NASASpaceFlight.com Forum

SpaceX Vehicles and Missions => SpaceX BFR - Earth to Deep Space => Topic started by: Chris Bergin on 02/16/2015 12:13 PM

Title: MCT Speculation and Discussion Thread 3
Post by: Chris Bergin on 02/16/2015 12:13 PM
Thread 1:
http://forum.nasaspaceflight.com/index.php?topic=33494.0

Thread 2:
http://forum.nasaspaceflight.com/index.php?topic=35424.0

Main NSF Articles:

http://www.nasaspaceflight.com/2014/03/spacex-advances-drive-mars-rocket-raptor-power/

http://www.nasaspaceflight.com/2014/07/spacex-roadmap-rocket-business-revolution/

http://www.nasaspaceflight.com/2014/08/battle-heavyweight-rockets-sls-exploration-rival/

And http://www.nasaspaceflight.com/?s=Raptor

L2 Info and Evaluations:
http://forum.nasaspaceflight.com/index.php?topic=35419.0 (Menu links in the opening post).

L2 MCT Rending Effort (ongoing, large collection):
http://forum.nasaspaceflight.com/index.php?topic=35307.0

--


Stay on topic and don't get crazy with the speculation please folks!
Title: Re: MCT Speculation and Discussion Thread 3
Post by: The Amazing Catstronaut on 02/16/2015 12:21 PM
Quote from:  RonM
What kind of trajectory can give a 100 day flight time to Mars? Can that be done with a single chemical rocket burn or would it be with a chemical rocket boost and SEP constant thrust?

I'd say that's a pretty pertinent question, although from the last thread I don't think RonM got an answer from anybody. I'm rather desperate to know the same, anybody got an idea?
Title: Re: MCT Speculation and Discussion Thread 3
Post by: jsgirald on 02/16/2015 01:47 PM
Quote from:  RonM
What kind of trajectory can give a 100 day flight time to Mars? Can that be done with a single chemical rocket burn or would it be with a chemical rocket boost and SEP constant thrust?

I'd say that's a pretty pertinent question, although from the last thread I don't think RonM got an answer from anybody. I'm rather desperate to know the same, anybody got an idea?

Have a look at Nasa's Trajectory Browser.
http://trajbrowser.arc.nasa.gov/

I was surprised to find that there are 128 days trajectories for just a bit over 6 km/s delta v.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: symbios on 02/16/2015 02:16 PM
Quote from:  RonM
What kind of trajectory can give a 100 day flight time to Mars? Can that be done with a single chemical rocket burn or would it be with a chemical rocket boost and SEP constant thrust?

I'd say that's a pretty pertinent question, although from the last thread I don't think RonM got an answer from anybody. I'm rather desperate to know the same, anybody got an idea?

Have a look at Nasa's Trajectory Browser.
http://trajbrowser.arc.nasa.gov/

I was surprised to find that there are 128 days trajectories for just a bit over 6 km/s delta v.

But 1,6 km/s of that is post Mars injection. This part will be greatly affected by what kind of post injection we are talking about.

2018 you can get a 80 day trajectory for a delta-v of 9,96 km/s but then 4,7 km/s of is post injection delta.

Will post injection delta-v be higher or lower for the planed landing profile then calculated in this tool?
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 02/16/2015 04:12 PM
Right. You can certainly do near 100 day trajectories all-chemical, ESPECIALLY if you refuel in a high orbit (high elliptical Earth orbit, EML1/2, or distant lunar retrograde) before your final departure burn (on flyby of Earth to get the biggest Oberth boost).

But there's evidence that SpaceX is now considering SEP as part of their MCT architecture (based on comments by Shotwell), although you don't get the impression that they've decided on it, yet.

...But I definitely don't think we should assume that EVERY opportunity will have a 100 day trajectory. In some years, the delta-v is just too high to be worth doing such a short trip. Also, if you extend the time by just a couple weeks (110-120 days), the delta-v requirements decrease dramatically, depending on the transit. So 100 days should be treated as more of a guideline than an absolute rule.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: JamesH on 02/16/2015 04:43 PM
From this video, MCT will be about 100x the size of an SUV.

https://www.youtube.com/watch?v=hwMIAKabRng&feature=youtu.be




Title: Re: MCT Speculation and Discussion Thread 3
Post by: MikeAtkinson on 02/16/2015 05:33 PM
From this video, MCT will be about 100x the size of an SUV.

We don't know whether this refers to internal volume of a SUV or external volume, if internal about 7m^3, if external maybe 15m^3 perhaps up to 22m^3.

We also don't know if it refers to total volume, pressurized volume or livable volume of the MCT.

700m^3 would be pretty small for the total MCT volume, while 2200m^3 would be very generous for the livable volume. Any of the other combinations seem possible to me, but if pressed I would go for 1500m^3 for the pressurized volume.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: SleeperService on 02/16/2015 05:41 PM
We also don't know if it is an African or European SUV...  ;)
Title: Re: MCT Speculation and Discussion Thread 3
Post by: MikeAtkinson on 02/16/2015 05:46 PM
But there's evidence that SpaceX is now considering SEP as part of their MCT architecture (based on comments by Shotwell), although you don't get the impression that they've decided on it, yet.

The exact quote is in answer to the question "and to power something for 8 months, and then presumably to turn around at some point, to get these people back home, you must be looking at some sort of renewable fuel?"

Quote
So we are looking at solar-electric propulsion, I think we are go to look at some other interesting propulsion (in-space propulsion) technologies, but our lift of both from the surface of Mars as well as Earth will probably be liquid oxygen and methane

I take this to mean that SpaceX are investigating various technologies, but they are not baselined for MCT at present.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: MikeAtkinson on 02/16/2015 05:51 PM
Quote
So we are looking at solar-electric propulsion, I think we are go to look at some other interesting propulsion (in-space propulsion) technologies, but our lift of both from the surface of Mars as well as Earth will probably be liquid oxygen and methane

I'm more interested in what these might be.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: SleeperService on 02/16/2015 05:54 PM
Quote
So we are looking at solar-electric propulsion, I think we are go to look at some other interesting propulsion (in-space propulsion) technologies, but our lift of both from the surface of Mars as well as Earth will probably be liquid oxygen and methane

I'm more interested in what these might be.

http://forum.nasaspaceflight.com/index.php?topic=36313.0
Title: Re: MCT Speculation and Discussion Thread 3
Post by: MikeAtkinson on 02/16/2015 06:11 PM
http://forum.nasaspaceflight.com/index.php?topic=36313.0

Not likely to be an EM drive in my opinion - I am skeptical that they work, even if they do work the reported thrust levels are too low (by several orders of magnitude) to be useful for a Mars transit.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lars-J on 02/16/2015 06:13 PM
http://forum.nasaspaceflight.com/index.php?topic=36313.0

Not likely to be an EM drive in my opinion - I am skeptical that they work, even if they do work the reported thrust levels are too low (by several orders of magnitude) to be useful for a Mars transit.

It's got to be at a minimum SEP level thrust or higher, otherwise it doesn't seem like it would be worth it.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: SleeperService on 02/16/2015 06:22 PM
Agreed. However the Chinese researchers and Shawyer have shown much greater thrust/KW...
The jury is out at the mo, but I think it is this line of work that comes under the 'interesting propulsion' description.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: CuddlyRocket on 02/16/2015 07:15 PM
Quote
So we are looking at solar-electric propulsion, I think we are go to look at some other interesting propulsion (in-space propulsion) technologies, but our lift of both from the surface of Mars as well as Earth will probably be liquid oxygen and methane

I'm more interested in what these might be.

Well, there's nuclear; but I'd be astonished if they were contemplating that! The only other ones I can think of are solar thermal and light sails, but neither seems to me to offer an advantage over chemical in this mission scenario. But then again, they're better engineers than I am! :)
Title: Re: MCT Speculation and Discussion Thread 3
Post by: RotoSequence on 02/16/2015 09:18 PM
Agreed. However the Chinese researchers and Shawyer have shown much greater thrust/KW...
The jury is out at the mo, but I think it is this line of work that comes under the 'interesting propulsion' description.

For now, we should dismiss anything more exotic than solar electric propulsion technologies, which have already been demonstrated and proven in space flight.

I don't think SpaceX is going to design anything around technologies that have not already been thoroughly researched. When you want to keep costs low, unproven technology is a liability. Technology that doesn't actually exist is unthinkable.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Impaler on 02/16/2015 10:39 PM
For a decent heliocentric transfer from EML1 using SEP you need about 1 mm/s acceleration, or 1 N per mt of vehicle mass.  That will get you to Mars in around 6 months and you will be at low velocity relative to Mars so you don't need to do any high-speed entry or airo-capture rather you can just spiral down which will take another month.  HALL thrusters and thin-film solar are adequate for this.

Faster transits require rapidly rising acceleration rates because your both going on a sharper more eccentric orbit around the sun and you have less total time in which to both accumulate and dissipate your speed.  If your willing to just accelerate and use Mars atmosphere for all your braking then you can reduce your needed acceleration for a given transit time as well as reducing your total propellent needs, but you get back the challenge of airo-capture maneuver which are still considered too dangerous for crew due to the highly variable nature of the Martian atmosphere.

I foresee several different ways SEP might be employed.  From minimal to maximum they are...

Limp-back-thrusters:  MCT has a DeltaV capability of ~4.5 km/s sized primarily for Mars Assent/Earth Escape and transits to Mars fully chemically, with or without assistance depending on desired speed.  On Mars it refuels and returns to LMO, at this point it deploys small solar arrays and returns to Earth via a very slow transfer using it's residual Methane/LOX or some Argon collected as a waste byproduct during the production of the latter propellents, any of these would yield high ISP and require very low propellent fractions.  Obviously this is applicable only for a cargo lander or a crew lander that's not taking anyone back to Earth. 

Primary Advantages:  large reduction in the demanded volume of Propellent production on Mars surface and reduction in chemical Delta-V capability needed on the MCT vehicle.  May allow early unmanned cargo vehicles that would otherwise be stranded on Mars to return and be reused.  Single vehicle design, works with any volume.

Primary Disadvantages: Electric thrusters capable of using low atomic mass propellents for long times not well established, can't return crew.  SEP system integration into lander inherently wasteful unless solar array is also used on surface which may make it heavy.


Cis-Lunar Tug:  MCT stages in LEO is refueled and then pushed to EML1 by a dedicated tug which immediately returns to LEO and never leaves cis-lunar space, tug is supplied with conventional Xenon/Krypton propellents launched from Earth for each pushing operation.  The MCT fleet is accumulated at EML1 until the transfer window opens at which point they all depart by chemical burns likely using lunar and Earth swing-by to maximize efficiency.  Landing on Mars and return to Earth are all chemical from their on out with Mars providing the propellents for Earth Return.  This will require crew to rendezvous with MCTs at EML1 via fast taxi craft such as Dragon, but any fleet-marshaling strategy requires the same rendezvous, this just puts the rendezvous at higher orbit which likely turns F9 launch into F9H launch.

Primary Advantages:  Significantly improves fraction of launch mass sent through TMI.  Alternatively faster transit may be had with the same TMI fraction.  Cargo containers outside of landers could be transported and only loaded into landers when in LMO to further increase efficiency of mass delivery.

Primary Disadvantages:  Two vehicle system, though SEP tug should be less development cost then lander.  Dock and rendezvous with autonomous vehicle necessary.  Requires a moderate volume and marshaling of vehicles to amortize Tug over.  Crew rendezvous slightly harder.  Dose not significantly effect MCT Delta-V capability need because it is driven by concurrent Mars-Assent and Earth-return needs.


Space-Freighter:  Combination of the above strategies in which SEP is used for ALL propulsion in-space and chemical thrusts in used only for Planetary assents/descents.  The marshaling of landers and cargo thus needs to be done in LEO with the spiral out to high orbit beginning months ahead of the Mars transfer window opening.  SEP vehicle would need to be larger then the tug concept if they pair 1:1 with landers, but could be massively larger if it carries multiple landers and cargo containers.  The landers descend with cargo and return with residual propellent multiple times which is transferred to the SEP vehicle and used to return to Earth keeping propellent tanks and mass to a minimum.  Both loading of cargo at Earth and unloading at Mars can be long-term operations taking the full time period between departure windows.

Primary Advantages:  Excellent mass transfer efficiency, on the order of 75% launch mass may be cargo containers once all vehicles are in place with 25% remainder being propellents.  Allows for large voluminous habitats to be attached to SEP vehicle which allow Landers to be relived of long-term habitation duty and function only as brief taxis with air-liner like densities.  Makes very efficient use of landers by using them to deposit multiple loads on Mars surface per synod, while putting lowest Delta-V needs and lowest habitation needs on lander, but at cost of higher re-usage between servicing needs.

Primary Disadvantages:   Requires large to huge volume to amortize over, including large and continual propellent production on Mars.  Requires on-orbit assembly of the largest concept SEP vehicle.  SEP vehicles of this size are beyond most current concepts and will require many MW of power pushing solar arrays well beyond current tech or even beyond near term goals of NASA.  Requires significant operations in LMO, loading containers into landers and transferring of propellent, likely autonomously.  Crew/Passengers need to rendezvous with vehicle in high Earth orbit as in tug scenario because of Van-Allen belt radiation.  Thrusters running off low atomic mass elements need more development.



Title: Re: MCT Speculation and Discussion Thread 3
Post by: JamesH on 02/17/2015 10:10 AM
Agreed. However the Chinese researchers and Shawyer have shown much greater thrust/KW...
The jury is out at the mo, but I think it is this line of work that comes under the 'interesting propulsion' description.

For now, we should dismiss anything more exotic than solar electric propulsion technologies, which have already been demonstrated and proven in space flight.

I don't think SpaceX is going to design anything around technologies that have not already been thoroughly researched. When you want to keep costs low, unproven technology is a liability. Technology that doesn't actually exist is unthinkable.

Although EM does like unusual technologies, and isn't afraid to try stuff out (the forthcoming Hyperloop test track for example), so I wonder if they are looking in to some of the newer techs for future use.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Cinder on 02/17/2015 11:08 AM
Yes, but especially for a group as keen to progress as quickly as possible as SpaceX, what concrete plans could they actually make if the technology in question is such an unknown?  We already know that as far as MCT goes, SpaceX is far ahead of the TRL of EM Drive.  You can only delay planning such a major part of a Mars Architecture as the MCT for the sake of such an unknown, for so long.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Ben the Space Brit on 02/17/2015 11:43 AM
This is me but I have this curious mental image of the first MCT landing beside the Mars One encampment and Elon Musk personally asking the camp commander's permission to disembark onto their planet.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: mikelepage on 02/17/2015 12:11 PM
Is there a publication anywhere with a graph modelling what proportion of the Mars craft mass budget would have to be dedicated to propulsion (be it chemical and/or SEP) versus transit time?  It would be neat to see it visualised.

The main reason for a fast transit is the radiation factor (~1.8 mSv/day Galactic Cosmic Rays as measured by Mars Curiosity rover during its transit which equates to 660 mSv per year).  This thread seems to confirm that as transit time -> 0 the proportion of the mass budget taken up by propellent/propulsion system mass increases dramatically.  That might mean there is a threshold at which it becomes more cost effective to devote the mass budget to more/better radiation shielding rather than more/faster propulsion system requirements.

I'm looking forward to hearing more about SpaceX's ideas for solutions to the radiation problem (specifically GCRs), because in the last interview I heard, it sounded like radiation originating from the sun was the only radiation source EM had considered ("just have a water column pointed towards the sun").  It stands to reason that all crew sleeping/living quarters will be at the centre of the craft, encased in water tanks + shielding materials, the thickest part of which will be pointed towards the sun.  Hopefully they can at least get it down to what the ISS astronauts experience (~0.8 mSv/day or 290mSv a year), although lower would be better since they will be out there for a lot longer.  Radiation workers - people who take x-rays and the like - generally have an annual limit of up to 80mSv for comparison, while the rest of us get the average background levels of ~5 mSv per year.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: fast on 02/17/2015 12:12 PM
For a decent heliocentric transfer from EML1 using SEP you need about 1 mm/s acceleration, or 1 N per mt of vehicle mass.  That will get you to Mars in around 6 months and you will be at low velocity relative to Mars so you don't need to do any high-speed entry or airo-capture rather you can just spiral down which will take another month.  HALL thrusters and thin-film solar are adequate for this.

Faster transits require rapidly rising acceleration rates because your both going on a sharper more eccentric orbit around the sun and you have less total time in which to both accumulate and dissipate your speed.  If your willing to just accelerate and use Mars atmosphere for all your braking then you can reduce your needed acceleration for a given transit time as well as reducing your total propellent needs, but you get back the challenge of airo-capture maneuver which are still considered too dangerous for crew due to the highly variable nature of the Martian atmosphere.

I foresee several different ways SEP might be employed.  From minimal to maximum they are...

Limp-back-thrusters:  MCT has a DeltaV capability of ~4.5 km/s sized primarily for Mars Assent/Earth Escape and transits to Mars fully chemically, with or without assistance depending on desired speed.  On Mars it refuels and returns to LMO, at this point it deploys small solar arrays and returns to Earth via a very slow transfer using it's residual Methane/LOX or some Argon collected as a waste byproduct during the production of the latter propellents, any of these would yield high ISP and require very low propellent fractions.  Obviously this is applicable only for a cargo lander or a crew lander that's not taking anyone back to Earth. 

Primary Advantages:  large reduction in the demanded volume of Propellent production on Mars surface and reduction in chemical Delta-V capability needed on the MCT vehicle.  May allow early unmanned cargo vehicles that would otherwise be stranded on Mars to return and be reused.  Single vehicle design, works with any volume.

Primary Disadvantages: Electric thrusters capable of using low atomic mass propellents for long times not well established, can't return crew.  SEP system integration into lander inherently wasteful unless solar array is also used on surface which may make it heavy.


Cis-Lunar Tug:  MCT stages in LEO is refueled and then pushed to EML1 by a dedicated tug which immediately returns to LEO and never leaves cis-lunar space, tug is supplied with conventional Xenon/Krypton propellents launched from Earth for each pushing operation.  The MCT fleet is accumulated at EML1 until the transfer window opens at which point they all depart by chemical burns likely using lunar and Earth swing-by to maximize efficiency.  Landing on Mars and return to Earth are all chemical from their on out with Mars providing the propellents for Earth Return.  This will require crew to rendezvous with MCTs at EML1 via fast taxi craft such as Dragon, but any fleet-marshaling strategy requires the same rendezvous, this just puts the rendezvous at higher orbit which likely turns F9 launch into F9H launch.

Primary Advantages:  Significantly improves fraction of launch mass sent through TMI.  Alternatively faster transit may be had with the same TMI fraction.  Cargo containers outside of landers could be transported and only loaded into landers when in LMO to further increase efficiency of mass delivery.

Primary Disadvantages:  Two vehicle system, though SEP tug should be less development cost then lander.  Dock and rendezvous with autonomous vehicle necessary.  Requires a moderate volume and marshaling of vehicles to amortize Tug over.  Crew rendezvous slightly harder.  Dose not significantly effect MCT Delta-V capability need because it is driven by concurrent Mars-Assent and Earth-return needs.


Space-Freighter:  Combination of the above strategies in which SEP is used for ALL propulsion in-space and chemical thrusts in used only for Planetary assents/descents.  The marshaling of landers and cargo thus needs to be done in LEO with the spiral out to high orbit beginning months ahead of the Mars transfer window opening.  SEP vehicle would need to be larger then the tug concept if they pair 1:1 with landers, but could be massively larger if it carries multiple landers and cargo containers.  The landers descend with cargo and return with residual propellent multiple times which is transferred to the SEP vehicle and used to return to Earth keeping propellent tanks and mass to a minimum.  Both loading of cargo at Earth and unloading at Mars can be long-term operations taking the full time period between departure windows.

Primary Advantages:  Excellent mass transfer efficiency, on the order of 75% launch mass may be cargo containers once all vehicles are in place with 25% remainder being propellents.  Allows for large voluminous habitats to be attached to SEP vehicle which allow Landers to be relived of long-term habitation duty and function only as brief taxis with air-liner like densities.  Makes very efficient use of landers by using them to deposit multiple loads on Mars surface per synod, while putting lowest Delta-V needs and lowest habitation needs on lander, but at cost of higher re-usage between servicing needs.

Primary Disadvantages:   Requires large to huge volume to amortize over, including large and continual propellent production on Mars.  Requires on-orbit assembly of the largest concept SEP vehicle.  SEP vehicles of this size are beyond most current concepts and will require many MW of power pushing solar arrays well beyond current tech or even beyond near term goals of NASA.  Requires significant operations in LMO, loading containers into landers and transferring of propellent, likely autonomously.  Crew/Passengers need to rendezvous with vehicle in high Earth orbit as in tug scenario because of Van-Allen belt radiation.  Thrusters running off low atomic mass elements need more development.



IMHO option three is the way to go ultimately, but in the nearest future MCT will have just small auxiliary SEP propulsion but mainly power system, it will supplement main chemical propulsion during long transits.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 02/17/2015 02:59 PM
Even if you have good electric propulsion, it's optimal to still do a small chemical burn on flyby of Earth as you leave for Mars, so there'll always be somewhat of a hybrid approach.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Joel on 02/17/2015 06:16 PM
Quote
So we are looking at solar-electric propulsion, I think we are go to look at some other interesting propulsion (in-space propulsion) technologies, but our lift of both from the surface of Mars as well as Earth will probably be liquid oxygen and methane

I'm more interested in what these might be.

Maybe they could beam power from SpaceX's 4000 comsats :)
Title: Re: MCT Speculation and Discussion Thread 3
Post by: aceshigh on 02/18/2015 10:39 AM
Have these MCT Speculation renders, by a guy called Root_Negative, been posted here at NSF already?

http://imgur.com/a/ObsNJ/embed#0

Title: Re: MCT Speculation and Discussion Thread 3
Post by: Ben the Space Brit on 02/18/2015 12:48 PM
Pure speculation but, when I visualise MCT, I visualise something like the Mars lander from the Constellation Mars DRM5 video. Like that spacecraft, I see it as having two modules - the mission vehicle and the propulsion module.

In essence, the crew vehicle is a a fully-contained surface to orbit to surface crew and cargo hauler, powered by Raptor-VAC. As it is going to be around 10m (33ft) diameter, it is just possible for it to provide artificial gravity during the cruise phase by rotating around its long axis. It lands on Mars, tanks up from storied ISRU methane and oxygen and then flies back to Medium Mars orbit.

The propulsion module, which may be SEP, NEP or something more exotic, will fly from EML2 to Phobos Station Keeping or PSK (orbiting at the same altitude as Phobos) and back.

The flight would be something like this:

CARGO (One-Way)
* Launch including core recovery
* SEI2 from LEO to TMI; U/S expended
* Hybrid aerocapture/propulsive deceleration into low Mars Orbit
* Hybrid aerodynamic/propulsive EDL

CREW (Two-Way - Reusable)
* Launch including core recovery
* SEI2 from LEO to EML2
   > U/S is on free-return trajectory and will carry out EDL for recovery and re-use at the next perigee
* Rendezvous with propulsion section
* TMI from EML2
* Cruise to Mars with longitudinal roll
* Brake to PSK using MPS
* Crew module detach and EDL for precision landing near pre-placed cargo/extant surface facility
* Surface ops (crew transfer, cargo offload, sample on-load, ISRU propellent on-load)
* Ascent to PSK & rendezvous with propulsion section
* ROI from PSK
* Brake to EML2
* Crew section detaches and returns to Earth by direct descent for refurbishment & reuse
* Propulsion section is refurbished at EML2 for reuse.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: dglow on 02/18/2015 02:07 PM
Have these MCT Speculation renders, by a guy called Root_Negative, been posted here at NSF already?

temp bana/ObsNJ/embed#0

I haven't seen them. Fix your link, please?
Title: Re: MCT Speculation and Discussion Thread 3
Post by: happyflower on 02/18/2015 05:44 PM
Have these MCT Speculation renders, by a guy called Root_Negative, been posted here at NSF already?

temp bana/ObsNJ/embed#0

I haven't seen them. Fix your link, please?

Here is the link to his post. It was pretty interesting stuff. He did some work with calculations as well.

http://www.reddit.com/r/spacex/comments/2vxxqd/the_future_spacecraft_of_spacex_a_fan_made_mct/

Title: Re: MCT Speculation and Discussion Thread 3
Post by: dglow on 02/18/2015 09:13 PM
Have these MCT Speculation renders, by a guy called Root_Negative, been posted here at NSF already?

temp bana/ObsNJ/embed#0

I haven't seen them. Fix your link, please?

Here is the link to his post. It was pretty interesting stuff. He did some work with calculations as well.

http://www.reddit.com/r/spacex/comments/2vxxqd/the_future_spacecraft_of_spacex_a_fan_made_mct/

Thank you, and wow.

I honor Root_Negative's spirit and creativity, but those designs seem, well, fragile. So many articulated pieces and parts (even the engines!), as though the problem was approached from a transformer mindset.

I love playing with toys designed like this, but would avoid flying on any such spacecraft. KISS, please.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lars-J on 02/18/2015 09:27 PM
Have these MCT Speculation renders, by a guy called Root_Negative, been posted here at NSF already?

temp bana/ObsNJ/embed#0

I haven't seen them. Fix your link, please?

Here is the link to his post. It was pretty interesting stuff. He did some work with calculations as well.

http://www.reddit.com/r/spacex/comments/2vxxqd/the_future_spacecraft_of_spacex_a_fan_made_mct/

Well, there's certainly out-of-the-box thinking on display. But also lunacy. 91 Raptors? :D
Title: Re: MCT Speculation and Discussion Thread 3
Post by: happyflower on 02/18/2015 10:42 PM
That was the very first thing that caught my eyes... Wow that's a lot of engines. He was confronted by this very question in the posts, and he did give an "answer" and did relate it to things stated by Musk and Shotwell. Of course its all assumptions on his part which is pretty much what everybody has so far (until SpaceX gives more information later). So there is method to his madness at any rate.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 02/18/2015 10:45 PM
I'm fairly certain MCT will need to be very highly structurally efficient, like a rocket stage. This will drive the appearance of the vehicle (as well as the aerodynamics of Mars entry).
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Impaler on 02/19/2015 02:38 AM
Well, there's certainly out-of-the-box thinking on display. But also lunacy. 91 Raptors? :D

Not to mention the 20 m monster core, and the floating oil-rig launch pad, and the 6 story tall landing capsule.   ::)
Title: Re: MCT Speculation and Discussion Thread 3
Post by: llanitedave on 02/19/2015 04:35 AM
I like it a lot.  You need ideas like that, and who knows, it may inspire other future designers.  I'd be very surprised if the MCT ends up like this, but if it did, I'd think it was cool!
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Vultur on 02/19/2015 05:36 AM
the radiation factor (~1.8 mSv/day Galactic Cosmic Rays as measured by Mars Curiosity rover during its transit which equates to 660 mSv per year).

...which isn't actually that bad if you're not ultra-risk-averse like NASA.


Quote
I'm looking forward to hearing more about SpaceX's ideas for solutions to the radiation problem (specifically GCRs), because in the last interview I heard, it sounded like radiation originating from the sun was the only radiation source EM had considered ("just have a water column pointed towards the sun").

Because that's the only one worth worrying about. GCR risks are very small from an early colonization viewpoint.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Ben the Space Brit on 02/19/2015 01:13 PM
Here is a question that may seem off-topic but isn't.

Most electric propulsion systems use noble gasses like Xenon as their propellent. I'm wondering if methane is compatible with SEP and, if so, what is the ISP like? The reason I'm asking is, if my MCT idea's electric drive can use the same propellent as the chemical engines on the crew vehicle, then, potentially, you can top up the propellent tanks on the propulsion section from tankers based on Earth and Mars, increasing the longevity of the vehicle.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: RanulfC on 02/19/2015 01:55 PM
Where do we have the "latest" specifications listing for the overall MCT at? The last set of figures I have is over 6 months old and I'm pretty sure there have been updates since :)

Randy
Title: Re: MCT Speculation and Discussion Thread 3
Post by: mikelepage on 02/19/2015 02:17 PM
the radiation factor (~1.8 mSv/day Galactic Cosmic Rays as measured by Mars Curiosity rover during its transit which equates to 660 mSv per year).

...which isn't actually that bad if you're not ultra-risk-averse like NASA.

Quote
I'm looking forward to hearing more about SpaceX's ideas for solutions to the radiation problem (specifically GCRs), because in the last interview I heard, it sounded like radiation originating from the sun was the only radiation source EM had considered ("just have a water column pointed towards the sun").

Because that's the only one worth worrying about. GCR risks are very small from an early colonization viewpoint.

Say what now? Sure, GCRs aren't going to fry you in the space of days like a solar proton event would, but we're still talking about whether you're going to get cancer in years or in decades.  Talking about being risk averse is the wrong terminology because that implies this is something that *might* happen, when with those radiation levels, cancer is a virtual certainty. 

I'm hoping to hear that at least MCT is designed with a decent amount of passive shielding in mind.  Even if we allow colonists to take a massive lifetime dose (say 6 Sv over the trip, which takes you to a ~2/3 chance of getting cancer), that still equates to a mission duration of only 9.1 years if we only use current levels of shielding.  Not an insurmountable problem, but clearly something has to improve: cause there's risk averse and then there's russian roulette.  Even just by planning your ship to keep crew quarters surrounded by water/fuel/resources (which you need to take with you anyway so zero mass gain) they should be able to cut that dose down by at least half.

Title: Re: MCT Speculation and Discussion Thread 3
Post by: Impaler on 02/19/2015 05:31 PM
Here is a question that may seem off-topic but isn't.

Most electric propulsion systems use noble gasses like Xenon as their propellent. I'm wondering if methane is compatible with SEP and, if so, what is the ISP like? The reason I'm asking is, if my MCT idea's electric drive can use the same propellent as the chemical engines on the crew vehicle, then, potentially, you can top up the propellent tanks on the propulsion section from tankers based on Earth and Mars, increasing the longevity of the vehicle.

Yes, HALL thrusters can run on other propellents, they need a small amount (~5% of total propellent) of something easy to ionize to catalyze the ionization of the remaining propellents through collisions.  ISP would rise significantly using low atomic mass elements found in conventional propellents, efficiency would drop though due to ionization energy costs.  The high ISP and low efficiency would thus give very low thrust per unit of power and the whole system would hinge on the power-density of the power-source, if it's high enough it would be viable.  Alternatively you can go real slow for cargo delivery.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: MikeAtkinson on 02/19/2015 06:18 PM
the radiation factor (~1.8 mSv/day Galactic Cosmic Rays as measured by Mars Curiosity rover during its transit which equates to 660 mSv per year).

...which isn't actually that bad if you're not ultra-risk-averse like NASA.

Quote
I'm looking forward to hearing more about SpaceX's ideas for solutions to the radiation problem (specifically GCRs), because in the last interview I heard, it sounded like radiation originating from the sun was the only radiation source EM had considered ("just have a water column pointed towards the sun").

Because that's the only one worth worrying about. GCR risks are very small from an early colonization viewpoint.

Say what now? Sure, GCRs aren't going to fry you in the space of days like a solar proton event would, but we're still talking about whether you're going to get cancer in years or in decades.  Talking about being risk averse is the wrong terminology because that implies this is something that *might* happen, when with those radiation levels, cancer is a virtual certainty. 

I'm hoping to hear that at least MCT is designed with a decent amount of passive shielding in mind.  Even if we allow colonists to take a massive lifetime dose (say 6 Sv over the trip, which takes you to a ~2/3 chance of getting cancer), that still equates to a mission duration of only 9.1 years if we only use current levels of shielding.  Not an insurmountable problem, but clearly something has to improve: cause there's risk averse and then there's russian roulette.  Even just by planning your ship to keep crew quarters surrounded by water/fuel/resources (which you need to take with you anyway so zero mass gain) they should be able to cut that dose down by at least half.

We know about one SpaceX strategy to avoid GCR's and can speculate on a few more.

SpaceX are planning on 3-4 month trips, which cuts down the GCR dose over the more conventional 6 months trips that most other missions have used.

Edit/CR: off-topic material regarding base/colony design and crew general medical matters deleted
Title: Re: MCT Speculation and Discussion Thread 3
Post by: CJ on 02/20/2015 06:57 AM

I've read through much of the two prior threads (and tried to skim the rest) but so far, in all the talk of MCT design, I can't see anything related to power?

What I'm getting at is that MCT will need a lot of electricity to provide life support and all other needs for up to 100 people, and that's without any of the speculated SEP.

I think we can safely assume they won't be using a very, very long extension cord, so that means MCT will have to generate said electrical power. No matter how it does so, that'll take mass.

IMHO, the only viable main source is solar due to mission duration, because I'm guessing that fuel cells plus the fuel would outmass the solar.   

So how much electric power is needed? Life support takes a lot. Is ISS a good model for this? If so, MCT is going to need about 10 times the solar arrays ISS has. I'm basing that guess on ISS being able to handle a crew of up to 10, MCT up to 100, and the fact that ISS is in darkness about half the time - but ISS orbits earth, while MCT will have to handle the lesser sunlight near Mars as well, about a 50% dropoff. The main solar arrays on ISS would cover more than half a football field according to NASA, so we're talking an array for MCT that covers five football fields? How much would that weigh? The arrays on ISS, if I remember right, produce about 38 watts per kilogram, and new tech can exceed that, but; they don't have the mass penalty of having to repeatedly and reliably extend and retract, and while retracted, handle high G loads. But, let's assume new tech overcomes the mass penalty entirely with a lighter array, and we can attain 38 watts per kilogram with an array that can repeatedly extend and retract.

ISS's power system produces somewhere in the realm of 100kw, so MCT's would need the capacity (at 1AU) of about 1000 kw. So that'd weigh about 26 tons, and also take up considerable volume when stowed. If SEP is involved, you're going to need an even larger array.

Why would it make sense to haul such a large mass in and out of deep grav wells at Earth and Mars? There's also the issue of it being a large additional mass and volume to protect with the TPS. The solar array could be made lighter if it didn't have to both retract and deal with significant G while stowed. This is part of why I find the concept that's popular here of MCT being a single solid vehicle that acts as an upper stage to BFR, refuels in Leo, flies to Mars and lands, refuels, then flies back to Earth and lands, to be implausible for both physical and fiscal reasons. Thus, my guess is that SpaceX's general concept for MCT (I doubt they have more than that, yet) is a very different beast; a transportation system with several components, rather than one single, enormous, solid vehicle that both flies between and lands on two very different worlds.     



 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: guckyfan on 02/20/2015 07:20 AM
Most of the weight of the ISS solar array comes from the fact that they work as heat rejection system too. The cooling ammonia circulates through them.

A new system might be as low as 1kg/kW. Maybe better calculate 2kg/kW to be on the safe side. Also much of the energy needs of ISS goes to experiments, not only life support. I am not sure but I would guess 2 or 3kW per person should be enough. I am basing this on the metabolism of people who consume the equivalent of ~300W. Producing oxygen from water is probably the single most energy consuming ECLSS activity and that should be around 500W, given present efficiency of electrolysis. In reality probably less because some of the oxygen would come from the Sabatier process using CO2 and the H2 that is a byproduct of electrolysis.

So I believe that 1000kg for the solar arrays is realistic. Thin film arrays should be easy to retract too. So 300kW at 150W/m˛ would be 2000 m˛.

Title: Re: MCT Speculation and Discussion Thread 3
Post by: Owlon on 02/20/2015 07:39 AM
ISS's power system produces somewhere in the realm of 100kw, so MCT's would need the capacity (at 1AU) of about 1000 kw. So that'd weigh about 26 tons, and also take up considerable volume when stowed. If SEP is involved, you're going to need an even larger array.

In short, modern technology can do much, much better than this and it's going to have to in order for the physics and economics of the MCT to work out. All current solar arrays have to survive launch while stowed, so they should be able to survive reentry, too; the big engineering issue is just that the MCT arrays need to be able to retract.

Current state of the art solar arrays are >10 times the specific power of the ISS arrays, and you probably need somewhat less than 10x the power the ISS produces due to scaling benefits of the ECLSS (plus hopefully newer, more efficient and advanced systems). Without doing some real engineering analysis, you can wind up with a weight for an MCT solar array anywhere from 1-100 tons depending on the assumptions, rounding, estimates, and hand-waving you use.

Keep in mind, too, that we won't be seeing 100 people on an MCT for a good long while, and the early flights will have smaller in-transit power needs compared to a full 100-person flight. There's a lot of room for improvement in solar arrays between now and, say, 2040.

EDIT: I'm assuming no SEP here, but the gist of of my post holds up either way
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Burninate on 02/20/2015 09:56 AM
Most of the weight of the ISS solar array comes from the fact that they work as heat rejection system too. The cooling ammonia circulates through them.

I was under the impression they had dedicated radiators for that - attached to the truss, but not part of the solar array wing.  Am I wrong?
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Ben the Space Brit on 02/20/2015 10:41 AM

I've read through much of the two prior threads (and tried to skim the rest) but so far, in all the talk of MCT design, I can't see anything related to power?

IMHO, solar would make the most sense and have the greatest fault tolerance. Fuel cells have a fixed lifespan and space-borne nuclear has huge practical unknowns that would, if I were Elon, reluctant to make it a primary option.

IF there was a huge breakthrough in fission or fusion reactor sizes and reliability in the next five years, SpaceX might decide to make MCT nuclear power but I wouldn't hold my breath even then.

If nuclear became practical, I'd still expect the crew section to be solar-powered (with the option of sucking ground-side power when down on Mars's surface) so it could operate independently of a reusable orbit-to-orbit propulsion stage.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: mikelepage on 02/20/2015 04:57 PM
Fairly sure solar power is the only solution that makes any sense for MCT in the near future.  Elon also put his opinion on record regarding fuel cells (I think it was regarding putting fuel cells in cars, but still): I think the quote was that he wished he could "stab that idea through the heart".

For the record, the panels on the ISS are not as easily improvable as one might think - they are already massively efficient (44%), but super expensive as panels.  All the recent improvements in solar panel technology to my understanding have been in getting cheaper technologies to achieve similar efficiencies.  The current record efficiency for thin film is currently 29% as far as I can tell (for Gallium Arsenide) but can have orders of magnitude less mass.  So I think it's not unlikely that SpaceX might actually go with panels that are less efficient that what is on ISS, but are better value for money.

ISS has 8 solar wings, each 12x35m = total area of 3360 square metres.  If we say MCT solar panels are somewhat less efficient than ISS (it can't be much better with today/near future tech), but that power use is somewhat more efficient (more people, efficiencies of scale, etc), I think it's still a reasonable estimate for the solar panel requirement for MCT to be 10x the area of ISS panels.  This gives us 33,600 square metres! (A circular area of 33600m2 is ~200m in diameter!).  Factoring in the distance of Mars (which receives 2.25x less sunlight for being at 1.5 AU), I think a solar array this size is fairly low for supporting 100 people, though it might be redundant enough for supporting initial flights of 10-20 or so.  Regardless, that's still a huge solar array: The question is where you will put all those panels.

I'm probably going to get roasted for bringing this up again (though I don't know why - this is a speculation & discussion thread after all), but I think it's fair to say that you obviously need to develop new techniques for unfurling solar panels that large, and that whatever technology you end up using to unfurl solar panels that large could surely be designed to work just as well for unfurling the lattice you need to implement spin gravity.  I'm calling it a lattice rather than a tether because any lattice suitable for supporting a solar panel array that size would have to be wide/stiff enough to address some of the same resonances which would make a simple tether problematic.  If the solar array designed to double as a lattice for spin gravity, you would have a way to generate the necessary energy as well as the option of full gravity.  Two crew modules, attached through a 1000x33m solar array lattice, gives 1 x g at 1.3rpm.  That solar array/lattice could potentially be launched separately, with the thin film solar cell component weighing as little as 8 tons (according to google, 0.25-1kg per m2 is the current weight range on thin film panels, though that will probably be halved again before MCT launches).

*retreats to a safe distance*.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: RanulfC on 02/20/2015 05:51 PM
Fairly sure solar power is the only solution that makes any sense for MCT in the near future.  Elon also put his opinion on record regarding fuel cells (I think it was regarding putting fuel cells in cars, but still): I think the quote was that he wished he could "stab that idea through the heart".

"Beamed power" not fuel cells :) (Specifically Earth beamed power compared to Solar which is NOT the same thing as power production on or near Mars I'll point out :) )
His main issue with fuel cells is the need for "fuel" to power them. The are an energy "storage" converter not a primary energy source. Nuclear and Solar are both primary sources.
On the other hand its been pointed out to him that you can (in most cases) re-crack the "exhaust" into fuel again but that comes right back to needing a "primary" power source to provide the energy to crack the components for the fuel cells :)

I'll point out here that while he may be right about terrestrial power beaming as a function of efficiency, (there's a lot of argument room in that using space based laser power beaming to terrestrial solar panels at night at the very least allows them to produce power when they normally wouldn't and delivery efficiency of over 90% has been demonstrated with tuned cells and laser :) ) the same does not necessarily apply to off-Earth use as getting you "primary power source" to your destination is often a determining factor rather than efficiency. For example a SEP propulsion stage that moves a cargo to High-Mars Orbit can then be re-purposed to provide primary and supplemental power for a Mars base or Colony either until a local power production and distribution grid can be set up or used in and of itself for as long as it can be maintained. It's "additive" in both economic moving of non-sensitive payload from Earth to Mars but also in providing power to surface operations when their "primary" supply (surface solar) is not operational for various reasons. (Sand storms or darkness for example using either microwave or laser beaming)

I suspect that at some point prior to actually going to Mars decisions will be made but not so "set-in-stone" that changes can't be made as technology advances :)

Quote
I'm probably going to get roasted for bringing this up again (though I don't know why - this is a speculation & discussion thread after all), but I think it's fair to say that you obviously need to develop new techniques for unfurling solar panels that large, and that whatever technology you end up using to unfurl solar panels that large could surely be designed to work just as well for unfurling the lattice you need to implement spin gravity.  I'm calling it a lattice rather than a tether because any lattice suitable for supporting a solar panel array that size would have to be wide/stiff enough to address some of the same resonances which would make a simple tether problematic.  If the solar array designed to double as a lattice for spin gravity, you would have a way to generate the necessary energy as well as the option of full gravity.  Two crew modules, attached through a 1000x33m solar array lattice, gives 1 x g at 1.3rpm.  That solar array/lattice could potentially be launched separately, with the thin film solar cell component weighing as little as 8 tons (according to google, 0.25-1kg per m2 is the current weight range on thin film panels, though that will probably be halved again before MCT launches).

*retreats to a safe distance*.

Don't think you'll get roasted... Probably only lightly singed at the most :)

Actually the pattern I've been seeing is the assumption that the solar panels will be "simply" rolled out onto the ground in the needed acreage and no planning or assumption of any extensive support or structure involved.

The thing is you are not going to need the amount of power in transit that you'll need on arrival so the in-space array will be very different from the on-Mars equipment I'm thinking.

Randy
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Krevsin on 02/20/2015 06:01 PM
WRT beamed power, I could easily see it as an eventual upgrade to the MCT, as a rectenna will probably be lighter than all the solar panels.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lars-J on 02/20/2015 06:11 PM
WRT beamed power, I could easily see it as an eventual upgrade to the MCT, as a rectenna will probably be lighter than all the solar panels.

When discussing power for the MCT - keep in mind that it will also need power when landed on Mars. So any arrays that it carries will need to function on Mars as well.

This will require a robust but lightweight deployment mechanism that also can function under martian gravity.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: CuddlyRocket on 02/20/2015 06:56 PM
In case any of you are wondering all posts about the effectiveness or otherwise of the Martian atmosphere as radiation shielding and anything similar have been deleted as off-topic to this thread which is about the design of SpaceX's MCT. (And if you wish to make the argument that it is relevant to the design specifically detail how in your post.)
Title: Re: MCT Speculation and Discussion Thread 3
Post by: oiorionsbelt on 02/20/2015 07:27 PM


When discussing power for the MCT - keep in mind that it will also need power when landed on Mars. So any arrays that it carries will need to function on Mars as well.

This will require a robust but lightweight deployment mechanism that also can function under martian gravity.
unless the MCT connects to surface power supply once it's landed.
 MCT could use solar in transit and nuclear on the surface.
Title: MCT Speculation and Discussion Thread 3
Post by: Lars-J on 02/20/2015 08:21 PM


When discussing power for the MCT - keep in mind that it will also need power when landed on Mars. So any arrays that it carries will need to function on Mars as well.

This will require a robust but lightweight deployment mechanism that also can function under martian gravity.
unless the MCT connects to surface power supply once it's landed.
 MCT could use solar in transit and nuclear on the surface.

True, but that won't be available for the first few flights. I suppose one of the early cargo landers could carry a large solar panel farm as its primary payload, but it needs to be placed by robots or crew before it can be used.

As far as nuclear on the surface, don't bet on that for the near term.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: oiorionsbelt on 02/20/2015 09:10 PM
Yes, from comments by Elon, I think we are vastly underestimating the roll of robots/androids in the Mars campaign.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 02/20/2015 10:12 PM
Just an FYI, but regenerative fuel cells aren't really lighter weight than the best lithium batteries, but they do have atrocious round-trip efficiency by comparison. Doesn't make sense. Just use a battery.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Impaler on 02/20/2015 10:18 PM
I agree MCT would need some kind of space-deployable solar system,  minimum it needs to keep navigation and comunication systems operation even when it is carrying only cargo.  When it carries passengers it likely has considerable life-support power needs as well.

The MCT surface power needs would be of two very different types though.  ISPP is going to need considerably more power then continued life-support.  I suspect that their would be two sets of solar-panels.

One set integrated into the MCT which is deploy-able and retractable in-space is composed of conventional thick silicon cells on blankets.  I could see this fitting under the nose-cone and being disk shaped with a diameter about equal to the MCT itself with an origami-style fold out/refold method, this would have the benefit of shading the vehicle during transit helping to maintain cyrogens and easing the work of any radiators systems which could operate in it's shade.  If deployed on the surface it would again act as shade for the vehicle and contribute to a reduction in refrigeration loads for propellents, this MIGHT be sufficient to justify the heavier support structure necessary to hold it up in the Martian wind-loads, otherwise it is retracted and stowed during surface stays.

A second solar-system that is stored in the cargo-hold as cargo and which is intended for surface use only, it would be thin-film roll based and be dedicated to Propellent production.  It would likely be of a VASTLY large area and likely has a peak power output of between 500 kw and 1 Mw depending on how much propellent we need and how fast we want to make it.  This system is likely to be left behind along with the other propellent production equipment and would be the back-bone power supply for a base.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: dglow on 02/20/2015 10:19 PM


When discussing power for the MCT - keep in mind that it will also need power when landed on Mars. So any arrays that it carries will need to function on Mars as well.

This will require a robust but lightweight deployment mechanism that also can function under martian gravity.
unless the MCT connects to surface power supply once it's landed.
 MCT could use solar in transit and nuclear on the surface.

True, but that won't be available for the first few flights. I suppose one of the early cargo landers could carry a large solar panel farm as its primary payload, but it needs to be placed by robots or crew before it can be used.

As far as nuclear on the surface, don't bet on that for the near term.

Whether solar or nuclear, there will need to be large power-source on Mars ahead of MCT's arrival. Won't we want to verify successful ISRU before launch?
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lars-J on 02/20/2015 11:21 PM


When discussing power for the MCT - keep in mind that it will also need power when landed on Mars. So any arrays that it carries will need to function on Mars as well.

This will require a robust but lightweight deployment mechanism that also can function under martian gravity.
unless the MCT connects to surface power supply once it's landed.
 MCT could use solar in transit and nuclear on the surface.

True, but that won't be available for the first few flights. I suppose one of the early cargo landers could carry a large solar panel farm as its primary payload, but it needs to be placed by robots or crew before it can be used.

As far as nuclear on the surface, don't bet on that for the near term.

Whether solar or nuclear, there will need to be large power-source on Mars ahead of MCT's arrival. Won't we want to verify successful ISRU before launch?

Yes, but careful with terminology. Does MCT imply crewed to you? It does not to me... And I would imagine that the first cargo MCT's that land ahead of the first crewed MCT's would be one way only - heavy haulers to put ISRU supplies and various robotics in place. Left in place to be the starting point of the base. (A great resource for space parts as well)

I would imagine that one of the MCT's would start some sort of ISRU demo to fill its tanks. This could also function as the backup crew return vehicle for the first expedition.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: dglow on 02/21/2015 01:27 AM
No, the MCT doesn't have to carry a crew. What MCT does imply to me is 'return trip'. If it's going to fly back it needs fuel. If you're going to make fuel you need power, hence my comment.

I agree with you on the need for demo mission(s) to validate ISRU in advance. I think this can/should/will be done with pre-MCT hardware, flown on a FH. Once you have that fuel, it can the be purposed for returning the first MCT.

Perhaps what's really being asked here is: will SpaceX's architecture include one-way landing vehicles (habs in Mars Direct), and should we consider those vehicles MCTs?
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Impaler on 02/21/2015 01:43 AM
I think all statements by Musk have been clear that they want their vehicles back, even if they are landing cargo.

I personally think we are only going to see one type of lander, all 'variants' will be variants in the cargo load-out only.  As little as possible will be integrated into the vehicle and as much as possible will be in the cargo, this includes all the Propellent production, all the Crew accommodations for in space or surface use.  This simplifies the vehicle, lightens it and makes it easier to get back.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Norm38 on 02/21/2015 02:37 AM
If the solar array designed to double as a lattice for spin gravity, you would have a way to generate the necessary energy as well as the option of full gravity.  Two crew modules, attached through a 1000x33m solar array lattice, gives 1 x g at 1.3rpm.

Interesting concept.  But if you're going to do spin gravity, design for 0.4g.  1g for people going to Mars is overkill.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: BobHk on 02/21/2015 03:38 AM
On the matter of solar collectors and power systems:

Above the Earth's atmosphere solar irradiance (radiant energy per unit area) is roughly 1373 w/m2 but drops to 610 w/m2 above Mars' atmosphere .1(pg7)  Irradiance close to the surface of Mars with the sun directly overhead on a clear day makes it about 590 w/m2.  At the equator you get 12 hours of daylight and 12 hours of night2, if you bother to land there.

Assuming there isn't a two week long dust storm and you can get good sunlight for 12 hours a day minimum (assuming no seasonal variations just to make it easier on our brains):

How large do your solar collectors and batteries have to be to avoid freezing to death if that (solar and batteries) is all you have?
Could said collectors be deployed from MCT without having to physically move them to the ground and lay them out? 
How would you maximize solar arrays (hull mounted and foldable?)?
What supplemental power systems should MCT have in the event of loss of solar array surface area or lack of sunlight for extended periods?

1: http://www.lpi.usra.edu/sbag/meetings/jan2011/presentations/day1/d1_1200_Surampudi.pdf (http://www.lpi.usra.edu/sbag/meetings/jan2011/presentations/day1/d1_1200_Surampudi.pdf)
2: http://tomatosphere.org/teachers/guide/grades-8-10/mars-agriculture (http://tomatosphere.org/teachers/guide/grades-8-10/mars-agriculture)
3: http://solarelectricityhandbook.com/solar-irradiance.html (http://solarelectricityhandbook.com/solar-irradiance.html) 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: guckyfan on 02/21/2015 06:11 AM
@BobHk

It is a very interesting topic. But this is not the thread for it. There are threads on this in the Mars section.

Title: Re: MCT Speculation and Discussion Thread 3
Post by: Llian Rhydderch on 02/21/2015 06:21 AM
No, the MCT doesn't have to carry a crew. What MCT does imply to me is 'return trip'. If it's going to fly back it needs fuel. If you're going to make fuel you need power, hence my comment.

I agree with you on the need for demo mission(s) to validate ISRU in advance. I think this can/should/will be done with pre-MCT hardware, flown on a FH. Once you have that fuel, it can the be purposed for returning the first MCT.

Perhaps what's really being asked here is: will SpaceX's architecture include one-way landing vehicles (habs in Mars Direct), and should we consider those vehicles MCTs?

The design for MCT will certainly be for a returnable craft, based on all that Musk has said.

However, that does not imply that 100% of all MCTs ever built will ply the two-way trade routes to Mars.

Some early MCTs are quite likely to remain on Mars as Terran-manufactured storage tanks, or to contain the purpose-built equipment for the collection and refinement of the requisite Methane and LOX for the return trip, or for the robots to set it all up.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: guckyfan on 02/21/2015 06:28 AM
The design for MCT will certainly be for a returnable craft, based on all that Musk has said.

However, that does not imply that 100% of all MCTs ever built will ply the two-way trade routes to Mars.

Some early MCTs are quite likely to remain on Mars as Terran-manufactured storage tanks, or to contain the purpose-built equipment for the collection and refinement of the requisite Methane and LOX for the return trip, or for the robots to set it all up.

I agree 100%. MCT including cargo will be designed reusable but no need to be dogmatic about it and expect even the first ever landed MCT back.

Title: Re: MCT Speculation and Discussion Thread 3
Post by: BobHk on 02/21/2015 01:25 PM
@BobHk

It is a very interesting topic. But this is not the thread for it. There are threads on this in the Mars section.

So the DESIGN of the MCT doesn't require the MCT to survive, even without a crew?  Speculation without basis in reality is a farce.  The power systems will require cost and mass savings in every other part of the craft impacting its design. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: dglow on 02/21/2015 05:36 PM
The design for MCT will certainly be for a returnable craft, based on all that Musk has said.

However, that does not imply that 100% of all MCTs ever built will ply the two-way trade routes to Mars.

Some early MCTs are quite likely to remain on Mars as Terran-manufactured storage tanks, or to contain the purpose-built equipment for the collection and refinement of the requisite Methane and LOX for the return trip, or for the robots to set it all up.

I agree 100%. MCT including cargo will be designed reusable but no need to be dogmatic about it and expect even the first ever landed MCT back.

Okay. It sounds like MCT, as discussed here, is a catch-all vehicle, regardless of whether it remains planted on Mars or taxis back and forth to Earth.

In that case, let's avoid the world 'reusable' and opt for more specificity: 'reflown' (taxi), 'repurposed' (prop factory, hab), etc.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Llian Rhydderch on 02/21/2015 06:03 PM
The design for MCT will certainly be for a returnable craft, based on all that Musk has said.

However, that does not imply that 100% of all MCTs ever built will ply the two-way trade routes to Mars.

Some early MCTs are quite likely to remain on Mars as Terran-manufactured storage tanks, or to contain the purpose-built equipment for the collection and refinement of the requisite Methane and LOX for the return trip, or for the robots to set it all up.

I agree 100%. MCT including cargo will be designed reusable but no need to be dogmatic about it and expect even the first ever landed MCT back.

Okay. It sounds like MCT, as discussed here, is a catch-all vehicle, regardless of whether it remains planted on Mars or taxis back and forth to Earth.

In that case, let's avoid the world 'reusable' and opt for more specificity: 'reflown' (taxi), 'repurposed' (prop factory, hab), etc.

Yeah, I think "MCT" as discussed here is the next in-space vehicle for SpaceX, to be launched on the BFR with Raptor methalox engines, which is capable of all of Earth launch, Mars transit, Mars EDL, Mars launch and Earth reentry, and certainly a number of other missions if needed.

But since SpaceX tends to optimize for cost, it makes sense that within that one overall design--qualified to reliably do a number of space transport tasks, including the transport of carbon-based lifeforms--they will have some variations to allow that one expensive-to-develop spacecraft to have multiple uses beyond the generic human transporter mission.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: MikeAtkinson on 02/21/2015 06:36 PM
The design for MCT will certainly be for a returnable craft, based on all that Musk has said.

However, that does not imply that 100% of all MCTs ever built will ply the two-way trade routes to Mars.

Some early MCTs are quite likely to remain on Mars as Terran-manufactured storage tanks, or to contain the purpose-built equipment for the collection and refinement of the requisite Methane and LOX for the return trip, or for the robots to set it all up.

I agree 100%. MCT including cargo will be designed reusable but no need to be dogmatic about it and expect even the first ever landed MCT back.

Okay. It sounds like MCT, as discussed here, is a catch-all vehicle, regardless of whether it remains planted on Mars or taxis back and forth to Earth.

In that case, let's avoid the world 'reusable' and opt for more specificity: 'reflown' (taxi), 'repurposed' (prop factory, hab), etc.

Dragon was designed for reuse, none have been reused yet. The Dragon has evolved in many significant ways.

F9 v1.1 was designed for flyback, landing and reuse. That has not occurred yet either. The F9 has evolved in the light of experience and as things in the original design have been implemented.

MCT will in my opinion be designed from the start to be flown back from Mars and reused. But the first few MCT may not be returned to Earth, and probably won't be reused. Just like Dragon and F9 the MCT will evolve as real data on performance is obtained and features are implemented.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: mikelepage on 02/23/2015 10:01 AM
Fairly sure solar power is the only solution that makes any sense for MCT in the near future.  Elon also put his opinion on record regarding fuel cells (I think it was regarding putting fuel cells in cars, but still): I think the quote was that he wished he could "stab that idea through the heart".

"Beamed power" not fuel cells :) (Specifically Earth beamed power compared to Solar which is NOT the same thing as power production on or near Mars I'll point out :) )
His main issue with fuel cells is the need for "fuel" to power them. The are an energy "storage" converter not a primary energy source. Nuclear and Solar are both primary sources.
On the other hand its been pointed out to him that you can (in most cases) re-crack the "exhaust" into fuel again but that comes right back to needing a "primary" power source to provide the energy to crack the components for the fuel cells :)

I'll point out here that while he may be right about terrestrial power beaming as a function of efficiency, (there's a lot of argument room in that using space based laser power beaming to terrestrial solar panels at night at the very least allows them to produce power when they normally wouldn't and delivery efficiency of over 90% has been demonstrated with tuned cells and laser :) ) the same does not necessarily apply to off-Earth use as getting you "primary power source" to your destination is often a determining factor rather than efficiency. For example a SEP propulsion stage that moves a cargo to High-Mars Orbit can then be re-purposed to provide primary and supplemental power for a Mars base or Colony either until a local power production and distribution grid can be set up or used in and of itself for as long as it can be maintained. It's "additive" in both economic moving of non-sensitive payload from Earth to Mars but also in providing power to surface operations when their "primary" supply (surface solar) is not operational for various reasons. (Sand storms or darkness for example using either microwave or laser beaming)

I suspect that at some point prior to actually going to Mars decisions will be made but not so "set-in-stone" that changes can't be made as technology advances :)
Agreed.  And wow did I get that wrong - that "stab through the heart" quote was the MIT interview right? should have looked it up :) I'm still fairly sure he's not a fan of fuel cells either, although now I'm not sure which interview I'm remembering.

I must admit I still don't see how MCT works without some component of it remaining in Mars orbit so I wouldn't be completely surprised to see space-based solar power beamed to a Mars base.  I'm expecting SpaceX will probably be the first to deploy a Mars satellite constellation for communication purposes, so maybe these satellites will be dual-purpose communication/energy (assuming the beaming technology can be demonstrated in the capcities needed before MCT goes). 

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I'm probably going to get roasted for bringing this up again (though I don't know why - this is a speculation & discussion thread after all), but I think it's fair to say that you obviously need to develop new techniques for unfurling solar panels that large, and that whatever technology you end up using to unfurl solar panels that large could surely be designed to work just as well for unfurling the lattice you need to implement spin gravity.  I'm calling it a lattice rather than a tether because any lattice suitable for supporting a solar panel array that size would have to be wide/stiff enough to address some of the same resonances which would make a simple tether problematic.  If the solar array designed to double as a lattice for spin gravity, you would have a way to generate the necessary energy as well as the option of full gravity.  Two crew modules, attached through a 1000x33m solar array lattice, gives 1 x g at 1.3rpm.  That solar array/lattice could potentially be launched separately, with the thin film solar cell component weighing as little as 8 tons (according to google, 0.25-1kg per m2 is the current weight range on thin film panels, though that will probably be halved again before MCT launches).

*retreats to a safe distance*.

Don't think you'll get roasted... Probably only lightly singed at the most :)

Actually the pattern I've been seeing is the assumption that the solar panels will be "simply" rolled out onto the ground in the needed acreage and no planning or assumption of any extensive support or structure involved.

The thing is you are not going to need the amount of power in transit that you'll need on arrival so the in-space array will be very different from the on-Mars equipment I'm thinking.

Randy

Out of curiosity why do you think MCT is going to consume more power upon arrival than during transit?  Surely the power use is proportional to the number of humans on board?

Perhaps the solar array lattice will be repurposed to be the space based solar power system around Mars upon arrival.  The dual MCTs undock from it and land on Mars, while the lattice moves via SEP to a geostationary orbit above the ground base such that it can provide 25h solar power to the base at night-time (incline the orbit such that it is never eclipsed by Mars itself).  MCTs which come back to Earth empty leave their solar arrays behind, while those which are crewed on the return trip are required to rendezvous with the array in orbit before beginning their trip.

If the solar array designed to double as a lattice for spin gravity, you would have a way to generate the necessary energy as well as the option of full gravity.  Two crew modules, attached through a 1000x33m solar array lattice, gives 1 x g at 1.3rpm.

Interesting concept.  But if you're going to do spin gravity, design for 0.4g.  1g for people going to Mars is overkill.

Depends if 0.4g is enough though, doesn't it?  Maybe it is, maybe it isn't, but I find it hard to believe that you can just ignore a couple of billion years of evolution at 1g without some serious long-term consequences.  It's not like the design constraints for making a 1g system are all that different from making a 0.4g system though, so why not preserve that ability to produce a 1g environment then gradually ramp it down?

Afterthought: I think this thread will get much more interesting once EM announces something.  I know how I would approach the problem, but I'm not the one with truckloads of cash.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: RanulfC on 02/24/2015 06:58 PM
Just an FYI, but regenerative fuel cells aren't really lighter weight than the best lithium batteries, but they do have atrocious round-trip efficiency by comparison. Doesn't make sense. Just use a battery.

I "think" the whole idea of MCT and Fuel Cells came up with a mention of a type that can use methane/LOX that got carried over from another ISRU conversation. The "connection" of course being "methane" was mentioned at some point, by someone, in both :)

I really don't see them being part of the SpaceX design philosophy due to the need for "fuel" in the first place. Colony design, probably, MCT use? Doubtful at best.

Randy
Title: Re: MCT Speculation and Discussion Thread 3
Post by: RanulfC on 02/24/2015 07:59 PM
Agreed.  And wow did I get that wrong - that "stab through the heart" quote was the MIT interview right? should have looked it up :) I'm still fairly sure he's not a fan of fuel cells either, although now I'm not sure which interview I'm remembering.

To be honest I've seen quite a number of "quotes" around, (not so much here but around the web) where Musk is supposed to have made the "stab-through-the-heart" comment relating to a BUNCH of different tech concepts but the only one I've actually seen from Musk is the Terrestrial beamed power concept.

I don't have a quote but I think you're right he's mentioned his preference for batteries over fuel cells somewhere.

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I must admit I still don't see how MCT works without some component of it remaining in Mars orbit so I wouldn't be completely surprised to see space-based solar power beamed to a Mars base.  I'm expecting SpaceX will probably be the first to deploy a Mars satellite constellation for communication purposes, so maybe these satellites will be dual-purpose communication/energy (assuming the beaming technology can be demonstrated in the capcities needed before MCT goes).

-Musk "said" that he didn't see an issue with "landing the whole thing" so it's an article of faith that's going to be the "baseline" design :)
Having said that I'll mention that I pointed out a "fully-reusable" but only landing what you need concept was suggested as an advanced Mars flyby mission earlier called "FLEM": http://www.wired.com/2014/01/to-mars-by-flyby-landing-excursion-mode-flem-1966/ (And I'm advocating a change of name as of this time. Suggest maybe "Landing Excursion Mode with Flyby" or LEMF :) )

-I highly suspect that Musk's dislike of Terrestrial Power Beaming is going to cause a significant "blind-spot" for application on Mars barring some compelling reason for doing so such as a SEP Mars propulsion stage and the various "PoWWoW" (PoWWoW: Power Without Wires, http://www.researchgate.net/publication/23857078_POwer_WithOut_Wire_(POWOW)_A_SEP_Concept_for_Space_Exploration, http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20020030127.pdf) concepts might come together. (I may have already pointed out that SpaceX tends to inherit Musk's bias and assumptions by default :) )

-Communications satellites are not going to have enough solar panels to allow power beaming unless they are HUGE. A more applicable duel-use would be Mars SEP for unmanned cargo or an MCT SEP stage per above.

-This might actually be more applicable to Mars Exploration and/or Mars Colony operations than Mars Colonial Transport operations.

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Out of curiosity why do you think MCT is going to consume more power upon arrival than during transit?  Surely the power use is proportional to the number of humans on board?

Myself I don't as I think the MCT is NOT going to be providing its own ISRU processing but be dependent on that being provided by the "colony" or organizational operations that it is supporting. However, the "initial" or precursor MCT flights will require either pre-positioned tankers or some other method of pre-flight propellant positioning OR (which is the general assumption here) it will be required to provide its own ISRU which will require higher power production than during flight.

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Perhaps the solar array lattice will be repurposed to be the space based solar power system around Mars upon arrival.  The dual MCTs undock from it and land on Mars, while the lattice moves via SEP to a geostationary orbit above the ground base such that it can provide 25h solar power to the base at night-time (incline the orbit such that it is never eclipsed by Mars itself).  MCTs which come back to Earth empty leave their solar arrays behind, while those which are crewed on the return trip are required to rendezvous with the array in orbit before beginning their trip.

As I noted the "assumption" is that everything that goes to Mars will be landed there so the idea that a "component" will be left in orbit doesn't get much traction around here. "I" on the other hand don't see a problem with it as it builds up capability with each flight. However I doubt that it would work leaving the arrays without some sort of "in-place" structure and power distribution system such as an orbital module/station/something to integrate them with each flight.

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Afterthought: I think this thread will get much more interesting once EM announces something.  I know how I would approach the problem, but I'm not the one with truckloads of cash.

"My" sneaky suspicion is that EM or someone actually monitors these forums and I will not at all be surprised if some concepts and ideas from here end up BEING announced "from the horses mouth" as it were :)
Not going to complain at ALL if some of my ideas end up being "borrowed" to get the job done. Not at ALL ;)

Randy
Title: Re: MCT Speculation and Discussion Thread 3
Post by: RanulfC on 02/24/2015 08:02 PM
Yes, from comments by Elon, I think we are vastly underestimating the roll of robots/androids in the Mars campaign.

I don't recall him saying anything about cell phone service on Mars but I suppose that's going to be a priority ;)


Randy
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Norm38 on 02/25/2015 03:17 AM
Depends if 0.4g is enough though, doesn't it?  Maybe it is, maybe it isn't, but I find it hard to believe that you can just ignore a couple of billion years of evolution at 1g without some serious long-term consequences.  It's not like the design constraints for making a 1g system are all that different from making a 0.4g system though, so why not preserve that ability to produce a 1g environment then gradually ramp it down?

On the way to spend considerable time in a 0.4g field is kind of late to find out 0.4g isn't enough. What do you do if it isn't?  Turn the ship around?
If people are that worried about it then we need to build a giant hamster wheel in LEO and put people on it for a few years before we even think about Mars.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: mikelepage on 02/26/2015 11:38 AM
Depends if 0.4g is enough though, doesn't it?  Maybe it is, maybe it isn't, but I find it hard to believe that you can just ignore a couple of billion years of evolution at 1g without some serious long-term consequences.  It's not like the design constraints for making a 1g system are all that different from making a 0.4g system though, so why not preserve that ability to produce a 1g environment then gradually ramp it down?

On the way to spend considerable time in a 0.4g field is kind of late to find out 0.4g isn't enough. What do you do if it isn't?  Turn the ship around?
If people are that worried about it then we need to build a giant hamster wheel in LEO and put people on it for a few years before we even think about Mars.

Hence, this thread:
http://forum.nasaspaceflight.com/index.php?topic=34036.0
Title: Re: MCT Speculation and Discussion Thread 3
Post by: mikelepage on 02/26/2015 01:32 PM
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Perhaps the solar array lattice will be repurposed to be the space based solar power system around Mars upon arrival.  The dual MCTs undock from it and land on Mars, while the lattice moves via SEP to a geostationary orbit above the ground base such that it can provide 25h solar power to the base at night-time (incline the orbit such that it is never eclipsed by Mars itself).  MCTs which come back to Earth empty leave their solar arrays behind, while those which are crewed on the return trip are required to rendezvous with the array in orbit before beginning their trip.

As I noted the "assumption" is that everything that goes to Mars will be landed there so the idea that a "component" will be left in orbit doesn't get much traction around here. "I" on the other hand don't see a problem with it as it builds up capability with each flight. However I doubt that it would work leaving the arrays without some sort of "in-place" structure and power distribution system such as an orbital module/station/something to integrate them with each flight.

If EM cared too much about what other people think, he'd still be trying to get funding for his supercapacitor research.  He's a pragmatist visionary (i.e. one that actually executes on a vision with compromises instead of holding out for an ideal solution).  If it turns out that it's easier to leave something in orbit, then he will.  I've always interpreted the "assumption" of MCT as being that everything with crew that goes to Mars will be landed (or have a fly by in case of abort) - but obviously the communication satellites have to be dropped off in orbit somehow, so I don't think it's a big stretch to suppose that other things will be left in orbit too.

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Afterthought: I think this thread will get much more interesting once EM announces something.  I know how I would approach the problem, but I'm not the one with truckloads of cash.

"My" sneaky suspicion is that EM or someone actually monitors these forums and I will not at all be surprised if some concepts and ideas from here end up BEING announced "from the horses mouth" as it were :)
Not going to complain at ALL if some of my ideas end up being "borrowed" to get the job done. Not at ALL ;)

Randy

Haha okay.  Me personally, I'm happy to be paid off with a Model S. P85 preferably.  My lips are sealed ;)
Title: Re: MCT Speculation and Discussion Thread 3
Post by: CJ on 02/26/2015 09:46 PM

-Musk "said" that he didn't see an issue with "landing the whole thing" so it's an article of faith that's going to be the "baseline" design :)
Having said that I'll mention that I pointed out a "fully-reusable" but only landing what you need concept was suggested as an advanced Mars flyby mission earlier called "FLEM": http://www.wired.com/2014/01/to-mars-by-flyby-landing-excursion-mode-flem-1966/ (And I'm advocating a change of name as of this time. Suggest maybe "Landing Excursion Mode with Flyby" or LEMF :) )

Thanks for the link on FLEM. Landing only what you need was also used for the Apollo missions. The early mission concepts called for landing the entire stack on the moon (that's why the SM engine was so oversized). It would have taken a Nova-class launcher to do it on one launch, or two Saturn 5 launches with earth-orbit rendezvous. The lunar-orbit rendezvous plan (the one actually used) was adopted because it would use a single Saturn 5 launch. The others needed one heck of a lot more Delta/V, hence much more upmass. And that's why I don't accept that landing the entire interplanetary part of MCT on Mars makes sense, save for, perhaps, one-way cargo missions. At the very least, I'd expect it to leave its massive solar array and even more massive heat-dissipation array in Mars orbit. IMHO, a  modular system just makes more sense, delta/V wise and cost wise. (And SpaceX optimizes for cost) 

Someone please correct me if I'm wrong, but the only place I've seen Musk's "land the whole thing" comment is in a 2012 interview, the same one where he also mentioned being five to six years away from a fully reusable F9 (which would include the second stage).

http://www.space.com/18596-mars-colony-spacex-elon-musk.html

Is there anything more recent? If not, why should we assume that landing the entire interplanetary part of MCT on Mars is any more cast-in-concrete than a reusable F9 second stage?

Secondly, has Musk, or any SpaceX official spokesperson, ever said anything about landing all of the interplanetary part of MCT on Earth? That's the aspect of the popular-in-this-thread design that I find the hardest to fathom.



Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lars-J on 02/26/2015 09:50 PM
Someone please correct me if I'm wrong, but the only place I've seen Musk's "land the whole thing" comment is in a 2012 interview, the same one where he also mentioned being five to six years away from a fully reusable F9 (which would include the second stage).

http://www.space.com/18596-mars-colony-spacex-elon-musk.html

Is there anything more recent? If not, why should we assume that landing the entire interplanetary part of MCT on Mars is any more cast-in-concrete than a reusable F9 second stage?

Unless something is said that contradicts it, then - yes - I think it should be a baseline of the discussion.

Otherwise you can just throw out ANY statement and just argue for your own person pet Mars architecture. And there is enough of that going on here. We have a Mars exploration sub-forum if you want to argue for something else, you can find it here: http://forum.nasaspaceflight.com/index.php?board=21.0

Secondly, has Musk, or any SpaceX official spokesperson, ever said anything about landing all of the interplanetary part of MCT on Earth? That's the aspect of the popular-in-this-thread design that I find the hardest to fathom.

That is based more on an assumption that MCT would be based on a reusable upper stage. Delta-V requirements are similar, and both would need to handle atmospheric landing and ascent.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: CJ on 02/27/2015 01:17 AM
Someone please correct me if I'm wrong, but the only place I've seen Musk's "land the whole thing" comment is in a 2012 interview, the same one where he also mentioned being five to six years away from a fully reusable F9 (which would include the second stage).

http://www.space.com/18596-mars-colony-spacex-elon-musk.html

Is there anything more recent? If not, why should we assume that landing the entire interplanetary part of MCT on Mars is any more cast-in-concrete than a reusable F9 second stage?

Unless something is said that contradicts it, then - yes - I think it should be a baseline of the discussion.

Otherwise you can just throw out ANY statement and just argue for your own person pet Mars architecture. And there is enough of that going on here. We have a Mars exploration sub-forum if you want to argue for something else, you can find it here: http://forum.nasaspaceflight.com/index.php?board=21.0

Ummm, based on those criteria, we should have taken as the basis for DSCVR mission discussions SpaceX's announcement that the second stage of the DSCVR mission would be disposed of in the sun? (Which would take about a 60kps delta/v post spacecraft sep). It also seems commonplace here to assume that the 100 person capacity is something for the far future, in spite of SpaceX comments to the contrary. What I'm saying is that you can't have it both ways.

I think it's quite reasonable to raise questions about issues with MCT design, because whatever design SpaceX has is necessarily fluid, even in basic concept, much as was Apollo in its early development phase. If something about what's assumed in this thread doesn't make sense, why not question it? This is, after all, a discussion thread.
Secondly, has Musk, or any SpaceX official spokesperson, ever said anything about landing all of the interplanetary part of MCT on Earth? That's the aspect of the popular-in-this-thread design that I find the hardest to fathom.

That is based more on an assumption that MCT would be based on a reusable upper stage. Delta-V requirements are similar, and both would need to handle atmospheric landing and ascent.

That's part of why I find it implausible; the delta/v requirements, when views against mass ratios. A BFR reusable upper stage, like any LV upper stage, has to be optimized for its purpose, which is launch delta/v. That means a very low ratio of dry mass to prop, much like the F9 upper stage, which is about 95% prop. Recovery will of course add mass, but nowhere near as much mass as making the upper stage into a spacecraft capable of manned landings on both Mars and Earth, as well as the interplanetary journey.  The upper stage of BFR simply has to (assuming it's a two stage and not a three stage vehicle) provide the lion's share of launch delta/v, on the order of 6kps. To do that, it has to have a low dry mass fraction. Even without payload, it'd have to have a dry mass/wet mass ratio (assuming a 362 ISP) of 82%. (82% of the stage mass would be prop). Every bit of capacity for useful upmass (be it a payload, base dry mass, recovery mass, or MCT structure) has to come out of that remaining 18%. That'd include the TPS needed to do an interplanetary-velocity reentry with considerable added mass, a very different thing than the orbital velocity very lightweight optimized second stage (the one they'll need to build anyway). Given the very mass-intensive requirements of an interplanetary vehicle (power, life support, heat radiators, consumables, living space, etc)  you simply cannot shoehorn all that, plus crew and/or cargo, into that 18%. The requirements for a launch vehicle reusable upper stage and a manned interplanetary spacecraft are just too different for the one-size-fits-all approach to work.

There's also the issue of the most important number in spaceflight, and it's not ISP, and it's certainly not thrust. It's the number preceded by the dollar sign, and the one-vehicle-does-everything approach, even if it proves possible, would be insanely expensive. If there's a more cost effective approach to MCT, that'll be the route SpaceX chooses, if their past is any guide to their future.

 
Edit: fixed quotes

   

 

 

   
Title: Re: MCT Speculation and Discussion Thread 3
Post by: CyclerPilot on 02/27/2015 02:28 AM
That's part of why I find it implausible; the delta/v requirements, when views against mass ratios. A BFR reusable upper stage, like any LV upper stage, has to be optimized for its purpose, which is launch delta/v. That means a very low ratio of dry mass to prop, much like the F9 upper stage, which is about 95% prop. Recovery will of course add mass, but nowhere near as much mass as making the upper stage into a spacecraft capable of manned landings on both Mars and Earth, as well as the interplanetary journey.  The upper stage of BFR simply has to (assuming it's a two stage and not a three stage vehicle) provide the lion's share of launch delta/v, on the order of 6kps. To do that, it has to have a low dry mass fraction. Even without payload, it'd have to have a dry mass/wet mass ratio (assuming a 362 ISP) of 82%. (82% of the stage mass would be prop). Every bit of capacity for useful upmass (be it a payload, base dry mass, recovery mass, or MCT structure) has to come out of that remaining 18%. That'd include the TPS needed to do an interplanetary-velocity reentry with considerable added mass, a very different thing than the orbital velocity very lightweight optimized second stage (the one they'll need to build anyway). Given the very mass-intensive requirements of an interplanetary vehicle (power, life support, heat radiators, consumables, living space, etc)  you simply cannot shoehorn all that, plus crew and/or cargo, into that 18%. The requirements for a launch vehicle reusable upper stage and a manned interplanetary spacecraft are just too different for the one-size-fits-all approach to work.

There's also the issue of the most important number in spaceflight, and it's not ISP, and it's certainly not thrust. It's the number preceded by the dollar sign, and the one-vehicle-does-everything approach, even if it proves possible, would be insanely expensive. If there's a more cost effective approach to MCT, that'll be the route SpaceX chooses, if their past is any guide to their future.

I think the MCT will need to have that 18ish percent dry mass whether its a 2nd or 3rd stage.  The mars launch and TEI is the most dV intensive leg in any case (8.5 km/s).  Even with the greatly reduced cargo/crew mass, the prop tanks need to be sized for this burn, not the TMI or the S2 burns.  (Although the S2 burn is close, which is why most designs have MCT/S2 combined).

I do agree with you that that tiny dry mass has to do A LOT.  Something has to give.  To make the numbers work, a lot of optimistic assumptions have to be made.  Advances have to made in almost all aspects of spacecraft design relative to state of the art (ISS) to trim dry mass.  SpaceX has demonstrated or is working on many of these (engine t/w, friction stir welding aluminum, pica-X, and most importantly: cost)

Like most, I think the crews will be much less at first (probably government chartered).  I used to be firmly in the combined S2 camp, but now I see S3 MCTs as viable with a smaller Raptor.  There are some merits to both ways and I can't wait until SpaceX reveals their design later this year.

Edit-quotes messed up
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lars-J on 02/27/2015 02:45 AM
Fix yer quotes! :)

I think it's quite reasonable to raise questions about issues with MCT design, because whatever design SpaceX has is necessarily fluid, even in basic concept, much as was Apollo in its early development phase. If something about what's assumed in this thread doesn't make sense, why not question it? This is, after all, a discussion thread.

There has to be a starting point for a discussion, and I see the most unique aspect of the MCT plan being this very concept - "land the whole thing" - as something that shouldn't just be dismissed too easily.

You obviously disagree. But is there a statement about "MCT" that *you* consider worthy of being a frame for the discussion? A reliable statement? Or do you think that Musk is just trolling us by throwing out random ideas?

Secondly, has Musk, or any SpaceX official spokesperson, ever said anything about landing all of the interplanetary part of MCT on Earth? That's the aspect of the popular-in-this-thread design that I find the hardest to fathom.

That is based more on an assumption that MCT would be based on a reusable upper stage. Delta-V requirements are similar, and both would need to handle atmospheric landing and ascent.

That's part of why I find it implausible; the delta/v requirements, when views against mass ratios. A BFR reusable upper stage, like any LV upper stage, has to be optimized for its purpose, which is launch delta/v. That means a very low ratio of dry mass to prop, much like the F9 upper stage, which is about 95% prop. Recovery will of course add mass, but nowhere near as much mass as making the upper stage into a spacecraft capable of manned landings on both Mars and Earth, as well as the interplanetary journey.  The upper stage of BFR simply has to (assuming it's a two stage and not a three stage vehicle) provide the lion's share of launch delta/v, on the order of 6kps. To do that, it has to have a low dry mass fraction. Even without payload, it'd have to have a dry mass/wet mass ratio (assuming a 362 ISP) of 82%. (82% of the stage mass would be prop). Every bit of capacity for useful upmass (be it a payload, base dry mass, recovery mass, or MCT structure) has to come out of that remaining 18%. That'd include the TPS needed to do an interplanetary-velocity reentry with considerable added mass, a very different thing than the orbital velocity very lightweight optimized second stage (the one they'll need to build anyway). Given the very mass-intensive requirements of an interplanetary vehicle (power, life support, heat radiators, consumables, living space, etc)  you simply cannot shoehorn all that, plus crew and/or cargo, into that 18%. The requirements for a launch vehicle reusable upper stage and a manned interplanetary spacecraft are just too different for the one-size-fits-all approach to work.

Indeed, the performance needed is significant. But this is also the case for a Mars SSTO -  a *minimum* of 4.1 km/s of delta-V is needed, and you would likely need at least 5km/s.

And I don't think anyone has claimed that the BFR upper stage would exactly match the "MCT". Merely that one would form the basis for the other. It would be its very nature be enormous with massive propellant tanks compared to its payload/crew volume. No one disputes that.

So let me repeat. A reusable BFR upper stage would not be the MCT. But... Having built one, it would be a good starting point for a Mars landing/ascent craft. And so on...
Title: Re: MCT Speculation and Discussion Thread 3
Post by: CJ on 02/27/2015 06:26 AM
Fix yer quotes! :)

oops, sorry. I'll go edit that.  :)

There has to be a starting point for a discussion, and I see the most unique aspect of the MCT plan being this very concept - "land the whole thing" - as something that shouldn't just be dismissed too easily.

You obviously disagree. But is there a statement about "MCT" that *you* consider worthy of being a frame for the discussion? A reliable statement? Or do you think that Musk is just trolling us by throwing out random ideas?

IMHO, a valid discussion starts with what we know, based on multiple statements; MCT is a transportation system for Mars. Second, it departs from earth orbit after fueling. And, most importantly, a valid discussion has to take into account the numbers - delta/v, ISP, mass ratios, and cost. And, IMHO, Elon Musk is a human being, and as such might not phrase every extemporaneous utterance with perfection, so IMHO something like "land the whole thing" might refer to the core of an interplanetary craft, rather than everything that's ever been attached. Might. It's also IMHO okay to make assumptions such as that, or that MCT lands on Earth. It's also equally okay to question such assumptions.

To be clear, I'm not dismissing "land the whole thing on Mars", I'm merely questioning it, or more exactly, the interpretation of it. It's landing the whole thing on both Earth and Mars that I find utterly implausible - which is why I was curious if they'd ever said such a thing. Even if they had, I'd be very highly skeptical, due to the physics.   

I'm not well-versed in SpaceX's announcements, which is why I tend to ask questions about what they've said.   

And no matter how definitive the statement, if it looks to me like it contradicts what's possible, I'll question it (just as I, and everyone else, did regarding disposing of the DSCOVR upper stage in the sun. That was both a definitive, clear statement, and also obviously impossible). I don't think they misstate things on purpose, but I do think they are human and thus occasionally make mistakes. Also, their plans change over time due to ongoing leaning and engineering reality (I'm merely implying that they're sane, not nefarious), so I'm inclined to a take a statement made years ago with a bigger dose of salt than I am one made yesterday.

Indeed, the performance needed is significant. But this is also the case for a Mars SSTO -  a *minimum* of 4.1 km/s of delta-V is needed, and you would likely need at least 5km/s.

And I don't think anyone has claimed that the BFR upper stage would exactly match the "MCT". Merely that one would form the basis for the other. It would be its very nature be enormous with massive propellant tanks compared to its payload/crew volume. No one disputes that.

So let me repeat. A reusable BFR upper stage would not be the MCT. But... Having built one, it would be a good starting point for a Mars landing/ascent craft. And so on...

Hrmmm. A BFR upper stage as a starting point? I do agree that it could well be an ideal one for Mars landing/ascent, because the F9 upper stage would be (except for the problem of getting RP1 ISRU). 

I'm perplexed by some of the delta/v numbers I'm seeing for launch from Mars. I may well be wrong (someone please correct me if so) but I came up with quite different numbers for Mars SSTO. I started with Earth LEO figures. LEO orbital velocity is about 7.8 kps, but launch takes about 9.4 kps, the difference being grav losses, air resistance, and engine back pressure during ascent - especially the early phase of ascent. So, the delta/v penalty is about (it varies a bit due to trajectory and vehicle design)  1.6 kps. Low Mars orbital velocity is 2.138 kps at 300 km altitude. Aerodynamic losses and engine back pressure losses should be negligible. That leaves mainly grav losses. An ascent from Mars, like the Apollo ascents from the moon, would use a less angled trajectory - tipover would occur almost instantly. Grav losses should be far less than a launch from earth, due to the much reduced ascent time to reach orbit, and also the far lower gravity. Yet, the delta/v penalty seems to be being assumed as being the same as it would be during an earth launch? That makes no sense to me. It's as if people are basing their delta/v penalty calcs on just on burn time * a loss factor, which is okay on Earth, but definitely not okay on Mars (assuming they're using the same formula). 
I'm ballparking the grav losses of a launch that averages 4 G from Mars to be around 420MS (someone please correct me) so total delta/v penalty for Mars to LMO at around 500 MS, including steering losses. That gives me a SSTO Mars delta/v of 2.638 kps. That's a lot different from the 4 or higher I see quoted all over the place. However, either I'm wrong, or all the delta/V maps and a whole lot of other sources are wrong, and I find it rather implausible that I'm right in that case - so where did I go wrong? 




That's part of why I find it implausible; the delta/v requirements, when views against mass ratios. A BFR reusable upper stage, like any LV upper stage, has to be optimized for its purpose, which is launch delta/v. That means a very low ratio of dry mass to prop, much like the F9 upper stage, which is about 95% prop. Recovery will of course add mass, but nowhere near as much mass as making the upper stage into a spacecraft capable of manned landings on both Mars and Earth, as well as the interplanetary journey.  The upper stage of BFR simply has to (assuming it's a two stage and not a three stage vehicle) provide the lion's share of launch delta/v, on the order of 6kps. To do that, it has to have a low dry mass fraction. Even without payload, it'd have to have a dry mass/wet mass ratio (assuming a 362 ISP) of 82%. (82% of the stage mass would be prop). Every bit of capacity for useful upmass (be it a payload, base dry mass, recovery mass, or MCT structure) has to come out of that remaining 18%. That'd include the TPS needed to do an interplanetary-velocity reentry with considerable added mass, a very different thing than the orbital velocity very lightweight optimized second stage (the one they'll need to build anyway). Given the very mass-intensive requirements of an interplanetary vehicle (power, life support, heat radiators, consumables, living space, etc)  you simply cannot shoehorn all that, plus crew and/or cargo, into that 18%. The requirements for a launch vehicle reusable upper stage and a manned interplanetary spacecraft are just too different for the one-size-fits-all approach to work.

There's also the issue of the most important number in spaceflight, and it's not ISP, and it's certainly not thrust. It's the number preceded by the dollar sign, and the one-vehicle-does-everything approach, even if it proves possible, would be insanely expensive. If there's a more cost effective approach to MCT, that'll be the route SpaceX chooses, if their past is any guide to their future.

I think the MCT will need to have that 18ish percent dry mass whether its a 2nd or 3rd stage.  The mars launch and TEI is the most dV intensive leg in any case (8.5 km/s).  Even with the greatly reduced cargo/crew mass, the prop tanks need to be sized for this burn, not the TMI or the S2 burns.  (Although the S2 burn is close, which is why most designs have MCT/S2 combined).

I do agree with you that that tiny dry mass has to do A LOT.  Something has to give.  To make the numbers work, a lot of optimistic assumptions have to be made.  Advances have to made in almost all aspects of spacecraft design relative to state of the art (ISS) to trim dry mass.  SpaceX has demonstrated or is working on many of these (engine t/w, friction stir welding aluminum, pica-X, and most importantly: cost)

Like most, I think the crews will be much less at first (probably government chartered).  I used to be firmly in the combined S2 camp, but now I see S3 MCTs as viable with a smaller Raptor.  There are some merits to both ways and I can't wait until SpaceX reveals their design later this year.

Edit-quotes messed up

I'm very eager for the reveal too. To be honest, I hope I'm wrong and the one-vehicle-does-it-all approach is viable, both physically and fiscally.

8.1 KPS for Mars surface to earth? that's darn near an earth launch SSTO of about 9.4 kps. I was assuming 5.91 kps delta/v needed for Mars surface through the TEI (Am I wrong in my numbers?), and that's assuming a less than ideal window, plus a small burn upon earth arrival. A F9 upper stage could do it, with as much or more payload as an all-up F9 can put in LEO. But 8.1 KPS at Raptor's postulated 362 ISP? You're looking at a vehicle thats about 90% fuel, leaving 10% for, well, everything. I thought the entire vehicle landing on Mars was doubtful at a needed 5.91 kps for departure, but if it's 8.1, that's vastly worse. Anyway, no matter which, Mars is a rather deep grav well, which is why I was thinking it'd make more sense to leave the mass that can stay in orbit, in orbit.

As for cost, look at how much (and how long) it's taking to go from Dragon 1 to Dragon 2. The R&D on something that's truly cutting-edge and the size of an airliner, and has to handle reentry and landing on two worlds, would be literally astronomical, if its even possible.

Title: Re: MCT Speculation and Discussion Thread 3
Post by: guckyfan on 02/27/2015 07:14 AM
Anyway, no matter which, Mars is a rather deep grav well, which is why I was thinking it'd make more sense to leave the mass that can stay in orbit, in orbit.

I don't want to reopen that discussion all over again. The one problem I see with that argument is: How do you propose to refuel the vehicle in Mars orbit for the flight back to earth?

My opinion is once the problem of landing a second stage back on earth is solved, landing MCT on both Mars and back on earth is the easiest, most straightforward solution. If that problem is not solved, everything else is moot anyway.

Title: Re: MCT Speculation and Discussion Thread 3
Post by: mikelepage on 02/27/2015 07:30 AM
Anyway, no matter which, Mars is a rather deep grav well, which is why I was thinking it'd make more sense to leave the mass that can stay in orbit, in orbit.

I don't want to reopen that discussion all over again. The one problem I see with that argument is: How do you propose to refuel the vehicle in Mars orbit for the flight back to earth?

My opinion is once the problem of landing a second stage back on earth is solved, landing MCT on both Mars and back on earth is the easiest, most straightforward solution. If that problem is not solved, everything else is moot anyway.

Interesting points.
Edit: Agreed that refueling anything in LMO complicates things.

Can I ask what you think about power supply then? Is it feasible to fold up a solar array (of the size required) so as to land with it at both destinations?  Or do you think there is a non-solar power solution in the works?

Title: Re: MCT Speculation and Discussion Thread 3
Post by: CJ on 02/27/2015 07:36 AM
Anyway, no matter which, Mars is a rather deep grav well, which is why I was thinking it'd make more sense to leave the mass that can stay in orbit, in orbit.

I don't want to reopen that discussion all over again. The one problem I see with that argument is: How do you propose to refuel the vehicle in Mars orbit for the flight back to earth?

My opinion is once the problem of landing a second stage back on earth is solved, landing MCT on both Mars and back on earth is the easiest, most straightforward solution. If that problem is not solved, everything else is moot anyway.

Sorry, I wasn't clear. I meant a modular design, so you'de leave just parts (solar arrays, heat radiators and coolant, habs, that sort of thing) in orbit. The vehicle core  could land on Mars, perhaps on an ascent-decent vehicle, or perhaps under its own power, and refuel. 

As for landing on Earth, Earth reentry, especially at interplanetary return velocities, is a very different thing to landing on Mars. Trying to design a single vehicle to handle multiple operating environments is very hard, and often results in performance issues. Amphibious cars come to mind, as do car/airplanes. It's also vastly different for an empty stage (extremely low mass to volume ratio) to a much denser, heavier spacecraft.  Just my opinion.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: The Amazing Catstronaut on 02/27/2015 07:36 AM
I don't want to reopen that discussion all over again. The one problem I see with that argument is: How do you propose to refuel the vehicle in Mars orbit for the flight back to earth?

My opinion is once the problem of landing a second stage back on earth is solved, landing MCT on both Mars and back on earth is the easiest, most straightforward solution. If that problem is not solved, everything else is moot anyway.

I suppose the advocates of leaving an orbital section in orbit are supposing that either some part of the crew or the craft (or both) isn't coming back with you; I.E, some of the flight hardware will end up going on a one-way trip. This probably has some basis since a heck of a lot of the proposed mars architectures of the past have mandated this as an necessity. In the example Musk has outlined, it's closer to optional.

I'm trying to figure out architectures where the return craft stays in orbit, without having to lug all your return fuel with you. Can it be done? Quite possibly, but I can't fathom it.

Edit:



Sorry, I wasn't clear. I meant a modular design, so you'de leave just parts (solar arrays, heat radiators and coolant, habs, that sort of thing) in orbit. The vehicle core  could land on Mars, perhaps on an ascent-decent vehicle, or perhaps under its own power, and refuel. 

As for landing on Earth, Earth reentry, especially at interplanetary return velocities, is a very different thing to landing on Mars. Trying to design a single vehicle to handle multiple operating environments is very hard, and often results in performance issues. Amphibious cars come to mind, as do car/airplanes. It's also vastly different for an empty stage (extremely low mass to volume ratio) to a much denser, heavier spacecraft.  Just my opinion.

Ahh, so you're saying the lander/MTC core would dock back up with the (mostly) interplanetary pertinent hardware once returning to mars orbit, then do all the pushing work to bring the whole spacecraft home?
Title: Re: MCT Speculation and Discussion Thread 3
Post by: CJ on 02/27/2015 07:55 AM


Sorry, I wasn't clear. I meant a modular design, so you'de leave just parts (solar arrays, heat radiators and coolant, habs, that sort of thing) in orbit. The vehicle core  could land on Mars, perhaps on an ascent-decent vehicle, or perhaps under its own power, and refuel. 

As for landing on Earth, Earth reentry, especially at interplanetary return velocities, is a very different thing to landing on Mars. Trying to design a single vehicle to handle multiple operating environments is very hard, and often results in performance issues. Amphibious cars come to mind, as do car/airplanes. It's also vastly different for an empty stage (extremely low mass to volume ratio) to a much denser, heavier spacecraft.  Just my opinion.

Ahh, so you're saying the lander/MTC core would dock back up with the (mostly) interplanetary pertinent hardware once returning to mars orbit, then do all the pushing work to bring the whole spacecraft home?

That's a guess of mine as to one possibility, which would save a lot of delta/v. However, sending the spacecraft home would mean LEO - I can't see it landing on Earth.

As to what kind of Mars orbit to leave the space-only hardware in, there are several possibilities. Leaving it in a high-energy orbit (the Martian equivalent of GTO) would save even more delta/v, but whether it's viable or not depends on vehicle performance issues.

However, if SEP is used, then it'd almost mandate leaving the SEP component in Mars orbit; it (plus the solar array) would mass quite a lot. 


Title: Re: MCT Speculation and Discussion Thread 3
Post by: JamesH on 02/27/2015 08:59 AM
I'd always wondered about the land everything comment, and just cannot see it (in my head, not done any numbers).

CJ's comments above match what I think - leave some stuff in orbit that you don't need on the ground. Solar arrays, comms gear, habitats, fuel tanks(?), SEP engines. Basically a frame work with a *big* lander to does the decent ascent. Maybe even other *non-returning* landers as well, satellites etc. Note, SEP could be used to keep orbital position.

On the ground the lander does what the lander does - discharge cargo etc. Then it refuels, returns to orbital stage, taking a load of extra fuel with it for the framework.

Non-returning landers would be permanent habitats, and designed as such. One way trip requires a different design approach. Or maybe one really big lander that splits up on the ground in to form a permanent hab plus a smaller ascent stage.

Point being, you don't want to take stuff down that is unused on the surface, then taken back up. That's a complete waste of energy. Also note that from a colonial approach the return lander does not need to be as big as the descent lander because it carrying fewer people.

Lots of options, but the ones that doesn't, to me, make sense, is one huge craft going up and down the gravity well.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: guckyfan on 02/27/2015 09:39 AM
Leaving habitats in orbit. You still need a smaller separate habitat to land people. You end up with two completely different designs for crew and cargo.

Leaving tanks in Mars orbit. How do they get refuelled? Tanks are lightweight and big volume. That helps with landing the whole thing.

Elon Musk keeps making the argument how important mass fraction is for reusability. Being able to disconnect and reconnect requires a lot of additional structural mass.

I don't see landing on Mars and on Earth so much different, once you go for vertical propulsive landing. Up to now landers are complex machines, think of the "minutes of terror" for Curiosity. Brake as much as you can with atmosphere then do the rest propulsively is a lot simpler. It does require fuel, that is true.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Ben the Space Brit on 02/27/2015 10:22 AM
I'm still thinking of a twin-module spacecraft (at least for the post-establishment crew and cargo transit to and from Mars).

My idea is a 10m-diameter aerospace craft optimised for a hybrid aerodynamic and propulsive EDL to Mars that can also do a somewhat inelegant 'flying brick' glide approach before a propulsive landing on Earth. If you wonder what it looks like, watch the old NASA Constellation DRA-5.0 video; I imagine MCT will look a lot like the landers proposed there.

There would be two distinct propulsion options available, depending on the mission. The MCTs would have Raptor-VACs, both for EDL at both ends of the mission as well as Mars ascent and orbital manoeuvring around Mars and cis-Lunar space. These would also be used for ROI in exploration-phase missions. There would also be a separate propulsion module, probably SEP or something more exotic. the MCT would dock to this at EML2 for the flight out to Mars and later return to for the return flight in colonial establishment and later phase missions.

In the initial 'exploration' phase mission, the MCT would direct insert to Mars from LEO using the BFR's Raptor-VAC upper stage for propulsion. The mission would be similar in most respects to Mars Direct in that there would be at least one one-way cargo precursor one Earth Departure window prior. The cargo module would stockpile LCH4, H20 and LOX to refuel the MCT once it has landed, ready for a later return flight.

During the 'Establishment' phase, robotics would be used to establish the basic ground facilities (power generation, labs, workshops and habitats; possibly also greenhouses). These will be deployed from a large number of one-way landers, which will be flying with reduced fuel load (some tanks replaced with cargo) and without life support. Other one-way flights would be basically the frame of landers constructed around hybrid reinforced inflatable hab modules.

Establishment phase missions would have a taste of Marsprojekt in the form of two crew transports accompanied by four or more one-way cargo landers. It is possible that the initial mission may divide in two with the crew of one MCT remaining on Mars for 500 days (between two Earth Departure windows) whilst the other returns directly to Earth with contingency scientific samples. The other MCT would remain behind to be returned on a later cycle.

To enable a higher cargo and crew load than would be possible with direct insert, two-way Establishment Phase missions would use a SEP propulsion module that would cycle between EML2 and the same orbital altitude as Phobos. The BFR upper stage would only be needed to send the MCT from LEO to EML2, which would mean a measurable increase of cargo delivered to Mars. Once again, the MCT would refuel on Mars's surface before returning, this time to the propulsion 'sled', which would be parked in the same orbital altitude as Phobos.

After the colony is secure, missions would become exclusively crew rotation, cargo delivery and results return, much like those currently flown to the ISS but on a vastly different scale, ambition and distance travelled.

BTW - Hellas Planitia is pretty much purpose-built as a location. The deeper location might make subsurface H20 frost easier to access. Although Mars's atmosphere is very thin, Hellas's below-mean-surface level altitude would add a small amount to the amount of atmospheric protection from solar and GCR radiation.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: JamesH on 02/27/2015 02:07 PM
Leaving habitats in orbit. You still need a smaller separate habitat to land people. You end up with two completely different designs for crew and cargo.

No wholly dissimilar though. Majority of parts are common.

Leaving tanks in Mars orbit. How do they get refuelled? Tanks are lightweight and big volume. That helps with landing the whole thing.

Take the fuel up in the lander that went down.  Ignore my comment on fuel tanks left in orbit, that's daft.  Just leave the interplanetary engines, habs etc in orbit. BA300's?


Elon Musk keeps making the argument how important mass fraction is for reusability. Being able to disconnect and reconnect requires a lot of additional structural mass.

So why take a load of mass you don't need on the surface down then up again?

I don't see landing on Mars and on Earth so much different, once you go for vertical propulsive landing. Up to now landers are complex machines, think of the "minutes of terror" for Curiosity. Brake as much as you can with atmosphere then do the rest propulsively is a lot simpler. It does require fuel, that is true.

They are not that different, but I'd leave the MCT framework in orbit round both planets and just use landers/ascenders at each end.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lars-J on 02/27/2015 03:28 PM
I'm perplexed by some of the delta/v numbers I'm seeing for launch from Mars. I may well be wrong (someone please correct me if so) but I came up with quite different numbers for Mars SSTO.

I merely consulted various delta-V charts that people have made and many assume to be correct. I haven't one the math myself. If you can demonstrate that they are incorrect, then that would be good news.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: BobCarver on 02/27/2015 03:50 PM
I'm perplexed by some of the delta/v numbers I'm seeing for launch from Mars. I may well be wrong (someone please correct me if so) but I came up with quite different numbers for Mars SSTO.

I merely consulted various delta-V charts that people have made and many assume to be correct. I haven't one the math myself. If you can demonstrate that they are incorrect, then that would be good news.

See John Whitehead's paper Mars Ascent Propulsion Trades with Trajectory Analysis: https://e-reports-ext.llnl.gov/pdf/307175.pdf
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Impaler on 02/28/2015 02:07 AM
I think people who are pounding their fists on "Land the Whole thing" are making a key unstated assumptions which is leading them to the in my opinion erroneous combined BFR-2nd-Stage / MCT conclusion.

They assume that ALL the vehicle mass that BEGINS the Trans-Mars-Injection will GO TO MARS.

This is absolutely unnecessary.  Just as SpaceX has worked to perfect in-atmosphere boots back they can and likely will do the same thing in space (where is it actually much easier) when doing TMI.

This means a perfectly NORMAL 2nd stage docked to MCT (actually they just never separate after launch) that is refueled (which we all agree is a definitely part of the architecture per EM statements).  Can send the MCT through TMI, immediately boost back to an Earth-atmosphere grazing trajectory and be recovered per it's normal recoverable-means (perhaps after a few atmospheric passes to bleed velocity) which again we all agree that it must have.

Thus "Land the whole thing " means land everything that was sent through TMI, not everything that reached LEO.  Huge difference, and this scenario is so much simpler relying on only the conventional 2 stage reusable rocket and LEO refueling as well as building upon boost-back experience that SpaceX has already got.

Lastly I think the combined 2nd-stage/MCT ideas are completely untenable for several other reasons as well.  The payload if it is on the top is dangerously high off the ground on a long-thin empty top-heavy tube landing on rough Martian terrain, non-starter.  If the payload is in the base of the vehicle then it is underneath the 2nd stage propellent and mass and has no abort from the first stage at any point during liftoff, another non-starter.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 02/28/2015 02:17 AM
Yeah, I had thought of that a few years ago back before we knew anything about what MCT was supposed to be (I'm sure I'm the 10,000th person to think of it) back when I was thinking of how to overcome the inherent difficulty of trying to get something economical and with high numbers of reuse when Mars and Earth only line up every ~26 months.

It's possible. But remember MCT will need to launch from Mars, too, and perhaps even straight to Earth. That's 5-7km/s delta-v (yes, it can be pretty low delta-v because you can take advantage of Mars' rotation and the low aero and gravity losses of Mars). Maybe MCT will strip out some of the unimportant and cheaply replaceable things for the trip back to help with that delta-v, but either way, that's a pretty good start on getting, say, 120 day trips from Earth to Mars (longer on the way back).

But in any case, it's likely the MCT would be fully fueled at near escape velocity in Earth orbit.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 02/28/2015 02:26 AM
Note my assumption is that MCT won't need multiple stages to ascend from Mars surface to Mars orbit, and probably won't be refueled in Mars orbit either but will go straight to trans-Earth-injection. Refueling will be in Earth orbit and on the surfaces of both planets, of course, but not likely in Mars orbit.

....however, knowing that there's a good (at least a 50:50?) chance now that the MCT architecture will now incorporate SEP kind of makes it difficult to predict what their likely course of action will be, since there are several ways that SEP could be used:

For instance:
1) only for prepositioning propellant in Earth orbit
2) perhaps also in Mars orbitperhaps for helping MCT return back to Earth
3) perhaps for speeding MCT along to Mars to get near 100-day transits
4) and is the SEP going to be a separate tug that stays in orbit? That seems definitely the most logical, although since MCT will already need significant power, it's possible it could also be integrated into MCT (the lander part), although this limits just how high performance it can be (since you'll want to minimize the SEP system mass and make it re-deployable). I doubt this last idea, but it's still possible. (If they use SEP, my bet is the SEP system will stay in orbit.)

We shall see.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Pipcard on 03/29/2015 02:54 PM
I have an interest in Robert Zubrin's "Mars Direct" plan. I see people talking about it and how the mass budgets/living space (for four people)/radiation considerations/etc. are "too optimistic."

If so, then what does that make the MCT?
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Ben the Space Brit on 03/29/2015 03:49 PM
If so, then what does that make the MCT?

Something intended for a very different model of Mars exploration than I think Zubrin or anyone else in NASA has aver seriously considered. Specifically: settlement first, exploration later.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: MikeAtkinson on 03/29/2015 05:16 PM
Mars direct, semi-direct and the various NASA DRM basically land a jab or two and a return stage or two total usable mass < 100 tonnes. It seems like SpaceX are going to land several cargo flights first, each of ~50 tonnes total usable mass for the first crew of > 200 tonnes. Similarly the first crew will have ~50 tonnes available during transit as compared to ~25 tonnes for Mars direct. As the MCT will provide power, cooling, comms, etc. the effective difference in payload mass is even greater.

Note that I have assumed that the first MCT flights have only half their design max payload. Mars direct had quite thin margins especially as whole systems (e.g. thermal control) were missing.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: MikeAtkinson on 03/29/2015 05:30 PM
....however, knowing that there's a good (at least a 50:50?) chance now that the MCT architecture will now incorporate SEP kind of makes it difficult to predict what their likely course of action will be

I think it very unlikely that SEP will be used. It doesn't gain SpaceX much and leads to more development expense. To be worthwhile SEP would have to run for over a decade, with very high reliability. Designing that reliability in is costly and testing it time consuming. In the end it swaps cheap fuel for expensive hardware, and moves all the cost upfront.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: meekGee on 03/29/2015 06:17 PM
...

....however, knowing that there's a good (at least a 50:50?) chance now that the MCT architecture will now incorporate SEP ...

...

I wasn't following that closely - was there more information made available, beyond Shotwell's comment that they are looking at a number of technologies including SEP?

I'm on the fence on whether SEP makes sense for Mars transit...  It will be nice to have more information from them.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: philw1776 on 03/29/2015 06:31 PM
A question from someone unschooled in celestial mechanics details.

Let's say that the MCT itself is SEP as Gwynne indicated as a possibility.  She also said that methalox was the propellant of choice for planetary launches, so this indicates that a possible MCT architecture has a deep space only SEP transporter.  We all know that the big issue with SEP is very low thrust even with large clusters of engines.

With an SEP architecture does it make sense for SpaceX to use a methalox tug using Raptor/BFR tech to launch a SEP transport to Mars from say L1 by diving towards the Earth, firing the high thrust methalox briefly at perigee giving the SEP transporter a kinetic energy boost and then the far less massive tug doing a boost-back to LEO where it's refueled.  Iterate. 

I am aware that this is far from the most energy efficient way to do this but if we accept SpaceX's claims that a re-usable BFR will be a relatively inexpensive launcher, would this approach help address SpaceX's stated desire for a quicker transit time yet low spacecraft mass (SEP ISP efficiencies) MCT?
Title: Re: MCT Speculation and Discussion Thread 3
Post by: MikeAtkinson on 03/29/2015 06:58 PM
A question from someone unschooled in celestial mechanics details.

Let's say that the MCT itself is SEP as Gwynne indicated as a possibility.  She also said that methalox was the propellant of choice for planetary launches, so this indicates that a possible MCT architecture has a deep space only SEP transporter.  We all know that the big issue with SEP is very low thrust even with large clusters of engines.

With an SEP architecture does it make sense for SpaceX to use a methalox tug using Raptor/BFR tech to launch a SEP transport to Mars from say L1 by diving towards the Earth, firing the high thrust methalox briefly at perigee giving the SEP transporter a kinetic energy boost and then the far less massive tug doing a boost-back to LEO where it's refueled.  Iterate. 

I am aware that this is far from the most energy efficient way to do this but if we accept SpaceX's claims that a re-usable BFR will be a relatively inexpensive launcher, would this approach help address SpaceX's stated desire for a quicker transit time yet low spacecraft mass (SEP ISP efficiencies) MCT?

One of the many challenges for the MCT design is furling and unfurling the solar panel. They are needed on the return trip so cannot be discarded. This is difficult enough for solar panels for MCT power, for SEP the panels have to be much lighter per unit area and this makes the task far harder.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: spacenut on 03/29/2015 07:42 PM
Vasmir (sp) can use oxygen and probably methane for propellant and it has higher thrust than other types from what I read.  Also, someone said EM did not discount the possibility of nuclear power to power either SEP or engines themselves.  SEP can continuously accelerate and decelerate to and from Mars maybe making the trip shorter.  Russia back in the 1960's developed a nuclear power supply that was 20 tons or less. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: MikeAtkinson on 03/29/2015 08:27 PM
Vasmir (sp) can use oxygen and probably methane for propellant and it has higher thrust than other types from what I read.  Also, someone said EM did not discount the possibility of nuclear power to power either SEP or engines themselves.  SEP can continuously accelerate and decelerate to and from Mars maybe making the trip shorter.  Russia back in the 1960's developed a nuclear power supply that was 20 tons or less.

There are numerous reasons why nuclear is not going to be used by SpaceX, time, cost and regulation are among them. SEP is solar electric propulsion, you meant NEP nuclear electric propulsion.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Jimmy Murdok on 03/29/2015 08:49 PM
Vasmir (sp) can use oxygen and probably methane for propellant and it has higher thrust than other types from what I read.  Also, someone said EM did not discount the possibility of nuclear power to power either SEP or engines themselves.  SEP can continuously accelerate and decelerate to and from Mars maybe making the trip shorter.  Russia back in the 1960's developed a nuclear power supply that was 20 tons or less.

Vasmir still has to demonstrate too much, I don't think unproven technology will be the choice.
Nuclear is a safe and good option, but still quite unproven in space and public opinion will probably kill it.

My vote is methalox for earth and mars ascent (with inmediate boostback to origin), hypergolics for descent (storable and safe option) and mix of chemical + solar-electric for transit.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: UberNobody on 03/30/2015 04:27 AM
So I've been looking over all the older videos where Musk talks about Mars, and I found a couple interesting bits in his talk at AIAA 2011.  Keep in mind, this is "old" and plans change, but I think there is some useful information.

https://www.youtube.com/watch?v=gYJyw8RGWyY

At 24:00, Elon talks about solar electric propulsion.  He figures that, if you need a bunch of solar panels to support the mission once at Mars, you could use them for SEP in-transit.  To infer from this, SEP is integrated into the MCT and is landed on Mars.  I don't think he is talking about keeping the SEP portion in orbit and beaming power to the surface.

Listening to him talk, I got to thinking: couldn't you just keep accelerating all the way to Mars?  Forget turning around half way through to slow down.  This isn't a "traditional" SEP mission, but one that starts with a chemical rocket burn.  If you can aerobrake over several orbits, I don't see the extra velocity as a huge problem, but I may be wrong.
Feel free to tear that idea to pieces.  I haven't had much time to think about it.

At 32:00, Elon talks about widening the departure window for Mars, or alternatively placing MCTs in highly elliptical parking orbits throughout the 26 month gap.  From more recent talks, it seems the latter (or a version of it) is still the plan.  I haven't heard much talk about elliptical parking orbits, just LEO and L1/L2.  Can anyone think of advantages to that approach?

I'd love to hear what you guys think about this.  Has the plan completely changed since then?  What evidence is there?
Title: Re: MCT Speculation and Discussion Thread 3
Post by: spacenut on 03/30/2015 04:47 AM
Why would a private companies 'space use only' nuclear reactor going to be regulated.  Maybe constructed to regulations.  The unit could be launched to L1 or L2, fueled, and started in space.  So any failure to launch wouldn't dump a running reactor into the ocean or crash in Africa somewhere, it will be just a structure or piece of equipment.  Chemical rockets would launch it as a unit to be docked with a MCT to power it up later.  Even NASA was only going to use a 3rd stage launched with a Saturn V and started in space before the NERVA program was shut down.  The NERVA rocket engines were tested in the desert somewhere and were fully functional units.  ISP was around 1,000 so it used far less fuel than an equivalent, (J2), upper stage engine.  Nuclear is the only option anyways for any large craft traveling past the asteroid belt, if we ever get to Mars.  For extremely fast and much shorter travel time nuclear is the only way to go.  Giant solar panels might be impractical for large human spacecraft.   

Otherwise it is going to be large metholox engines, possibly refueled in space. 

If the travel time is compacted in a 6 month time frame every two years.  A very large fuel depot could be built at L1 or L2 for the MCT to refuel there to continue on. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: meekGee on 03/30/2015 04:52 AM
So I've been looking over all the older videos where Musk talks about Mars, and I found a couple interesting bits in his talk at AIAA 2011.  Keep in mind, this is "old" and plans change, but I think there is some useful information.

https://www.youtube.com/watch?v=gYJyw8RGWyY

At 24:00, Elon talks about solar electric propulsion.  He figures that, if you need a bunch of solar panels to support the colony, you could use them for SEP.  To infer from this, SEP is integrated into the MCT and is landed on Mars.  I don't think he is talking about keeping the SEP portion in orbit and beaming power to the surface.

Listening to him talk, I got to thinking: couldn't you just keep accelerating all the way to Mars?  Forget turning around half way through to slow down.  This isn't a "traditional" SEP mission, but one that starts with a chemical rocket burn.  If you can aerobrake over several orbits, I don't see the extra velocity as a huge problem, but I may be wrong.
Feel free to tear that idea to pieces.  I haven't had much time to think about it.

At 32:00, Elon talks about widening the departure window for Mars, or alternatively placing MCTs in highly elliptical parking orbits throughout the 26 month gap.  From more recent talks, it seems the latter (or a version of it) is still the plan.  I haven't heard much talk about elliptical parking orbits, just LEO and L1/L2.  Can anyone think of advantages to that approach?

I'd love to hear what you guys think about this.  Has the plan completely changed since then?  What evidence is there?

That's an interesting talk.

He's kind of reserved about SEP.  What he says is simple fact - you need energy on the surface, so it's a waste not to have it as a booster while in transit.  But it's a challenge to make it matter (or be positive net gain even)

There are two straight takeaways though:
- He's definitely thinking solar for surface power
- The main propulsion method is chemical - SEP might be an accelerator.

He mentions (even back then) 12-15 tons to the surface of Mars with an FH.  That's pretty interesting, I think this must include refueling.  (And clearly one-way)

And as usual...  Amazing to look back 4 years. 

EDIT:
At 35:00 he does go into the advantages of nuclear power on the surface.  He was knocking it earlier for electric propulsion.  Still highly hypothetical though.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: MikeAtkinson on 03/30/2015 08:46 AM
Why would a private companies 'space use only' nuclear reactor going to be regulated. 

Because they would be designed, built and tested on Earth.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: AncientU on 03/30/2015 12:02 PM
Why would a private companies 'space use only' nuclear reactor going to be regulated. 

Because they would be designed, built and tested on Earth.
And launched...
Title: Re: MCT Speculation and Discussion Thread 3
Post by: meekGee on 03/30/2015 02:22 PM
Why would a private companies 'space use only' nuclear reactor going to be regulated. 

Because they would be designed, built and tested on Earth.
And launched...

But on the up side, if reason prevails, they will only be subject to regulations pertaining to the transport of unused fuel rods, as applied to "transport by a rocket", and not subject to regulations pertaining to the operation of a nuclear reactor.

IF reasons prevails.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: philw1776 on 03/30/2015 03:10 PM
Gwynne Shotwell recently spoke that SEP is under consideration, as well as others.  What the others are...who knows?

I believe SX will use SEP with methalox assist at planetary departure and arrival.  Elon has said that he favors shorter transit profiles so that lets out the typical 30+ day SEP only spiral out from Earth L2 or whatever, and the 30+ day SEP only spiral in to Mars LEO. I'm betting on a methalox tug for Earth Oberth effect departure to meet the faster transit times.

Here's an informative paper that describes SEP Mars missions and SEP + chemical mission profiles.  SLS based but celestial mechanics remains the same.

http://spirit.as.utexas.edu/~fiso/telecon/Oleson_3-6-13/

I'll bet that the MCT architecture Elon said he'd reveal at year's end does not survive this decade without substantial revision. That is not a bad thing in my view.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Pipcard on 03/30/2015 03:41 PM
If people think Mars Direct underestimated the mass to support 4 people on a Mars round trip, how do people expect the MCT to send 100 people to Mars with 100 tonnes of mass?
Title: Re: MCT Speculation and Discussion Thread 3
Post by: guckyfan on 03/30/2015 03:51 PM
If people think Mars Direct underestimated the mass to support 4 people on a Mars round trip, how do people expect the MCT to send 100 people to Mars with 100 tonnes of mass?

100 people to Mars means infrastructure is already there to accomodate them. No problem at all. It will happen in the colony extension phase.

Initially much smaller numbers of people will be sent. Maybe 8 or 10 at the first crewed flight. And even then a lot of necessary infrastructure, at least for water and fuel ISRU, will be awaiting them on the ground.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: spacenut on 03/30/2015 04:37 PM
When talking nuclear, I'm talking some type of small nuclear unit purchased off the shelf, like something light enough to already be approved, and only launch approval would be required such as a small nuclear unit that is used on say a small naval vessel or submarine.  One of the nuclear carriers had 8 small nuclear power plants on board.  They are larger now, but that was in the 1960's or 70's.  GE is working on a small plant that can be transported by one truck. 

I also believe some type of fuel depot will have to be developed for refueling a large craft of any type.  Something along the lines that can be refueled continuously with F9R's or FHRs.  Even if using a nuclear rocket, it will still have to have some type of fuel to superheat.  Hydrogen was used in the 1960's but it could be something that chemical rockets would also use. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Pipcard on 03/30/2015 04:45 PM
Even if the 100-people per MCT is for a later phase of Mars colonization, it still means that there is only one metric tonne of ship per person. 10 metric tonnes if only 10 people are going. The Mercury capsule only weighed about a couple tonnes, and that was to support one astronaut for a few hours.

And this is a journey of several months.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Krevsin on 03/30/2015 04:51 PM
When talking nuclear, I'm talking some type of small nuclear unit purchased off the shelf, like something light enough to already be approved, and only launch approval would be required such as a small nuclear unit that is used on say a small naval vessel or submarine.  One of the nuclear carriers had 8 small nuclear power plants on board.  They are larger now, but that was in the 1960's or 70's.  GE is working on a small plant that can be transported by one truck. 
Still doesn't answer the crux of the issue, namely that people kinda go insane whenever the word "nuclear" is involved. It's a political issue, not a tech one.

On a similar but different topic, regardless of whether or not it's off the shelf hardware, it'll probably require some significant reworking and certification to work (or indeed, be allowed to work) in space, and of course let's not forget the mass penalties that carrying a nuclear reactor would entail.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: guckyfan on 03/30/2015 04:53 PM
Even if the 100-people per MCT is for a later phase of Mars colonization, it still means that there is only one metric tonne of ship per person. The Mercury capsule only weighed about a couple tonnes, and that was to support one astronaut for a few hours.

No. It means there will be 1t of payload per person, including that person, supplies and ECLSS. I suspect that ECLSS has become less heavy and more efficient since Mercury.

Assuming 120 days transfer time and assuming 5kg/person/day supplies as in the ISS it sounds doable. I expect though that supplies will be much smaller, given an advanced ECLSS.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: spacenut on 03/30/2015 06:40 PM
I like the idea of settlement first, exploration later. 

When talking about how the architecture will be.  I think SEP for continuous round trips to Mars and back like Buz Aldrins cycler idea.  The cycler using SEP can go between earth and Mars on a continuous basis for supplies and equipment. 

The human transfer either needs to be higher speed or with artificial gravity of some sort, even if only Mars gravity for a smaller diameter.  I do agree a large BFR will be needed to launch the larger components and humans.  However the Falcon heavy could stay busy supplying 50 ton parts for a SEP tug to a cycler, then the cycler transferring it to Mars, then landing.  The equipment and supplies would not have to come back, just the humans. 

I also think once the equipment is sent to Mars, humans would need to go to make sure it is working properly.  I also think twice what is needed for human survival for x number of colonists should be sent for redundancy.  Then humans could go on two year stints and come back to check their physical changes.  Later longer stints could be done, in multiples of 2 like 4, 6,8 years etc.   
Title: Re: MCT Speculation and Discussion Thread 3
Post by: spacenut on 03/30/2015 06:46 PM
Also, once cyclers are in place, larger ones could be built with artificial gravity.  Once someone comes back from a long stint, gravity could gradually be increased on the return to have people re-acclimate to one G for earth return.  1/2 G out, 1/2 G increasing to 1G on return. 

A fast trip there, say 3 months, wouldn't be a problem acclimating to the Mars gravity.  Fast trip back after a 2 year stint, might be hard to acclimate to 1 G on return, not counting G forces coming back through the atmosphere, unless they use something like Dream Chaser with lower G's on decent. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Ludus on 03/30/2015 10:00 PM
When talking nuclear, I'm talking some type of small nuclear unit purchased off the shelf, like something light enough to already be approved, and only launch approval would be required such as a small nuclear unit that is used on say a small naval vessel or submarine.  One of the nuclear carriers had 8 small nuclear power plants on board.  They are larger now, but that was in the 1960's or 70's.  GE is working on a small plant that can be transported by one truck. 

I also believe some type of fuel depot will have to be developed for refueling a large craft of any type.  Something along the lines that can be refueled continuously with F9R's or FHRs.  Even if using a nuclear rocket, it will still have to have some type of fuel to superheat.  Hydrogen was used in the 1960's but it could be something that chemical rockets would also use.

I don't think many people on NSF are bothered by the idea of launching reactors but out in the real world the idea of launching far more radioactive material than has ever been launched in history and the risk of an accident scattering it in somebody's backyard creates more problems politically than it's worth unless it's critically important.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Burninate on 03/30/2015 10:15 PM
Even if the 100-people per MCT is for a later phase of Mars colonization, it still means that there is only one metric tonne of ship per person. 10 metric tonnes if only 10 people are going. The Mercury capsule only weighed about a couple tonnes, and that was to support one astronaut for a few hours.

And this is a journey of several months.

Because both "100 people" and "100 tons to Mars" and "reusable" have been mentioned, and the combination is so extreme, I think it's best to interpret the mass part conservatively:  MCT will land 100 tons useful payload (humans, rovers, food, experiments) on the Martian surface, and bring it back to the Earth-Moon system, but that structural mass, fuel mass, and even ISRU hardware is not included in this figure.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 03/30/2015 10:32 PM
1) Nuclear electric sucks compared to solar electric in the inner solar system for propulsion.
2) there are no small "off the shelf" nuclear units that would be relevant
3) nuclear tech is something SpaceX has exactly zero experience with and we have no reason to think SpaceX cares to change that
4) an entire jet airliner weighs 200-250kg per passenger, including luggage, emergency life support, cockpit, etc. Mercury is not a good example of weight-optimized design for a 100-person spacecraft. SpaceX will necessarily not have luxurious, spacious accommodations (because they could charge less and have more people). Assume they will have a very mass-efficient design by necessity.
5) 5kg/day consumables is needlessly conservative. SpaceX can do better.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: guckyfan on 03/31/2015 03:28 AM
2) there are no small "off the shelf" nuclear units that would be relevant
3) nuclear tech is something SpaceX has exactly zero experience with and we have no reason to think SpaceX cares to change that

Though, if they become available off the shelf they would not hesitate to use them. It would greatly reduce the need for batteries during night.

4) an entire jet airliner weighs 200-250kg per passenger, including luggage, emergency life support, cockpit, etc. Mercury is not a good example of weight-optimized design for a 100-person spacecraft. SpaceX will necessarily not have luxurious, spacious accommodations (because they could charge less and have more people). Assume they will have a very mass-efficient design by necessity.
5) 5kg/day consumables is needlessly conservative. SpaceX can do better.

Absolutely. And in a zero g environment it all can be done quite mass efficient. I mentioned those 5kg because it is what is supplied to the ISS and some argue that is the reference and needs to be calculated with. But absolutely it can be done with less. Inspiration Mars calculated with way less than 1kg. But they were on the extreme side.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Impaler on 03/31/2015 04:26 AM
SpaceX has already said that they consider HALL effect thrusters which are the clear optimum electric thruster type to use on a Mars transit (ISP is in the sweet spot), are so simple and common that they feel they can mass produce them in the thousands in-house for their satellite network.  They will also likely be producing their own solar panels for said satelites.  It will be quite trivial for them to leverage this production chain and the expertise they gain from it into the MCT, it's looking more and more like the path of least resistance.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: spacenut on 03/31/2015 02:00 PM
EM did mention nuclear as an option.  He would probably use thorium if he did since it is safer and cooler.  I think Germany is the only one working on this now.  I have read also that GE is working on a small reactor that can burn the old spent fuel rods around the country.  Australia has expressed interest in this and would gladly take everyones spent fuel rods from around the world.  No need to process or mine the fuel.  Even third world countries could use these because the spent fuel rods can't be made into bombs.  I know a BFR could launch a small reactor with the MTC for use on Mars, especially at night.  Probably wouldn't weight more than a large solar array with battery backup for night use. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: docmordrid on 03/31/2015 02:06 PM
EM did mention nuclear as an option.  He would probably use thorium if he did since it is safer and cooler.  I think Germany is the only one working on this now.
>

The US and China are working on a thorium  reactor (http://fortune.com/2015/02/02/doe-china-molten-salt-nuclear-reactor/), and AIUI India is also in the hunt .
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 03/31/2015 03:27 PM
EM did mention nuclear as an option.
I remember no such thing.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: philw1776 on 03/31/2015 04:04 PM
It's been discussed elsewhere on this site (don't remember where) but I could see Magnetoshell Plasma Aerocapture as a technology utilized by SpaceX on their Mars missions...

https://s3-us-west-2.amazonaws.com/pnwmsnw/Kirtley_MSNW_NIAC_12MAR_final.pdf

Potential of huge reduction in heat shield entry mass and thereby fuel and spacecraft mass.  Allows faster transfer orbits to Mars (high V aerobraking) minimizing that transit time that EM has expressed concerns about.

Title: Re: MCT Speculation and Discussion Thread 3
Post by: spacenut on 03/31/2015 04:08 PM
From what I read EM did in 2007 if they can overcome the safety issue otherwise he prefers solar.  If they get these small thorium reactors up and going, I'll bet if they are light enough to launch, and put off x amount of power, compared to larger heavier solar, he will use it.  I know also he invested in a solar manufacturer in Buffalo, NY.  I think it all adds up.  He will use this solar factory to make solar for Mars, and use his Tesla technology for Martian vehicles. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 03/31/2015 04:13 PM
From what I read EM did in 2007 if they can overcome the safety issue otherwise he prefers solar.  If they get these small thorium reactors up and going, I'll bet if they are light enough to launch, and put off x amount of power, compared to larger heavier solar, he will use it.  I know also he invested in a solar manufacturer in Buffalo, NY.  I think it all adds up.  He will use this solar factory to make solar for Mars, and use his Tesla technology for Martian vehicles.
No, he never said that.

Besides, nuclear is heavier.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: spacenut on 03/31/2015 06:17 PM
I will get the link when I get off work.  It was on a NatGeo interview if I remember. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: sheltonjr on 03/31/2015 08:04 PM
From what I read EM did in 2007 if they can overcome the safety issue otherwise he prefers solar.  If they get these small thorium reactors up and going, I'll bet if they are light enough to launch, and put off x amount of power, compared to larger heavier solar, he will use it.  I know also he invested in a solar manufacturer in Buffalo, NY.  I think it all adds up.  He will use this solar factory to make solar for Mars, and use his Tesla technology for Martian vehicles.
No, he never said that.

Besides, nuclear is heavier.

I do not think you can make that statement with the "Matter of Fact" that you claim.

I would like to see the weight of a Mars Solar solution that has the following capabilities: (Based on a real reactor that ran decades ago)

1) 1.25 MWatts of electrical power, 5 years, 24.5 Hours/668 days a year (Available all the time)
2) Near zero maintenance. Just add fuel monthly (15 minute job)
3) 700C waste process heat for ISRU and materials processing
4) Size of a small SUV + Power generation and radiators
5) Estimate weight 5-8 MT

If more power is required, the size scales really well.

Kirk Sorenson with FLIBE Energy may be ready to build a space molten salt reactor in 10 years. Terestrial Energy of Canada may be a better fit and ready earlier since they are only building a burner type reactor.

Here is a post I did on this reactor last year
Aircraft Reactor Experiment post
Title: Re: MCT Speculation and Discussion Thread 3
Post by: spacenut on 03/31/2015 10:07 PM
This is what I was talking about.  I didn't know it only weighted 5-8 tons.  Even in America today solar is not practical in the Midwest, the south and mountain states.  To many clouds and rainy weather and the greatest use of power, thus nukes, coal, natural gas, and hydro. 

Mars has sun all the time except at night, so I think maybe a combination of solar-small nuclear would work.  Use the power off the small nuke for manufacturing processes and the solar for lighting and smaller use.  It might take 10 acres of solar panels to get enough power for manufacturing, but only a few sq ft for a nuke power plant.  It could also be buried. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: philw1776 on 03/31/2015 10:49 PM
Several problems with nuclear...

"May be available in 10 years" 
Strong political aversion to all things nuclear with no sign of change.
The BIG $$$ is being spent on solar R&D.  Yes I'm aware of Silicon Valley investment in sundry nuke businesses, but it's small change.
Solar has flown in space for ages and more solar will fly in the next 10 years vs ZERO US space fission flights.

More mundane:
Elon ever the showman has positioned himself as Mr Solar.  He will take flack & opposition from his myriad green acolytes were he to commit the heresy of utilizing nuclear. That bad press and rabid opposition by jilted girlfriends could pose serious problems for all his concerns.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: happyflower on 04/01/2015 06:18 AM
SpaceX has already said that they consider HALL effect thrusters which are the clear optimum electric thruster type to use on a Mars transit (ISP is in the sweet spot), are so simple and common that they feel they can mass produce them in the thousands in-house for their satellite network.  They will also likely be producing their own solar panels for said satelites.  It will be quite trivial for them to leverage this production chain and the expertise they gain from it into the MCT, it's looking more and more like the path of least resistance.

I'm a visual person. Credit NASA
HALL thruster http://www.nasa.gov/sites/default/files/thumbnails/image/hall-thruster.jpg (http://www.nasa.gov/sites/default/files/thumbnails/image/hall-thruster.jpg)
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 04/01/2015 12:57 PM
This is what I was talking about.  I didn't know it only weighted 5-8 tons.  Even in America today solar is not practical in the Midwest, the south and mountain states.  To many clouds and rainy weather and the greatest use of power, thus nukes, coal, natural gas, and hydro. 

Mars has sun all the time except at night, so I think maybe a combination of solar-small nuclear would work.  Use the power off the small nuke for manufacturing processes and the solar for lighting and smaller use.  It might take 10 acres of solar panels to get enough power for manufacturing, but only a few sq ft for a nuke power plant.  It could also be buried.
Nonesense, those aren't real figures. No such space rated nuclear reactor exists and those that flew in the past were at least ten times heavier per watt than solar.

The weight of the reactor itself is only a small part of the total. Space radiators are huge and heavy, plus you need the generator itself and especially for crewed missions the shielding. Plus you need to somehow reuse it, which poses problems with maintenance of the now-hot reactor and surrounding areas.

Nuclear works great on Earth where mass isn't a concern and you can dump heat into a body of water or the dense atmosphere. But in the inner solar system, solar beats the crap out of nuclear and for a far cheaper price. It has nothing to do with politics. Solar is simply superior for this task, and if you are willing to pay for development for new developments, it would be FAR better.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 04/01/2015 01:11 PM
Also, for surface power, nuclear requires buring of the reactor (with a rover) and a 1 km long cable to be far enough away from the base. It doesn't take merely a few square feet, it requires a large exclusion zone, FAR bigger than the footprint of a solar field.

But at least surface nuclear power makes some sense and is competitive, unlike in-space power where solar blows nuclear away.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: spacenut on 04/02/2015 03:55 PM
I was thinking about something this size that can either be used to power the space craft itself or even to power a Mars colony.  They are small and if they can be delivered by truck should be light enough to at least be lifted to orbit on a Falcon Heavy. 

http://phys.org/news145561984.html

Title: Re: MCT Speculation and Discussion Thread 3
Post by: RoboGoofers on 04/02/2015 08:15 PM
From the bottom of the article you linked:

Quote
Update (November 12, 2008): The Nuclear Regulatory Commission (NRC) contacted PhysOrg.com to state that the NRC has no plans to review the Hyperion design in the near future, although the NRC and Hyperion have had preliminary talks. Because the Hyperion design is unique, the NRC expects that it will take significant time to ensure safety requirements. In a response to a letter from October 2008, the NRC stated:
“Hyperion Power Generation is in the early stages of development of this design, and very little testing information is available for this design concept. Hyperion Power Generation has indicated that it will submit technical reports to support a pre-application review in late FY 2009. The NRC cannot engage in any meaningful, formal technical interaction with the potential applicant until we receive those reports. Because of the very limited amount of test data and lack of operating experience available for a uranium hydride reactor, the NRC staff anticipates that a licensing review would involve significant technical, safety, and licensing policy issues.”

So in other words, it's not even ready for earthbound use...

edit: If you look at they wikipedia page for Gen4 Energy (http://en.wikipedia.org/wiki/Gen4_Energy) (formerly Hyperion) you'll see that the revised concept is a little more involvedl.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: spacenut on 04/02/2015 08:20 PM
However, small nuclear power plants are doable.  Russia has done one, don't know the details.  Many European and Japanese are interested, especially the salt and thorium reactors.  SpaceX hasn't even landed the first stage of Falcon 9 nor have they developed the Raptor engine yet.  Advances in nuclear power might be available by they time Raptor, BFR, and MTC come on line and smaller units could be available by then. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 04/02/2015 09:07 PM
In the meantime, what about advances in solar and battery technology by that time, both of which have been advancing much faster than nuclear tech?
Title: Re: MCT Speculation and Discussion Thread 3
Post by: RoboGoofers on 04/02/2015 09:09 PM
space reactors would be developed just like they are on earth:

1. Prove it's viable on paper= Years of studies
2. Prove it's viable in practice= Years of construction, regulation, and more studies
3. Build for production= Years of construction and regulation.

As far as i'm aware, none of the earthbound small reactors have gotten past step 1, so are at least a decade away. A small space-based reactor would likely need a decade or more after FH is deemed reliable just for step 2. It would be much more dangerous and complex than JWST, and look how long that is taking.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Jimmy Murdok on 04/02/2015 09:20 PM
However, small nuclear power plants are doable.  Russia has done one, don't know the details.  Many European and Japanese are interested, especially the salt and thorium reactors.  SpaceX hasn't even landed the first stage of Falcon 9 nor have they developed the Raptor engine yet.  Advances in nuclear power might be available by they time Raptor, BFR, and MTC come on line and smaller units could be available by then.

Old space nuclear reactors were heavy and inneficient. 2 Russian ones made a mess reentering.

Solar panels are around 300W/kg (correct me if wrong)

Best nuclear space reactor you can expect is the Russian ROSATOM (in funded development):
- 1MW Electric power
- 3MW Termical power
- Fast neutrons, Gas refrigeration, Brayton cicle
- 6,8 Tons ---> 1MW/6,8T -> 147W/kg

I think it's interesting to workout this technology but not for crewed missions, solar is far better.
For Mars surface it makes much more sense.

Deep article (in spanish) http://danielmarin.naukas.com/2012/10/28/rusia-y-su-remolcador-espacial-nuclear/
Brief press note http://russianspacenews.com/rosatom-and-kurchatov-institute-making-thermo-nuclear-battery-for-space/
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Jimmy Murdok on 04/02/2015 10:16 PM
space reactors would be developed just like they are on earth:

1. Prove it's viable on paper= Years of studies
2. Prove it's viable in practice= Years of construction, regulation, and more studies
3. Build for production= Years of construction and regulation.

As far as i'm aware, none of the earthbound small reactors have gotten past step 1, so are at least a decade away. A small space-based reactor would likely need a decade or more after FH is deemed reliable just for step 2. It would be much more dangerous and complex than JWST, and look how long that is taking.

I'm not going to expand because this is OT but:
- Small space based reactors did flew in the past, few dozens between URSS and USA from 60's to 80's.
- Until they are activated they are less dangerous than plutonium RTG.
- They are less complex than JWST (at least less expensive).
- Still less efficient and more complex than solar but for few applications they are cool.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Elmar Moelzer on 04/03/2015 12:55 AM
In my humble opinion, why go small with a nuclear reactor? Go in the GW scale and all of a sudden they become a lot more efficient and don't bother with nuclear electric. Go nuclear thermal.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 04/03/2015 06:15 AM
Yeah, as long as it's a paper rocket, why stop there? Make it a terawatt! ~
Title: Re: MCT Speculation and Discussion Thread 3
Post by: spacenut on 04/03/2015 05:29 PM
Is the MTC lander for Mars supposed to land 100 tons of CARGO, or the whole spacecraft be 100 tons? 

What would an unfueled MTC lander weigh without fuel?

How many launches of fuel to fill the MTC before departing for Mars? 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: BobHk on 04/03/2015 05:34 PM
Is the MTC lander for Mars supposed to land 100 tons of CARGO, or the whole spacecraft be 100 tons? 

What would an unfueled MTC lander weigh without fuel?

How many launches of fuel to fill the MTC before departing for Mars?

Feb 2014 Musk Said : "It's going to put over 100 tons of cargo on Mars."

Title: Re: MCT Speculation and Discussion Thread 3
Post by: nadreck on 04/04/2015 02:48 AM
If I wanted a fast trajectory to Mars, I would launch getting as much benefit from hyperbolic velocity (Oberth Effect) as possible, so much so that if SEP was used maybe it is used to provide a braking for most of the trip to bring the encounter velocity to a level that a first atmospheric braking would leave the vehicle in an elliptical orbit of Mars and be within the margins of the TPS.

For cargo flights going on minimum energy flights, use SEP to a highly elliptical orbit ready for a methalox TMI burn that gets the most benefit from hyperbolic velocity at the least cost, then maybe SEP from there. Or maybe it was an SEP tug that orbit.

I see it as a given that SpaceX will do everything possible to make their MCT tank systems store methalox long term.

Title: Re: MCT Speculation and Discussion Thread 3
Post by: Elmar Moelzer on 04/04/2015 04:57 AM
Yeah, as long as it's a paper rocket, why stop there? Make it a terawatt! ~
I never said that. But a Gigawatt Thermal is fairly standard as far as nuclear reactor sizes go and IIRC the power to weight ratio of nuclear reactors scales almost volumetrically. So why not go with a more powerful reactor? Why the obsession with small reactors? Phoebus and NERVA NRX were all way over a Gigawatt and certainly for good reason.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Burninate on 04/04/2015 09:09 AM
Yeah, as long as it's a paper rocket, why stop there? Make it a terawatt! ~
I never said that. But a Gigawatt Thermal is fairly standard as far as nuclear reactor sizes go and IIRC the power to weight ratio of nuclear reactors scales almost volumetrically. So why not go with a more powerful reactor? Why the obsession with small reactors? Phoebus and NERVA NRX were all way over a Gigawatt and certainly for good reason.
I was looking at reactors the other night in the interest of examining the Ad Astra '39 days' drivel, where they assume 200MWe from a 50 ton reactor.
1) This scaling law is not something I observed.  Some of the best TWRs were of smaller reactors, actually - but there are uncertain selection effects, it may just be that only the ones optimized for low mass mentioned mass.
2) Radiator mass scales slower
3) My target was 600MWt / 300MWe, and figures using planned reactors ranged from ~1000T (SSTAR and RAPID-L, which match space-designated reactor SAFE-400) to ~5000T.  These are outside the reasonable scope of MCT.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: MikeAtkinson on 04/04/2015 10:16 AM
Lets sum up what  know (or at least reasonably can expect) of MCT.

Payload to Mars surface 100 tonnes - initial flights are likely to have lower payload mass, perhaps 50 tonnes.

Up to 100 passengers and crew - initial flights are likely to carry far less, perhaps around 10.

100 SUV volume - it is unclear if this is external volume which could be 2000m3 or internal volume perhaps 700m3. It is also unclear if this refers to total MCT volume or usable cargo volume or pressurized volume.

Something like 2 cargo flights to each crew flight - cargo flights are probably the major cost driver.

Launched on a 100-200 tonne BFR (fully reusable) - equivalent to 200-300 tonnes expendable rocket. It is probably possible to go as low as 50 or as high as 600 tonnes (reusable), but these seem to go away from the optimum.

Cargo and crew flights will use a similar MCT configuration - technologies that are only useful for crew flights are unlikely.

MCTs to be returned to Earth so that they can be reused within 1 synod. This might not apply to early flights, some might be left on Mars, others might be returned later.

Reflight within 1 synod implies fast cargo flights. Most architectures employ low energy cargo flights which save on IMLEO.

Crew accommodations are just cargo. It seems likely that crew and cargo MCT are almost identical with all additions for crew being treated as cargo.

Methane/Oxygen main fuel and lots of it.

Main engine is raptor. Used for TMI, Mars ascent, TEI, also probably used for Mars landing.

Raptor size is in the range 500-1500klb. Optimisation still probably taking place. Landings on Mars using Raptor at higher thrusts would be 'sporty', but not impossible given the range of potential MCT masses and throttling levels.

Fully reusable - both MCT and BFR. This has implications for Mars and Earth entry descent and landing.

Land the whole MCT on Mars. The simplest architecture. Given that the MCT will be large and fully reusable and uses Mars derived propellants it is difficult to improve on this.

Propellant transfer in LEO, either from tankers to MCT, or from tankers to propellant depot to MCT.

Multiple tanker flights per MCT. Could be as high has 12 or as low as 3 depending on BFR size, MCT size, etc. perhaps 6 is a reasonable estimate.

Multiple constraints means that the MCT design is hard. All aspects of the flight (Earth launch, TMI/TEI, transit, Mars EDL, Mars surface ops, Earth EDL) put constraints on the MCT, it is a very difficult problem to satisfy them all. Finding it impossible to meet all of them would be the most likely reason to change from a land-it-all, return-it-all in 1 synod using methane architecture.

It is highly probable that Solar power will be used during transit. Lightest and cheapest solution, but it does create difficulties in furling the solar sails for landing.

It is likely that Solar power will be used during surface ops. Cheap and easy to scale.

Electric Propulsion may be used during transit. But probably only as a secondary propulsion system for attitude control, course corrections

There seem to be 3 possible shapes for the MCT:
1. Capsule - similar to Dragon - SpaceX has lots of experience in this, but perhaps not enough lift for Mars to give a reasonable payload fraction landed - scaling Red Dragon would give a heat shield over 20m in diameter.
2. Bullet - similar to fairing - most space efficient, used on DRM 5.0, but perhaps too tail-heavy either during Mars descent or Earth descent.
3. Semi-lifting - something like ESA's IXV perhaps, gives more lift than capsules.
All three have advantages and disadvantages.

Vertical landing is likely. As this avoids the problems with horizontal landings -  load paths in 2 directions, a separate set of landing engines and does not need raising to the vertical for launch from Mars.

Separate landing engines are possible. Better match to thrust required, could possibly be used for LAS, keeps exhaust well away from martian surface which reduces debris. But add extra mass and complexity.

No Nuclear. There are no suitable reactors off-the-shelf, creating one would be time consuming, very costly and impose great regulatory burdens on the entire architecture.

Initial crews live in the MCT.

Early designs of the MCT are likely to be quite different from those at the colony stage. More experience, better technology, economies of scale and competition will all affect the MCT over several generations. 100 people for $500k each is likely 50 years away, lots can happen in that time.

The MCT and BFR factory will be built near the launch site. If there are more than one launch site, probably near water as well.

The launch site location is unknown. Noise is a major constraint, few if any places on the coast are suitable, perhaps launch from a short distance off-shore.

Two possible configurations of BFR/MCT:
1. MCT is the second stage of the BFR, with mission kits for tanker, propellant depot, crew and cargo roles.
2. MCT is payload on a two stage BFR. It would then probably make sense for the tanker and propellant depot roles to be a stretched upper stage variant, while the MCT takes on other roles.
The first option allows a larger MCT (+payload) for the size of BFR at the expense of even more constraints on the MCT design. The second option is more flexible and probably easier, but at the expense of designing an extra reusable stage.

LEO rendezvous. Use of L1 does not seem to be part of the plan. Putting the mission together at L1 gives the advantage of staging, but it seems unlikely that BFR can get a fully loaded MCT to L1 in a single launch, even with a SEL tug. Assuming BFR launch is cheap, the added complexity of L1 does not seem worth it.

No use of Lunar propellants. Production of lunar propellants and launch are highly likely to be more expensive than using BFR tanker flights.

Direct return injection. The MCT launches and directly injects into an Earth return orbit. No stops in low Mars orbit, no propellant depot on a Mars moon. A MCT sized to go from LEO to the Mars surface is also sized correctly to go from the Mars surface back to Earth in one go (perhaps with a smaller but still substantial payload). Schemes to refuel in Mars orbit, may save a bit of propellant production on Mars but only at the expense of increased complexity.

Testing. The MCT will be thoroughly tested in LEO before flights are attempted to Mars. Multiple landings on Mars will be made before the first crew landing, multiple return flights will be made before the first crew return.

Early MCT crew may be launched on Dragon. Early crews are likely to be in the order of 10 people, it is likely that it will be cheaper to launch them on Dragon than to man rate the BFR/MCT. The MCT can also be refuelled over months using tankers without needing the crew on board (this stops the propellant depot becoming a gating item).

The cost of moving to Mars will be higher than $500k. Add in necessary equipment and supplies and cost to expand the base/colony to accommodate one more person and the true cost (long term) is probably an order of magnitude higher.

The BFR and MCT may have other uses. Other short term uses might be one way of paying for the development. SpaceX have a record of getting customers to pay for development flights.

Development over the next 5 years will not be payed for from the satellite constellation. It will take at least that long for the satellite business to be profitable, in the mean time that will be a vast capital expense.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Semmel on 04/04/2015 11:14 AM
Very nice summary MikeAtkinson, thank you! Might be worth starting Thread 4 with your post as first entry.

The BFR and MCT may have other uses. Other short term uses might be one way of paying for the development. SpaceX have a record of getting customers to pay for development flights.

I have the same hunch. Think what NASA would be able to pay for a few tonnes of cargo (i.e. robots) to Mars on the first flights. Sure, they want to use SLS instead but I have a hard time imagining they would pass on that opportunity. If not NASA, there are a bunch of other organisations  from countries around the world that could take such opportunity. Like Russia, China, Europe, Japan, India or even Brazil. Given that they would only have to design the surface robot but neither the interplanetray stage and landing equipment, the engineering task is much, much simpler. It would be an economically sound opportunity by SpaceX to offer such service.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: guckyfan on 04/04/2015 12:08 PM
Great post MikeAtkinson

Really worth to be fixed as the first post of a new thread. But this one is quite new with only 8 pages. Maybe a mod could move or copy it to the front?

One very minor point. Elon Musk has recently - this year - mentioned a ratio cargo/crew of 10 to one. It really does not matter as those things are clearly not planned through yet. Every ratio is a crude guess at this point.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: MikeAtkinson on 04/04/2015 12:40 PM
Very nice summary MikeAtkinson, thank you! Might be worth starting Thread 4 with your post as first entry.

The BFR and MCT may have other uses. Other short term uses might be one way of paying for the development. SpaceX have a record of getting customers to pay for development flights.

I have the same hunch. Think what NASA would be able to pay for a few tonnes of cargo (i.e. robots) to Mars on the first flights. Sure, they want to use SLS instead but I have a hard time imagining they would pass on that opportunity. If not NASA, there are a bunch of other organisations  from countries around the world that could take such opportunity. Like Russia, China, Europe, Japan, India or even Brazil. Given that they would only have to design the surface robot but neither the interplanetray stage and landing equipment, the engineering task is much, much simpler. It would be an economically sound opportunity by SpaceX to offer such service.

Thanks for your kind words.

I don't see robotic missions to Mars as something that NASA would do in the near term. Large robots are expensive, probably too expensive for discovery missions and are unlikely to be funded soon as a flagship mission. Similarly for near or medium term large telescopes, there is no science budget for them, even if they could be launched cheaply on BFR.

I think you would have to look to the human space flight and technology budgets. The technology budget has been pretty small for far too long, and in the great scheme of solar system exploration would be better spent on ECLSS, planetary rovers (manned and unmanned) and a host of other technologies which have not been matured to a readyness level of 6 or more. That leaves the human spaceflight budget.

If (and its still a big if) BFR/MCT look credible and cheap and are well into development, SpaceX would have an argument for replacing SLS/Orion with BFR/MCT for ARM. Similarly we know that ISS is likely to be replaced by some form of private station, possibly based on Bigelow modules. BFR could launch that station, an entire ISS in 2-3 launches! More interestingly, MCT could be fitted out with science racks and act as attached and free floating long duration science labs. Finally, we know that sections of NASA are still interested in the Moon, its not difficult to envisage various ways MCT could be used for Lunar exploration, anything beyond LEO allows SpaceX to practice refuelling and various other things necessary for Mars missions, even if they do not land on the Moon themselves.

Outside of NASA space tourism is a possible market. BFR/MCT is probably two big for near term space tourism and will I think not initially be man rated, however it would make a good target for tourists, instead of them going to a Bigelow station, they could go to an MCT fitted out for short term tourist stays. After MCT is man rated launching tourists on MCT should be cheaper than Dragon, there would be no need for a Bigelow station with its attendant costs and each fresh batch of tourists would stay in a fresh clean habitat.

Looking back in 10 years time I expect the ideas above will seem amusing and that with hindsight something else will appear obvious (perhaps even "MCT was a rotten idea, why did we ever take it seriously"). However, these ideas show, I think, that SpaceX could have a reasonable expectation of getting much of the development and testing paid for by customers who have no interest in Mars.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: MikeAtkinson on 04/04/2015 12:52 PM
Great post MikeAtkinson

Really worth to be fixed as the first post of a new thread. But this one is quite new with only 8 pages. Maybe a mod could move or copy it to the front?

One very minor point. Elon Musk has recently - this year - mentioned a ratio cargo/crew of 10 to one. It really does not matter as those things are clearly not planned through yet. Every ratio is a crude guess at this point.

Thanks.

I remember now that Elon said that, like most things he says it is open to interpretation. Did he mean:

1. we will send 10 cargo missions before the first crew mission, after that the ratio will be different (less).
2. early missions will be 10 cargo to 1 crew mission, later on that ratio will be less.
3. we don't know what the ratio will be for early missions, but looking at it from first principles when we are in the colony phase it will be about 10 to 1.
4. we don't know, it might be 2 to 1 or it might be 20 to 1, lets call it 10 to 1 as a placeholder.
5. each 10 crew need 1 cargo mission, we are sending 10 crew on the first manned mission, but they will need a couple of extra cargo flights to get things going.

My, perhaps completely wrong, guess is that it is close to 2 cargo flights per crew flight (almost 30 tonnes per crew member) for the first few synods, with perhaps a few cargo test missions to start things off.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: spacenut on 04/04/2015 03:34 PM
Another thing.  IF these small nuclear power plants, self contained type they are talking about, ever get developed within this time frame, one might be taken to a Mars colony for additional power. 

I can also understand 10 cargo to 1 human transfer.  You need methane, oxygen, power (solar panels), food, seeds, habitats, electric vehicles, trucks, earth moving, and towing, greenhouses, water tanks for aquaculture and fish.  That is a lot of equipment. 

I can also believe there will be dual equipment for redundancy if something breaks down. 

I can also understand a 500k lb powered Raptor engine.  Say 30 for the launch vehicle, also vacuum versions for the transfer to Mars.  Small enough to land a big rocket softly, but enough of them for take off to return to earth. 

So from this information, for he first colony, he will need at least 12 BFRs, probably more, to be launched continuously during the window of opportunity.  Say one per day, or per week, or one as soon as refueling and refurbishing can be done. 

Does anyone know how long it takes to liquefy a certain volume of oxygen and methane with existing equipment?

The natural gas company I worked for liquefied gas during the summer when gas was abundant and cheap, but took 3-4 months to liquefy enough for 2 months winter use.  These tanks were very large, around 50-75 meters in diameter, two walls, 3' between the walls where a vacuum was pulled, like a giant thermos bottle.  I wasn't with that group, so I know very little about how much volume they could liquefy in a given time.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: spacenut on 04/04/2015 03:38 PM
Do you guy's think SpaceX might test the MTC by launching to the moon, landing, and returning to earth?  This would test it's landing ability, and its take-off  and return ability without a long trip to Mars and back.  Then try for Mars and back to test it's ability for the longer trips. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: philw1776 on 04/04/2015 04:19 PM
Enjoyed the MCT speculative post.  I take most exception to this...

"Electric Propulsion may be used during transit. But probably only as a secondary propulsion system for attitude control, course corrections"

Don't know why this is so as both Elon & Gwen have said they're looking at SEP Solar Electric Propulsion "among other {un-named} alternatives.  Lots of non-SpaceX R&D $ and flights advancing SEP technology for space that SpaceX could leverage off in the MCT to Mars realistic timeframe.

I agree wholeheartedly that what gets built will deviate in unexpected ways from both our initial expectations and yes from SpaceX's ToBeAnnounced 1st public architecture release, late this year or likely later.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: MikeAtkinson on 04/04/2015 05:40 PM
The way I look at it is this:

Is the system necessary - the main engines are, ECLSS is, heat shield is.

For those systems that are necessary, is there a cheaper way to do them.

If they aren't necessary, then do they confer some other benefit, that overrides the disadvantages.

In the case of SEP, it is not necessary. It is expensive in terms of design and hardware cost. It complicates the mission architecture and does not gain anything that throwing a bit more propellant at it doesn't do (propellant is cheap).

To provide useful propulsion for MCT a SEP system two orders of magnitude larger than any previous one is needed. Scaling up is not going to be easy, keeping the cost reasonable is going to be hard. Deploying the SEP,  then getting it all back into the MCT reliably each year for the lifetime of the vehicle is especially hard. There is nowhere on Earth that the deployment can be tested.

When my boss asks me to make a design change that is a bad idea, but not silly, I say "I'll look into it" I think this is what Elon did, rather than reject SEP outright he made a noncommittal statement.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 04/04/2015 06:09 PM
Who says SEP is expensive as far as hardware costs go? SpaceX certainly doesn't think so for their constellation satellites.

Doesn't mean it will be used for MCT, but don't assume SpaceX would hamstring themselves with super-expensive hardware when they know they can produce that hardware much cheaper.

(The reason they might not use extensive SEP would be architectural: you probably would want to keep the SEP portion in orbit instead of landing on Mars and Earth as the rest of MCT would, and this would complicate things somewhat.)
Title: Re: MCT Speculation and Discussion Thread 3
Post by: philw1776 on 04/04/2015 07:42 PM
The way I look at it is this:

Is the system necessary - the main engines are, ECLSS is, heat shield is.

For those systems that are necessary, is there a cheaper way to do them.

If they aren't necessary, then do they confer some other benefit, that overrides the disadvantages.

In the case of SEP, it is not necessary. It is expensive in terms of design and hardware cost. It complicates the mission architecture and does not gain anything that throwing a bit more propellant at it doesn't do (propellant is cheap).

To provide useful propulsion for MCT a SEP system two orders of magnitude larger than any previous one is needed. Scaling up is not going to be easy, keeping the cost reasonable is going to be hard. Deploying the SEP,  then getting it all back into the MCT reliably each year for the lifetime of the vehicle is especially hard. There is nowhere on Earth that the deployment can be tested.

When my boss asks me to make a design change that is a bad idea, but not silly, I say "I'll look into it" I think this is what Elon did, rather than reject SEP outright he made a noncommittal statement.

Not as said.
Plus, when asked directly in the video how the MCT would get to Mars , Shotwell said "We're looking into SEP"
That is far from noncommittal.

Point being, to the best of our knowledge, not being in SpaceX, all management statements of record has SEP being a prime consideration for propulsion. It may not be selected in the end, but if we're basing speculation on what SX says, and want to post an accurate summary of their statements, SEP is under consideration for FAR more than positional thrusters.

Title: Re: MCT Speculation and Discussion Thread 3
Post by: BobHk on 04/04/2015 08:10 PM
So their options beyond chemical, nuclear thermal and SEP are?  Solar sail?  Really what tech that is available will cut transit time other than SEP or nuclear thermal?

Title: Re: MCT Speculation and Discussion Thread 3
Post by: docmordrid on 04/04/2015 11:24 PM
So their options beyond chemical, nuclear thermal and SEP are?  Solar sail?  Really what tech that is available will cut transit time other than SEP or nuclear thermal?

NASA just dumped millions into NextSTEP's 3 year SEP development. The recipients are MSNW for an ELF thruster, Ad Astra for VASIMR and AeroJet (Hall?)  Any bets?

NextSTEP.... (http://www.nasa.gov/press/2015/march/nasa-announces-new-partnerships-with-us-industry-for-key-deep-space-capabilities/)

NSF Advanced thread.... (http://forum.nasaspaceflight.com/index.php?topic=36787.0)
Title: Re: MCT Speculation and Discussion Thread 3
Post by: BobHk on 04/05/2015 12:29 AM
If an ELF can use a really cheap low atomic mass fuel its a winner...but it seems a lot less mature as a thruster vs the HALL.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 04/05/2015 01:51 AM
SpaceX is using Hall thrusters for the constellation, one would imagine it would be their choice if SpaceX goes SEP as they said they might.


(And nowhere did SpaceX mention the possibility of nuclear power for MCT, so it's off topic for this thread.)
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Elmar Moelzer on 04/05/2015 01:54 AM
SpaceX is using Hall thrusters for the constellation, one would imagine it would be their choice if SpaceX goes SEP as they said they might.


(And nowhere did SpaceX mention the possibility of nuclear power for MCT, so it's off topic for this thread.)
I remember SpaceX and Elon Musk mentioning NTRs and nuclear power on several occasions. No positive confirmation but we don't have that for SEP either.
The ELF could be really good. MSNW has had really good experimental results from it.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: darkenfast on 04/05/2015 02:57 AM
Regarding launch sites: has anyone ever set a limit for what can be launched from the KSC/CCAFS area before noise or possible blast starts to cause damage outside of the security area or off-site?  The 130-ton SLS will be about 10 million pounds of thrust and it will go from LC39.  Can a 15-million pound thrust BFR launch from the same general area?
Title: Re: MCT Speculation and Discussion Thread 3
Post by: go4mars on 04/05/2015 02:10 PM
Regarding launch sites: has anyone ever set a limit for what can be launched from the KSC/CCAFS area before noise or possible blast starts to cause damage outside of the security area or off-site?  The 130-ton SLS will be about 10 million pounds of thrust and it will go from LC39.  Can a 15-million pound thrust BFR launch from the same general area?
There's a thread for that.
http://forum.nasaspaceflight.com/index.php?topic=2594.0
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Ben the Space Brit on 04/05/2015 05:34 PM
Regarding 'what is and is not necessary' for the complete MCT spacecraft: I've been hearing figures for VASMIR-powered flight to Mars of around 5 or 6 weeks one-way. With this sort of flight duration, is any kind of gravity simulation of the spacecraft strictly necessary, especially assuming that, in between transfer orbits, the crew would be spending most or all of their time on Mars's surface?
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Hauerg on 04/05/2015 05:47 PM
Regarding 'what is and is not necessary' for the complete MCT spacecraft: I've been hearing figures for VASMIR-powered flight to Mars of around 5 or 6 weeks one-way. With this sort of flight duration, is any kind of gravity simulation of the spacecraft strictly necessary, especially assuming that, in between transfer orbits, the crew would be spending most or all of their time on Mars's surface?
Methinks that works only if you can get the energy to power the engine for free from hyperspace.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: spacenut on 04/05/2015 08:17 PM
Max for Kennedy pads 39A and B were about 12 million lbs. thrust, based on an 8 engine Nova rocket using same engines as Saturn V. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: MikeAtkinson on 04/05/2015 09:32 PM
Max for Kennedy pads 39A and B were about 12 million lbs. thrust, based on an 8 engine Nova rocket using same engines as Saturn V.

Sound suppression technology might be better now.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: MikeAtkinson on 04/05/2015 09:36 PM
Regarding 'what is and is not necessary' for the complete MCT spacecraft: I've been hearing figures for VASMIR-powered flight to Mars of around 5 or 6 weeks one-way. With this sort of flight duration, is any kind of gravity simulation of the spacecraft strictly necessary, especially assuming that, in between transfer orbits, the crew would be spending most or all of their time on Mars's surface?

Don't believe all you hear. VASMIR is no better than at least a couple of other technologies. As always with electric propulsion is finding a large power source in a low mass package.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Doesitfloat on 04/05/2015 09:48 PM
Does anyone know how long it takes to liquefy a certain volume of oxygen and methane with existing equipment?

The natural gas company I worked for liquefied gas during the summer when gas was abundant and cheap, but took 3-4 months to liquefy enough for 2 months winter use.  These tanks were very large, around 50-75 meters in diameter, two walls, 3' between the walls where a vacuum was pulled, like a giant thermos bottle.  I wasn't with that group, so I know very little about how much volume they could liquefy in a given time.
Large volume of LNG
See the LNG tankers.
The Grand Aniva carries 36,671 tons of LNG.
Gotta luv a ton of gas. 8)
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Burninate on 04/05/2015 10:46 PM
Regarding 'what is and is not necessary' for the complete MCT spacecraft: I've been hearing figures for VASMIR-powered flight to Mars of around 5 or 6 weeks one-way. With this sort of flight duration, is any kind of gravity simulation of the spacecraft strictly necessary, especially assuming that, in between transfer orbits, the crew would be spending most or all of their time on Mars's surface?
http://www.reddit.com/r/Futurology/comments/31795t/nasa_selects_companies_to_develop_superfast_deep/cq0b8uf
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 04/06/2015 12:39 AM
SpaceX is using Hall thrusters for the constellation, one would imagine it would be their choice if SpaceX goes SEP as they said they might.


(And nowhere did SpaceX mention the possibility of nuclear power for MCT, so it's off topic for this thread.)
I remember SpaceX and Elon Musk mentioning NTRs and nuclear power on several occasions...
Nope. There WAS a presentation mentioning it by a former employee (Markusic, now working at Firefly), but this was later disavowed by SpaceX and as far as we know was ONLY his idea. Musk has NEVER mentioned using NTR or nuclear power as a real possibility (certainly not "several occasions"). Prove me wrong (should be simple to do if you're right), or you're off-topic.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 04/06/2015 12:53 AM
Here are all the times Musk has mentioned nuclear on shitelonsays.com:
"On the nuclear side, I think that's tough. It's really tough taking up a lot of nuclear fuel in a rocket. People have a hard time with establishing nuclear power stations, how would you like one that's flying over your head and might crash? I mean, we all might think that's a good idea, but we're in the minority."
(this part is about nuclear in space)

Nuclear on the ground:
"I'm quite confident that solar power will be the single largest source of electrical energy for humanity in the future. It will be combined with other things, of course, such as hydro power, geothermal, and I actually think nuclear is not a terrible option, so long as you're not located in a place that's susceptible to natural disasters. That, also I think, defies common sense. So long as there are not huge earthquakes or weather systems that have names coming at you, then I think nuclear can be a sensible option. There are much safer and better ways of generating nuclear energy - I'm talking fission here - than existed in the past when nuclear reactors first came out. At some point in the future it would be nice to make fusion work, of course. That'd be quite good, but in the mean time I think indirect fusion, being solar power, is a good thing to do. That's what Solar City is doing, it's really trying to improve the economics of solar power, and they're doing a great job."

Nuclear on surface of Mars:
"[Question about robotic precursor missions.] Yeah, yeah, I think that'd be - like, we have rovers on Mars already, so I think we'll see more robots on Mars and we'll probably want to make sure the propellant depot works - it'd be an automated propellant depot and there is some question as to, what do you do for power generation on Mars? Do you have a nuclear reactor? Then you've got to carry the nuclear fuel there, and reactors are fairly heavy. Do you do some lightweight solar power system? Like, maybe big inflatable solar arrays or something like that. So, just power generation on Mars, I think is an interesting problem, and then just figuring out how to get all the bits of efficiency right for creating, say, methane and oxygen on Mars. Ya know, Mars has got a CO2 atmosphere and there's a lot of water buried in the soil that you can get to."

Nuclear power as part of a broad array of power sources for electric cars:
" The great thing about electric cars is you can generate the electricity from a wide range of renewable sources like hydro, geothermal, wind, solar and nuclear where it's safe to do so."

In every case, he seems to be saying nuclear is not a particularly amazing option and generally solar is better (safer) or less heavy.

I agree with him (although I don't think nuclear is quite as dangerous as he's implying), for the record. But especially in space, solar is much, much better.

Nowhere does he give a hint that it's a likely fit for MCT, certainly not nuclear-thermal.


So nuclear power is off-topic.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: spacenut on 04/06/2015 02:12 AM
I know about the large natural gas ships.  The same tanks on the ships, we use on the ground.  I was wondering how long it would take to fill a natural gas powered rocket.  Same with lox.  Can you launch a Raptor with MTC per day if MTC is metholox powered? Per week, bi-weekly.  It takes time to liquefy one of these ships, or the storage tanks.  We took 3-4 months to liquefy the equivelant of one if those ships. 

On MCT, would argon for a SEP powered ship be a better source of fuel vs xenon for in space use?  Argon if more plentiful and is the 3rd most abundant gas after nitrogen and oxygen in the atmosphere. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 04/06/2015 02:58 AM
Yeah, Argon is better than Xenon due to the high flight rate (Xenon is better technically but is much rarer). And really, with thousands of flights per yer, Xenon isn't an option (it'd require a thousand times the current Xenon production rate to keep up)
Title: Re: MCT Speculation and Discussion Thread 3
Post by: spacenut on 04/06/2015 04:33 PM
That's what I thought, so it seems more research and development should be done using argon.  I know MCT might not be electric, but using what is currently available upsized, how big an area would the solar panels be to move a 100-200 ton MCT to Mars and back? 

Seems like flight adjustment thrusters would be great using electric-argon since hypergols are dangerous with a lot of human interaction and a lot of transfers to Mars. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Vultur on 04/10/2015 05:23 AM
Regarding 'what is and is not necessary' for the complete MCT spacecraft: I've been hearing figures for VASMIR-powered flight to Mars of around 5 or 6 weeks one-way. With this sort of flight duration, is any kind of gravity simulation of the spacecraft strictly necessary, especially assuming that, in between transfer orbits, the crew would be spending most or all of their time on Mars's surface?

I don't think it's necessary even at 8 months. Maybe even a negative - you can get more use out of limited space in zero-g.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Ben the Space Brit on 04/10/2015 11:53 AM
FWIW, I'm still thinking of two distinct crewed flight modes:

The first would use a Raptor cluster for TMI and the MCT's own engines for ROI and would sacrifice payload weight for fuel bunkerage.

The second would have a separate electric propulsion module that would stage from EML-2 and remain in the same orbital altitude as Phobos at Mars. The advantage of the second option would be more of the internal volume could be used for crew, consumables and cargo. Electric propulsion is high-reliability so eliminating large enough propellent tanks for a chemical ROI would be low risk.

The main uncrewed flight mode would resemble the first crewed flight mode and would be used for one-way cargo delivery. The inside of the MCT would be almost entirely stripped out in favour of cargo racks, pressurised cargo pods or a composite-hulled habitat module.

The MCT itself would be an aerodynamic configuration not dissimilar to the X-37 in shape but with folding fins and wings. Its primary propulsion system would be eight Merlin-M in four dual clusters at the four corners. The aft two clusters can be vectored aft or down. The TPS will be designed for Earth EDL; the design would allow a certain degree of gliding performance but would still require either ditching at sea or a propulsive landing on Earth. Due to Mars's thin atmosphere, Martian EDL would be all-propulsive.

All launches would be identical with a BFR. The only significant differences would be in the tasking of the Raptor VAC upper stage. If there is the mission has an electric propulsion module, then the U/S will only need to send the MCT to EML-2, meaning that it can lift more payload into the LEO parking orbit.

I just love the thought of watching a 10m-diameter stub-winged spacecraft setting down on the shuttle landing strip. Shades of Thunderbirds!

[Edit]
Forgot to mention: The Flight Deck and passenger launch cabin would be in the nose of the MCT. Underneath the aerodynamic shell this element would be a scaled-up Dragon that can be ejected from the MCT in the event of an emergency during ascent from Earth and would allow for the crew to return to Mars's surface (and the colony) in the event of a serious failure in Mars orbit.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: The Amazing Catstronaut on 04/10/2015 12:34 PM
FWIW, I'm still thinking of two distinct crewed flight modes:

Its primary propulsion system would be eight Merlin-M in four dual clusters at the four corners.

I don't agree with the lifting body idea - I really don't think it adds much in the way of functionality and might create a lot more structural trouble than it is worth. Yeah, lifting bodies are cool and I'd also love to see a Thunderbird in real life. However, Thunderbirds didn't really exhibit the world's best understanding of physics when it came to spacecraft. Or aircraft. Or minisubs. However, I'm interested by the "Merlin-M" concept.

What kind of specs are you thinking for this, Ben? I'm assuming the "M" stands for "Methane" here.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Ben the Space Brit on 04/10/2015 12:42 PM
What kind of specs are you thinking for this, Ben? I'm assuming the "M" stands for "Methane" here.

Yeah, basically a Merlin-VAC but using LCH4 as its propellent.

The objective specifications of Merlin-M would be about the same thrust with about 360s-380s vacuum impulse. It's possible that eight engines for landing and early ascent is excessive but, if so, it at least provides a degree of redundancy.

Raptor is probably going to be a very big engine at least in terms of volume and it might not be practical to fit it to MCT itself. If that is the case, then Merlin-M steps in as a 'baby Raptor'.

FWIW, it is important not to overstate my MCT concept's lift-generating capability. It is never more than 'controlled fall' and is meant to allow for steering in the event of having to navigate through weather on approach and give the flight crew a few options in the event they need to find an alternate LZ. As it is VL, that could potentially be anywhere suitably size, such as a large enough (empty) parking lot. Most of the aerodynamics are intended to allow for the maximum volume utilisation from a 10m-barrel LV without having to squeeze the mission vehicle inside a PLF.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: The Amazing Catstronaut on 04/10/2015 12:48 PM

Yeah, basically a Merlin-VAC but using LCH4 as its propellent.

The objective specifications of Merlin-M would be about the same thrust with about 360s-380s vacuum impulse. It's possible that eight engines for landing and early ascent is excessive but, if so, it at least provides a degree of redundancy.

Raptor is probably going to be a very big engine at least in terms of volume and it might not be practical to fit it to MCT itself. If that is the case, then Merlin-M steps in as a 'baby Raptor'.

Oh wow! Kudos for the zippy response time.  :D

That makes a lot of sense - it seems reasonable to apply the "Lots of engines = redundancy" principle for the MTC if you're going do do the same for the LV. Besides, SpaceX already has experience with getting 9+ engines to work coherently without much in the way of mishap, so that's a sound idea there. I wouldn't be too shocked if that is what comes to fruition.

A dual engine landing would be an interesting thing to witness, to be sure (with possibly/probably more for Earth landing, I'm not sure how it scales).

Edit: Aaah, I've got you. Apologies, I misread your first statement.

Giving the MTC more aero control whilst returning through the Earth's atmosphere would certainly be intriguing - I can imagine the footage of it reorienting for the terminal burn - would certainly be majestic.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: philw1776 on 04/15/2015 12:41 AM
I'll speculate that the 1st stage of the BFR or MCT or whatever it's called will look thick & squat compared to the Falcon 9 pencil.  More stable as a vertical landing vehicle.  I'm in for >10meters diameter as well.  If you're gonna put up a craft capable of carrying 50-100 people for months to Mars, a tiny tube is not a good design starting point.  Yes, I'm aware of Bigelow.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Ben the Space Brit on 04/15/2015 10:52 AM
@philw1776,

Maybe this is me but I see the BFR (the Raptor-powered launch vehicle) and the MCT as two distinct projects and two distinct vehicles. The BFR (which I think of as 'Condor') is basically just a 120-ish t IMLEO launcher. MCT is the payload.

Look at pictures of the hypothetical 'Falcon-XX' and add Falcon-style landing legs and you've got a good idea of what BFR looks like. What MCT will look like is anyone's guess. It could be quite an elaborate design, straight out of Space: 1999 if it launches in a PLF.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lampyridae on 04/15/2015 11:09 AM
Look at pictures of the hypothetical 'Falcon-XX' and add Falcon-style landing legs and you've got a good idea of what BFR looks like. What MCT will look like is anyone's guess. It could be quite an elaborate design, straight out of Space: 1999 if it launches in a PLF.

That would be awesome. Elrond Musk, make it so!
Title: Re: MCT Speculation and Discussion Thread 3
Post by: spacenut on 04/15/2015 02:37 PM
I too think a short wide BFR and MCT would be able to land better without toppling over.  Also I like the idea of say electric tugs going from ELM 2 to high Mars orbit and back.  A Falcon Heavy could bring argon propellant to resupply the tug and either another one, or a BFR would take cargo to the tug.  The MCT would be for human transport only along with some food/water supplies.  The tug to take a 100 tons of cargo or cargo MCT to Mars slowly even during a long trips when humans are not in the 6 month window.  Colonization cargo could be carried on a continuous bases with ISRU equipment, soil moving equipment, mining equipment, smelting equipment, solar arrays, etc.  Even high Mars orbit solar panels parallel with the Mars sun orbit for continuous electricity that could be beamed to a colony at night using microwaves or lasers.  So I think the MCT could do far more than just go to Mars and come back during a 6 month window, but during off months the tug infrastructure could be put in place with non perishable cargo transported once this infrastructure is in place.  NASA could pay to use it also. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: sheltonjr on 04/15/2015 02:58 PM
 ;D It drives me crazy! Seems like half the posts about the MCT cannot get the acronym right. How hard is it to spell MTC???  ;D
Title: Re: MCT Speculation and Discussion Thread 3
Post by: spacenut on 04/15/2015 03:05 PM
Fixed it. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/16/2015 12:35 AM
@philw1776,

Maybe this is me but I see the BFR (the Raptor-powered launch vehicle) and the MCT as two distinct projects and two distinct vehicles. The BFR (which I think of as 'Condor') is basically just a 120-ish t IMLEO launcher. MCT is the payload.

Look at pictures of the hypothetical 'Falcon-XX' and add Falcon-style landing legs and you've got a good idea of what BFR looks like. What MCT will look like is anyone's guess. It could be quite an elaborate design, straight out of Space: 1999 if it launches in a PLF.

As I've posted over on the Raptor thread, I think you are on the right track for it's overall size. 

http://forum.nasaspaceflight.com/index.php?topic=34197.msg1357465#msg1357465

120mt-ish, Saturn V-class.  But I disagree that BFR and MCT will be two different things.  I think they'll be an integrated system, not unlike STS.  STS wasn't an LV and a spacecraft, it was a whole system that flew together.  That's why we've never heard any seperate name for the booster.  It's always just been referred to as by SpaceX and Elon as "MCT".  And in fact, in Elon's Reddit interview, he basically said that here:

Quote
Question:
Mars. Could you please clarify what the Mars Colonial Transporter actually is? Is it a crew module like Dragon, a launch vehicle like Falcon, or a mix of both? Does it have inflatable components? Is MCT just a codename?
  Elon's Answer:
 
The Mars transport system will be a completely new architecture. Am hoping to present that towards the end of this year. Good thing we didn't do it sooner, as we have learned a huge amount from Falcon and Dragon.

He also makes reference to there being just a booster using the sea level version of Raptor, and the spaceship using the vacuum version of Raptor.  While I suppose he could mean a two-stage stack when he says "booster", typical reference to booster just meanst he 1st stage, so I take this to mean MCT is a two stage integrated system, with the spacecraft integrated onto the upper stage, and BLEO missions are staged in LEO where that spacecraft is fueled up.
Think of a Saturn INT-21, where a spacecraft and TPS system (and landing legs) were integrated into the S-II stage. 
If the spacecraft is part of the stage and not a payload, the dry mass of the stage is included in the LEO capability.  The Saturn INT-21 could have put nearly 120mt payload into LEO.  The drymass of the S-II was about 45mt.  That means if Saturn INT-21 was an MCT, it could place 165mt in LEO. 
So what sort of capability could such an S-II sized spacecraft/stage fueled all the way up in LEO have?

Someone could model that accurately, but to do just a quick and dirty comparative analysis.
 
The S-IVB could get 45mt plus it's own dry mass of 16mt, plus whatever residuals were left in it at separation, through TLI, obviously.   That's 61mt+ (depending on the mass of residuals).
And that would be more if the S-IVB didn't need to do the final part of the ascent burn that it needed to do while flying on the while Saturn V stack.  So it wasn't fully fueled while in LEO, prior to the TLI burn.  If it way, maybe it's total TLI would be closer to 70mt?  Let's assume 70mt if fully fueled in LEO for an example.

The S-II carried about 4.2X more propellant than the S-IVB, and had a little better mass fraction.  So 4.2X the TLI capacty of the S-IVB (including it's own dry mass) would be about 294mt (assuming close to 70mt through TLI for a fully fueled S-IVB in LEO).  The S-IVB and S-II used the same engine with the same impulse, so I think that's a reasonable comparison.
And I think TMI capacity of a stage is around 80-82% of TLI?  So assuming 80%, that's 235mt through TMI.   That'd allow for a 135mt MCT and 100mt of useful payload.
Raptor will be about 40s less impulse than the S-II's J2 engines, so that 235mt would need to be derated for that, but for example if you derate say 20% (guess) for that lower impulse, that's still 188mt total.  An 88mt Spacecraft and 100mt of payload.  That's still very plausible.  The spacecraft could be lighter than that even.  The lighter the spacecraft and smaller MCT's booster needs to be to get it up into LEO with stowed cargo.

Again, that's just a rough example, but now we are talking about a stack more in the class Saturn INT-21, with maybe 15 Raptors (7.5Mlbs of thrust total), rather than something double that size or more with 30 Raptors or more as some of speculated.
15 Raptors would also make a fairly good MPS.  15 around with a central engine that should be able to handle the dry mass of the stage by itself.  500,000lbs of thrust can just barely hover a 226mt dy mass core core.  And I doubt the MCT booster will be that or more if it were to only have 15 engines for 7.5Mlbs of thrust.    The dry mass of the heavy S-1C was only 137mt dry.  So one Raptor should be able to handle it, and be more at the top of it's throttle range, rather than down at the bottom of it.

As MCT will be designed primarily for crews and for going to Mars (not unmanned payloads to GTO), that is a pretty good and neat and simple configuration.  It's reusable, so as long as it can get the minimal dry mass spacecraft into LEO, there's benefit to fly a smaller stack more often, instead of a larger stack less often, to get the economics of reusabilty to work better.

But what if someone has an umanned payload they want to send to escape or GTO?  Well, FH will handle most of that.  If there's an unmanned payload larger than that, MCT could launch with an expendable in-space stage mounted with the payload in a PLF on the nose of MCT.  Fortunately, SpaceX already has such a stage in the Falcon Upper stage.  I imagine it could throw quite a bit of uncrewed mass to GTO or escape if it was delivered fully fueled or mostly fulled fuled to LEO.
So there'd be options there as well. 

That's my current guestimate for MCT anyway, from reading Elon's recently clues.  :-)
Title: Re: MCT Speculation and Discussion Thread 3
Post by: dglow on 04/16/2015 07:02 AM
In every case, he seems to be saying nuclear is not a particularly amazing option and generally solar is better (safer) or less heavy.

I agree with him (although I don't think nuclear is quite as dangerous as he's implying), for the record. But especially in space, solar is much, much better.

Nowhere does he give a hint that it's a likely fit for MCT, certainly not nuclear-thermal.

One important detail that's often missed: if you need heat, especially on an industrial scale, nuclear is far more efficient than solar. It will be an important power source on Mars.

But agree re: MCT; in space that same heat generation is a liability.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Ben the Space Brit on 04/16/2015 12:17 PM
@philw1776,

Maybe this is me but I see the BFR (the Raptor-powered launch vehicle) and the MCT as two distinct projects and two distinct vehicles. The BFR (which I think of as 'Condor') is basically just a 120-ish t IMLEO launcher. MCT is the payload.

Look at pictures of the hypothetical 'Falcon-XX' and add Falcon-style landing legs and you've got a good idea of what BFR looks like. What MCT will look like is anyone's guess. It could be quite an elaborate design, straight out of Space: 1999 if it launches in a PLF.

As I've posted over on the Raptor thread, I think you are on the right track for it's overall size. 

http://forum.nasaspaceflight.com/index.php?topic=34197.msg1357465#msg1357465

120mt-ish, Saturn V-class.  But I disagree that BFR and MCT will be two different things.  I think they'll be an integrated system, not unlike STS.  STS wasn't an LV and a spacecraft, it was a whole system that flew together.  That's why we've never heard any seperate name for the booster.  It's always just been referred to as by SpaceX and Elon as "MCT".  And in fact, in Elon's Reddit interview, he basically said that here:

I have thought about the 'integrated U/S and payload' option. I'll tell you why I think that a separate upper stage is required: If the BFR core booster is anything like the one on Falcon-9, it will only burn for the first two or so minutes of the flight before RTLS. That will mean that the U/S will need to run for a very long time, around six minutes, just to reach LEO parking orbit. It will require a huge amount of propellent to shift a 100t payload that far. Combine that with the TMI fuel load and you suddenly have only a tiny mass budget left for the mission payload and the MCT will have to be towing around huge and mostly-empty fuel tanks for most of the mission.

A separate upper stage means that you can use Tsilokovsky's cheat to best effect. Dump the second set of ETO (and, for some flight profiles, TMI) tanks and engine so more of the MCT's mass and volume budget can be used for mission payload and in-mission propellent rather than redundant Earth ascent and departure mass and volume. A separate upper stage also allows the BFR to be used as a cargo hauler to launch the SEP propulsion module and other cargo like carrying racks for smaller (5m-diameter or smaller) one-way cargo landers.

[Edit]
Just an additional point about MCT's return to Earth. I've done some admittedly minimal research. Apparently, the largest ever mass returned by parachute is 86,000lbs or about 40t (A Minuteman missile). Depending on how much of that 100t IMLEO mass is used up before re-entry, it is not an engineering impossibility to use a parachute descent with propulsive velocity cancellation at zero feet for MCT!
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Hauerg on 04/16/2015 12:28 PM
But you do need those big tanks on the MCT for the fuel for the Mars to Earth trip. Not so different from the second stage functionality.
Also most likely it will be refuelled on it's way to mars anyway, so not THAT big tanks.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: JasonAW3 on 04/16/2015 03:35 PM
Does anyone know how long it takes to liquefy a certain volume of oxygen and methane with existing equipment?

The natural gas company I worked for liquefied gas during the summer when gas was abundant and cheap, but took 3-4 months to liquefy enough for 2 months winter use.  These tanks were very large, around 50-75 meters in diameter, two walls, 3' between the walls where a vacuum was pulled, like a giant thermos bottle.  I wasn't with that group, so I know very little about how much volume they could liquefy in a given time.
Large volume of LNG
See the LNG tankers.
The Grand Aniva carries 36,671 tons of LNG.
Gotta luv a ton of gas. 8)

If they plan on using an LNG carrier for the Methane, I hope that they set up an off shore station for offloading the LNG to the BFR Tank Farm. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Ben the Space Brit on 04/16/2015 04:16 PM
But you do need those big tanks on the MCT for the fuel for the Mars to Earth trip. Not so different from the second stage functionality.

Not necessarily. Depending on the exact mission plan, MCT may only need enough fuel for MTO (Mars to Orbit).
Title: Re: MCT Speculation and Discussion Thread 3
Post by: JasonAW3 on 04/16/2015 04:20 PM
But you do need those big tanks on the MCT for the fuel for the Mars to Earth trip. Not so different from the second stage functionality.
Also most likely it will be refuelled on it's way to mars anyway, so not THAT big tanks.

Might be able to drill holes big enough for the tankage in the regolith, and bury them.  Should act as a good insulator.  (Remember, depending upon where you are on Mars, it can get to 77 degrees Fahrenheit in the martian summer).
Title: Re: MCT Speculation and Discussion Thread 3
Post by: guckyfan on 04/16/2015 04:51 PM

I have thought about the 'integrated U/S and payload' option. I'll tell you why I think that a separate upper stage is required: If the BFR core booster is anything like the one on Falcon-9, it will only burn for the first two or so minutes of the flight before RTLS. That will mean that the U/S will need to run for a very long time, around six minutes, just to reach LEO parking orbit. It will require a huge amount of propellent to shift a 100t payload that far. Combine that with the TMI fuel load and you suddenly have only a tiny mass budget left for the mission payload and the MCT will have to be towing around huge and mostly-empty fuel tanks for most of the mission.

We do know that MCT will be mostly empty in LEO. It will be refuelled for the flight to Mars.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/16/2015 05:35 PM

I have thought about the 'integrated U/S and payload' option. I'll tell you why I think that a separate upper stage is required: If the BFR core booster is anything like the one on Falcon-9, it will only burn for the first two or so minutes of the flight before RTLS. That will mean that the U/S will need to run for a very long time, around six minutes, just to reach LEO parking orbit. It will require a huge amount of propellent to shift a 100t payload that far.

Yes, I agree.  In fact, I think that will be the plan.  The MCT stack...again...will look a lot like the Saturn INT-21 stack (or even the Saturn 1B stack), as in, the upper stage is very large in relation to the booster.  We're used to these BLEO optimized ELV's like Atlas and Delta where the upper stage is very small compared to the booster.  But they both use high ISP booster engines and so the more dV they can get from the booster, the lighter/smaller/more efficient they can make the upper stage.  Which maximizes GTO performance in a 2-stage LV. 
However, Saturn 1B and INT-21 were only going to LEO.  They have relatively short burning and high powered boosters (about 2.5 minutes burn time each if I recall correctly).  That actually works very well if you want the bring the booster back to the launch site.  You really do want it going "low and slow", because the faster and farther it is, the more propellant you need to get it back.  Better to make a short burning overpowered booster, and put that extra propellant on the upper stage.
And it won't necessarily need a huge amount of propellant.  Again, The Saturn INT-21 would have gotten nealy 120mt payload into LEO....plus it's own dry mass of 45mt.  That's 165mt into LEO.  The S-II was hydrolox with about 40s better ISP than Raptor-vac will have...but LH2 is also a lot less dense than LCH4.  So while you need more propellant mass to do the same job due to the lower impusle, it's denser.  So I wouldn't imagine the MCT/spacecraft/upper stage to be much different in size than the Saturn S-II stage....and get 165mt of combined mass into LEO.  The S-II is a big stage, but not hugely big like you are speculating here.   Once in LEO, it will be dry, and then subsequent  MCT launches fill it up in orbit.  Then it would burn for TMI.

I sort of expect the stack to look something like these. (see below).


Combine that with the TMI fuel load and you suddenly have only a tiny mass budget left for the mission payload and the MCT will have to be towing around huge and mostly-empty fuel tanks for most of the mission.

No, you're thinking about it wrong.  It's ascent propellant is burned all up to get it's own dry mass plus 100mt of payload to LEO.  Then it's refueled in LEO propr to TMI.  It's also refueled on the MArs surface prior to surface ascent and TEI. 
See my previous post as to my rough calculations on what an Saturn S-II sized MCT should be able to do if fueled up in LEO.  It should be able to get 100mt of paylaod plus it's own dry mass of up to about 88mt through TMI. (very rough calculation).   Is that not within Elon's comments about what he is planning MCT to do?


A separate upper stage means that you can use Tsilokovsky's cheat to best effect. Dump the second set of ETO (and, for some flight profiles, TMI) tanks and engine so more of the MCT's mass and volume budget can be used for mission payload and in-mission propellent rather than redundant Earth ascent and departure mass and volume. A separate upper stage also allows the BFR to be used as a cargo hauler to launch the SEP propulsion module and other cargo like carrying racks for smaller (5m-diameter or smaller) one-way cargo landers.


But a combined stage/spacecraft means you don't have to have the mass of two stages to LEO, just one.  You get double duty out of your stage mass. 
And an integrated upper stage still would allow MCT to be a cargo hauler.  See my previous post.  If smaller paylaods going BLEO, add a fueled F9US under the paylaod on top as an expendable "kick stage".
For larger payloads going BLEO, you stage in LEO like you would for a Mars mission, and fuel up MCT. 
It's not the most efficient as an uncrewed heavy payload launcher, but that's not really it's purpose, is it?

Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/16/2015 05:55 PM
But you do need those big tanks on the MCT for the fuel for the Mars to Earth trip. Not so different from the second stage functionality.
Also most likely it will be refuelled on it's way to mars anyway, so not THAT big tanks.

Yup.

The reusable F9US already hinted at all of this...just instead of a separate Dragon capsule on top, it'd be integrated into the sage itself.  I would expect the MCT spacecraft to look like a large version of that.

I know many are thinking the MCT spacecraft will look like a really big DRagon capsule, but I don't think so.  It'll look more like the biconic aeroshell in NASA's DRM, but be a whole stage/spacecraft rather than a jettisonable aeroshell.  That way the engines are at the aft and don't need to retract behind a heat shield.  And there's a reason NASA liked the biconic shape, it offers a lot more surface area to the Mars atmosphere for desceleration than a smaller capsule bottom. 

MCT Mars mission sequence"

Image 2:  MCT separating from the booster during ascent (use some imagination here, I'm borrowing a NASA graphic for their DRM 5.  But it shows my 2-part MCT concept)
Image 3:  MCT being refueled in LEO (picture a 2nd MCT there instead of the gold in-space stage, doing propellant transfer)
Image 4:  MCT entering the Martion atmosphere.
Image 5:  MCT on the surface of Mars.
 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lars-J on 04/16/2015 06:03 PM
But you do need those big tanks on the MCT for the fuel for the Mars to Earth trip. Not so different from the second stage functionality.

Not necessarily. Depending on the exact mission plan, MCT may only need enough fuel for MTO (Mars to Orbit).

The MCT still needs very large tanks. The delta V from Mars surface to low Mars orbit is not that much lower than what a second stage would need. It is till significant.

Delta-V:
Earth to LEO 2nd stage: 6000-7000 m/s
Mars to LMO SSTO: 4000 m/s

So you still need very large tanks.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/16/2015 07:00 PM
But you do need those big tanks on the MCT for the fuel for the Mars to Earth trip. Not so different from the second stage functionality.

Not necessarily. Depending on the exact mission plan, MCT may only need enough fuel for MTO (Mars to Orbit).

The MCT still needs very large tanks. The delta V from Mars surface to low Mars orbit is not that much lower than what a second stage would need. It is till significant.

Delta-V:
Earth to LEO 2nd stage: 6000-7000 m/s
Mars to LMO SSTO: 4000 m/s

So you still need very large tanks.

Even larger, as I think MCT would need to do a direct return from Mars surface though TEI?

Unless they set up a tanker in LMO, which I suppose there's no reason they couldn't.  Have an unmanned MCT land on Mars, Fill up, and go to LMO and wait for the outbound crew MCT.  Transfer prop in LMO and this the tanker returns to the surface and the crew MCT returns to Earth.
The only problem with that is how is the tanker MCT resupplied with LH2 fuel stock to make more methalox?  Unless you have a way to produce it reliable on the surface (a small surface crew stays and makes it from surface water ice they mine and electrolyze maybe?)

So I guess I always assumed MCT would launch from the surface of Mars directly through TEI.  It wouldn't be carrying nearly so much payload on the outbound trip as that would be offloaded on the surface, but it'd still have a crew of 4 or 6 or 10 or whatever (early exploratiory mission) plus provisions.

Later during colonization, I suppose the outbound MCT's would have few or no crew if they could be brought back fully remotely. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: philw1776 on 04/16/2015 07:22 PM
These interesting MCT architectures...what about the SEP possibility that Elon and recently Gwynne have each mentioned?  Elon has also said that they have "learned a lot" from the F9R project, so much that he was glad the BFR/MCT architecture was still in flux.  Deployable SEP implies to me that there may be 2 distinct components to the MCT and it's not monolithic.  A re-usable interplanetary vehicle with SEP and housing for humans that carries a multi-use re-usable Mars lander/ Mars return to orbit/ Earth re-entry "classical" MCT that possibly looks like the MCT concept posted a couple posts earlier.

Title: Re: MCT Speculation and Discussion Thread 3
Post by: spacenut on 04/16/2015 07:42 PM
90% of what goes to Mars for colonization is going to be earth equipment, housing, solar panels, greenhouses, ISRU equipment, etc.  Only 10% will be for human transportation.  Therefore large SEP in space tugs will probably carry most of the non perishable equipment and cargo, and land it on Mars.  SEP tug will return to L1 or L2 to pick up additional SEP fuel (I prefer argon because it is more plentiful), and more cargo to take to Mars.  All this can take place in the 18 months Mars is not close to earth.  Then humans can transport in MCT refueled in space to get to Mars. 

I think some of the equipment landed on Mars should be on wheels so it can move closer together.  That is so landers returning to earth can refuel.  At least the fuel storage equipment should be mobile to be able to move to the landers to refuel them. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Semmel on 04/16/2015 08:33 PM
Lets say this following map is roughly correct (exact numbers vary depending on transfer anyway):
http://i.imgur.com/SqdzxzF.png

deltaV
TMI: ~4000 m/s
LMO: ~3800 m/s
TEI: ~2500 m/s

Then it would make sense to design BFR+MCT as a two-part vehicle.
It needs at least 4000 m/s deltaV, which can just be part of the second stage going into orbit.

Refuelling in Mars orbit is maybe possible but probably way too complicated. It adds so many failure modes that it is probably not considered unless absolutely necessary.
So in this case, MCT needs at least 3800+2500 m/s = 6300 m/s of dV on its way back. Considering that it will loose a lot of its cargo on Mars, the same vehicle that has 4000 m/s on its way to Mars might just have 6500 m/s on its way back. No need to refuel in Mars orbit in the first place.

Some margin would be required, especially because it needs to be able to select the transfer window and for human spaceflight, margin is required anyway. So lets say the stage has a dV capacity of 5000 m/s on its way to Mars.

That means, the BFR booster stage would require around 4500 m/s dV capacity, including 10% margin for reusing it. From this (I admit rather simplified) considerations, MCT would look roughly like this:

BFR 1rst stage: > 4500 m/s dV
MCT (= 2nd stage): >5000 m/s dV

The question is, is it possible to build a tanker 2. stage that can be lifted by the BFR 1rst stage that refuels MCT in LEO? I dont know how much mass in fuel for the MCT would be required to achieve 5000 m/s dV. There must be some tradeoff optimum somewhere where the mass of the fuel transporter matches the mass of the MCT fully fuelled. I dont know how to do such a calculation, but I am sure someone here can do that. But first, is there a fundamental flaw in my thoughts?
Title: Re: MCT Speculation and Discussion Thread 3
Post by: guckyfan on 04/16/2015 09:56 PM
@Semmel

One nitpick. You need to add Mars landing which will need very roughly 1km/s delta/v.

Earth landing requires much less so you can neglect it on first approximation.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/16/2015 11:36 PM
Lets say this following map is roughly correct (exact numbers vary depending on transfer anyway):
http://i.imgur.com/SqdzxzF.png

deltaV
TMI: ~4000 m/s
LMO: ~3800 m/s
TEI: ~2500 m/s

Then it would make sense to design BFR+MCT as a two-part vehicle.
It needs at least 4000 m/s deltaV, which can just be part of the second stage going into orbit.

Refuelling in Mars orbit is maybe possible but probably way too complicated. It adds so many failure modes that it is probably not considered unless absolutely necessary.
So in this case, MCT needs at least 3800+2500 m/s = 6300 m/s of dV on its way back. Considering that it will loose a lot of its cargo on Mars, the same vehicle that has 4000 m/s on its way to Mars might just have 6500 m/s on its way back. No need to refuel in Mars orbit in the first place.

Some margin would be required, especially because it needs to be able to select the transfer window and for human spaceflight, margin is required anyway. So lets say the stage has a dV capacity of 5000 m/s on its way to Mars.

That means, the BFR booster stage would require around 4500 m/s dV capacity, including 10% margin for reusing it. From this (I admit rather simplified) considerations, MCT would look roughly like this:

BFR 1rst stage: > 4500 m/s dV
MCT (= 2nd stage): >5000 m/s dV

The question is, is it possible to build a tanker 2. stage that can be lifted by the BFR 1rst stage that refuels MCT in LEO? I dont know how much mass in fuel for the MCT would be required to achieve 5000 m/s dV. There must be some tradeoff optimum somewhere where the mass of the fuel transporter matches the mass of the MCT fully fuelled. I dont know how to do such a calculation, but I am sure someone here can do that. But first, is there a fundamental flaw in my thoughts?

Yea, that's kinda what I was thinking in general.  Thanks for throwing some actual [rough] numbers to it, and fleshing it out some.  I'm leaning more and more this way, not only from it's economical and simplicity merits, but mainly from my take on the clues Elon's been dropping to us.

Myself I agree that refueling in Mars orbit for the return would add complexity.  But that complexity may be necessary of MCT can't feasibly be made to have enough dV to get from the surface of Mars to the surface of earth in one direct shot. 

Does anyone know how much dV the Saturn S-II stage had?  Just as a rough comparison of one large upper stage to another?

Or how much dV the Saturn S-1C stage had, as rough comparison to the MCT 1st stage?

Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/16/2015 11:51 PM
Ultimately, I think Elon just got inspired by this:

http://matterhorn1959.blogspot.com/2007/08/rocket-to-moon-under-douglas.html

;-)
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/16/2015 11:56 PM
90% of what goes to Mars for colonization is going to be earth equipment, housing, solar panels, greenhouses, ISRU equipment, etc.  Only 10% will be for human transportation.  Therefore large SEP in space tugs will probably carry most of the non perishable equipment and cargo, and land it on Mars.  SEP tug will return to L1 or L2 to pick up additional SEP fuel (I prefer argon because it is more plentiful), and more cargo to take to Mars.  All this can take place in the 18 months Mars is not close to earth.  Then humans can transport in MCT refueled in space to get to Mars. 

I think some of the equipment landed on Mars should be on wheels so it can move closer together.  That is so landers returning to earth can refuel.  At least the fuel storage equipment should be mobile to be able to move to the landers to refuel them.

I think Elon might be warming to the idea of SEP down the road once they get to actualy colonization mode, for the reasons you mention.  I think first Elon was against, but I think he's made a few comments more recently warming to it, if I recall correctly.  (Someone correct me if that's wrong).

But for the initial "learning" and "exploration" phases, of which I'm sure they'll be heavily partnered with NASA for (they won't let a rocket go to Mars without their guys on it.  ;-)  ), I'm sure it'll be more basic chemical propulsion.   SEP is efficient, but MCT will be designed to get 100mt to the Mars surface, and LCH4 and LOX are both cheap propellants.  So if it can get the job done affordably, there's not much hurry for some larger cargo system using SEP which would require a lot of additional investment by SpaceX.

Title: Re: MCT Speculation and Discussion Thread 3
Post by: Impaler on 04/17/2015 02:43 AM
These integrated 2nd stage concepts have some unavoidable problems.

*  No possible abort during launch, the propellent mass is simply too high for the large vehicle to have any appreciable acceleration away from an exploding 1st stage.  For our early missions when crews are just a handful of explorers it's easy enough to put them on F9 to rendezvous with the MCT that launches un-manned.  But for the full blown system you clearly need to be using this vehicle as a crewed launch vehicle and it is impossible to see how you can put people in this vehicle and rescue them when a launch failure happens.

* Highly unstable landing on Mars, with is extreme height your in great danger of toppling over.  Even if cargo hold is in the bottom as Lobo's sketch indicates the tanks above are going to have residual propellent, and center of mass will be higher above the ground then the leg base is wide.  We have seen how difficult it is to keep F9 first stage strait on landing and that is on a flat surface.  On Mars your surface can be both rocky AND it can give-way during landing or even after, say if subsurface ice sublimates you end up like the Leaning tower of Pisa.

Both these problems make the system more dangerous then I think is acceptable.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: go4mars on 04/17/2015 03:56 AM
We do know that MCT will be mostly empty in LEO. It will be refuelled for the flight to Mars.
Do we know that?  At one point I was assuming the tanker/upper stages could refuel each other and probably MCT,  probably at  L4 or L5, but I haven't read anything that specifies the depot architecture.   Not even what the transferred fluid will be.  Argon?  Silane?  Methane & oxygen? Methane only?    Some combination of the 4?   

Does the TMI tanker stage also use 1000 isp silane ramjets for propulsive descent at Mars, and for ascent from Mars? 

So many questions outstanding about the architecture that it's tough to state that the MCT is refuelled in LEO for the flight to Mars.       ...though I've been busy and might have missed the statement.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: BobHk on 04/17/2015 04:12 AM
Will MCT really need great honking large tanks when its taking off from Mars 90-100mT lighter than it arrived?
Title: Re: MCT Speculation and Discussion Thread 3
Post by: guckyfan on 04/17/2015 05:49 AM
We do know that MCT will be mostly empty in LEO. It will be refuelled for the flight to Mars.

Do we know that? 
................
So many questions outstanding about the architecture that it's tough to state that the MCT is refuelled in LEO for the flight to Mars.       ...though I've been busy and might have missed the statement.

Yes we do know that. Elon Musk did mention that they will refuel in LEO. We do know that Raptor is developed as the MCT engine, so we do know the fuel would be LOX and methane.

Title: Re: MCT Speculation and Discussion Thread 3
Post by: hkultala on 04/17/2015 05:59 AM
We do know that MCT will be mostly empty in LEO. It will be refuelled for the flight to Mars.

Do we know that? 
................
So many questions outstanding about the architecture that it's tough to state that the MCT is refuelled in LEO for the flight to Mars.       ...though I've been busy and might have missed the statement.

Yes we do know that. Elon Musk did mention that they will refuel in LEO.

This part is the part needing reference. When / where did he say that?

Quote

We do know that Raptor is developed as the MCT engine, so we do know the fuel would be LOX and methane.

This part is so trivial and commonly known it's not even worth mentioning.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: guckyfan on 04/17/2015 06:40 AM
Quote
Yes we do know that. Elon Musk did mention that they will refuel in LEO.


This part is the part needing reference. When / where did he say that?

I am quite sure it was in the reddit AMA. Most readers will know.

Quote

We do know that Raptor is developed as the MCT engine, so we do know the fuel would be LOX and methane.

This part is so trivial and commonly known it's not even worth mentioning.

It was in response to this quote by go4mars:

Quote
I haven't read anything that specifies the depot architecture.   Not even what the transferred fluid will be.  Argon?  Silane?  Methane & oxygen? Methane only?    Some combination of the 4?   
Title: Re: MCT Speculation and Discussion Thread 3
Post by: GORDAP on 04/17/2015 12:27 PM
Lets say this following map is roughly correct (exact numbers vary depending on transfer anyway):
http://i.imgur.com/SqdzxzF.png

deltaV
TMI: ~4000 m/s
LMO: ~3800 m/s
TEI: ~2500 m/s

Then it would make sense to design BFR+MCT as a two-part vehicle.
It needs at least 4000 m/s deltaV, which can just be part of the second stage going into orbit.

Refuelling in Mars orbit is maybe possible but probably way too complicated. It adds so many failure modes that it is probably not considered unless absolutely necessary.
So in this case, MCT needs at least 3800+2500 m/s = 6300 m/s of dV on its way back. Considering that it will loose a lot of its cargo on Mars, the same vehicle that has 4000 m/s on its way to Mars might just have 6500 m/s on its way back. No need to refuel in Mars orbit in the first place.

...

Why do we always seem to insist upon stopping in Mars orbit on the return trip?  I think a direct launch from Mars surface to TEI saves considerable delta V (though I'm having trouble getting my hands on the exact figure - does anyone have this?).  So I think the required return trip is well under the 6300 m/s figure above, right?  If so, this would match even better to that required for the outbound trip.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: cuddihy on 04/17/2015 12:46 PM
But you do need those big tanks on the MCT for the fuel for the Mars to Earth trip. Not so different from the second stage functionality.

Not necessarily. Depending on the exact mission plan, MCT may only need enough fuel for MTO (Mars to Orbit).

The MCT still needs very large tanks. The delta V from Mars surface to low Mars orbit is not that much lower than what a second stage would need. It is till significant.

Delta-V:
Earth to LEO 2nd stage: 6000-7000 m/s
Mars to LMO SSTO: 4000 m/s

So you still need very large tanks.

The only problem with that is how is the tanker MCT resupplied with LH2 fuel stock to make more methalox?  Unless you have a way to produce it reliable on the surface (a small surface crew stays and makes it from surface water ice they mine and electrolyze maybe?)

The current NASA DRM projects making water and feedstock from capturing water vapor in the Martian atmosphere, using zeolite bed that absorbs water even at Martian pressures and temperatures but evolves it under heat. If this works, it may not even be too heavy--the main issue is the power needed. But it's small compared to power required for Sabatier--if you're making fuel/O2 via Sabatier anyway, makes sense to also get the H2 locally as well from atmospheric vapor.
So potentially an MCT depot truck could cycle between the Martian surface and orbit, delivering fuel and Lox without resupply until it breaks...
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Semmel on 04/17/2015 12:57 PM
@Semmel

One nitpick. You need to add Mars landing which will need very roughly 1km/s delta/v.

Earth landing requires much less so you can neglect it on first approximation.

Ohh, I forgot that. Right, but 1000 m/s sounds like a lot. How comes that number s so high? Even in Mars thin atmosphere it should be possible to bleed off more speed than that.. or am i completely mistaken there?

Anyway, with additional dV for landing, thats just an even stronger argument that a tanking operation in mars orbit is not necessary.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Semmel on 04/17/2015 01:07 PM
Why do we always seem to insist upon stopping in Mars orbit on the return trip?  I think a direct launch from Mars surface to TEI saves considerable delta V (though I'm having trouble getting my hands on the exact figure - does anyone have this?).  So I think the required return trip is well under the 6300 m/s figure above, right?  If so, this would match even better to that required for the outbound trip.

When going to orbit first, you can coast to the proper point to do the TEI. It does not depend on the launch time directly. When going directly from Mars surface to TEI, the timing has to be spot on. Thats an operational risk that is avoided by getting into orbit first.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: QuantumG on 04/17/2015 01:29 PM

Why do we always seem to insist upon stopping in Mars orbit on the return trip?  I think a direct launch from Mars surface to TEI saves considerable delta V (though I'm having trouble getting my hands on the exact figure - does anyone have this?).  So I think the required return trip is well under the 6300 m/s figure above, right?  If so, this would match even better to that required for the outbound trip.

Because once you have mass in Mars orbit it doesn't make much sense to send that mass down to the surface and back up again. The only way direct launch to TEI works is if you make a full sized return vehicle with all the required supplies from Martian resources... i.e., the deep future. In the short term, any resources needed for the return journey - excluding possibly propellant - will be derived from Earth resources, so the best way to utilize them is by not sending them down to the Martian surface only to be returned to orbital velocities.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: guckyfan on 04/17/2015 01:31 PM
One nitpick. You need to add Mars landing which will need very roughly 1km/s delta/v.

Ohh, I forgot that. Right, but 1000 m/s sounds like a lot. How comes that number s so high? Even in Mars thin atmosphere it should be possible to bleed off more speed than that.. or am i completely mistaken there?

Honestly I have no idea, really. It depends on so many parameters. But it will be supersonic and I don't think that will be just above speed of sound of 300m/s. 1000m/s may  be high. But it will be a value that unlike on earth cannot be neglected even for first approximation.

Anyway, with additional dV for landing, thats just an even stronger argument that a tanking operation in mars orbit is not necessary.
My opinion too. refuelling in Mars orbit adds a lot of complexity. They won't do it early. I do have the hope that some day much later with a lot of traffic and the right kind of volatiles on Phobos they may produce propellant there to refuel after Mars ascent.

Title: Re: MCT Speculation and Discussion Thread 3
Post by: guckyfan on 04/17/2015 01:48 PM
Because once you have mass in Mars orbit it doesn't make much sense to send that mass down to the surface and back up again. The only way direct launch to TEI works is if you make a full sized return vehicle with all the required supplies from Martian resources... i.e., the deep future. In the short term, any resources needed for the return journey - excluding possibly propellant - will be derived from Earth resources, so the best way to utilize them is by not sending them down to the Martian surface only to be returned to orbital velocities.

So you assume that MCT will not touch down on Mars? That does not save anything really. MCT does need to be refuelled. For refuelling you need another craft that ferries fuel from the martian surface to MCT. That vehicle then needs to land back on Mars. It needs to be serviced on Mars. You need a landing craft and have to transfer huge amounts of cargo, both small packs and large pieces of infrastructure like habitats, cranes, heavy construction equipment from the interplanetary craft to the lander. A huge complex operation.

For all those reasons I believe MCT will land on Mars. It then ascends and flies back to earth. I indeed don't think it will go into orbit but go directly to TMI. Whatever is the best way of minimizing delta-v needed for earth return.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Semmel on 04/17/2015 02:11 PM
Because once you have mass in Mars orbit it doesn't make much sense to send that mass down to the surface and back up again. The only way direct launch to TEI works is if you make a full sized return vehicle with all the required supplies from Martian resources... i.e., the deep future. In the short term, any resources needed for the return journey - excluding possibly propellant - will be derived from Earth resources, so the best way to utilize them is by not sending them down to the Martian surface only to be returned to orbital velocities.


I dont think thats true. To make a fuel depot in Mars orbit with fuel from Earth you need to break the fuel into the orbit, which is around 3000 m/s dV (assuming 1000 m/s for landing) more than the lander would need. So fuel wise, it is much much cheaper to just land the stuff than to bring it into orbit. Doing an aero-capture is hell of a lot more risky..

Edit: I miscalculated, sorry. The dV difference is just over 1000 m/s dV. So it might just be possible to send 3 MCTs to Mars, one with fuel to the surface, one with fuel into orbit and one that goes back. So that leaves 2 MCTs tranded and one that is coming back. If the one that goes to mars takes the equipment to refuel with it and leaves it on mars, no MCTs have to be sacrificed. All in all, if the fuel is not produced on the surface, its more expensive to bring a MCT back than to just leave it there. That just convinced me that fuel production is a hard requirement for the whole idea to make sense economically.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: GORDAP on 04/17/2015 03:04 PM
Why do we always seem to insist upon stopping in Mars orbit on the return trip?  I think a direct launch from Mars surface to TEI saves considerable delta V (though I'm having trouble getting my hands on the exact figure - does anyone have this?).  So I think the required return trip is well under the 6300 m/s figure above, right?  If so, this would match even better to that required for the outbound trip.

When going to orbit first, you can coast to the proper point to do the TEI. It does not depend on the launch time directly. When going directly from Mars surface to TEI, the timing has to be spot on. Thats an operational risk that is avoided by getting into orbit first.

Semmel, doesn't this just move the requirement for doing a precisely timed burn from Mars surface to Mars orbit?  And it doesn't seem to be a very important requirement at that.  Say you miss your window today; just launch tomorrow.  In any event, it doesn't strike me as important enough to counter the need for hundreds (or thousands?) of m/s delta v.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Semmel on 04/17/2015 04:32 PM
Semmel, doesn't this just move the requirement for doing a precisely timed burn from Mars surface to Mars orbit?  And it doesn't seem to be a very important requirement at that.  Say you miss your window today; just launch tomorrow.  In any event, it doesn't strike me as important enough to counter the need for hundreds (or thousands?) of m/s delta v.

I would love to believe that its that significant. In this case, of course it makes sense to do a direct transfer. However, I would guestimate the savings in the area of tens m/s of dV, not hundreds. I am not sure that it is possible to target timing and TEI injection trajectory well enough directly from the surface. In my laymans understanding, it is easier to do the TEI from orbit because it is easier to compensate for inaccuracies.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: cuddihy on 04/17/2015 05:01 PM
No, you can do this with three MCTs, or should I say two MCTs and one martian orbit depot. Only one of the MCTs needs to leave Mars and return to earth, the other two serve as a martian orbital fuel depot and a fuel ferry respectively. Here's how it would work: cycle 1 a MCT lands on Mars with the Sabatier plant, zeolite water producer, power source, and empty or deployable tankage.

It captures H2O & CO2 from the Martian atmosphere, converts them to Lox/Methane conveniently stored at Martian temperatures.

This is autonomously transferred back to the MCT.

Cycle 2 you launch an empty MCT, perhaps with additional empty fuel tanks, to Martian orbit to serve as a depot. Then either cycle 2 or 3 you start launching your manned missions. The MCTs returning to earth can refuel in orbit to do a faster transfer or to have more payload. If stuff goes bad you have spare MCTs to serve as refundant transport to earth.

From then on the first two MCTs stay at Mars and keep performing the same function for later MCTs until they break. That's a scalable architecture and requires MCT reusability, and overall delta V and thrust to accomplish.

Lot of automation required however.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: nadreck on 04/17/2015 05:19 PM
Will MCT really need great honking large tanks when its taking off from Mars 90-100mT lighter than it arrived?
Except if it is putting fuel in a depot then it probably takes off with full tanks anyway even though no cargo.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Eerie on 04/17/2015 06:56 PM
But for the full blown system you clearly need to be using this vehicle as a crewed launch vehicle and it is impossible to see how you can put people in this vehicle and rescue them when a launch failure happens.

Ehm, you know airplanes, right? They transport hundreds of people without a rescue systems. When they fail, everyone on board dies. It just happens rarely enough for the society to accept the risk.

But does it even matter? NASA used an airplane glued to the side of a giant rocket for 30 years, with no rescue system and a magnificent 1/67 chance of death...
Title: Re: MCT Speculation and Discussion Thread 3
Post by: RanulfC on 04/17/2015 07:14 PM
But for the full blown system you clearly need to be using this vehicle as a crewed launch vehicle and it is impossible to see how you can put people in this vehicle and rescue them when a launch failure happens.

Ehm, you know airplanes, right? They transport hundreds of people without a rescue systems. When they fail, everyone on board dies. It just happens rarely enough for the society to accept the risk.

How old are you? If you're over 25 you should be aware that crashes were MUCH more common even 20 years ago than today and MUCH higher before that. Society "accepted" it (but complained a lot anyway) because air travel was fast and relatively "safe" and people were more concerned with "time" than safety.
(The math did show that you were more likely to die in a car crash than a plane crash but cars rarely carried over 70 passengers so "individually" the odds were on your side :) )

Rockets are inherently more dangerous than aircraft. They are put under more stress and perform across a much greater envelope than any aircraft and it is NOT that hard to design in sufficient safety to mitigate almost all the dangers involved so why NOT do so?

Quote
But does it even matter? NASA used an airplane glued to the side of a giant rocket for 30 years, with no rescue system and a magnificent 1/67 chance of death...

And THAT could have been prevented by an installed escape system from the start. The problem WAS that NASA strapped an "airplane" to the side of a rocket in the first place but they were constrained in a manner that left them little choice but to take that route. In doing so they had to accept  a higher risk and the odds caught up them. Twice.

The same thing happened to them twice with the Apollo program as well, only then they had the budget and authority to change the system to prevent such things from occurring again. The design and construction of the Shuttle left no such options open. SpaceX knows better and have set out to ensure that their rockets which they KNOW are unsafe from the start WILL have those options for human payloads. There is NO reason to assume they will suddenly change their mind with the MCT or BFR. Society be damned this is a COMPANY decision and the reasoning is straight forward and logical. I don't see them changing their path for some marginal performance gains.

Randy
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Eerie on 04/17/2015 07:32 PM
The same thing happened to them twice with the Apollo program as well, only then they had the budget and authority to change the system to prevent such things from occurring again. The design and construction of the Shuttle left no such options open. SpaceX knows better and have set out to ensure that their rockets which they KNOW are unsafe from the start WILL have those options for human payloads. There is NO reason to assume they will suddenly change their mind with the MCT or BFR. Society be damned this is a COMPANY decision and the reasoning is straight forward and logical. I don't see them changing their path for some marginal performance gains.

I'm not saying SpaceX shouldn't have a rescue system on an MCT. Just that it is not beyond the realm of possibility that at some point MCT will not have one. Having a rescue system does not reduce the chance of death to 0% either, the system itself can fail. It's always a matter of profit vs. risk.

I'd like to have a rescue system on the airplanes that I take, but alas...
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lars-J on 04/17/2015 07:44 PM
But for the full blown system you clearly need to be using this vehicle as a crewed launch vehicle and it is impossible to see how you can put people in this vehicle and rescue them when a launch failure happens.

Ehm, you know airplanes, right? They transport hundreds of people without a rescue systems. When they fail, everyone on board dies. It just happens rarely enough for the society to accept the risk.

How old are you? If you're over 25 you should be aware that crashes were MUCH more common even 20 years ago than today and MUCH higher before that. Society "accepted" it (but complained a lot anyway) because air travel was fast and relatively "safe" and people were more concerned with "time" than safety.
(The math did show that you were more likely to die in a car crash than a plane crash but cars rarely carried over 70 passengers so "individually" the odds were on your side :) )

Rockets are inherently more dangerous than aircraft. They are put under more stress and perform across a much greater envelope than any aircraft and it is NOT that hard to design in sufficient safety to mitigate almost all the dangers involved so why NOT do so?

Wow. Not hard? What planet are you from... This has to be one of the most stunning proclamations I have read on this forum. There will always be mass penalties and engineering compromises. Making the Shuttle as safe as you seem to want it would have crippled it.

Accept the risk and move on. You yourself wrote "Rockets are inherently more dangerous than aircraft", so more risks will be expected and accepted. If this bothers you, others will gladly take your place in line.

Here's the ultimate safe vehicle for you: One that doesn't go anywhere.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: nadreck on 04/17/2015 08:17 PM
Look, the level of acceptable risk varies greatly from one activity to another, and just because aircraft crashes and rocket explosions are more interesting than automobile accidents on city streets and on highways the public perception of the risk is not related to actual risk, but to the outcome of the worst case scenario that they see.

http://en.wikipedia.org/wiki/List_of_motor_vehicle_deaths_in_U.S._by_year (http://en.wikipedia.org/wiki/List_of_motor_vehicle_deaths_in_U.S._by_year)

If you look at the table in the above article, you can see that in 1921 it was (measuring by fatalities per vehicle mile driven) 5 times more life threatening to drive than it was in 1972 - when seat belts were just becoming mandatory and just before the first energy crisis. At that time many people opined, it was in fact virtually a truism, that cars were much safer before WWII because they moved slower and that acccidents were much less severe with far lower a risk of fatality. Obviously that was not true.  Cars today, again based on same statistics in the article above, are 4 times safer than in 1972 and more than 20 times saver than 1921. However public perception does not acknowledge that.

http://en.wikipedia.org/wiki/Aviation_safety#Comparison_to_other_modes_of_travel (http://en.wikipedia.org/wiki/Aviation_safety#Comparison_to_other_modes_of_travel)

now putting that all into a comparative context (and note that the Space Shuttle is in the list) look at the table I am linking to above. I think the comparison from the point of view of someone deciding the safest way to get from A to B should be based on the fatalities per billion kilometers travelled, I would argue that the fairest comparison is by fatalities  per billion hours. In either case, even though your mother probably wouldn't agree, walking is more dangerous than driving or flying.

Can we do better than the shuttle with Dragon, CST-100, MCT? I am sure we can, but the proof is in the pudding as they say and I expect to see a massive reduction in the risk with the Dragon/CST-100 generation, and a further increase in the next, however a single accident will change public perception. You really don't hear anyone telling you how dangerous walking is do you?
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/17/2015 08:48 PM
Impaler.  Good comments.  A few additional ones in response.

These integrated 2nd stage concepts have some unavoidable problems.

*  No possible abort during launch, the propellent mass is simply too high for the large vehicle to have any appreciable acceleration away from an exploding 1st stage.  For our early missions when crews are just a handful of explorers it's easy enough to put them on F9 to rendezvous with the MCT that launches un-manned.  But for the full blown system you clearly need to be using this vehicle as a crewed launch vehicle and it is impossible to see how you can put people in this vehicle and rescue them when a launch failure happens.


The MCT going to MArs would launch first, and be uncrewed.  Several subsecquent launches would come up bringing propellant and other provisions.  Lastly would come up the crew and probably the LH2 feedstock for making the methalox on the surface.
So the Mars-MCT doesn't need an LAS system.  The other LEO-MCT could have one, as it could withstand the mass penalty of it.  It would just then take more launches to get the adequate propellant, provisions, and crew to the Mars-MCT prior to departure. 

However, we need to really ask ourselves, what would the LAS on the LEO-MCT need to be?  If the 2nd stage -is- the Spacecraft, then really the only "abort" scenario is if the booster is failing during the first 2-2.5 minutes of ascent.  Once staging has occured and the upper stage lit, there's really no abort option.  If it blows up, there's a LOC.  If there's some other issue, it can actually divert to an alternate landing area and come back down and land before reaching orbit.

If the MCT spacecraft where to have landing thrusters like Dragon, the LEO-MCT could be built with enough of them to do an emergency separation from the booster and much the spacecraft away from the booster.

So you really need to look at what and how you are aborting.  MCT landing engines should be able to do an emergency separation in any condition but a catestrophic booster explostion....and those would be pretty rare.  If you feel you need to be able to abort during a full booster explostion, more landing thrusters could be added, or a large tractor down, or something else.  Again, that wouldn't be needed for the Mars MCT as that would launch unmanned.
And as you say, earlier flights where the system doesn't have a lot of flights under it's belt, they may launch the crews on Dragon.  I can't imagine early Mars missions would have more than like 14 people anyway.  Two Dragons can do that. 


* Highly unstable landing on Mars, with is extreme height your in great danger of toppling over.  Even if cargo hold is in the bottom as Lobo's sketch indicates the tanks above are going to have residual propellent, and center of mass will be higher above the ground then the leg base is wide.  We have seen how difficult it is to keep F9 first stage strait on landing and that is on a flat surface.  On Mars your surface can be both rocky AND it can give-way during landing or even after, say if subsurface ice sublimates you end up like the Leaning tower of Pisa.

Both these problems make the system more dangerous then I think is acceptable.

Hard to know if the cargo would be on the bottom, or on top and use a swing out crane or something.
This stability issue will be the issue with any vertical lander, and I don't know if SpaceX is looking at anything but a a vertical lander.  So issues of landing will be inherrent whether my integrated stage concept, or a separate dedicated spacecraft.
Remember, whatever that spacecraft looks like, it will need to carry enough propellant on board to get itself back to Earth.  So it will be tall no matter what, unless they switch to a horizontal lander or something. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/17/2015 08:53 PM
Lets say this following map is roughly correct (exact numbers vary depending on transfer anyway):
http://i.imgur.com/SqdzxzF.png

deltaV
TMI: ~4000 m/s
LMO: ~3800 m/s
TEI: ~2500 m/s

Then it would make sense to design BFR+MCT as a two-part vehicle.
It needs at least 4000 m/s deltaV, which can just be part of the second stage going into orbit.

Refuelling in Mars orbit is maybe possible but probably way too complicated. It adds so many failure modes that it is probably not considered unless absolutely necessary.
So in this case, MCT needs at least 3800+2500 m/s = 6300 m/s of dV on its way back. Considering that it will loose a lot of its cargo on Mars, the same vehicle that has 4000 m/s on its way to Mars might just have 6500 m/s on its way back. No need to refuel in Mars orbit in the first place.

...

Why do we always seem to insist upon stopping in Mars orbit on the return trip?  I think a direct launch from Mars surface to TEI saves considerable delta V (though I'm having trouble getting my hands on the exact figure - does anyone have this?).  So I think the required return trip is well under the 6300 m/s figure above, right?  If so, this would match even better to that required for the outbound trip.

Myself, I only mentioned refueling in Mars orbit on the way out if it was technically necessary.  If it's not, direct return would obviously be much more simple and the way to go. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/17/2015 09:07 PM
No, you can do this with three MCTs, or should I say two MCTs and one martian orbit depot. Only one of the MCTs needs to leave Mars and return to earth, the other two serve as a martian orbital fuel depot and a fuel ferry respectively. Here's how it would work: cycle 1 a MCT lands on Mars with the Sabatier plant, zeolite water producer, power source, and empty or deployable tankage.

It captures H2O & CO2 from the Martian atmosphere, converts them to Lox/Methane conveniently stored at Martian temperatures.

This is autonomously transferred back to the MCT.

Cycle 2 you launch an empty MCT, perhaps with additional empty fuel tanks, to Martian orbit to serve as a depot. Then either cycle 2 or 3 you start launching your manned missions. The MCTs returning to earth can refuel in orbit to do a faster transfer or to have more payload. If stuff goes bad you have spare MCTs to serve as refundant transport to earth.

From then on the first two MCTs stay at Mars and keep performing the same function for later MCTs until they break. That's a scalable architecture and requires MCT reusability, and overall delta V and thrust to accomplish.

Lot of automation required however.

I think that would be something later on, once there's some sort of permanent base set up as a precursor to a colony.  But initionally, they'll be exploring around various different locations on Mars, probably partnered with NASA, which will pick up a lot of the tab for logistics, support and surface equipment.  So they'll need to send MCT's to various locations around Mars.

During this exploration phase, I think they'll do something like Zubrin's Mars Direct.  Except it'll be more like "Mars REALLY Direct".    Really with a minimal exploration crew of like 5 or 6, MCT can make it's own propellant while they are on the surface.  But if they want another level of safety, they can land an MCT 2 years ahead of the crewed mission, and then let it fuel itself up.  Then the crewed MCT comes down (like Mars Direct).  They can start refueling the crewed MCT, but transnfer to the 1st one for the return trip.  The 2nd MCT can then return home autonomously (why not?) later once it's fueled itself. 
If there was a problem with the first MCT, then they still have the 2nd MCT. 

It's similar to what Zubrin proposed, but just with once common spacecraft rather than two. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/17/2015 10:17 PM
The same thing happened to them twice with the Apollo program as well, only then they had the budget and authority to change the system to prevent such things from occurring again. The design and construction of the Shuttle left no such options open. SpaceX knows better and have set out to ensure that their rockets which they KNOW are unsafe from the start WILL have those options for human payloads. There is NO reason to assume they will suddenly change their mind with the MCT or BFR. Society be damned this is a COMPANY decision and the reasoning is straight forward and logical. I don't see them changing their path for some marginal performance gains.

I'm not saying SpaceX shouldn't have a rescue system on an MCT. Just that it is not beyond the realm of possibility that at some point MCT will not have one. Having a rescue system does not reduce the chance of death to 0% either, the system itself can fail. It's always a matter of profit vs. risk.

I'd like to have a rescue system on the airplanes that I take, but alas...

Well again, here's the thing.  There -are- rescue systems on airplanes.  Just not one that will get all the people on board safely if the plane suddenly blows up in mid air.  If there was one, it'd never get off the ground.  -There- is the analogy. 

Airplanes are build with redudant wiring and control system, so they can be flown if primary systems fail.  Commercial airlines must be able to still fly safely and land with the loss of 1 engine.  (A 747 can tolerate 1 of 4 engines failing, the 737, 777, etc can fly with 1 of 2 engines failing).  There's reserve oxygen in case of sudden depressurization, seat coushions float and there's life rafts and rescue beacons in case of a water landing, and there's inflatable slides in case of an emergency ground landing so people can get off without a ladder there.  And the engien cowling must contain turbine baldes that come off so they don't fly out and rip into the fusilage.

There's really only a few catestrophic failure modes that there isn't some sort of rescue system built into them for.  (explosion mid air, wing or tail ripped off, massive fuselage failure)  It's deemed that those are rare, and it would make operating the plane inpractical.

So why would MCT be any different?
There will be backup systems, and fail-safes, and things like that whereever possible.  If there's some sort of booster failure (short of a sudden explosion) then the Raptor engines and/or the landing engines can light and push the spacecraft away from the failing booster, and then it can divert to an emergency landing zone.
The booster will have multiple engines and can tolerate an engine failure during ascent, and I would imagine ditto for the Spacecraft.    It will have a cluster of Raptors to land on on Mars and Earth to tolerate engine out, or it will have clusters of landing thrusters like Dragon, which also will tolerate and engine out (or 2)
Sitting on Mars, it'll probably have more engines than are necessary to get it off the surface and through TEI, so it can handle and engine failing at lift off. 
And each MCT can come back to Earth where it can be properly maintained and serviced, rather than trying to do it in orbit or on the Mars surface.

So again, what exact failure modes are we trying to protect against that won't already be protected against, and why?

Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/17/2015 10:28 PM
My opinion too. refuelling in Mars orbit adds a lot of complexity. They won't do it early. I do have the hope that some day much later with a lot of traffic and the right kind of volatiles on Phobos they may produce propellant there to refuel after Mars ascent.

Yea, I think if there's any feasbile way to have MCT do a direct return, that would have a lot of advantages over LMO staging and refueling.  And as others have said, fuel can be made on the surface, so that's really where you want to put all of your hardware if you can.  And it takes more fuel to brake into Mars orbit than to just land.  If you aren't making fuel on the surface, then there's a big efficiency issue with orbital rendezvous vs. direct return.  Which was why Direct return was shelved in favor of LOR or Apollo.  They weren't making fuel on the surface so they wanted to keep every kg brought to the surface at a minimum.  But that's not the case with in-situ propellant generation.  If there was fuel to be had on the lunar surface, then it would have been more efficient to land everything, and do a direct return back (because you wouldn't have had to carry your ascent and TEI propellant with you) 
The lunar lander could have just been the Apollo CSM with legs essentially.  And that's essentially what we are looking at with MCT.
And there's actually even more reason to do it on Mars because of the Mars atmosphere that can provide some of the dV required to land, where that doesn't exist on the Moon. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: llanitedave on 04/18/2015 12:17 AM
But for the full blown system you clearly need to be using this vehicle as a crewed launch vehicle and it is impossible to see how you can put people in this vehicle and rescue them when a launch failure happens.

Ehm, you know airplanes, right? They transport hundreds of people without a rescue systems. When they fail, everyone on board dies. It just happens rarely enough for the society to accept the risk.

How old are you? If you're over 25 you should be aware that crashes were MUCH more common even 20 years ago than today and MUCH higher before that. Society "accepted" it (but complained a lot anyway) because air travel was fast and relatively "safe" and people were more concerned with "time" than safety.
(The math did show that you were more likely to die in a car crash than a plane crash but cars rarely carried over 70 passengers so "individually" the odds were on your side :) )

Rockets are inherently more dangerous than aircraft. They are put under more stress and perform across a much greater envelope than any aircraft and it is NOT that hard to design in sufficient safety to mitigate almost all the dangers involved so why NOT do so?

Wow. Not hard? What planet are you from... This has to be one of the most stunning proclamations I have read on this forum. There will always be mass penalties and engineering compromises. Making the Shuttle as safe as you seem to want it would have crippled it.

Accept the risk and move on. You yourself wrote "Rockets are inherently more dangerous than aircraft", so more risks will be expected and accepted. If this bothers you, others will gladly take your place in line.

Here's the ultimate safe vehicle for you: One that doesn't go anywhere.


If SpaceX loses an MCT or BFR full of paying customers, they will face a bigger risk of bankruptcy than the passengers themselves risked prior to buying tickets.  It's in SpaceX's interest to make those craft as safe as possible.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lars-J on 04/18/2015 12:25 AM
Here's the ultimate safe vehicle for you: One that doesn't go anywhere.

If SpaceX loses an MCT or BFR full of paying customers, they will face a bigger risk of bankruptcy than the passengers themselves risked prior to buying tickets.  It's in SpaceX's interest to make those craft as safe as possible.

Only up to a point. The same applies to the manufacturer of any vehicle, or owner of any fleet.

If you don't think you are rolling the dice every time you cross the street, drive/ride in car, sit on a train, fly in an aircraft, then you are kidding yourself.

Again, if you want complete safety, don't fly at all. Problem solved.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: spacenut on 04/18/2015 12:41 AM
If they are going to Mars, they probably will make them sign a waiver.  It was their decision.  They knew the dangers. 

On the other side, launch failures are rare these days.  Even the shuttle with all it's dangers only lost two out of over 100+ launches.  Soyuz percentage is about the same. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Impaler on 04/18/2015 12:58 AM
Impaler.  Good comments.  A few additional ones in response.

These integrated 2nd stage concepts have some unavoidable problems.

*  No possible abort during launch, the propellent mass is simply too high for the large vehicle to have any appreciable acceleration away from an exploding 1st stage.  For our early missions when crews are just a handful of explorers it's easy enough to put them on F9 to rendezvous with the MCT that launches un-manned.  But for the full blown system you clearly need to be using this vehicle as a crewed launch vehicle and it is impossible to see how you can put people in this vehicle and rescue them when a launch failure happens.


The MCT going to MArs would launch first, and be uncrewed.  Several subsecquent launches would come up bringing propellant and other provisions.  Lastly would come up the crew and probably the LH2 feedstock for making the methalox on the surface.
So the Mars-MCT doesn't need an LAS system.  The other LEO-MCT could have one, as it could withstand the mass penalty of it.  It would just then take more launches to get the adequate propellant, provisions, and crew to the Mars-MCT prior to departure. 

However, we need to really ask ourselves, what would the LAS on the LEO-MCT need to be?  If the 2nd stage -is- the Spacecraft, then really the only "abort" scenario is if the booster is failing during the first 2-2.5 minutes of ascent.  Once staging has occured and the upper stage lit, there's really no abort option.  If it blows up, there's a LOC.  If there's some other issue, it can actually divert to an alternate landing area and come back down and land before reaching orbit.

If the MCT spacecraft where to have landing thrusters like Dragon, the LEO-MCT could be built with enough of them to do an emergency separation from the booster and much the spacecraft away from the booster.

So you really need to look at what and how you are aborting.  MCT landing engines should be able to do an emergency separation in any condition but a catestrophic booster explostion....and those would be pretty rare.  If you feel you need to be able to abort during a full booster explostion, more landing thrusters could be added, or a large tractor down, or something else.  Again, that wouldn't be needed for the Mars MCT as that would launch unmanned.
And as you say, earlier flights where the system doesn't have a lot of flights under it's belt, they may launch the crews on Dragon.  I can't imagine early Mars missions would have more than like 14 people anyway.  Two Dragons can do that. 


* Highly unstable landing on Mars, with is extreme height your in great danger of toppling over.  Even if cargo hold is in the bottom as Lobo's sketch indicates the tanks above are going to have residual propellent, and center of mass will be higher above the ground then the leg base is wide.  We have seen how difficult it is to keep F9 first stage strait on landing and that is on a flat surface.  On Mars your surface can be both rocky AND it can give-way during landing or even after, say if subsurface ice sublimates you end up like the Leaning tower of Pisa.

Both these problems make the system more dangerous then I think is acceptable.

Hard to know if the cargo would be on the bottom, or on top and use a swing out crane or something.
This stability issue will be the issue with any vertical lander, and I don't know if SpaceX is looking at anything but a a vertical lander.  So issues of landing will be inherrent whether my integrated stage concept, or a separate dedicated spacecraft.
Remember, whatever that spacecraft looks like, it will need to carry enough propellant on board to get itself back to Earth.  So it will be tall no matter what, unless they switch to a horizontal lander or something.

Thx for the reply Lobo and for taking these issues seriously.

You speak of a 'Mars-MCT' and 'LEO-MCT' but I've always assumed one type of vehicle, and unless the LEO variant is staged different from the 'combined 2nd stage' design used on the Mars variant then it has the same abort difficulty. 


Abort both static at the launch pad and during the first stage burn is generally the most dangerous part of a rocket launch so having this a 'black zone' is very serious even if the time period is brief.  Catastrophic booster explosion (or a loss of guidance control on the Booster which is going to force a self-destruct) is indeed TEH scenario for which abort systems are designed, virtually ever disaster scenario necessitating abort starts with or goes through a catastrophic booster explosion.  I am though less concerned with the MCT itself blowing up during assent even when it is acting as a 2nd or even 3rd stage. 

But I am quite confident that no amount of engines can be attached to this large MCT to push it away from the first stage, you would need more engines on it then are in the first stage.  Think about the masses and accelerations.  The first stage of BFR is likely to have 20+ raptor engines and it accelerates the whole rocket off the launch pad at a small fraction of a G, aka Thrust:Weight is just slightly >1.  That second stage is maybe a third of the total mass on the launch pad but to effectively abort you need Thrust:Weight of around 5, meaning you would need an absurd ~30 engines to push the second stage away at abort speed, and that's assuming it can even withstand that much acceleration.

A traditional 'capsule on 2 stages' that the F9 uses would still be difficult challenge to abort, I think it will need something like 6-8 Raptor engines around it like the Super-Draco's on the Dragon capsule.

As for the cargo placement within the vehicle, I have to imagine that with a vertical landing the cargo being in the nose is absolutely prohibitive because of the top-heavy nature, it would be virtually guaranteed to fall over, the logistics of unloading are just another headache.  The low, nearly ground level cargo hold depicted in your sketch seems to me the only viable means to do such a vehicle.



Title: Re: MCT Speculation and Discussion Thread 3
Post by: AncientU on 04/18/2015 05:55 PM
If SpaceX loses an MCT or BFR full of paying customers, they will face a bigger risk of bankruptcy than the passengers themselves risked prior to buying tickets.  It's in SpaceX's interest to make those craft as safe as possible.

If they are to see their Mars goals achieved, they will lose more than one MCT/BFR.
Great deeds are not for the faint of heart (i.e., there's no free lunch).
The obsession with avoiding risk in our society is pathological.

Note that many airlines have lost a load of paying passengers, and this even today when commercial flight is routine (and safer than driving).  The reasons that they go bankrupt are not the inherent risks of flying.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Eerie on 04/18/2015 06:03 PM
The obsession with avoiding risk in our society is pathological.

I think this is more about NASA being a symbol. Cars, airplanes... those are routine risks. But astronauts are the High Priests of the religion of Progress, and people today don't like martyrs or human sacrifices.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Impaler on 04/18/2015 10:41 PM
What's pathological is this belief by Space-Cadets that all the problems with our space program be be boiled down to 'timidness' and 'spinelessness', and taking greater risks with human life will magically yield the glory they seek.

It is a simplistic, self-gratifying message that conforms to the general anti-government ideology and 'nanny state' bogyman of the political right-wing.  But it bears no resemblance to reality, NASA engineers when faced with envelope pushing performance demands and inadequate funding (both the fault of Congress) have in fact sacrificed safety REPEATEDLY and become quite cavalier in doing so.

SpaceX success has been based on internally NOT making the mistakes Congress cripples NASA with, Musk adequately funded the company and it's internal development and he dose not make absurd performance demands.  This gives them the engineering headroom to make their system SAFER then NASA equivalents. 

Elon is smart, he knows this is what space travel needs to be if it has any chance of succeeding as a means of colonization.  People with large amounts of disposable income (and very good earning potential if they stay on Earth) are not going to accept 1-2% chances of dieing in a fireball on the launch pad to go to Mars, Mars is not THAT attractive of a place.  This is not 1620 in which religious dissidents and peasants in Europe consider a leaky boat to America better then wars and plagues in their home land, and even then the death rate in crossing the Atlantic was only 2% on the Mayflower, people are going to rightfully demand better then that after 500 years of improved living standards and technology development.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Owlon on 04/19/2015 01:12 AM
What's pathological is this belief by Space-Cadets that all the problems with our space program be be boiled down to 'timidness' and 'spinelessness', and taking greater risks with human life will magically yield the glory they seek.

It is a simplistic, self-gratifying message that conforms to the general anti-government ideology and 'nanny state' bogyman of the political right-wing.  But it bears no resemblance to reality, NASA engineers when faced with envelope pushing performance demands and inadequate funding (both the fault of Congress) have in fact sacrificed safety REPEATEDLY and become quite cavalier in doing so.

SpaceX success has been based on internally NOT making the mistakes Congress cripples NASA with, Musk adequately funded the company and it's internal development and he dose not make absurd performance demands.  This gives them the engineering headroom to make their system SAFER then NASA equivalents. 

Elon is smart, he knows this is what space travel needs to be if it has any chance of succeeding as a means of colonization.  People with large amounts of disposable income (and very good earning potential if they stay on Earth) are not going to accept 1-2% chances of dieing in a fireball on the launch pad to go to Mars, Mars is not THAT attractive of a place.  This is not 1620 in which religious dissidents and peasants in Europe consider a leaky boat to America better then wars and plagues in their home land, and even then the death rate in crossing the Atlantic was only 2% on the Mayflower, people are going to rightfully demand better then that after 500 years of improved living standards and technology development.

Nobody is somehow blaming this on the "nanny state". Decades down the line, launch may very well be the part of a journey to Mars least likely to fail. At some point it doesn't make sense to make design compromises in a low-margin system to catch every failure mode. It's not likely to be feasible to build a launch escape system that works on Mars, and not every abort from a failing booster on Earth is going to require a high-g escape.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 04/19/2015 01:23 AM
I can imagine an abort system which would work on Mars just fine. In fact, Dragon (or something similar) should do the job just fine since you could just shut down the engines on your ascent vehicle (the thin atmosphere doesn't transmit explosions much, so there's less urgency to out-run it) then land vertically Red-Dragon-style after boosting a bit away. It'd be plenty feasible. Not sure if it's necessary (or worth it), though.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: NovaSilisko on 04/19/2015 01:36 AM
How many times have we had this discussion on aborts with no definite conclusion again?
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 04/19/2015 01:47 AM
How many times have we had this discussion on aborts with no definite conclusion again?
People keep saying it can't feasibly be done, but that only shows they haven't thought very hard about it. Of course, whether or not it's worth it is far more subjective and probably can't even be answered this decade (speaking in the context of Mars colonization or large base level of activity).
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Impaler on 04/19/2015 06:21 AM
Nobody is somehow blaming this on the "nanny state". Decades down the line, launch may very well be the part of a journey to Mars least likely to fail. At some point it doesn't make sense to make design compromises in a low-margin system to catch every failure mode. It's not likely to be feasible to build a launch escape system that works on Mars, and not every abort from a failing booster on Earth is going to require a high-g escape.


That's a straw-man, I'm pointing out how someones proposal has ZERO abort capability in THE most dangerous time and place of a launch in THE most dangerous class of vehicle ever conceived by man and your accusing me of essentially demanding infinite safety. 

Telling a person that a new Car design should have a seat belt is not the same thing as demanding that cars be made out of pillow and go no more then 5 mph.  Basic safety systems in launch vehicles are well established and expecting that they at least maintain that standard is the only reasonable position on this issue.

If a person can not think of a MCT design that is at least as safe as a Falcon 9 launch then they should go back to the drawing board because Elon and SpaceX ain't interested.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Ben the Space Brit on 04/19/2015 12:36 PM
FWIW, I repeat my proposal that the nose of MCT be essentially an up-sized (say, 5m-diameter) Dragon 2.0. During ascent and descent phases, the crew and passengers ride in there. In the event of an emergency, the aerodynamic outer shell of the MCT is jettisoned and the 'Super-Dragon' escape pod flies clear of the MCT with the objective of a safe landing as near to the launch site as possible (Mars) or just safe land- or sea-fall (Earth).
Title: Re: MCT Speculation and Discussion Thread 3
Post by: AncientU on 04/19/2015 12:57 PM
What's pathological is this belief by Space-Cadets that all the problems with our space program be be boiled down to 'timidness' and 'spinelessness', and taking greater risks with human life will magically yield the glory they seek.

...NASA engineers when faced with envelope pushing performance demands

This Space-Cadet (actually, I'm a scientist and space enthusiast for 50+ years) never referred to NASA...
But if you choose to wear it, it's your shoe.

The point I was making is that the SpaceX Mars goals are not compatible with zero risk tolerance.  Having the trip to Mars always decades in the future is the only zero risk strategy.

Note: What is pathological, in my thinking, is our society's (in US of A) aversion to perceived risk, based in part on our lack of technical education to judge actual risk.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: AncientU on 04/19/2015 01:18 PM
As to MCT's LAS, I think it will have none.  This is because I'm one of the small minority here that think MCT will not take off from Earth with crew aboard.  Cargo, yes.  Provisions, yes. Heat shield for Earth re entry, no. Fuel for TMI, no.

 I don't think the 'fleet' of MCTs will ever return to Earth's surface.  Not sure about Mars surface either... after all, 'land the whole thing' is only four words.  And those words were in reference to the Mars end of the trip.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Burninate on 04/19/2015 01:32 PM
The only way a complete MCT would be capable of launch abort would be if it was launched with a minimal fuel load relative to its large capacity.  Full tanks don't work for high-G abort at max Q, there just isn't enough thrust.

This would require:

1) That crew is not onboard, because it will take months/years to fill those tanks and crew won't want to spend all that time waiting in orbit

2) That the MCT not be used to achieve orbit.  This means that there need to be two or more likely 3 stages *below* the MCT.

Better to just send the crew up at a later date, after the MCT is fueled in orbit.
-----

A nosecone capsule has been a repetitive conclusion in my designs.  I keep trying to remove it and finding it's congruent with some other purpose.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 04/19/2015 02:08 PM
If you don't think MCT will land back on Earth or even on Mars, then you are saying SpaceX will need to develop 2 additional large vehicles to do so. Dragon certainly isn't cheap enough to do this. Sounds like a very complicated and expensive architecture.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: RonM on 04/19/2015 02:28 PM
I think there will be at least two versions of MCT.

In the exploration phase, each flight will have a small crew. The first version of the MCT will be mainly cargo for setting up a base and exploring. It will not have a LAS and the small crew can be sent up to the MCT on a single Dragon while the MCT is being refueled for the trip to Mars.

The colonization version will need a LAS because with a large crew of up to a hundred they will have to launch with the MCT. A dozen or more Dragon launches to transfer the crew to the MCT doesn't make sense. The crew compartment will probably be on top and could be separated from the rest of the MCT during an emergency, making it easier to develop a LAS. This version of MCT will benefit from lessons learned from the first version.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: AncientU on 04/19/2015 02:39 PM
If you don't think MCT will land back on Earth or even on Mars, then you are saying SpaceX will need to develop 2 additional large vehicles to do so. Dragon certainly isn't cheap enough to do this. Sounds like a very complicated and expensive architecture.

Today's Dragon-2 is affordable for crew.  Reuse of first stages and Dragons will improve that cost.
Affordable for transferring small crews, that is (10-20 people).  That seems sufficient for the next ten years.
If cheap enough is constrained to the $500k/passenger, then no known combination of vehicles can qualify.

On-orbit refueling is the biggest challenge if MCT is going to land at the Mars end (besides MCT itself, of course). If a full propulsive landing of people on Mars is not part of MCT's design, then there will be additional technology needing development to get crew down (safely).  Taking back off from Mars using ISRU is incredibly more complicated and expensive than crew transfer.

Note: Making a 20-30 passenger Dragon-3 is not that difficult.




Title: Re: MCT Speculation and Discussion Thread 3
Post by: Impaler on 04/19/2015 02:43 PM
This Space-Cadet (actually, I'm a scientist and space enthusiast for 50+ years) never referred to NASA...
But if you choose to wear it, it's your shoe.

The point I was making is that the SpaceX Mars goals are not compatible with zero risk tolerance.  Having the trip to Mars always decades in the future is the only zero risk strategy.

Note: What is pathological, in my thinking, is our society's (in US of A) aversion to perceived risk, based in part on our lack of technical education to judge actual risk.

Space-Cadet-ism is an attitude and has nothing to do with technical experience or education, having these things just makes the attitude that much more inexcusable.

Again claiming that criticism of an unsafe vehicle design is a 'zero risk strategy' is a blatant straw-man.  I am not saying that we should stay on the ground forever, I am saying that SpaceX vehicle designs are not going to throw all safety concerns out the window for maximizing performance.

As to MCT's LAS, I think it will have none.  This is because I'm one of the small minority here that think MCT will not take off from Earth with crew aboard.  Cargo, yes.  Provisions, yes. Heat shield for Earth re entry, no. Fuel for TMI, no.

 I don't think the 'fleet' of MCTs will ever return to Earth's surface.  Not sure about Mars surface either... after all, 'land the whole thing' is only four words.  And those words were in reference to the Mars end of the trip.

Then what vehicle gets the passengers to orbit?  The goal is to be capable of taking 100 people per MCT, I can't see this being done with dozens of F9 flights as this would kill the cost competitiveness of the system.  Also everything we have been told about MCT says it will come back to Earth, Musk pounds on this point at every opportunity, it is GOSPEL.  If you don't believe it then your saying MCT development with FAIL, Musk would never even bother bringing a non reusable MCT to market.

The only way a complete MCT would be capable of launch abort would be if it was launched with a minimal fuel load relative to its large capacity.  Full tanks don't work for high-G abort at max Q, there just isn't enough thrust.

This would require:

1) That crew is not onboard, because it will take months/years to fill those tanks and crew won't want to spend all that time waiting in orbit

2) That the MCT not be used to achieve orbit.  This means that there need to be two or more likely 3 stages *below* the MCT.

Better to just send the crew up at a later date, after the MCT is fueled in orbit.
-----

A nosecone capsule has been a repetitive conclusion in my designs.  I keep trying to remove it and finding it's congruent with some other purpose.

All good points, but I think what will be done is that the MCT will be a 12-15m diameter capsule and will perform Dragon style abort with sidewall mounted raptor engines.  The main propellent tanks will be empty on launch but a number of smaller pressurized tanks will provide the brief burst necessary for abort as well as allow the raptor to start-up rapidly by bypassing the turbo-pump which takes too long to spin up.

The synod window and the refueling time will ultimately drive SpaceX toward the massive 'space liner' SEP vehicle that carries a few MCT rather then 'fleets' of MCT themselves just individually departing, that will happen only in the early exploration phase before real colonization and real volume demand.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: AncientU on 04/19/2015 08:58 PM
1...I am not saying that we should stay on the ground forever, I am saying that SpaceX vehicle designs are not going to throw all safety concerns out the window for maximizing performance.

2...everything we have been told about MCT says it will come back to Earth, Musk pounds on this point at every opportunity, it is GOSPEL.

3... dozens of F9 flights 


1. SpaceX isn't into maximizing 'performance' -- quite the opposite -- and they won't start MCT down that path.  It is a proven dead end.  (BTW, I believe that F9 delivers cargo with more margin than STS delivered crew, so safety is built into all vehicles.)

2. MCT will come back -- yes. ("We need them back, they're expensive" or some such.) 
But to an Earth landing -- reference for said GOSPEL required.

3. Nothing requires Dragon or its spawn to remain 7 passenger vehicles.
F9 v1.2 will be no where near its capacity when launching D-2.  The technology for a 20-30 passenger Dragon variant for shuttling people is a comparably easy derivative of D-2 -- using propulsive land landings.
FH can loft:
Quote
a mass equivalent to a 737 jetliner loaded with passengers, crew, luggage and fuel
Note: 737s carry from 100-200 passengers depending on configuration. 
A 100 passenger to LEO SuperDragon would also be nothing compared to MCT/BFR/ISRU/etc.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Ben the Space Brit on 04/20/2015 02:09 PM
FH can loft:
Quote
a mass equivalent to a 737 jetliner loaded with passengers, crew, luggage and fuel
Note: 737s carry from 100-200 passengers depending on configuration. 
A 100 passenger to LEO SuperDragon would also be nothing compared to MCT/BFR/ISRU/etc.

A bit misleading as the 737 doesn't need pressurisation against hard vacuum, reaction control system motors, a life-support system and other things. Additionally, there are volume limitations (due to bending loads) that mean 53t IMLEO requires a lot denser a payload than a pressurised crew/passenger cabin.

Cost-effectiveness is going to be SpaceX's gospel. As matters stand, in-orbit refurbishment will be harder than landing and refurbishment in the OPF or somewhere similar. That may change in the future but, planning for now, IMO at least, returning the MCT to Earth surface for refurbishment is likely to be the easier and more cost-effective option.


[edit]
Corrected typo
Title: Re: MCT Speculation and Discussion Thread 3
Post by: matthewkantar on 04/20/2015 03:10 PM
2. MCT will come back -- yes. ("We need them back, they're expensive" or some such.) 
But to an Earth landing -- reference for said GOSPEL required.

There are good reasons to land on Earth.

-The atmosphere allows you to kill most of your velocity without need of propellant.
-There is plenty of cheap propellant on Earth to refill the vehicle.
-Refurbishment not really an option in orbit without some really expensive facilities.

Enjoy, Matthew
Title: Re: MCT Speculation and Discussion Thread 3
Post by: RanulfC on 04/20/2015 03:21 PM
Wow. Not hard? What planet are you from... This has to be one of the most stunning proclamations I have read on this forum.

That assumes you actually "read" what a wrote which is pretty obvious you didn't :)

Quote
There will always be mass penalties and engineering compromises. Making the Shuttle as safe as you seem to want it would have crippled it.

Which is why I specifically said that the Shuttle design did NOT allow it.

Quote
Accept the risk and move on. You yourself wrote "Rockets are inherently more dangerous than aircraft", so more risks will be expected and accepted. If this bothers you, others will gladly take your place in line.

Of course, only macho people with no fear of danger and no perception of the risk, (it's all the same after all) need apply.... ::::sigh:::: The actual process which SpaceX has used is to NOT "accept-the-risk-and-move-on" but to UNDERSTAND the risk and move to mitigate it. That's how transportation systems become safer and more useful. If this bothers you, well, your out of luck because its the way society accepts new transportation methods and operations.

You don't NEED to "accept the risk" because engineering the majority of the risk OUT of the system is pretty easy and cheap unless you "compromise" yourself into a corner with the design. Rockets ARE more inherently dangerous than aircraft but that in no way means they are more "risky" as long as you are smart in design and operations. (Don't compromise yourself into a corner)

Rather than continue to accept the "risks" of flying we have stepped up and engineered and modified operations to greatly reduce the risk of flying. Your 'statement' would indicate you see no reason we should have ever bothered...

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Here's the ultimate safe vehicle for you: One that doesn't go anywhere.

In fact that IS the primary "answer" for risk assessment: Don't do anything or go anywhere "risky". But real-world/mission requirements mean that is not an option for most cases and therefore you look to reduce and control what risk factors you CAN in order to successfully complete the mission/task. Risk management is the process of accepting that "risk" is out there and assessing what the worst thing that can happen is and how mitigate the risk of it happening and/or the amount of damage that such an outcome will produce. The idea is that you can never reduce the "risk" to zero but you can and should reduce it (and the effects of a 'bad' outcome) to the lowest factor possible.

Randy
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/20/2015 04:15 PM

Thx for the reply Lobo and for taking these issues seriously.

You speak of a 'Mars-MCT' and 'LEO-MCT' but I've always assumed one type of vehicle, and unless the LEO variant is staged different from the 'combined 2nd stage' design used on the Mars variant then it has the same abort difficulty. 


No, I'm referring to one common spacecraft platform, but by Mars-MCT, I mean the spacecraft staged in LEO being fueled and provisioned to go to Mars.  And by LEO-MCT I mean the spacecraft/stages that will be coming up to fuel up and provision the Mars-MCT.  Not unlike ULA's ACES LEO depot concept, except the stages would be reusable rather than expendable.  And the Mars-MCT itself would act as the Depot.  In ULA's plan, EELV's would launch without payload, and the upper stages would take the extra residuals to the depot and pump them into it.  Once there was enough propellant in the depot, an upper stage with Orion or a lunar lander would come up, the stage would get fueled up, and then it would burn for TLI.

http://www.ulalaunch.com/uploads/docs/Published_Papers/Exploration/DepotBasedTransportationArchitecture2010.pdf

http://www.ulalaunch.com/uploads/docs/Published_Papers/Exploration/AffordableExplorationArchitecture2009.pdf

 
So that's basically what I'm referring to.   The LEO-MCT wouldn't need some of the equipment the Mars MCT had, like a Sabatier reactor, etc.  I would envision the MCT's coming up as tankers would have pretty minimal (if any at all) crew accommodations as they'd be unnecessary.  But would still be the same basic platform.   Think if a Dv2 capsule configured for crew or for cargo, or for a few crew and some cargo.  Same spacecraft, but just configured a little different depending on need.


Abort both static at the launch pad and during the first stage burn is generally the most dangerous part of a rocket launch so having this a 'black zone' is very serious even if the time period is brief.  Catastrophic booster explosion (or a loss of guidance control on the Booster which is going to force a self-destruct) is indeed TEH scenario for which abort systems are designed, virtually ever disaster scenario necessitating abort starts with or goes through a catastrophic booster explosion.  I am though less concerned with the MCT itself blowing up during assent even when it is acting as a 2nd or even 3rd stage. 

But I am quite confident that no amount of engines can be attached to this large MCT to push it away from the first stage, you would need more engines on it then are in the first stage.  Think about the masses and accelerations.  The first stage of BFR is likely to have 20+ raptor engines and it accelerates the whole rocket off the launch pad at a small fraction of a G, aka Thrust:Weight is just slightly >1.  That second stage is maybe a third of the total mass on the launch pad but to effectively abort you need Thrust:Weight of around 5, meaning you would need an absurd ~30 engines to push the second stage away at abort speed, and that's assuming it can even withstand that much acceleration.

A traditional 'capsule on 2 stages' that the F9 uses would still be difficult challenge to abort, I think it will need something like 6-8 Raptor engines around it like the Super-Draco's on the Dragon capsule.


Which is why I was speculating they probably won't try to have an "traditional" abort system.  It would just be impractical.  However, as long as the booster isn't suddenly exploding, in the event of a LOM booster failure, you should be able to shut the booster engines down and light the upper stage engines and do an emergency staging.  And then divert MCT to a contingency emergency landing area.  Not unlike STS.  STS has been panned for not having an LAS system (by me at times too), but it actually could have survived some different abort scenarios.  It did abort to orbit one launch when it had a SSME failure.   Other abort modes would have had it doing an emergency jettison and return to launch site or go to various other location.  One major problem with that of course is if it had to jettison while the SRB's were burning, as they can't be shut down.  It'd have to jettison into possibly a hypersonic slipstream if it couldn't jettison the SRB's early.  If it became unstable it could break up.  But that really wouldn't be the case with MCT, as it would always be on top of the booster and would have enough engine thrust to push it away from the booster once the booster was shut down.  (All of the engines would have to malfunction and not shut down in order for this to not be possible...which is pretty unlikely). 
So barring a booster suddenly exploding, or all it's engines failing on and at full throttle, MCT should be able to abort itself in all/most other failure modes.
Again, remember, any LAS system is just a matter of what sort of failure modes you are trying to protect against.  An airliner had safety/abort capabilities to handle most failures.  But if you tried to protect against the aircraft blowing up or breaking apart in flight, the plane could never get off the ground.  So they don't try.  But they are protected against loosing an engine, and various electrical and control failures.  There are hundreds of people on them and they are considered "safe" and "acceptable". 


As for the cargo placement within the vehicle, I have to imagine that with a vertical landing the cargo being in the nose is absolutely prohibitive because of the top-heavy nature, it would be virtually guaranteed to fall over, the logistics of unloading are just another headache.  The low, nearly ground level cargo hold depicted in your sketch seems to me the only viable means to do such a vehicle.

That could very well be.  I would think it would make more sense to put it at the bottom in a cargo area between the MPS and the bottom of the tanks (like an integral interstage section...as shown in the picture I posted).  But I don't know enough about rocket engineering to know if there's any prohibitive engineering challenges in doing that or not.   Maybe the crew hab could be just above the cargo deck?
Seems very odd to have the crew under the tank...very un-spaceship-like, but I can't really think of an obviously reason it couldn't be done.  Would make egress and ingress much easier as the crew would just have to get one deck up from the cargo deck, and one would assume the cargo deck would have some sort of deployable ramp so large rover/cargo can be unloaded if they aren't wanting to use a crane.  (Also as shown in the picture I posed)


Title: Re: MCT Speculation and Discussion Thread 3
Post by: RanulfC on 04/20/2015 04:24 PM
The same thing happened to them twice with the Apollo program as well, only then they had the budget and authority to change the system to prevent such things from occurring again. The design and construction of the Shuttle left no such options open. SpaceX knows better and have set out to ensure that their rockets which they KNOW are unsafe from the start WILL have those options for human payloads. There is NO reason to assume they will suddenly change their mind with the MCT or BFR. Society be damned this is a COMPANY decision and the reasoning is straight forward and logical. I don't see them changing their path for some marginal performance gains.

I'm not saying SpaceX shouldn't have a rescue system on an MCT. Just that it is not beyond the realm of possibility that at some point MCT will not have one. Having a rescue system does not reduce the chance of death to 0% either, the system itself can fail. It's always a matter of profit vs. risk.

No it does NOT reduce the risk to 0% it however greatly reduces the risks of certain outcomes. While it's always about profit vs risk it is about balancing those factors, especially in an transportation system as reduced risk of loss of vehicle/cargo/passengers directly relates to profit.

Quote
I'd like to have a rescue system on the airplanes that I take, but alas...

Come up with one that can be economically introduced and actually reduces the risks of vehicle/cargo/passenger loss (most don't or are only applicable to a limited segment of the overall operations) and you will become a multi-billionaire over night. Meanwhile continued active risk management and system improvement has reduced the risk of flying to a very low level compared to even 20 years ago. A "rescue" system for an airplane is much harder to engineer, (and vastly less "cheap") than one for a launch vehicle.

If they are to see their Mars goals achieved, they will lose more than one MCT/BFR.
Great deeds are not for the faint of heart (i.e., there's no free lunch).
The obsession with avoiding risk in our society is pathological.

If this were at all true we would have NO people taking risks at all which would (for one) eliminate all "extreme" sports and activities. The fact that these activities are on the rise and are becoming "safer" while still providing the same experience and thrill to a wider audience pretty much proves this to be a typical "pop" analysis with no substance.

SpaceX has lost vehicles and payloads before, but they have moved away from design and operations where that was "common" in the direction of reduced risk of failure without sacrificing economy. They are in fact NOT accepting "greater risk" in order to get the job done but reducing the risk in order to get the job done successfully. If you can't see the difference you're missing the point.

The obsession with avoiding risk in our society is pathological.

I think this is more about NASA being a symbol. Cars, airplanes... those are routine risks. But astronauts are the High Priests of the religion of Progress, and people today don't like martyrs or human sacrifices.

People LOVE martyrs and as long as the "sacrifice" is considered worthwhile society is willing to accept a VERY high price as has been proven over and over again in the past and will again in the future. Your reasoning is flawed at the core. NASA is very careful in risk management due to the fact that they no longer have unlimited budget and political/public support as hey did at the beginning of the Apollo. The REASON for this (and why NASA has become much more risk averse than that time) is simply that during Apollo NASA accepted and took risks that ended up in deaths, accidents and a general loss of public/political trust and support. Society had decided that they no longer accepted "martyrdom" for astronauts because they no longer viewed the sacrifice as acceptable.

SpaceX is NOT willing to accept the risk of killing people in their vehicles and has worked towards mitigating the risk that this will happen as much as possible. This is why people will NOT fly on the Dragon-V1 as SpaceX has not developed nor plan on deploying a LES on that vehicle. No matter how many people are willing to volunteer to fly on it SpaceX is unwilling to pursue that path. (SpaceX is unwilling to create martyrs for the OPPONENTS of commercial manned space flight, which is the SMART move I'd say but it would seem a lot of people see this as being to "risk adverse")

Quote
Note that many airlines have lost a load of paying passengers, and this even today when commercial flight is routine (and safer than driving). The reasons that they go bankrupt are not the inherent risks of flying.

No the main reason companies in commercial flight go broke is because they do NOT adhere to or operate in a risk-reduced mode and they eventually get caught and have to pay the price. Aircraft flight today is very much safer than airline flight 20 years ago. It is HUGELY more safer than 40 years ago. This has been due to a steady progression of safety standards, operations and modifications as well as improving technology.

This is an example of risk mitigation in progress, a process that far to many see as UNWANTED in the far more inherently risky rocket launch vehicle system. Why? Because most of these people do not understand that while space travel is on the cusp of becoming almost routine that does NOT mean that it is safer or that the risk is less. 40 years ago air travel was 'routine' but it was FAR from safe by todays standards. It has taken time, effort and money to reach the point were are at today and it will take at LEAST a similar effort to do the same with space transportation.

For routine space travel to become "safe" enough for society to accept the inherent risks means that the majority people have to believe that the benefits outweigh the risks and that only happens when the risks are mitigated to a level where this happens.

NASA has to reduce risk to a level that is acceptable to the political and public interests to which it has to answer. Those are very much higher than the ones SpaceX has to answer to outside of NASA contracts but SpaceX is determined to reduce the risks possible to a level where the "risk" of colonizing Mars is low enough to allow the benefits of such activity to proceed. That does not mean and has never meant "zero" risk but it DOES require risk mitigation to reduce the risks to the required level.

Randy
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/20/2015 04:44 PM
FWIW, I repeat my proposal that the nose of MCT be essentially an up-sized (say, 5m-diameter) Dragon 2.0. During ascent and descent phases, the crew and passengers ride in there. In the event of an emergency, the aerodynamic outer shell of the MCT is jettisoned and the 'Super-Dragon' escape pod flies clear of the MCT with the objective of a safe landing as near to the launch site as possible (Mars) or just safe land- or sea-fall (Earth).

If you're going to do that, why not jut build a separate "super-dragon" and send the crew up separately from MCT for EOR?  Why have the added compexity of a spacecraft on another spacecraft?

And to expand on that more, when I mentioned different configurations of MCT depending on the need, there's really no reason you could have a "crew-MCT" which would trade it's normal paylaod mass for some sort of full LAS system.  Additional rapid light abort engines or whatever, but this would be the only version of MCT that would launch with a crew and it would be intended to ferry crews to and from LEO.
This version could loft 100 crew to LEO, but very little else due to it's LAS system.
This allows the use of the new common Spaceship design (although modified) rather than needed a whole new spacecraft development in "super-Dragon".

Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/20/2015 04:47 PM

Better to just send the crew up at a later date, after the MCT is fueled in orbit.

@this.

But then you need a spacraft that will carry the crew up to the Mars-MCT that has been fueled and provisioned and readied in LEO.  So the question then remains, what sort of launch abort scenarios will -it- be able to handle?
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/20/2015 05:15 PM
2. MCT will come back -- yes. ("We need them back, they're expensive" or some such.) 
But to an Earth landing -- reference for said GOSPEL required.

There are good reasons to land on Earth.

-The atmosphere allows you to kill most of your velocity without need of propellant.
-There is plenty of cheap propellant on Earth to refill the vehicle.
-Refurbishment not really an option in orbit without some really expensive facilities.

Enjoy, Matthew

I respect Ancient's views a lot, but my inclunation too is that MCT's will be desinged to land on Mars, and on Earth.  That way there won't need to be any propulsive injection into Mars orbit or Earth orbit.  Plus then the spacecraft comes back to Earth were it can most easily be refitted and repaired and redied for the next mission.  That's a much more difficult thing to do in orbit.  And again, when you can make your fuel on the planetary surface, then there's not the need to leave as much mass as possible in orbit as there was for Apollo, and as there is with conventional Mars plans where all the fuel is brought from Earth.  If fuel can be made on the Mars surface, (and on Earth surface) then you want to get your spacecraft down there to it if you can.   You don't need to be as fuel efficient as if you had to bring it all with you (as we did for Apollo). 
And if you design your spacecraft to handle EDL on Mars (unlike a spacecraft like the LEM that never saw an atmosphere), then it's not much of a stretch to design it to handle EDL on Earth as they both have comparative EDL criteria.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: The Amazing Catstronaut on 04/20/2015 05:43 PM
Agreed with Lobo - Apollo, as one Nasa presentation demonstrated in great detail, also had a godawful amount of "Do or die" burns and staging events - things that absolutely had to go right first time with no auxiliary solution and if they didn't work out, you were going to run out of consumables and die horribly. Or do a subterranean   lithobreak and die fast. Or just explode. If any of these contingencies had occurred, we'd be remembering Apollo as one of Mankind's most historic Babel moments, and probably wouldn't even be considering going BEO today.

Lowering complexity by having an integrated "do everything" transfer hab that also serves as your cargo/crew lander and Earth return capsule is going to help prevent any Babel moments from stymying manned BEO space travel for generations on end.

Title: Re: MCT Speculation and Discussion Thread 3
Post by: sheltonjr on 04/20/2015 05:52 PM
OK, here are my thoughts, opinions and speculation concerning the MCT with current topics.

Launch Abort System
I cannot see a conventional rocket 5-6g LAS being practical on the MCT. The engines and weight penalty would be too severe and they would be too powerful to be used again in any portion of the remainder of the flight. Also, I do not think one is necessarily required.

The big gotcha that requires a LAS is booster explosion and I believe that with current and near term technology, the risks of a booster explosion should be manageable and near zero based on the following improvements.

My educated guess on what causes a booster explosion is the rapid detonation of uncontrolled fuel and oxidizer. Which means somehow there is a big leak next to something hot.  There is a lot of hot stuff at the end of the rocket, and eliminating that does not seem feasible. So therefore our primary goal is should prevent unwanted leaks of fuel and oxidizer.

The first obvious cause for a leak is structural failure in the tank or piping.
SpaceX has shown that reliability and re-usability are more important than payload performance to orbit and have greater structural margin than other unmanned rockets, and since they are designing the rocket to survive re-entry, a tougher structural environment, It must be designed not to fail. Aircraft do not have spare wings, their spar is designed to survive with a comfortable safety factor.   I believe the  BFT/Raptor/MCT system will be able to lift about 200-225MT to LEO in fully re-usable mode. The BFR has enough performance that SpaceX can ensure the structural integrity of vehicle. On-board vibration and stress monitors will monitor and record any unexpected limits for inspection after landing. A Health and Usage Monitoring System (HUMS).

Solid rocket motor failure.
Do not use them. They difficult to inspect, They cannot be test fired, and they cannot be turned off once started.

A failure of a turbo-pump/combustion chamber that produces shrapnel that penetrates the tanks and lines.
With modern sensors and computing engine performance can be quickly monitored and shutdown if trends or limits are reached. SpaceX has demonstrated this already on a Falcon 9 mission, and with their architecture of using many engines they can safely do this without loss of mission or vehicle. The design of the Raptor engine with hydro-static bearings and separate fuel and  oxidizer pumps that eliminates a seal failure should greatly reduce the possibility of a engine RUD.  SpaceX has also demonstrated that they are willing to take the weight/performance penalty of putting debris shields between the engines.

Others
I am sure there are others, but I hope you see what I am getting at.

If the booster does fail, the MCT must safely separate from the booster and land on land or water. For this I do not think it needs 5-6G worth of thrust for a 225MT payload.  My guess is the MCT dry mass is around 65MT and with a max payload of 100MT allows the MCT to launch with 70MT of fuel. This should be enough perform some LEO missions like visiting a space station and doing a launch abort and propulsive landing if required.

Also instead of adding massive thrust to the payload, the other option is to add a lot of drag to the stage. And surprise it already exists.  In case of booster failure, separate the MCT and then deploy the first stage landing legs to add drag to the first stage in a hurry.  (I do not think I have heard this concept mentioned before by anyone. True??)

 
MCT Flight Plan
I believe the MCT flight plan is exactly what Elon Musk has said it would be. "Land the whole thing", Return to Earth for reuse, for the following reasons.

Slowing ~180MT in LMO is going to use a lot of propulsive dv, or risky areo-braking, and I do not know what the benefit is besides possibly making the MCT more comfortable with inflatable modules and other systems that could not survive re-entry.

A big argument for not returning the MCT to Earth terra-firma is the waste of lifting the MCT to orbit in the first place.  But if you evaluate the actual mass evolved in a MCT mission to Mars.  My hypothetical MCT design has a 225MT to LEO BFR lifting the MCT/Payload/60MT fuel to LEO and then topping of another 400MT of fuel from 2 BFR Tanker missions. Therefor total fuel load is 460MT and total mass for TMI is 626MT. 

The MCT mass is just 10% of mission mass, and to have the advantage of having the MCT on Earth where it can be inspected/repaired/reloaded/upgraded is well worth the fuel cost of lifting that 65MT MCT into orbit over & over again.

I also have the opinion that the MCT will be gutted on Mars before it is returned. If no one is returning with the MCT than everything that is not required for the return will be removed by the colonist for their use. It is adding to the available payload to Mars. Examples are: Mattresses, bunks, computers, entertainment devices, food processing equipment, life-support, toilets and sinks and even some non-structural bulkheads and dividers. Everything that is useful for the trip to Mars will also be useful on Mars. If designed and built in a modular way with proper disconnects, They should be able to safely remove all these items, and they will have to be replace back on earth before the next mission.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: AncientU on 04/20/2015 09:56 PM
2. MCT will come back -- yes. ("We need them back, they're expensive" or some such.) 
But to an Earth landing -- reference for said GOSPEL required.

There are good reasons to land on Earth.

-The atmosphere allows you to kill most of your velocity without need of propellant.
-There is plenty of cheap propellant on Earth to refill the vehicle.
-Refurbishment not really an option in orbit without some really expensive facilities.

Enjoy, Matthew

You and others continue to make a good argument for landing on Earth, so I'm not surprised to be in the minority here.  My return to Earth (but don't land) approach mainly works if return is actually to cis-Lunar space, preferably EML-2 (or 1, for easier refit).  Once you head to LEO, might as well land the whole thing.  But, that means lots of advantages of remaining in space disappear. 

To comment on your points above:
-The atmosphere is an extremely cheap option for killing velocity.  No argument there.
-Plenty of cheap fuel on Earth is irrelevant.  Yes, it's cheap to get back to LEO, but you have to refuel there again with not-so-cheap fuel.
-Refurbishment of an in-space vehicle that has been in space for less than a year (and is obviously still working) is not a drastic expense.  Anyway, what did Scotty and the engineering crew do on that long trip back to Earth?

The thing that isn't mentioned here is the logistical challenge of getting all the MCT fleet back into orbit and refueled when the launch window is approaching.  Having the vehicles already in orbit and only having to top off fuel (and crew at the last minute) makes the 'fleet' concept viable.  Otherwise, it's going to be a mad scramble with many single failures having potential to untie the best-laid-plans bundle.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/21/2015 12:22 AM
Agreed with Lobo - Apollo, as one Nasa presentation demonstrated in great detail, also had a godawful amount of "Do or die" burns and staging events - things that absolutely had to go right first time with no auxiliary solution and if they didn't work out, you were going to run out of consumables and die horribly. Or do a subterranean   lithobreak and die fast. Or just explode. If any of these contingencies had occurred, we'd be remembering Apollo as one of Mankind's most historic Babel moments, and probably wouldn't even be considering going BEO today.

Lowering complexity by having an integrated "do everything" transfer hab that also serves as your cargo/crew lander and Earth return capsule is going to help prevent any Babel moments from stymying manned BEO space travel for generations on end.

Aa multi-use piece of hardware is less mass/fuel efficient at each separate job than a dedicated piece of hardware.  But being able to gas up when you get there really helps make fuel efficiency less of a constraint, which means a dual purpose vehicle, or tri-purpose vehicle can withstand the mass pentalty it incurs by not being dedicated.

However, in that same vein, getting more uses out of a single spacecraft can have a mass-reduction effect. (As well as the obvious economic value) With Saturn V/Apollo, there was essentially 7 different spacecraft/components.
1)  S-1C
2) S-II
3) S-IVB
4) LEM DM
5) LEM AM
6) Apollo CM
7)  Apollo SM

So with MCT, 2-7 would all be handled by the same piece of hardware.  It would required refueling in LEO, which NASA really wasn't ready to do in the 60's for Apollo given their time schedule, and it requires refueling on Mars, wich NASA definately wasn't ready to try to do on the Moon in the 60's. 
But if you can do those two things, then the 2nd stage that takes you do orbit (S-II), and then can be refueled and used as your Earth departure stage (S-IVB).  And then has landing thrusters and a heat shield so it can be used as your lander (LEM DM).  And then has ascent engines so it can be used as your ascent module (LEM AM), and your Mars departure stage (Apollo Service Module).  Finally, since it still had that heat sheild and those landing engines, it can be used as your Earth Return Vehicle (Apollo Command module.

The LEM AM and DM used a common crew cabin, as did the Apollo CM and SM, and the LEM DM didn't have it's own RCS system as the AM had one.  So they -did- consolidate where they could.  This MCT plan just does more of it. 

It's like Zubrin's Mars Direct plan, but with two pieces instead of four.  Zubrin had the 2-stage Ares LV, the crew hab module, and the Earth Return Vehicle.  This MCT plan just blends the ERV with the Hab module and the Ares 2nd stage.  To simplify even further.  Zubrin's Mars Direct didn't include LEO refueling, so it needed the Ares 2nd stage to be separate and expandable from the other two space craft.

Besides simplicity and economics, another advantage in getting so much use out of the same hardware is then you can really invest more in each system without the multiping effect of having to do that for the other pieces.  For example, with Apollo, if you wanted engine out redundancy for the whole mission, then you need to invest in additional redundant engines on 6 of those 7 pieces (not the CM as it had no main propulsion)  You'd need another F-1 on the S-1C, another J2 on the S-II and S-IVB.  Anther DM engine, and another AM engine, as well as a 2nd engine on the SM.  That's a lot of additional engines and plumbing to add that in, so Apollo didn't.
However, with a 2 piece MCT, you just have one additional engine on the booster, and one additional engine on the spacecraft.  So now perhaps it's not such a huge mass hit to add in engine out redundancy in all phases of the mission?  That extra MCT engine means there's no LOC during ascent if an engine fails, and no LOC during TMI if an engine fails, and no LOC during powered landing if an engine fails, and no crew stranded on the surface of Mars if an engine fails on the surface.  Ditto for TMI and for Earth EDL.
  If you add in redundancies to the ECLSS system, you have just one system to add that too, not two or three or even four as would be needed in NASA's DRM 5.0 mission plan.  You can really invest into each system becuase there's only one of them on one common spacecraft and you can afford (mass wise) multiple redundancies.

And really, this isn't much of a reach.  Rocketplane Kistler was going to basically do just this on a LEO scale.  This basically just expands on that.  And the K-1 was proposed to be a commercial crew supplier too.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/21/2015 12:26 AM
It is a simplistic, self-gratifying message that conforms to the general anti-government ideology and 'nanny state' bogyman of the political right-wing.  But it bears no resemblance to reality, NASA engineers when faced with envelope pushing performance demands and inadequate funding (both the fault of Congress) have in fact sacrificed safety REPEATEDLY and become quite cavalier in doing so.


Impaler,

I respect your comments, but take some issue with you here.  Setting aside your political accusation as it would be OT to get into, I think you are looking at the situation with SLS and projecting that historically on NASA.  Issues with CxP and even the compromises/limitations of STS are more the blame of NASA not being pragmatic and realistic with their budget situation, than Congress no longer giving them a blank check as they did in the ealy Apollo days.  Something like Direct,  which NASA did look at a version of it in ESAS, could have worked much better within realistic budgets than CxP did.  But -NASA- wanted the larger-than-Saturn V HLV and a new CLV that essentially only reproduced what EELV's were already doing.  They also dictated Orion, vs. more affordable Orbital Space Plane concepts in the early 2000's...one of which became CST-100 later.   
So a lot of the issues over the years have been self inflicted, not so much Congress-inflicted.  (Although of course various political pressures of various Presidents and Congress's have always pulled on NASA in different ways.  They are a government agency after all.)


SpaceX success has been based on internally NOT making the mistakes Congress cripples NASA with, Musk adequately funded the company and it's internal development and he dose not make absurd performance demands.  This gives them the engineering headroom to make their system SAFER then NASA equivalents. 


You are contradicting yourself.  Either NASA should be able to work adequately, even successfully, with even modest budgets like SpaceX has, or SpaceX shouldn't be in business any more because they've not had anything like NASA's budgets to work under....and thus should be crippled and be bankrupt.

So SpaceX has done a lot, with a lot less, than the budgets NASA has been working with from Congress...which you are blaming for not funding enough?

That doesn't quite make sense to me.  ;-)



Title: Re: MCT Speculation and Discussion Thread 3
Post by: Impaler on 04/21/2015 01:42 AM
I think I've correctly put my finger on the root of the repeated claims by many on these forums that space-craft need to be designed with LESS safety features and safety margin.  It has ideological roots, indeed MOST opinions about space and space exploration, and the design of the vehicles to do it with stem from deep ideological beliefs.  RanulfC has stated it better then I why this anti-safety belief is wrong.

With regard to the seeming contradiction, their is no single 'platonic' number of dollars being the true 'cost' for any group to do a specific task, every group has it's own unique cost to do anything.

SpaceX is clearly more efficient with their money then NASA is, what ever the underlying reasons for that are (their are many) is irreverent for this point.  The allocation of money for each entity to achieve a goal can either be adequate or inadequacy for THAT entity, it makes no difference if another entity would need more or less to do the same job.  If NASA would need $100 dollars to do a job and is given $50 they are inadequately funded, even if SpaceX could do the same job for $20, and if Elon allocates $20 for SpaceX to do that job internally they the funding is adequate for them. 

We know that MANY NASA development efforts fail (more fail then succeed) and funding is a major reason why, but to our knowledge no SpaceX development effort has yet failed, though this might just be a case of not talking about failures.  We do know that when the Falcon-1 blew up 3 times in a row Elon put in his last dollar and pushed them over the top, the fact he had already capitalized the company to go through 3 failures and had money is reserve for a 4th try shows he is good at adequately capitalizing an effort to see it through rocky times, this is important, most people will only capitalize/estimate/budget with rose colored glasses on, aka only enough to do the job if everything goes right.

Historically Congress had made excessive technological demands with inadequate funding given what NASA would have needed to do the job, STS being the prime example.  Apollo succeeded because NASA administrators quadrupled their cost estimates and Congress did not blink.  SLS has basically been designed by Congress so their is no cost-safety trade off for NASA to even make if they wanted too, the program just proceeds as a glacial pace due to low funding instead.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: hkultala on 04/21/2015 01:51 AM
I think I've correctly put my finger on the root of the repeated claims by many on these forums that space-craft need to be designed with LESS safety features and safety margin.  It has ideological roots, indeed MOST opinions about space and space exploration, and the design of the vehicles to do it with stem from deep ideological beliefs.  RanulfC has stated it better then I why this anti-safety belief is wrong.

With regard to the seeming contradiction, their is no single 'platonic' number of dollars being the true 'cost' for any group to do a specific task, every group has it's own unique cost to do anything.

SpaceX is clearly more efficient with their money then NASA is, what ever the underlying reasons for that are (their are many) is irreverent for this point.  The allocation of money for each entity to achieve a goal can either be adequate or inadequacy for THAT entity, it makes no difference if another entity would need more or less to do the same job.  If NASA would need $100 dollars to do a job and is given $50 they are inadequately funded, even if SpaceX could do the same job for $20, and if Elon allocates $20 for SpaceX to do that job internally they the funding is adequate for them. 

We know that MANY NASA development efforts fail (more fail then succeed) and funding is a major reason why, but to our knowledge no SpaceX development effort has yet failed, though this might just be a case of not talking about failures.

Parachute returnal of first staged did fail.

The stages did not widthstand the return to atmosphere at high speeds. So they had to switch away from parachutes to using retro-burn and powered landing.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Impaler on 04/21/2015 02:55 AM
Parachute returnal of first staged did fail.

The stages did not widthstand the return to atmosphere at high speeds. So they had to switch away from parachutes to using retro-burn and powered landing.

Your only proving my point, SpaceX has a 'return first stage by any means' development program which is adequately funded that they can continue it if the first stab (parachute) dose not work.  By your definition Thomas Edison 'failed' to develop the light-bulb 999 times, but this is silly because it is one development arc of trying a thousand different filament materials.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: matthewkantar on 04/21/2015 03:07 AM

The thing that isn't mentioned here is the logistical challenge of getting all the MCT fleet back into orbit and refueled when the launch window is approaching.  Having the vehicles already in orbit and only having to top off fuel (and crew at the last minute) makes the 'fleet' concept viable.  Otherwise, it's going to be a mad scramble with many single failures having potential to untie the best-laid-plans bundle.

Getting the MCT back on Earth does not imply leaving it there until the last minute. If you have a dozen of them, they can be put in orbit any time prior to the Mars launch window opening.

If the vehicle is truly reusable, the propellant to get it into earth orbit is cheap, and the propellant to refill it in orbit is the same price weather the stage set down on Earth or not.

When I first heard of the idea to land the thing back on Earth, it went against everything I thought about how a Mars colonization should work, but it makes more and more sense.

Matthew
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lars-J on 04/21/2015 03:46 AM
I think I've correctly put my finger on the root of the repeated claims by many on these forums that space-craft need to be designed with LESS safety features and safety margin.  It has ideological roots, indeed MOST opinions about space and space exploration, and the design of the vehicles to do it with stem from deep ideological beliefs.  RanulfC has stated it better then I why this anti-safety belief is wrong.

You have done no such thing - all you have done is provide a series of straw man statements that only appear to show a fundamental lack of understanding of other people's positions. To further label the opposing set of arguments as "anti-safety" just illustrates this perfectly.

Spend more time explaining your *own position*, spend less time arguing against what you *think* opponents are saying.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: guckyfan on 04/21/2015 05:52 AM

The thing that isn't mentioned here is the logistical challenge of getting all the MCT fleet back into orbit and refueled when the launch window is approaching.  Having the vehicles already in orbit and only having to top off fuel (and crew at the last minute) makes the 'fleet' concept viable.  Otherwise, it's going to be a mad scramble with many single failures having potential to untie the best-laid-plans bundle.

Getting the MCT back on Earth does not imply leaving it there until the last minute. If you have a dozen of them, they can be put in orbit any time prior to the Mars launch window opening.

If the vehicle is truly reusable, the propellant to get it into earth orbit is cheap, and the propellant to refill it in orbit is the same price weather the stage set down on Earth or not.

When I first heard of the idea to land the thing back on Earth, it went against everything I thought about how a Mars colonization should work, but it makes more and more sense.

Matthew

Interesting arguments. MCT may have a weight of 80t that need to be relaunched. However getting people and cargo up there is also not achieved without some vehicle with mass. Assume it weighs only 40t instead of 80 there would be 40t launch mass saved. That's less than 10% of total mass in LEO required for the trip. That small saving comes at the cost of developing a separate vehicle, having to do maintenance in orbit, transfering people and all kinds of cargo, from boxes to large infrastructure pieces from one vehicle to another in orbit.

I can imagine that people who have thought in the scale of NASA DRMs and their associated cost for a long time have trouble seeing 40 or 80t as small though.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: MikeAtkinson on 04/21/2015 07:25 AM
A big reason for returning the MCT to Earth is that cargo can be loaded on it there (most flights will be for cargo). People with their carry on luggage are easy to transfer in space (i.e. through a narrow docking port), supplies and tools are easy as well as demonstrated with ISS, water and other fluids can be pumped. But transferring a large 50 tonne hab or a 10 tonne pressurised rover is difficult - no doubt it could be done, but it is completely outside our current experience base. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: guckyfan on 04/21/2015 07:28 AM
supplies and tools are easy as well as demonstrated with ISS

Easy is relative. It takes them forever to transfer 2 or 3t of cargo.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: AncientU on 04/21/2015 11:30 AM

The thing that isn't mentioned here is the logistical challenge of getting all the MCT fleet back into orbit and refueled when the launch window is approaching.  Having the vehicles already in orbit and only having to top off fuel (and crew at the last minute) makes the 'fleet' concept viable.  Otherwise, it's going to be a mad scramble with many single failures having potential to untie the best-laid-plans bundle.

Getting the MCT back on Earth does not imply leaving it there until the last minute. If you have a dozen of them, they can be put in orbit any time prior to the Mars launch window opening.

If the vehicle is truly reusable, the propellant to get it into earth orbit is cheap, and the propellant to refill it in orbit is the same price weather the stage set down on Earth or not.

When I first heard of the idea to land the thing back on Earth, it went against everything I thought about how a Mars colonization should work, but it makes more and more sense.

Matthew

Now you are shuttling crew separately again, so no need for a LAS... Where we started this discussion.  Cargo loading is a challenge still as MikeAtkinson pointed out, but cargo doesn't need a LAS. 

So, return to Earth surface to refit and provision the MCT, then launch asap so pre-fueling can start well before the fleet sails.  Crew comes up last.  Makes sense. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: guckyfan on 04/21/2015 11:47 AM
Now you are shuttling crew separately again, so no need for a LAS... Where we started this discussion.  Cargo loading is a challenge still as MikeAtkinson pointed out, but cargo doesn't need a LAS. 

So, return to Earth surface to refit and provision the MCT, then launch asap so pre-fueling can start well before the fleet sails.  Crew comes up last.  Makes sense.

That does not follow. Launch all of the cargo MCT early and refuel them. Top off any boiloff before TMI. But launch the much smaller number of crew MCT late.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: spacenut on 04/21/2015 11:58 AM
Any private company can operate more efficiently than any government agency.   That is a fact.  Government is a bureaucracy top down.  Too many people to going through with too many rules.  Government can't fire unproductive employees like a private company.  Government has higher pay and more benefits for their workers in a lot of cases.  Private companies can focus on goals and objectives.  NASA has to do this and that for every congressional district that has a NASA office.  That is exactly why the Soviet Union failed and why China adapted capitalism.  NASA could do more if they could stay focused on one goal at a time and chose the right contractors to design rockets to do the stated goal instead of designing rockets by committee.  NASA did more in the 60's because they chose the right rocket for the right job.  There were several competitors with different plans to get to the moon, but NASA got their doing it the cheapest way possible.  They were going to use a Nova rocket and have a direct landing, until docking and the LEM were offered as a lower cost alternative. 

SpaceX has one goal in mind - MARS.  Whatever they do is designing and testing so they can achieve that goal.  Launching satelites and supplying the space station is just a means of getting money to eventually build the BFR and MCT.  Whatever they learn with Falcon 9 will be applied to the BFR and MCT. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: AncientU on 04/21/2015 12:28 PM
Now you are shuttling crew separately again, so no need for a LAS... Where we started this discussion.  Cargo loading is a challenge still as MikeAtkinson pointed out, but cargo doesn't need a LAS. 

So, return to Earth surface to refit and provision the MCT, then launch asap so pre-fueling can start well before the fleet sails.  Crew comes up last.  Makes sense.

That does not follow. Launch all of the cargo MCT early and refuel them. Top off any boiloff before TMI. But launch the much smaller number of crew MCT late.

I guess that I'm assuming (and we know why that's dangerous) that cargo MCTs will still have a basic crew to maintain systems, replace failed modular components, etc. as is the majority of ISS crew time spent.  The 100 passenger 'cargo' would be on separate space ships, but there would still be the basic crew.  It would be possible to have these trips fully autonomous, but then small things would risk lives and the ships themselves. We could send purely autonomous rovers to Mars, too, but we have kept humans in the loop because it's too hard to make a drone situationally smart.

OK, some cargo can be completely autonomous, but it has to be expendible. Completely. And redundant.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 04/21/2015 12:34 PM
You need an LAS when you launch from Mars as much (or as little) as you do when launching from Earth. Sending crew up separately is thus pointless.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: go4mars on 04/21/2015 01:19 PM
You need an LAS when you launch from Mars as much (or as little) as you do when launching from Earth. Sending crew up separately is thus pointless.
You're assuming that the upper stage/tanker stage/ISRU stage doesn't land on Mars to launch MCT from Mars. 

Assuming no upper stage/workhorse stage presumes that MCT can't have an abort system analogous to dragons.

Those could be a reasonable assumption based on some old quotes, but they are uncertain.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: spacenut on 04/21/2015 01:24 PM
If the LAS is hypergolic and not used with earth launch, it could be used for Mars launch also, like Dragon 2.  Parachutes would also be required if it is used.  On Mars half the fuel could be used on launch escape and maybe half used to land without parachutes since the gravity is lower.  So that has to be carried all the way there and back. 

It seems like the MCT maybe should just come back to earth orbit to refuel and pick up a modular storage unit to load in the cargo bay to fly back to Mars.  Cargo crews could be transferred using a simple Dragon docking.  A mechanical arm/crane could be installed on MCT for unloading on Mars and reloading in LEO.  To me that would save a BFR launch every time there is a return to earth.  One or two Falcon heavies could resupply the MCT cargo with a Falcon 9 Dragon replacement crew. Also with each 6 month window every 18 months, enough food, fuel, etc, would have to be brought for long term storage.  So say you can launch 20 MCT's in a 6 month window, that is a lot of MCTs launched in a few weeks, probably one or two a day from Florida and Texas.  So 36 or at most 72 colonists with cargo flights each 18 months.  Then again, it depends on the size of the BFR to haul up the MCT.  Also how fast they can liquefy natural gas and liquid oxygen to fuel this many beasts.  Some cargo flights might have to go unmanned during the off months.

Something else, since Falcon 9 can carry 7 to orbit, just say 6 with personal belongings.  Four could stay on Mars with each cargo haul and two return.  If it takes nine MCT cargo flights for every one human flight, then that is 36 colonists with every 9 cargo flights.  Maybe there will be no need for 100 colonists at a time.  Just 4 at a time with each cargo flight, because with all the solar panels needed for abundant power, battery backup at night, basalt melting equipment, excavation equipment, small cranes, modular housing, food, clothing, space suits, rovers, communication equipment, ice hauling trucks, storage units, aquaphonic equipment, hydrophonic equipment, seeds, plants, fish, and at least one MCT capable of hauling people back to earth in event of some type of major catastrophe. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 04/21/2015 01:44 PM
You need an LAS when you launch from Mars as much (or as little) as you do when launching from Earth. Sending crew up separately is thus pointless.
You're assuming that the upper stage/tanker stage/ISRU stage doesn't land on Mars to launch MCT from Mars. 
you're right because that would be dumb.

Quote
Assuming no upper stage/workhorse stage presumes that MCT can't have an abort system analogous to dragons.
There are other possible methods of abort.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Semmel on 04/21/2015 02:02 PM
You need an LAS when you launch from Mars as much (or as little) as you do when launching from Earth. Sending crew up separately is thus pointless.

I was wondering about that exact same fact or some time. It is pretty hard to design a LAS that works on Mars and Earth. I am not aware of any concept doing that. If both are different, I have a hard time imagining that two different LAS fly on the same vehicle.

Also when leaving Mars, what is the point of having a LAS? When the rocket fails, it and all its resources will be lost. How can the people survive on Mars without it? So to have a LAS on Mars to make sense, the colony infrastructure must have the margin to support the aborted colonists until a resupply ship arrives and they can be brought back with the next MCT. Is that realistic? Especially in the beginning?
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lampyridae on 04/21/2015 02:07 PM
A big reason for returning the MCT to Earth is that cargo can be loaded on it there (most flights will be for cargo). People with their carry on luggage are easy to transfer in space (i.e. through a narrow docking port), supplies and tools are easy as well as demonstrated with ISS, water and other fluids can be pumped. But transferring a large 50 tonne hab or a 10 tonne pressurised rover is difficult - no doubt it could be done, but it is completely outside our current experience base. 

If only we had decades of experience with a very large, reusable spacecraft that could load and unload large cargo modules in space...
Title: Re: MCT Speculation and Discussion Thread 3
Post by: JamesH on 04/21/2015 02:09 PM
You need an LAS when you launch from Mars as much (or as little) as you do when launching from Earth. Sending crew up separately is thus pointless.

You don't need an LAS on Mars, at least at first.

If the launch goes wrong, any LAS would result in the crew being stranded on Mars too far from any help to be saved anyway. Grim, but, I suspect, true. As the population increases, there will be more chance of recovery, so then you think of LAS.

Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lampyridae on 04/21/2015 02:27 PM
Well, that assumes you don't want to budget for a fuelled-up descent stage to go over and fetch yonder stranded crew. One ballistic hop, collect six or so suited crew in the cargo bay, and back to base. LAS mass is the real issue (although arranging the other stuff would be onerous).
Title: Re: MCT Speculation and Discussion Thread 3
Post by: sheltonjr on 04/21/2015 02:43 PM
I was wondering about that exact same fact or some time. It is pretty hard to design a LAS that works on Mars and Earth. I am not aware of any concept doing that. If both are different, I have a hard time imagining that two different LAS fly on the same vehicle.

Also when leaving Mars, what is the point of having a LAS? When the rocket fails, it and all its resources will be lost. How can the people survive on Mars without it? So to have a LAS on Mars to make sense, the colony infrastructure must have the margin to support the aborted colonists until a resupply ship arrives and they can be brought back with the next MCT. Is that realistic? Especially in the beginning?

A reasonable MCT taking off from Earth on top of a booster will mass about 225MT of vehicle/payload/fuel; 65/100/60. A distributed LAS like Dragon 2 with the 8 superDracos but using CH4/LOX would need a thrust of 250MT to safely separate from a non-exploding booster, which I contend will be rare and deployment of first stage landing legs acting as a large drag to separate the stage from the MCT. DeltaV to Mars is 5000 m/s after fully fueling in LEO.

See my post here for some justification of some of the above: http://forum.nasaspaceflight.com/index.php?topic=36805.msg1362199#msg1362199

The same reasonable MCT taking off from MARS fully fueled will mass 535MT of vehicle/payload/fuel; 65/10/460. On Mars the weight on the MCT is 201MT, Launch from Mars to Earth will rely on redundancy with engine out capability and on a very bad day, RTLS or land down range. DeltaV to Earth is 7325 m/s after fully fueling on Mars with ISRU CH4/LOX.

In summary, the new smaller CH4/LOX engines mounted on the MCT will serve as Earth LAS. TMI, Mars Propulsive re-entry, Mars launch engines and Earth propulsive re-entry. It seems doable, just need to work out the minor details.  ;)

EDIT: Added summary paragraph
Title: Re: MCT Speculation and Discussion Thread 3
Post by: spacenut on 04/21/2015 02:55 PM
Sounds like they need to develop a Methane Merlin.  They already have the engine, just need to adjust the piping and injectors.  Using the same turbopumps and as much hardware as possible it would probably only get 60-75% of he thrust of kerolox.  Just guessing, someone would have to roughly figure that.  Also the crew area and the cargo/fuel area could be separated in emergency. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: guckyfan on 04/21/2015 02:58 PM
In summary, the new smaller CH4/LOX engines mounted on the MCT will serve as Earth LAS. TMI, Mars Propulsive re-entry, Mars launch engines and Earth propulsive re-entry. It seems doable, just need to work out the minor details.  ;)

Fully my opinion too. Abort will be rare. If it happens, both stages will separate, fly for a while to burn off fuel, just like airplanes do. They then will fly back to the launch site for a soft landing. That capability will not cover every borderline accident ending in a fireball. But these will be even much more rare than the need for abort will be.

And it can be done with Raptor at the presently targeted thrust. No need for separate abort engines.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: sheltonjr on 04/21/2015 03:12 PM
Sounds like they need to develop a Methane Merlin.  They already have the engine, just need to adjust the piping and injectors.  Using the same turbopumps and as much hardware as possible it would probably only get 60-75% of he thrust of kerolox.  Just guessing, someone would have to roughly figure that.  Also the crew area and the cargo/fuel area could be separated in emergency. 

The theoretical advantages in safety/reliability/re-usability of the Raptor with hydro-static bearings, improved ISP from stage combustion, and separate fuel and oxidizer turbo-pumps would be lost if using the gas generator cycle of the Merlin engine.

But is a small 20MT/40Klb thrust Raptor feasible? Wise?

Is it possible to have Raptor turbo-pumps driving multiple combustion chambers? A turbo-pump fail then would take out multiple engine chambers. 

SpaceX has a large trade-space in the designing the MCT. Both fun and a nightmare.  ;D
Title: Re: MCT Speculation and Discussion Thread 3
Post by: spacenut on 04/21/2015 03:27 PM
Yes, the MCT could only use a few Raptors vs a lot on the booster.  Haven't thought about the whole MCT separating and flying back for landing.  If it is like 9-1 like Falcon 9 first and second stage, and it looks like 30 Raptors on first stage BFR then at least 3-4 Raptors on MCT. 

How low a throttle are they figuring on Raptor?  Seems like it would have to throttle low to land on Mars or only use fewer engines.  However would it be enough to fast separate from booster on earth launch. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: sheltonjr on 04/21/2015 03:44 PM
In summary, the new smaller CH4/LOX engines mounted on the MCT will serve as Earth LAS. TMI, Mars Propulsive re-entry, Mars launch engines and Earth propulsive re-entry. It seems doable, just need to work out the minor details.  ;)

Fully my opinion too. Abort will be rare. If it happens, both stages will separate, fly for a while to burn off fuel, just like airplanes do. They then will fly back to the launch site for a soft landing. That capability will not cover every borderline accident ending in a fireball. But these will be even much more rare than the need for abort will be.

And it can be done with Raptor at the presently targeted thrust. No need for separate abort engines.

For discussion, I am assuming you are talking about the 250MT/500Klb Raptor. If throttleable to 40% would provide a minimum thrust of 100MT/200Klb.

For Earth LAS, I agree this is usable. But that would require the engine to be mounted on the bottom of the MCT and somehow use through the heat shield with a very large vacuum nozzle. No redundancy available.

For TMI, Also works and would be optimum with no cosine losses. No redundancy available.

For Mars EDL. Good for initial part of EDL, but too much thrust for landing. Minimum thrust in 100MT and MCT weight on mars will be near 60MT.  Hover-Slam again and far from ideal. Thrust from center mounted engine will cause landing debris to possible damage the MCT. No redundancy available.

Mars Launch to Earth. Works. No redundancy available.

After typing all that, I see two problems. Lack of redundancy and how to mount a large engine with a large vacuum nozzle through the heat shield.

The only way to solve the redundancy problem is split the thrust into more engines. This then makes some of the other problems easier to find solutions too and opens up the trade space.

Smaller engines can be mounted on the side like Dragon 2, or behind the heat shield with more manageable smaller doors.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: RanulfC on 04/21/2015 03:57 PM
Impaler,

I respect your comments, but take some issue with you here.  Setting aside your political accusation as it would be OT to get into, I think you are looking at the situation with SLS and projecting that historically on NASA.  Issues with CxP and even the compromises/limitations of STS are more the blame of NASA not being pragmatic and realistic with their budget situation, than Congress no longer giving them a blank check as they did in the ealy Apollo days.  Something like Direct,  which NASA did look at a version of it in ESAS, could have worked much better within realistic budgets than CxP did.  But -NASA- wanted the larger-than-Saturn V HLV and a new CLV that essentially only reproduced what EELV's were already doing.  They also dictated Orion, vs. more affordable Orbital Space Plane concepts in the early 2000's...one of which became CST-100 later.   
So a lot of the issues over the years have been self inflicted, not so much Congress-inflicted.  (Although of course various political pressures of various Presidents and Congress's have always pulled on NASA in different ways.  They are a government agency after all.)

Lobo, while I respect your opinion and all.... :)

-SLS requirements were "directed" by Congress for no technical reason OTHER than a stated requirement for a certain size payload that would "require" the use of Solid Rocket Boosters as advised to certain Congressmen by certain "experts" in his home state. This is on record, as is the fact that NASA in the form of Bolden was TOLD this would be a hard requirement for the new NASA launch system and was enshrined in the "law" authorizing the design and construction of the SLS. That NASA has gotten "away" with designing a less capable "first" version is both a budgetary decision and a lack of any viable "alternative" showing up for the SRBs so that the original "requirement" no longer strictly applies. (This will change IF LRBs are suggested again)

-CxP/Ares-I/V were top-down directed which is why DIRECT never stood a chance of happening despite the very high internal NASA support for it. Griffin wanted a "Mars Direct" booster (ARES-V) and that was the goal and purpose he sold to Congress. Despite the lack of support and budget FROM Congress it was accepted as the program-of-record and no alternatives were considered. It was well understood IN NASA that no expansion of the budget was going to happen and that CxP-et-al were going to be far to expensive to develop and that a full change to a Mars Direct architecture was not in the cards which is why DIRECT was offered.

-The OSP program had ONE major conclusion that is continually overlooked: By following the requirements of what NASA actually NEEDED rather than what the program name "suggested" (Orbital Space PLANE) all the contractors found that the BEST and most cost EFFECTIVE vehicle to meet the mission requirements was a capsule design and not a "plane" or lifting body vehicle. The final version of the "winning" design, (when in fact the Boeing capsule design out-scored all the other concepts on all factors) was a hypersonic lifting body design that landed by parafoil and airbags BECAUSE the original "winner" with wings was unable to meet the economic and payload goals of the competition. The current Orion is a less capable version of the dismissed Boeing entry to the OSP contest, built by the company who during development of their "winning" design fully admitted that a capsule design was superior and more fit the requirements as long as "philosophical assumptions due to nomenclature" were ignored.

-NASA has issues I will agree, the biggest being there is STILL a large sub-culture that was spoiled by the "get-it-done-no-matter-the-cost" Apollo era funding and support regime and refuse to believe or understand what an aberration that was and why it will never happen again. But the fact that Congress has a historic lack of support for NASA, specifically for manned space flight and a outright hostility towards any proposals for expanding operations or capability in any case, and has actively OPPOSED any suggestions in currently and in the past pretty much shows that even if NASA got its act together today it would have no choice but to continue along the path constrained by Congressional will.

Quote
SpaceX success has been based on internally NOT making the mistakes Congress cripples NASA with, Musk adequately funded the company and it's internal development and he dose not make absurd performance demands.  This gives them the engineering headroom to make their system SAFER then NASA equivalents. 

You are contradicting yourself.  Either NASA should be able to work adequately, even successfully, with even modest budgets like SpaceX has, or SpaceX shouldn't be in business any more because they've not had anything like NASA's budgets to work under....and thus should be crippled and be bankrupt.

So SpaceX has done a lot, with a lot less, than the budgets NASA has been working with from Congress...which you are blaming for not funding enough?

That doesn't quite make sense to me.  ;-)

You're comparing a company that has adequate funding for the development and operations that it plans and carries out, directed by an individual who clearly knows what his goals are and makes only incremental changes to accommodate experience as its gained, with a government agency which is told to do one thing, given inadequate funding and support for, yet is tasked to ensure that "all" resources, personnel and facilities, spread over multiple states and sometimes nations, are fully utilized, (again often without adequate budget to do so) and often finds funding diverted (by line item "adjustment") to other priorities and projects with no notice or consultation, is told to change goals and objectives every 4 years or so and more often than not given one goal by one "boss" (Administration) while told to ignore that goal in favor of the goal of another boss (Congress) who actually controls the money and resources available to that agency.

And your confused on the "why" one would be able to perform a specific task better than the other? :)

Due to the differences between them it is impossible to "compare" SpaceX and NASA, the former is focused on putting people on Mars while making a profit from space access and this focus includes everyone from the top down. The latter while having a high internal population that are also focused on expanded space access and goals such as the Moon and Mars and much more have a "top" that is not overly concerned with space access and no interest in manned spaceflight or goals beyond seeing NASA's money spent in the right place and to the right people. And NASA in and of itself is only a very tiny segment of their interest and no where near a highly placed one at that.

To bring this "on-topic" as much as possible; SpaceX is building the MCT, NASA would never be allowed to do so.

Randy
Title: Re: MCT Speculation and Discussion Thread 3
Post by: RanulfC on 04/21/2015 04:08 PM
MCT engine placement:

Several options are possible, ranging from "DRragon-ish" side rockets to base mounted firing through the heat-shield. I'll note that if the MCT base is big enough studies for SERV showed that protective doors were not needed for Earth entry. I wouldn't doubt that its quite possible the Raptors will be arranged in a similar "virtual" plug-nozzle engine in fact.
http://pmview.com/spaceodysseytwo/spacelvs/sld034.htm

It would make sense for the BFR booster to use a similar engine arrangement as well.

Randy
Title: Re: MCT Speculation and Discussion Thread 3
Post by: spacenut on 04/21/2015 06:13 PM
MCT could be a horizontal type heat shield to slow down, then flip up the nose and land vertically. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/21/2015 06:25 PM

The thing that isn't mentioned here is the logistical challenge of getting all the MCT fleet back into orbit and refueled when the launch window is approaching.  Having the vehicles already in orbit and only having to top off fuel (and crew at the last minute) makes the 'fleet' concept viable.  Otherwise, it's going to be a mad scramble with many single failures having potential to untie the best-laid-plans bundle.

Getting the MCT back on Earth does not imply leaving it there until the last minute. If you have a dozen of them, they can be put in orbit any time prior to the Mars launch window opening.

If the vehicle is truly reusable, the propellant to get it into earth orbit is cheap, and the propellant to refill it in orbit is the same price weather the stage set down on Earth or not.

When I first heard of the idea to land the thing back on Earth, it went against everything I thought about how a Mars colonization should work, but it makes more and more sense.

Matthew

Interesting arguments. MCT may have a weight of 80t that need to be relaunched. However getting people and cargo up there is also not achieved without some vehicle with mass. Assume it weighs only 40t instead of 80 there would be 40t launch mass saved. That's less than 10% of total mass in LEO required for the trip. That small saving comes at the cost of developing a separate vehicle, having to do maintenance in orbit, transfering people and all kinds of cargo, from boxes to large infrastructure pieces from one vehicle to another in orbit.

I can imagine that people who have thought in the scale of NASA DRMs and their associated cost for a long time have trouble seeing 40 or 80t as small though.

Yes, all of the "conventional wisdom" that's been out for some time now (aside from Zubrin's Mars Direct and Semi-Direct) has involved dedicated in-space components like a large Mars Transfer Vehicle, which brakes into Mars orbit, and deploys a separate crew lander, and Mars Ascent Vehicle.  Even the most recent proposal by Boeing had SLS staging at EML2 with a large reusable ion drive MTV with disposable kick stage.
So we're sort of conditioned to think there needs to be dedicated in-space vehicles, as well as a lot of in-space staging and contruction.  The idea that there might just be one vehicle that is launched whole, then fueled and provisioned in LEO, but not -constructed- there, and then sends itself to Mars and directly down to the surface, and then get itself back of of Mars and back to the Earth's surface seems very unorthodox and we keep thinking there must be something wrong with that concept.  Or that it wouldn't be as capable of having large dedicated in-space components and such.  Even Zubrin's Mars Direct had two vehicles, a MTV/Hab lander for the outbound trip, and then a MAV/ERV craft for the return trip.
That those two crafts would be combined into just one, and then that craft may be combined with the LV's upper stage, is kinda hard to get our minds around at first.  We feel like we are trying to divide by zero to get so few components.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/21/2015 06:36 PM
supplies and tools are easy as well as demonstrated with ISS

Easy is relative. It takes them forever to transfer 2 or 3t of cargo.

Yes, but MCT to MCT docking port may be larger than the ISS's docking ports, and time is on their side.  They just launch the Mars MCT into LEO as early as needed to get the follow X number of refueling, provisioning, and finally crew MCT's up and docked to it prior to the TMI window.  If the last MCT comes up with the crew and their personal items and various smaller cargo, they could take a few days to transfer those items while they are getting settled in and checking out the Mars-MCT prior to departure. 

But yes, I'm sure they'll launch MCT with as much cargo already stowed on the Earth's surface as is possible, and keep in-orbit transfers to a minimum.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/21/2015 06:43 PM

The thing that isn't mentioned here is the logistical challenge of getting all the MCT fleet back into orbit and refueled when the launch window is approaching.  Having the vehicles already in orbit and only having to top off fuel (and crew at the last minute) makes the 'fleet' concept viable.  Otherwise, it's going to be a mad scramble with many single failures having potential to untie the best-laid-plans bundle.

Getting the MCT back on Earth does not imply leaving it there until the last minute. If you have a dozen of them, they can be put in orbit any time prior to the Mars launch window opening.

If the vehicle is truly reusable, the propellant to get it into earth orbit is cheap, and the propellant to refill it in orbit is the same price weather the stage set down on Earth or not.

When I first heard of the idea to land the thing back on Earth, it went against everything I thought about how a Mars colonization should work, but it makes more and more sense.

Matthew

Now you are shuttling crew separately again, so no need for a LAS... Where we started this discussion.  Cargo loading is a challenge still as MikeAtkinson pointed out, but cargo doesn't need a LAS. 

So, return to Earth surface to refit and provision the MCT, then launch asap so pre-fueling can start well before the fleet sails.  Crew comes up last.  Makes sense.

Yup exactly. 

Shuttling crew separately is almost a must for this type of scenario, as it will take at least several weeks to fuel up, provision, and check out Mars-MCT while in LEO prior to departure.  Even best case scenarios I don't know that SpaceX could turn round a HLV launch pad faster than a week or two.   So if we're talking maybe 6 support launche in addition to the initial launch that places Mars-MCT in LEO, that could be a couple of months of LEO staging.  You don't want the crew just loitering there for 2 months or more ahead of then a 4-6 month trip to Mars.  You bring the crew up just prior to departure and minimize their exposure to zero g and radiation.  The only time Mars-MCT would launch with a crew would be when launching itself off the surface of Mars.  So there's no dedicated LAS system needed on it. 
That would be on (if there is one) a LEO taxi version of MCT that would be set up specifically to ferry crews to LEO.  (And from LEO if there were a Bigelow station or something there.  Such a configured MCT would make a great vehicle for servicing a LEO space station).
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/21/2015 06:51 PM
You need an LAS when you launch from Mars as much (or as little) as you do when launching from Earth. Sending crew up separately is thus pointless.

???

How exactly would an LAS system operate/beenfit MCT when launching itself off the surface of Mars?  I don't get that.  If it suffers a catesphrophic explosion, there's no way to get the crew away as it's all one spacecraft.  It's not a booster and spacecraft as it is when launching from Earth. 

If it suffers an engine failure during Mars ascent, you make sure it has engine out capability.  That's your "abort".
It if suffers some sort of problem that it just cannot continue from, then it lands itself down range, and will be marooned.
(This contingency would have a reserve MCT on the surface somewhere in the vicinity that the crew can then get to.  Just as was Zubrin's Mars Direct and Semi direct plan.  So there was always a backup craft).

If it blows up, you loose the crew.  However, I've never seen a Mars plan which would have any different result on Mars Ascent.  NASA's DRM 5.0 plans don't have any sort of LAS system on the MAV, nor did Zubrin's Mars Direct or Semi-Direct (at least that I recall). 

What sort of LAS system do you propose would benefit MCT during Mars Ascent?
Title: Re: MCT Speculation and Discussion Thread 3
Post by: The Amazing Catstronaut on 04/21/2015 07:08 PM
MCT could be a horizontal type heat shield to slow down, then flip up the nose and land vertically.

Might lead to an offset CoG, which is great for reentry control. In space, can cause minor problems. I'm sure it's something many other spacecraft have dealt with before without performance hits and any negatives will be ultimately inconsequential.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/21/2015 07:13 PM
A reasonable MCT taking off from Earth on top of a booster will mass about 225MT of vehicle/payload/fuel; 65/100/60. A distributed LAS like Dragon 2 with the 8 superDracos but using CH4/LOX would need a thrust of 250MT to safely separate from a non-exploding booster, which I contend will be rare and deployment of first stage landing legs acting as a large drag to separate the stage from the MCT. DeltaV to Mars is 5000 m/s after fully fueling in LEO.

See my post here for some justification of some of the above: http://forum.nasaspaceflight.com/index.php?topic=36805.msg1362199#msg1362199

The same reasonable MCT taking off from MARS fully fueled will mass 535MT of vehicle/payload/fuel; 65/10/460. On Mars the weight on the MCT is 201MT, Launch from Mars to Earth will rely on redundancy with engine out capability and on a very bad day, RTLS or land down range. DeltaV to Earth is 7325 m/s after fully fueling on Mars with ISRU CH4/LOX.

In summary, the new smaller CH4/LOX engines mounted on the MCT will serve as Earth LAS. TMI, Mars Propulsive re-entry, Mars launch engines and Earth propulsive re-entry. It seems doable, just need to work out the minor details.  ;)

EDIT: Added summary paragraph

Exactly.  Except the methlox engine on MCT/Spacecraft will also serve as the LV's 2nd stage, and get itself to LEO empty, where it will be fueled up.  A cluster of say, 5 Raptors in an S-II like cross pattern on MCT/Spacecraft would give it pleanty of 2nd stage/Earth ascent power, and would give it multiple scenarios for dealing with an engine out without getting it's thrust off kilter to the centerline of mass, during the various phases of the mission.    I doubt more than one or two engines would be needed for any phase of the mission after LEO insertion.  Either two oppose pairs of outside engined could work together and keep the thrust in the centerline.  Or the central engine could burn itself to do it, except perhaps MArs ascent where it may need two engines at least to get itself off Mars. 

I sort of picture the MCT/booster being about 15 engines, 14 around and one in the center to land it back at the launch site after a "low and slow" staging.    And MCT/spacecraft to have 5 engines in the cross pattern, only 4 of which (2Mlbs of thrust, almost double what the Saturn S-II stage had) would be needed to get to LEO. 
Although, if there's an engine failure during Earth ascent, they may abort the rest of the mission rather than to continue with a failed engine.  Once they do the TMI burn, they are committed to the rest of the mission, but they could call it off if there's any issues prior to then.   But such an MCT engine pattern could withstand pone engine failure and even two, depending on which two engines failed.  That's not a bad safety margin.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: RanulfC on 04/21/2015 07:18 PM
What sort of LAS system do you propose would benefit MCT during Mars Ascent?

The kind of LAS that allows it to land the crew who have (unlike Mars Direct or the NASA DRMs) a "colony" or at least an outpost-beginnings-of-a-colony to rescue them :)

You harp on the "conventional wisdom" and yet are falling prey to it yourself :) Maybe think of it as a "lifeboat" instead of a LAS?

Randy
Title: Re: MCT Speculation and Discussion Thread 3
Post by: RanulfC on 04/21/2015 07:26 PM
MCT could be a horizontal type heat shield to slow down, then flip up the nose and land vertically.

Might lead to an offset CoG, which is great for reentry control. In space, can cause minor problems. I'm sure it's something many other spacecraft have dealt with before without performance hits and any negatives will be ultimately inconsequential.

It's doable but the main point will be whether the MCT is more cylindrical or squat I suppose. Most of the reason a lot of the Mars manned ELD concepts show a "side" entry profile it to increase the area of a cylinder where as if the vehicle is more "squat" (Dragon like if you will) then the base has more area to help slow down so "side" entry is not needed.

In either case it only works well up to a certain size and mass where your area can't be increased fast enough and the overall mass is getting to high for aerobraking to be effective.

At which point the "ParaShield" begins to look particularly attractive :)
http://spacecraft.ssl.umd.edu/academics/791S12/791S12L10.ParaShield.pdf
http://spacecraft.ssl.umd.edu/publications/2010/SpaceOps2010ParaShieldx.pdf
http://www.techscience.com/doi/10.3970/fdmp.2012.008.453.pdf
http://nia-cms.nianet.org/RASCAL/2010-Winning-Papers/UMD-(Grad)-RASC-AL-2006.aspx
http://arc.aiaa.org/doi/abs/10.2514/2.3373

Randy
Title: Re: MCT Speculation and Discussion Thread 3
Post by: sheltonjr on 04/21/2015 07:35 PM
Yup exactly. 

Shuttling crew separately is almost a must for this type of scenario, as it will take at least several weeks to fuel up, provision, and check out Mars-MCT while in LEO prior to departure.  Even best case scenarios I don't know that SpaceX could turn round a HLV launch pad faster than a week or two.   So if we're talking maybe 6 support launche in addition to the initial launch that places Mars-MCT in LEO, that could be a couple of months of LEO staging.  You don't want the crew just loitering there for 2 months or more ahead of then a 4-6 month trip to Mars.  You bring the crew up just prior to departure and minimize their exposure to zero g and radiation.  The only time Mars-MCT would launch with a crew would be when launching itself off the surface of Mars.  So there's no dedicated LAS system needed on it. 
That would be on (if there is one) a LEO taxi version of MCT that would be set up specifically to ferry crews to LEO.  (And from LEO if there were a Bigelow station or something there.  Such a configured MCT would make a great vehicle for servicing a LEO space station).

Here is my Alternative architecture.

SpaceX has designed a depot that uses the re-usable second stage as a depot. The only difference is it contains the fuel transfer fittings and connections under a hinged dome at the top. May also include solar panels on the side like Dragon 2 to provide power for the vehicle and cyro-coolers.  The BFR launches and the first stage does a RTLS. The second stage continues to orbit and should have left over 225MT of fuel.

1st Launch. Depot BFR launches to LEO. 225 MT of fuel (Example)

2nd Launch. Depot BFR launches to LEO and transfers fuel first Depot withholding enough fuel for de-orbit Earth return. Depot now contains 440 MT of fuel.

3rd Launch. MCT BFR launches to LEO and rendezvous with Depot. MCT is launched with 60 MT of fuel and only requires 400 MT to top off. This leaves 30 MT spare for boil off and other contingencies. Transfer should take no more than a day.

I would schedule the MCT to launch to LEO 1-2 week prior to TMI. This will give time for scrubs due to weather or other reasons. The two depot/tanker launches would probably be in the couple months before TMI.

Depot can de-orbit after refueling the MCT or stay in orbit to receive other tankers. SpaceX has flexibility in which has a financially advantage.

This is based on my MCT system that has a fully resuable 225MT LEO BFR. A smaller launcher will require more depot tanker visits. But this is a big reason why I think SpaceX has not shrunk the BFR/MCT, only the Raptor engine.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/21/2015 07:37 PM

After typing all that, I see two problems. Lack of redundancy and how to mount a large engine with a large vacuum nozzle through the heat shield.


You don't.  You make MCT a biconic aeroshell shape and land it on it's aft.  It's not like SpaceX wasn't planning to do just that with their reusable F9US concept.  See my post here up thread:

http://forum.nasaspaceflight.com/index.php?topic=36805.msg1360318#msg1360318


Smaller engines can be mounted on the side like Dragon 2, or behind the heat shield with more manageable smaller doors.

Smaller methalox landing thrusters can be used if the Raptor main engines are unsuitable.   Used in the same way superdracos will be used on Dv2, in four pair around the perimeter of the MPS.  Needing them vs. just landing on the Raptors will be something SpaceX will have to determine during development.

If they can land on the Raptor(s) then that's obviously more mass efficint than haveing a 2nd engine system.  However, the propulsive landing is critical to the crews lives, and so you'd want maximum reliability there, so it may be worth that trade.  And engine out in all other phases can be compensated for with the right Raptor engine arrangement, but there's no margin for error at landing.

However, if you had a cluster of 5 Raptor engines in a cross pattern on MCT, shortly before terminal landing you light all 5 of them.  Within a few seconds the computer will let you know if any of them failed to light, and then the appropriate engines can be shut back down to just have the center engine stay lit to land MCT, of if that engine failed, it'd keep an outter pair lit to land MCT so the thrust lines stays in the vehicle centerline.  As long as there's enough time for such an operation, then the Raptors -should- be able to be used to land MCT, -if- they had adequate throttle range...or hover-slam is acceptable. 
How reliably they get hover slam to work with the F9R booster will probably play a factor.

Assuming MCT is a biconic aeroshell design, the cluster of 5 engines could actually be started up prior to terminal landing while MCT has it's belly towards the supersonic slipstream.   MCT could actually sort of "fly" this way, and the engines don't have to be lit -into- the supersonic slipstream as they would if the aft was oriented towards the ground. (which solves that potential problem)  This could be done after terminal velocity has been reached, but early enough so that the Raptors can be started up (I'm assuming there's a certain startup lag to them, they won't be instantly on like superdracos) and verified operational.  Any engine that doesn't light, will then be compensated for.  Then with the help of the gimbaling main firing engine(s), the RCS system will orient the aft to the ground and the legs will deploy for terminal landing. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: sheltonjr on 04/21/2015 07:50 PM
Exactly.  Except the methlox engine on MCT/Spacecraft will also serve as the LV's 2nd stage, and get itself to LEO empty, where it will be fueled up.  A cluster of say, 5 Raptors in an S-II like cross pattern on MCT/Spacecraft would give it pleanty of 2nd stage/Earth ascent power, and would give it multiple scenarios for dealing with an engine out without getting it's thrust off kilter to the centerline of mass, during the various phases of the mission.    I doubt more than one or two engines would be needed for any phase of the mission after LEO insertion.  Either two oppose pairs of outside engined could work together and keep the thrust in the centerline.  Or the central engine could burn itself to do it, except perhaps MArs ascent where it may need two engines at least to get itself off Mars. 

I sort of picture the MCT/booster being about 15 engines, 14 around and one in the center to land it back at the launch site after a "low and slow" staging.    And MCT/spacecraft to have 5 engines in the cross pattern, only 4 of which (2Mlbs of thrust, almost double what the Saturn S-II stage had) would be needed to get to LEO. 
Although, if there's an engine failure during Earth ascent, they may abort the rest of the mission rather than to continue with a failed engine.  Once they do the TMI burn, they are committed to the rest of the mission, but they could call it off if there's any issues prior to then.   But such an MCT engine pattern could withstand pone engine failure and even two, depending on which two engines failed.  That's not a bad safety margin.

The concept of the combined MCT/Second stage is appealing and what I first thought also. But after looking at the numbers, I cannot reconcile the difference in the required thrust for the second stage and what the MCT requires.

If we are using the 500K Raptor. This is a good fit, but the MCT only requires one of them, while the second stage would require 3-5. The 1.6 Mlb Raptor. No way.

I also think the combined MCT/Second Stage makes the MCT really tall and puts the cargo/habitat area to high. A dedicated MCT design with smaller tanks I hope can have the fuel tanks on top and cargo at the bottom. Structural vehicle design is farther outside my wheelhouse, so I have no fact to back that one up.

Both second stage and the MCT will have to return to Earth so many want to combine them. But I do not think it works. I believe that the second stage will be its own entity and will have the same re-entry profile as the first stage. It will have to reserve more fuel to de-orbit from higher orbits. When your payload capability is greater than 200 MT you have the mass margin to make it work.

Thanks Lobo, Randy, SpaceNut. This is an enjoyable sharing of ideas on what the MCT may be. I hope Elon does provide us more by the end of the year.  ;)

EDIT: Added part about vehicle being to tall. spelling
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/21/2015 07:51 PM
What sort of LAS system do you propose would benefit MCT during Mars Ascent?

The kind of LAS that allows it to land the crew who have (unlike Mars Direct or the NASA DRMs) a "colony" or at least an outpost-beginnings-of-a-colony to rescue them :)

You harp on the "conventional wisdom" and yet are falling prey to it yourself :) Maybe think of it as a "lifeboat" instead of a LAS?

Randy

So...you want to have the crew habitat separate off MCT?  Like the Enterprise separating it's saucer section?   And then waiting on the surface wherever they land for rescue by the Mars colonists who are still on the surface at the base?  The hab would act as the lifeboat?
How would that work mechnically?  And how would that lifeboat land?  Parachutes won't slow it enough by themselves, and a propulsive landing system would then require it's own seprate system from the rest of MCT.  I don't know that that would be feasible, or if it could escape and -exploding- MCT fuel tank.
And what if you want the crew hab section to be below the tanks rather than above them to make ingress and egress on the surface easier?  How do you separate?

And if MCT is not exploding, why have a lifeboat at all?  Have redundant engines on MCT so it can still make TEI with the loss of an engine.  If the failure is such that they can't make TEI, then MCT is already it's own lifeboat and lander.  It'd just abort and land downrange, where the crew can wait to be rescued by a colony if one exists, or get to a backup MCT pre-positioned on the Mars surface, as Zubrin conceived.
It would, presumably, be designed to land with engine out redundancy.  Why would you want the crew off the spacecraft that's already designed to sustain them?

That's what I'm not getting in yours and Robotbeat's line of reasoning there.  :-)

Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/21/2015 08:09 PM
Exactly.  Except the methlox engine on MCT/Spacecraft will also serve as the LV's 2nd stage, and get itself to LEO empty, where it will be fueled up.  A cluster of say, 5 Raptors in an S-II like cross pattern on MCT/Spacecraft would give it pleanty of 2nd stage/Earth ascent power, and would give it multiple scenarios for dealing with an engine out without getting it's thrust off kilter to the centerline of mass, during the various phases of the mission.    I doubt more than one or two engines would be needed for any phase of the mission after LEO insertion.  Either two oppose pairs of outside engined could work together and keep the thrust in the centerline.  Or the central engine could burn itself to do it, except perhaps MArs ascent where it may need two engines at least to get itself off Mars. 

I sort of picture the MCT/booster being about 15 engines, 14 around and one in the center to land it back at the launch site after a "low and slow" staging.    And MCT/spacecraft to have 5 engines in the cross pattern, only 4 of which (2Mlbs of thrust, almost double what the Saturn S-II stage had) would be needed to get to LEO. 
Although, if there's an engine failure during Earth ascent, they may abort the rest of the mission rather than to continue with a failed engine.  Once they do the TMI burn, they are committed to the rest of the mission, but they could call it off if there's any issues prior to then.   But such an MCT engine pattern could withstand pone engine failure and even two, depending on which two engines failed.  That's not a bad safety margin.

The concept of the combined MCT/Second stage is appealing and what I first thought also. But after looking at the numbers, I cannot reconcile the difference in the required thrust for the second stage and what the MCT requires.

If we are using the 500K Raptor. This is a good fit, but the MCT only requires one of them, while the second stage would require 3-5. The 1.6 Mlb Raptor. No way.

I also think the combined MCT/Second Stage makes the MCT really tall and puts the cargo/habitat area to high. A dedicated MCT design with smaller tanks I hope can have the fuel tanks on top and cargo at the bottom. Structural vehicle design is farther outside my wheelhouse, so I have no fact to back that one up.

Both seconds stage and the MCT will have to return to Earth so many want to combine them. But I do not think it works. I believe that the second stage will be its own entity and will have the same re-entry profile as the first stage. It will have to reserve more fuel to de-orbit from higher orbits. When your payload capability is greater than 200 MT you have the mass margin to make it work.

MCT may need two Raptors to get off the surface, depending on it's actual fueled mass.

2nd stage on Earth will probably need 3-5 Raptors.  But Elon already said the "spacecraft and booster will have multiple engines", so it's presumed the plan is for the MCT spacecraft to have more than just one.

But here's the thing, if MCT/Spacecraft has 5 Raptors, and need 4 of them to get itself to LEO, then it has engine out redundancy.  If it only needs one for TMI or TEI, then it has multiple engine out redundancy.
If it lands on Raptors rather than separate landing thrusters. it will have multiple engine out redundancy.
And if it need two Raptors to get off the surface of Mars, again, it will have multiple engine out redundancy.  If it only needs one or two engines to land back on EArth...again...it will have multiple engine out redundancy.   Those extra engines are only "needed' during ascent from Earth, and are extra weight after that.  But they provide the engine out redundancy that Apollo never had, and was the big fear of LOC if the SMME failed during LOI, they would fly off into deep space and die.  If the LEM DMME failed during descent they could abort back to LLO with the AM...which was the only time there was any redundancy.  If the LEM AMME failed to light, the crew died on the lunar surface....Nixon even had a speech prepared for this event.  And if the SMME failed to light for TEI the crew died in LLO.  So I don't know that having those extra engines that aren't really "required" after MCT gets into LEO is the detriment you are thinking here.  Especially if MCT can land on them (unknown), then a separate landing thruster system would not be needed, which balances the extra mass to take them with you.  It then means MCT has just one common MCT platform with the same MPS.   A separate 2nd stage and MCT/Spacecraft aren't needed. 

Again, this is my working theory that will either become more plausible if it survives criticism, or need to be revisited and revised if it does not survive critisim.  Which is as it should be for any theory.  :-)



Thanks Lobo, Randy, SpaceNut. This is an enjoyable sharing of ideas on what the MCT may be. I hope Elon does provide us more by the end of the year.  ;)


Absolutely agree!

Title: Re: MCT Speculation and Discussion Thread 3
Post by: RanulfC on 04/21/2015 08:15 PM
Thanks Lobo, Randy, SpaceNut. This is an enjoyable sharing of ideas on what the MCT may be. I hope Elon does provide us more by the end of the year.  ;)

Oh he will... I predict it will be something on the order of "the walls will be painted green" just to keep this thread going strong ;)

Randy
Title: Re: MCT Speculation and Discussion Thread 3
Post by: nadreck on 04/21/2015 08:17 PM
I sort of picture the MCT/booster being about 15 engines, 14 around and one in the center to land it back at the launch site after a "low and slow" staging.    And MCT/spacecraft to have 5 engines in the cross pattern, only 4 of which (2Mlbs of thrust, almost double what the Saturn S-II stage had) would be needed to get to LEO. 
Although, if there's an engine failure during Earth ascent, they may abort the rest of the mission rather than to continue with a failed engine.  Once they do the TMI burn, they are committed to the rest of the mission, but they could call it off if there's any issues prior to then.   But such an MCT engine pattern could withstand pone engine failure and even two, depending on which two engines failed.  That's not a bad safety margin.

I would see the having 4 gimballed engines on the MCT that at one extreme of the gimbal range are parallel to the side of the MCT which slopes inward by about 30° from the vertical and at the other extreme point straight 'down' to be 100% efficient.  At 500klbf thrust any two could land you on Mars even when they are gimballed parallel to the hull for landing (to reduce potential to the damage from debris kicked up from untreated Mars surface also landing on two engines in the last stages of landing pointed in opposite directions could allow for the craft to keep from damaging anything in one particular direction if landing near existing facilities on unprepared surface). I also see these as outboard of the body of the craft and maybe an extensible TPS section protects each of them (probably to reduce the area needing protection) the engines are also flush to the hull during atmospheric entry.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: RanulfC on 04/21/2015 08:45 PM
What sort of LAS system do you propose would benefit MCT during Mars Ascent?

The kind of LAS that allows it to land the crew who have (unlike Mars Direct or the NASA DRMs) a "colony" or at least an outpost-beginnings-of-a-colony to rescue them :)

You harp on the "conventional wisdom" and yet are falling prey to it yourself :) Maybe think of it as a "lifeboat" instead of a LAS?

So...you want to have the crew habitat separate off MCT?  Like the Enterprise separating it's saucer section?   And then waiting on the surface wherever they land for rescue by the Mars colonists who are still on the surface at the base?  The hab would act as the lifeboat?

Could be but I'd suspect it would be simply a "capsule" on the MCT used only for take off and landing rather than the whole "hab" area.

Quote
How would that work mechanically?

Well if we assume the MCT itself is shaped like a burrito... :)

It fully depends on the overall design of the MCT itself but it COULD be as simple as the top being a modified DragonV3 or some such.

Quote
And how would that lifeboat land?  Parachutes won't slow it enough by themselves, and a propulsive landing system would then require it's own seprate system from the rest of MCT.  I don't know that that would be feasible, or if it could escape and -exploding- MCT fuel tank.

They are "hover-slamming" a recoverable booster stage... Again it depends on what the MCT design is but it could be as simple as parachutes and a set of solid retro rockets to cushion the landing shock ala Soyuz. It's not that complicated really.

Quote
And what if you want the crew hab section to be below the tanks rather than above them to make ingress and egress on the surface easier? How do you separate?

Your fixated with the crew travelling all the way to and from Mars in the "hab" and that being the ONLY habitable part of the ship :) Think of it as the MCT version of the Shuttle "P-suits" used for take off and landing only. They are only used for a short portion of the overall trip but they ARE used for the parts where they would be most effective.

Quote
And if MCT is not exploding, why have a lifeboat at all?  Have redundant engines on MCT so it can still make TEI with the loss of an engine.  If the failure is such that they can't make TEI, then MCT is already it's own lifeboat and lander.  It'd just abort and land downrange, where the crew can wait to be rescued by a colony if one exists, or get to a backup MCT pre-positioned on the Mars surface, as Zubrin conceived.
It would, presumably, be designed to land with engine out redundancy.  Why would you want the crew off the spacecraft that's already designed to sustain them?

That's what I'm not getting in yours and Robotbeat's line of reasoning there.  :-)

In spacecraft life boats and LES are ONLY usable on or very near the surface of a planet. You NEVER 'abandon ship' in space. It's FAR to useful. Having said that what is being suggested is a continuation of SpaceX's already stated policy of making spaceflight as safe as possible. (As opposed to 'totally' safe which is impossible)

Engine out capability I would figure as a given as it's been SpaceX policy since the failures of the Falcon-1 so I don't see a reason it wouldn't apply to the MCT. (And every reason that it would in fact) I would reject the notion that the MCT would go to TEI if had a failure though. Any engine failure and I highly doubt THAT MCT will be going to Mars or Earth. They will abort and try again when the engines are fixed. It would make more sense (even early on) to abort back to the surface of Mars as a more survivable option. It's the failure where the MCT can not in fact land itself where some sort of LAS would come into play. IF you assume the entire MCT is something like a giant Dragon capsule then a life boat LAS makes little sense of course but that also assumes that the MCT CAN act as its own LAS which is not clear given a need to re-propellant on-orbit unless its using up it's own abort propellant to GET to orbit. (Both at Earth and Mars)

Continuing the 'logic' we note that the DragonV2 can use its propulsion to land on Earth IF it doesn't abort, now carry that through to MCT. If it has to abort from the BFR, yet normal operations require it to be refueled in Earth orbit, will it be able to land BACK on Earth if has to use its on-board propellant to abort? Or are we going to assume a change in SpaceX policy and figure they will just "write-off" the crew and passengers if a failure occurs?

In my mind there's no way that the entire MCT is going to have a LAS but that the MCT can act as its own LAS is possible as is a portion of the vehicle being a "life-boat" type escape vehicle. That would make good sense in any situation where the abilities of the MCT to reach Earth or Mars orbit come into effect. (In most of THOSE cases there is not saving the MCT anyway and your only option is to abandon ship) The trade comes in figuring where those scenarios come to the point where your crew has time to take action or not and figuring from there.

I think people are trying to hard to 'make' the MCT only as safe as an airplane (lose the plane, lose the crew and passengers but that's "ok" because we accept that for airplanes) when in fact its better and not much more complicated to give yourself backups and options with a rocket transport.

(One of the things that bugged me about every Bono designed rocket transport I've seen of his is that the CREW got an escape pod and too bad for the passengers. Talk about a not-incentive to go with the design :) )

Randy
Title: Re: MCT Speculation and Discussion Thread 3
Post by: RanulfC on 04/21/2015 08:47 PM
Since we're talking engines arrangements, how about fifteen raptor combustors around a plug nozzle heat shield? :)

Randy
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Semmel on 04/21/2015 09:45 PM
One more question regarding the MCT: How do engines and a heat shield work together? I can only come up with bad ideas:

1. The engines are the heat shield. They need to be active during reentry, otherwise they would not survive.

2. The engines are mounted like the superdracos on Dragon 2. But that would probably conflict with the large engine bells that are required.

3. There is a deployable heat shield of some sort.

4. The engines are deployable and sit on arms that move outwards from the centre body of the MCT. Adds a lot of failure modes.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/21/2015 11:26 PM
It fully depends on the overall design of the MCT itself but it COULD be as simple as the top being a modified DragonV3 or some such.


The "Ship within a ship" concept that has been mentioned before is certainly a possibility.  I tend to doubt it for a few reasons, but there's not technical reason it couldn't be so that I can thing of. 
Mainly I think that almost any abort scenario that the ship within a ship concept can handle, having the MCT itself be the lifeboat, and build extra redundancy into it, also can handle.  Neither can save the crew from an exploding fuel tank on Mars ascent.   So I just don't know that you really gain much from it. 
Perhaps moreso for Earth ascent, but not much for Mars ascent....that I can see anyway.


They are "hover-slamming" a recoverable booster stage... Again it depends on what the MCT design is but it could be as simple as parachutes and a set of solid retro rockets to cushion the landing shock ala Soyuz. It's not that complicated really.

 You'd need far more than Soyuz's meager retro burn to keep the crew alive.  Probably better just to go all propulsive rather than mess with a chute at all in this case.  I don't think a chute will supply enough dV to be worth having.  The crew will die one way or other if the landing engines don't work, but with a chute, the crew will die of either the parachute -or- landing engines don't work.  Probably better just to put more fuel in the engines and land fully propulsively


Engine out capability I would figure as a given as it's been SpaceX policy since the failures of the Falcon-1 so I don't see a reason it wouldn't apply to the MCT. (And every reason that it would in fact) I would reject the notion that the MCT would go to TEI if had a failure though. Any engine failure and I highly doubt THAT MCT will be going to Mars or Earth. They will abort and try again when the engines are fixed. It would make more sense (even early on) to abort back to the surface of Mars as a more survivable option. It's the failure where the MCT can not in fact land itself where some sort of LAS would come into play. IF you assume the entire MCT is something like a giant Dragon capsule then a life boat LAS makes little sense of course but that also assumes that the MCT CAN act as its own LAS which is not clear given a need to re-propellant on-orbit unless its using up it's own abort propellant to GET to orbit. (Both at Earth and Mars)

I think you missed my point here some.  If there was an engine out during Earth ascent. MCT could still make it to LEO.  An "abort to orbit".  That would be much more desirable than trying to land somewhere downrange, because they can they orbit back to a reentry window that will take them back to the launch site.  But I'm sure if an MCT engine failed before LEO, they would scrub the mission.
However, after that, they are committed.  If an engine fails during the TMI burn, they could perhaps correct to a free return trajectory and come back, but it might be better to go to the surface and make use of an existing contingency MCT already waiting there (ala Mars Direct).
If an engine fails during EDL, they also can then transfer to the contingency MCT on the surface for the return home.  If an engine fails during Mars ascent, you could abort back to the surface if early enough, and then transfer to the contingency MCT, but once you are too far up I'd think you'd just keep buring all the way through TEI, as you still have sufficient operational engines, and with a cluster of 5, actually could withstand another engine failure.


Continuing the 'logic' we note that the DragonV2 can use its propulsion to land on Earth IF it doesn't abort, now carry that through to MCT. If it has to abort from the BFR, yet normal operations require it to be refueled in Earth orbit, will it be able to land BACK on Earth if has to use its on-board propellant to abort? Or are we going to assume a change in SpaceX policy and figure they will just "write-off" the crew and passengers if a failure occurs?

??
First, I'm talking of sending up a crew on an MCT that's outfitted specifically for crew transfer.  That means, it wouldn't get to LEO empty, as the Mars MCT loaded with cargo would.  It would get to LEO with enough propellant to land itself again.  Same with the tanker MCT's that would fill the MARs-MCT up in orbit.  They all need enough residual propellant to land...or else they'd be expendable.  Fotuantely, that won't require that much propellant. 
So let's say MCT aborts while on the booster.  The booster is shut down, and probably legs deployed to help slow it down, MCT fires it's engine early and does an emergency separation.  As the booster will probably typically stage about the time F9 does now, MCT could do a RTLS abort up until staging.    In this abort mode, MCT may "fly" itself around a bit to burn off enough propellant so that it doesn't land too heavy as it would have a full propellant load during such a booster abort.

Once the booster is staged normally, an MCT engine failure after that could be tolerated (with engine out capability) and MCT aborts to orbit, as the shuttle did on STS-51F.  At that point it would orbit around to the proper return window and return to launch site. 

Why does any of this involve SpaceX just "writing off" the crew and passengers?  MCT would always have enough propellant to land.  I'm not sure what's unclear?


In my mind there's no way that the entire MCT is going to have a LAS but that the MCT can act as its own LAS is possible as is a portion of the vehicle being a "life-boat" type escape vehicle. That would make good sense in any situation where the abilities of the MCT to reach Earth or Mars orbit come into effect. (In most of THOSE cases there is not saving the MCT anyway and your only option is to abandon ship) The trade comes in figuring where those scenarios come to the point where your crew has time to take action or not and figuring from there.


I agree, I just don't think that any sort of separate lifeboat could really protect against an exploding booster or MCT.  -Maybe- an exploding booster as there may be enough distance between the booster and lifeboat, but if the MCT tanks explode, the crew, even in a lifeboat on top, will still be very close to them.  (but, as always, I could be wrong.  ;-)  )
And if it can't protect against an exploding MCT, then why have it?  Just make MCT the lifeboat, as I outlined.  It would be like STS, only safer in that your TPS system wouldn't be subject to debris shedding from the ET.  You could still have a Challenger like incident, but not a Columbia like one.  At least not one caused by tank debris shedding. 

This would assume that there's no pad abort options, again, like STS.  Maybe a full up lifeboat could protect against something like that.  An Antares like failure where it lifts off but then fails to achineve enough lift and stalls.  It would be pretty hard to give MCT enough power to get itself up and away from that situation.  But then again, is a lifeboat launch compartment in MCT the best way to handle that?  Or just have a separate crew launch vehicle?  I can't see early missions having more than 5-10 people.  Dragon v2 could put 7 people on a Mars-MCT, and it'd already have an LAS system capable of pad abort, and exploding-booster abort.  Two Dragons could put a crew of 14 on an MCT bound for Mars. 
A decade or two later when there might actually be colonization, maybe they either make a Dv3 that can take colonists up to MCT en masse?  Or they make a version of MCT that actually has a full propulsive LAS system capable of doing a pad abort?  Put enough engines on it and it'll get itself up and off the booster, and be designed to have enough propellant left to land somewhere near the pad, away from the explosion.  Make a "super dragon" version of MCT for mass passenger transport?

Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/21/2015 11:32 PM
One more question regarding the MCT: How do engines and a heat shield work together? I can only come up with bad ideas:

1. The engines are the heat shield. They need to be active during reentry, otherwise they would not survive.

2. The engines are mounted like the superdracos on Dragon 2. But that would probably conflict with the large engine bells that are required.

3. There is a deployable heat shield of some sort.

4. The engines are deployable and sit on arms that move outwards from the centre body of the MCT. Adds a lot of failure modes.

Agreed.  So you resolve this by not having the engines in the heat shield at all.  That gets back to the biconic aeroshell with engines at the aft.  Essentially a wingless Spaceshuttle that lands on it's SSME's. 

Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 04/22/2015 12:19 AM
You need an LAS when you launch from Mars as much (or as little) as you do when launching from Earth. Sending crew up separately is thus pointless.

???

How exactly would an LAS system operate/beenfit MCT when launching itself off the surface of Mars?  I don't get that.  If it suffers a catesphrophic explosion, there's no way to get the crew away as it's all one spacecraft....
One just lacks a certain imaginative creativity if one can't figure out any way to do it.

Anyway, I wasn't trying to say a LAS should be used for Mars ascent, but if you're dead set on using one for Earth ascent, you might as well get it to work for Mars ascent, too. Yes, it is possible. The thin atmosphere of Mars and the fact that it's fairly easy to just cut the engines on a liquid rocket make it possible. Everyone should probably be suited up, though.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 04/22/2015 12:24 AM
...
Also when leaving Mars, what is the point of having a LAS? When the rocket fails, it and all its resources will be lost. How can the people survive on Mars without it? So to have a LAS on Mars to make sense, the colony infrastructure must have the margin to support the aborted colonists until a resupply ship arrives and they can be brought back with the next MCT. Is that realistic? Especially in the beginning?
In the context of a colony, it's absolutely realistic.

If SpaceX is serious about large scale Mars settlement (and every indication is that they will be), then except for the first few synods, a single extra set of MCT passengers wouldn't be even the slightest burden. What you're doing here is carrying over thinking from when we used to only think about Mars exploration in terms of a half dozen or so people on a base. That isn't relevant except in the slimmest corner case for the MCT.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 04/22/2015 12:27 AM
...However, I've never seen a Mars plan which would have any different result on Mars Ascent.  NASA's DRM 5.0 plans don't have any sort of LAS system on the MAV, nor did Zubrin's Mars Direct or Semi-Direct (at least that I recall). 
...
Of course not, because no other detailed Mars plan was seriously considering full scale colonization. MCT isn't being built for mere exploration, it's being built to shuttle people (and equipment) to and from a colony. It's right in its name.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: spacenut on 04/22/2015 12:32 AM
Earth's LEO is about 100-120 miles or so.  What is Mars LEO?  If one can achieve orbit on Earth in say 5-10 minutes or so, Mars should be about 40 miles and 2-5 minutes.  Might not really need a LAS if it is a fairly quick launch. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Elmar Moelzer on 04/22/2015 03:11 AM
One more question regarding the MCT: How do engines and a heat shield work together? I can only come up with bad ideas:

1. The engines are the heat shield. They need to be active during reentry, otherwise they would not survive.

2. The engines are mounted like the superdracos on Dragon 2. But that would probably conflict with the large engine bells that are required.

3. There is a deployable heat shield of some sort.

4. The engines are deployable and sit on arms that move outwards from the centre body of the MCT. Adds a lot of failure modes.
There are plenty of base first reentry concepts for SSTOs as well. Gary Hudson would be able to tell about those {Phoenix SSTO comes to mind).
One could also arrange them away from the base as a kind of aerospike/truncated spike/plug. There were concepts for that (Aerospike Test Vehicle).
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Hyperion5 on 04/22/2015 03:16 AM
One more question regarding the MCT: How do engines and a heat shield work together? I can only come up with bad ideas:

1. The engines are the heat shield. They need to be active during reentry, otherwise they would not survive.

Can't say this seems like a good idea, though obviously with enough testing it might be mastered. 

2. The engines are mounted like the superdracos on Dragon 2. But that would probably conflict with the large engine bells that are required.

Well considering the vehicle will be landing on Mars, you actually don't need large engine nozzles to get great Isp out of staged combustion methane-oxygen engines in a near vacuum.  Best example?  The closest known engine design to the Raptor is an under-design (seemingly perpetually so) engine from KBKhA called the RD-0162.  It would put out 226 tf of thrust in a vacuum with an Isp of 356 seconds.  Scaling up to a Raptor gets you about a 1.75 m nozzle.  Luckily there are two things going on that make this much more manageable. 

1) You don't need that large of a nozzle, as a SC methalox engine can produce 345-350 seconds of Isp out of a more compact nozzle. 
2) The MCT is going to be a very wide craft (14-17 meters in diameter is very plausible).  Proportionately 8 Raptor engines with SL-optimized nozzles should fit just fine into the sides of such a vehicle. 

3. There is a deployable heat shield of some sort.

This is a bad idea?  Aside from one of our L2 experts being enamored of the idea, you'll have to explain to me why NASA engineers and other visionaries have used this approach multiple times in their concepts.  See the attached pictures. 

4. The engines are deployable and sit on arms that move outwards from the centre body of the MCT. Adds a lot of failure modes.

Can't say I'd go for this.  The winning option is either #3 on its own or a combination of options 2 & 3. 


Agreed.  So you resolve this by not having the engines in the heat shield at all.  That gets back to the biconic aeroshell with engines at the aft.  Essentially a wingless Spaceshuttle that lands on it's SSME's.

Given the number of designs with engines embedded behind deployable heat shield doors, I would think the "wingless" Space Shuttle design is far from given.  The simplicity of landing with a Dragon-style vertical lander on Mars is not something to be given up lightly. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: sanman on 04/22/2015 03:53 AM
So will MCT use "hoverslam" when landing on Earth and Mars? Musk said it's going to be using "many engines", with the same throttleability limits in both cases.

But while Mars has lower gravity than Earth, it also has greater terminal velocity. So is it automatically the case that for Mars landing fewer engines will be used, and for Earth landing more of those engines would be used?

Since MCT will be bigger and heavier, will the thrust-to-weight ratio be > 1 under the minimum throttle value?

Are vehicular mass constraints going to dictate the engine configuration, or will engine configuration constraints dictate the vehicular mass?

Title: Re: MCT Speculation and Discussion Thread 3
Post by: sanman on 04/22/2015 04:02 AM
Earth's LEO is about 100-120 miles or so.  What is Mars LEO?  If one can achieve orbit on Earth in say 5-10 minutes or so, Mars should be about 40 miles and 2-5 minutes.  Might not really need a LAS if it is a fairly quick launch.

Can you even have LAS for SSTO? I thought MCT on Mars is going to be SSTO.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 04/22/2015 05:15 AM
Earth's LEO is about 100-120 miles or so.  What is Mars LEO?  If one can achieve orbit on Earth in say 5-10 minutes or so, Mars should be about 40 miles and 2-5 minutes.  Might not really need a LAS if it is a fairly quick launch.

Can you even have LAS for SSTO? I thought MCT on Mars is going to be SSTO.
Unpressurized escape pod.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Impaler on 04/22/2015 05:24 AM

2) The MCT is going to be a very wide craft (14-17 meters in diameter is very plausible).  Proportionately 8 Raptor engines with SL-optimized nozzles should fit just fine into the sides of such a vehicle. 

This is what my money is on, 4 pairs of 2 engines just like Dragon, this gives huge thrust for escaping an exploding booster (at 2,300 kN per raptor, MCT could mass up to 370 MT while still having the T:W of ~5 like Dv2), huge redundancy for landing on any pair of opposing engines and keeps the interior volume of the vehicle clear and the heat-shield monolithic.  Power to weight ratios of SpaceX engines are high and this means the performance cost of high and even surplus engines is mitigated substantially, at 100:1 T:W these 8 raptors only mass 18 MT.

Note that Lobo's earlier 5 engine configuration in which a central engine penetrates the heat-shield and is used for landing isn't viable because that central engine can't gimble, which is absolutely necessary for controlling the hover-slam.  The engine-through heat-shield concept is only viable for high altitude deceleration and even then it's though that the engines will need to be angled to the side so the vehicles remains stable and doesn't 'wobble' on it's own plume, when landing you simply must have a gimbling engine or multiple engines with adjustable thrust.

Lastly several people have commented that no abort is needed for 'cargo' variant MCT because their are no people on board to save.  But this ignored that SpaceX would VERY MUCH like to save the MCT itself from being destroyed, so it can you know be REUSED (provided that is is a whole vehicle escape system as with Dragon).  Having no LAS for a cargo carrying rocket is the normal thing in expendable rocketry because they are equally 'gone' if the launch is a success or failure, but it dose not hold that it's superfluous upon a reusable vehicle.  On Earth we have lots of systems to to keep trains from derailing and we use these systems on both passenger and freight trains because we want to reuse both types of trains many times, so it seems reasonable that we have one variant that hauls everything and has a single abort system.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: hkultala on 04/22/2015 06:04 AM

2) The MCT is going to be a very wide craft (14-17 meters in diameter is very plausible).  Proportionately 8 Raptor engines with SL-optimized nozzles should fit just fine into the sides of such a vehicle. 

This is what my money is on, 4 pairs of 2 engines just like Dragon, this gives huge thrust for escaping an exploding booster (at 2,300 kN per raptor, MCT could mass up to 370 MT while still having the T:W of ~5 like Dv2),

No, it does not. It gives practically no thrust for escaping exploding booster. It only gives huge thrust couple of seconds too late.

High-pressure staged combustion has just too slow thrust response to be useful as abort motor.

Pressure fed or solids are good for abort motors. (also hybrids would work but they seems to have other problems)
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Impaler on 04/22/2015 07:35 AM
I mentioned the spin up time issue on an earlier post, should have mentioned it again.  Some modification of the engine would be need to get the start time of a pressure fed system, I'm thinking small pressure tanks to feed the engine (bypassing the turbo-pump) for a second or two until the spin up of the pump is complete.  Yes this is speculative engineering on my part.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: R7 on 04/22/2015 12:53 PM
I mentioned the spin up time issue on an earlier post, should have mentioned it again.  Some modification of the engine would be need to get the start time of a pressure fed system, I'm thinking small pressure tanks to feed the engine (bypassing the turbo-pump) for a second or two until the spin up of the pump is complete.  Yes this is speculative engineering on my part.

If you suddenly raise the pressure inside combustion chamber by pressure feeding (requires additional injectors for LOX in ORSC) and igniting propellants how do you stop the combusting gases from flowing upstream via regular fluid routes to pump and turbine outlets? And where do you direct all TPA pump outlets and turbine exhaust during spin up, those don't want to go into the combustion chamber its pressure is greater?
Title: Re: MCT Speculation and Discussion Thread 3
Post by: JasonAW3 on 04/22/2015 01:43 PM

2) The MCT is going to be a very wide craft (14-17 meters in diameter is very plausible).  Proportionately 8 Raptor engines with SL-optimized nozzles should fit just fine into the sides of such a vehicle. 

This is what my money is on, 4 pairs of 2 engines just like Dragon, this gives huge thrust for escaping an exploding booster (at 2,300 kN per raptor, MCT could mass up to 370 MT while still having the T:W of ~5 like Dv2), huge redundancy for landing on any pair of opposing engines and keeps the interior volume of the vehicle clear and the heat-shield monolithic.  Power to weight ratios of SpaceX engines are high and this means the performance cost of high and even surplus engines is mitigated substantially, at 100:1 T:W these 8 raptors only mass 18 MT.

Note that Lobo's earlier 5 engine configuration in which a central engine penetrates the heat-shield and is used for landing isn't viable because that central engine can't gimble, which is absolutely necessary for controlling the hover-slam.  The engine-through heat-shield concept is only viable for high altitude deceleration and even then it's though that the engines will need to be angled to the side so the vehicles remains stable and doesn't 'wobble' on it's own plume, when landing you simply must have a gimbling engine or multiple engines with adjustable thrust.

Lastly several people have commented that no abort is needed for 'cargo' variant MCT because their are no people on board to save.  But this ignored that SpaceX would VERY MUCH like to save the MCT itself from being destroyed, so it can you know be REUSED (provided that is is a whole vehicle escape system as with Dragon).  Having no LAS for a cargo carrying rocket is the normal thing in expendable rocketry because they are equally 'gone' if the launch is a success or failure, but it dose not hold that it's superfluous upon a reusable vehicle.  On Earth we have lots of systems to to keep trains from derailing and we use these systems on both passenger and freight trains because we want to reuse both types of trains many times, so it seems reasonable that we have one variant that hauls everything and has a single abort system.

Interesting thought here;  If the MCT lander is configured similar to the Dragon V2 in engimne layout, it may be possible to hang a low mass cargo carrier with a one shot heat shield under the main craft, in many ways, like the Dragon trunk.

     If so, should a MCT lander have to abort to orbit, it could eject the cargo module, allowing it to either crash or attempt a parachute descent independant of the main craft itself, thus freeing up fuel to abort to orbit.

     Should the MCT lander and cargo module successfully land, one could detach the Lander, loft it up a few hundred feet and land nearby.  The cargo could then be offloaded and the module could be sealed up and used as a habitat module.  (This also assumes a "stand off" distance above the martian surface as well as the use of the one shot heat shield as an insulating layer between the surface and the module itself).

     The Lander would then be refueled from IRSU sources, for it's flight back to Earth.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: spacenut on 04/22/2015 02:25 PM
In order for SpaceX to avoid having to build multiple launch pads for BFR and MCT, I think the MCT maximum diameter should be 12m if they are to use Kennedy and the BFR maximum 12 million lbs thrust.  Otherwise a lot of expense would have to go out to build launch facilities to handle multiple launches in a narrow window of time.  NASA might agree to build pad 39C that was originally planned or give up their SLS pad for dual launches from Kennedy. 

So I think MCT will be 12 m and not like a capsule but like the wingless shuttle idea combining 2nd stage with MCT.  This would require possibly refueling in LEO with fuel being launched to a large station able to control boil off during the off months when not going to Mars and back.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: MikeAtkinson on 04/22/2015 03:51 PM
3. There is a deployable heat shield of some sort.

This is a bad idea?  Aside from one of our L2 experts being enamored of the idea, you'll have to explain to me why NASA engineers and other visionaries have used this approach multiple times in their concepts.  See the attached pictures. 

I think its probably a bad idea - but maybe it turns out to be the least bad option.

Single point of failures are bad, even a free return trajectory would not help as the heatshield would be needed at Earth as well.

Perhaps with multiple redundant actuators and deployment early enough so that there is time to sort out problems (in extreme by a spacewalk) it would be acceptable.

But even if it is acceptable on its own as a feature, it would preclude other options, e.g. using the main engines for landing.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: MikeAtkinson on 04/22/2015 03:57 PM
2. The engines are mounted like the superdracos on Dragon 2. But that would probably conflict with the large engine bells that are required.

Well considering the vehicle will be landing on Mars, you actually don't need large engine nozzles to get great Isp out of staged combustion methane-oxygen engines in a near vacuum.  Best example?  The closest known engine design to the Raptor is an under-design (seemingly perpetually so) engine from KBKhA called the RD-0162.  It would put out 226 tf of thrust in a vacuum with an Isp of 356 seconds.  Scaling up to a Raptor gets you about a 1.75 m nozzle.  Luckily there are two things going on that make this much more manageable. 

1) You don't need that large of a nozzle, as a SC methalox engine can produce 345-350 seconds of Isp out of a more compact nozzle. 
2) The MCT is going to be a very wide craft (14-17 meters in diameter is very plausible).  Proportionately 8 Raptor engines with SL-optimized nozzles should fit just fine into the sides of such a vehicle. 

Engines mounted on the sides would use differential thrust for steering. A SC engine has a rather slow throttle response and so would be difficult to use in that situation.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: MikeAtkinson on 04/22/2015 04:05 PM
So will MCT use "hoverslam" when landing on Earth and Mars? Musk said it's going to be using "many engines", with the same throttleability limits in both cases.

But while Mars has lower gravity than Earth, it also has greater terminal velocity. So is it automatically the case that for Mars landing fewer engines will be used, and for Earth landing more of those engines would be used?

Since MCT will be bigger and heavier, will the thrust-to-weight ratio be > 1 under the minimum throttle value?

Are vehicular mass constraints going to dictate the engine configuration, or will engine configuration constraints dictate the vehicular mass?

Another big problem is engines that are optimised for landing on Mars (i.e. to all intents and purposes vacuum) cannot be used to land on Earth due to flow separation in their nozzles.

There are a number of ways round this, the one I think is best overall is to use altitude compensation (e.g. ED) nozzles. This would allow extra expansion for first stage Raptor engines (perhaps 10-20 s extra Isp on average).
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lars-J on 04/22/2015 05:22 PM
Note that Lobo's earlier 5 engine configuration in which a central engine penetrates the heat-shield and is used for landing isn't viable because that central engine can't gimble, which is absolutely necessary for controlling the hover-slam.

Unless you are referring to another concept, his latest images showed a lifting body with a side heat shield that would flip and land vertically. Not using a bottom heat shield.

The engine-through heat-shield concept is only viable for high altitude deceleration and even then it's though that the engines will need to be angled to the side so the vehicles remains stable and doesn't 'wobble' on it's own plume, when landing you simply must have a gimbling engine or multiple engines with adjustable thrust.

What is this wobble on its own plume idea, and where did you get it from? And since when does an engine need to be angled to the side? Have you not seen the supersonic retro-propulsion that has been demonstrated by F9R in many flights now?
Title: Re: MCT Speculation and Discussion Thread 3
Post by: RanulfC on 04/22/2015 05:24 PM
3. There is a deployable heat shield of some sort.

This is a bad idea?  Aside from one of our L2 experts being enamored of the idea, you'll have to explain to me why NASA engineers and other visionaries have used this approach multiple times in their concepts.  See the attached pictures. 

I think its probably a bad idea - but maybe it turns out to be the least bad option.

Single point of failures are bad, even a free return trajectory would not help as the heatshield would be needed at Earth as well.

Perhaps with multiple redundant actuators and deployment early enough so that there is time to sort out problems (in extreme by a spacewalk) it would be acceptable.

But even if it is acceptable on its own as a feature, it would preclude other options, e.g. using the main engines for landing.

Last isn't really true. In most concepts the deployable is around the base of the vehicle increasing the overall area but not getting in the way of the engines. With a wide enough base you overall heating load is far lower and your engines don't need a great deal of protection to survive reentry heating. (SERV as an example, ParaShield as another)

Randy
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Eerie on 04/22/2015 06:24 PM
3. There is a deployable heat shield of some sort.

This is a bad idea?  Aside from one of our L2 experts being enamored of the idea, you'll have to explain to me why NASA engineers and other visionaries have used this approach multiple times in their concepts.  See the attached pictures. 

I think its probably a bad idea - but maybe it turns out to be the least bad option.

Single point of failures are bad, even a free return trajectory would not help as the heatshield would be needed at Earth as well.

Deployable heat shields have some options for failures.

For example, if it fails to open during Mars landing, there could be a pyrotechnic system of last resort, with no moving parts, that just blows the shield off. Then you can't come back to Earth without switching to a rescue vehicle somewhere, but at least you won't die on impact.

If the shield fails to close after launch from Mars, then perhaps it could be closed manually by doing EVA. There are plenty of time in transfer.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: nadreck on 04/22/2015 06:33 PM
The engine-through heat-shield concept is only viable for high altitude deceleration and even then it's though that the engines will need to be angled to the side so the vehicles remains stable and doesn't 'wobble' on it's own plume, when landing you simply must have a gimbling engine or multiple engines with adjustable thrust.

What is this wobble on its own plume idea, and where did you get it from? And since when does an engine need to be angled to the side? Have you not seen the supersonic retro-propulsion that has been demonstrated by F9R in many flights now?

Hmm, there is a reason to have, on landing and takeoff, engines angled on the side. If you see the discussion of Dr. Phil Metzger's paper on landing on unprepared Martian surface at http://forum.nasaspaceflight.com/index.php?topic=29053.msg1346980#msg1346980 (http://forum.nasaspaceflight.com/index.php?topic=29053.msg1346980#msg1346980) (there is a link to his paper there), I think it argues for that angling, however I could see a system where the engines were gimballed to be able to point straight down at one extreme of the gimbal range and lie flush to the side of the inward slopping cone shape of the craft (say 30° from the vertical) at the other extreme. That angle would reduce the area that would need extra TPS (small extending heat shield) on Mars atmospheric entry.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Burninate on 04/22/2015 06:41 PM
2. The engines are mounted like the superdracos on Dragon 2. But that would probably conflict with the large engine bells that are required.

Well considering the vehicle will be landing on Mars, you actually don't need large engine nozzles to get great Isp out of staged combustion methane-oxygen engines in a near vacuum.  Best example?  The closest known engine design to the Raptor is an under-design (seemingly perpetually so) engine from KBKhA called the RD-0162.  It would put out 226 tf of thrust in a vacuum with an Isp of 356 seconds.  Scaling up to a Raptor gets you about a 1.75 m nozzle.  Luckily there are two things going on that make this much more manageable. 

1) You don't need that large of a nozzle, as a SC methalox engine can produce 345-350 seconds of Isp out of a more compact nozzle. 
2) The MCT is going to be a very wide craft (14-17 meters in diameter is very plausible).  Proportionately 8 Raptor engines with SL-optimized nozzles should fit just fine into the sides of such a vehicle. 

Engines mounted on the sides would use differential thrust for steering. A SC engine has a rather slow throttle response and so would be difficult to use in that situation.

This is something I'd like to talk about some more.

RCS thrusters need high throttle control frequency, relatively low thrust, fast light/relight, and durability over many ignition cycles.  It would be really nice to use methane and oxygen for this: is there anything possible in this niche, or is hydrazine necessary?  Alternately: Are there green propellant options that fit here?
Title: Re: MCT Speculation and Discussion Thread 3
Post by: spacenut on 04/22/2015 06:52 PM
I also think SpaceX should develop their Raptor engine like the BE-3 that can throttle from 30% to 110%.  That would make for easier landing on earth or Mars. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: spacenut on 04/22/2015 06:59 PM
Landing could be done downwind of a space colony location and use electric space trucks to haul items to the colony location.  The trucks could use Tesla batteries and could be recharged at a solar panel location.  Every item could be designed to be towed or hauled by a space truck.  Once initial colony is in place the trucks could be used as battery banks for nighttime use at the colony, and only a few trucks used to haul ice for the water and hydrogen processing ISRU unit.  Hopefully ice can be found below the surface and extracted out of the soil around the colony.  Smooth landing areas could be made in the process or smooth areas for future colony construction and or solar panel layouts. 

A truck could be brought with each MCT lander.  They could be built from aluminum and with batteries might weigh 2.5 tons on earth based on the weight of a Tesla.  It would probably weigh less since it will probably be open similar to the moon buggy.  They could be made to couple together to haul trailers of ice or equipment like a train for heavier items.  One truck might have a front end loader, one a backhoe attachment, one just a bed.  All with front and rear ring connectors hitches, since they would be easier to connect with gloved hands.  Items will weigh only 40% what they weigh on earth.  There would be a power coupler on each end for train type hauling. 

Just some ideas of what could be brought by a 100 or even a 50 ton MCT cargo hauler. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 04/22/2015 07:01 PM
You can use methane/LOx for thrusters, provided you have a good ignition system.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: nadreck on 04/22/2015 07:07 PM
Landing could be done downwind of a space colony location and use electric space trucks to haul items to the colony location.  The trucks could use Tesla batteries and could be recharged at a solar panel location.  Every item could be designed to be towed or hauled by a space truck.  Once initial colony is in place the trucks could be used as battery banks for nighttime use at the colony, and only a few trucks used to haul ice for the water and hydrogen processing ISRU unit.  Hopefully ice can be found below the surface and extracted out of the soil around the colony.  Smooth landing areas could be made in the process or smooth areas for future colony construction and or solar panel layouts.

If you read the paper I quoted, one of the primary dangers is damage to the craft itself from blow back, another is destabilizing the surface beneath the craft for relaunch, and the blow out that could damage existing installations could throw for several kilometers. So, angled out and being sure that the plumes point away from existing installations is the probably way to go for the first round of landings. Then site preparation for future ones at that location can begin, but landings at other locations that aren't yet prepared will have to be handled the same way the first ones were.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: spacenut on 04/22/2015 07:17 PM
Yes, haven't thought about the dust and debris throwback.  Then that goes back to mounting the engines like Dracos higher up on the sides.  This would definitely require deep throttling of each engine to balance the landing and take-off.  Combustion chambers and plumbing could possibly be the same for the BFR and the MCT, but the nozzles entirely different. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 04/22/2015 07:35 PM
Landing could be done downwind of a space colony location and use electric space trucks to haul items to the colony location.  The trucks could use Tesla batteries and could be recharged at a solar panel location.  Every item could be designed to be towed or hauled by a space truck.  Once initial colony is in place the trucks could be used as battery banks for nighttime use at the colony, and only a few trucks used to haul ice for the water and hydrogen processing ISRU unit.  Hopefully ice can be found below the surface and extracted out of the soil around the colony.  Smooth landing areas could be made in the process or smooth areas for future colony construction and or solar panel layouts.

If you read the paper I quoted, one of the primary dangers is damage to the craft itself from blow back, another is destabilizing the surface beneath the craft for relaunch, and the blow out that could damage existing installations could throw for several kilometers. ...
I am certain the "several kilometers" part would only be relevant on the Moon. Mars' atmosphere and higher gravity prevents debris from a landing from traveling anywhere near that far.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Hyperion5 on 04/22/2015 08:14 PM
3. There is a deployable heat shield of some sort.

This is a bad idea?  Aside from one of our L2 experts being enamored of the idea, you'll have to explain to me why NASA engineers and other visionaries have used this approach multiple times in their concepts.  See the attached pictures. 

I think its probably a bad idea - but maybe it turns out to be the least bad option.

Single point of failures are bad, even a free return trajectory would not help as the heatshield would be needed at Earth as well.

Deployable heat shields have some options for failures.

For example, if it fails to open during Mars landing, there could be a pyrotechnic system of last resort, with no moving parts, that just blows the shield off. Then you can't come back to Earth without switching to a rescue vehicle somewhere, but at least you won't die on impact.

If the shield fails to close after launch from Mars, then perhaps it could be closed manually by doing EVA. There are plenty of time in transfer.

I would agree that there are at least some options for failures.  I have to admit when I saw the word "deployable" here, I thought of 2 different things.  The first is of course a conventional deployable heat shield like you mentioned.  The second is deployable heat shield doors.  Obviously you would not want to open these at any point during reentry or even during Earth launch.  To abort as well as land on Earth and Mars, you would use 8 angled Raptor engines mounted in the MCT's sides.  These would fire at full throttle for aborts on Earth launches and be throttled back for landings on Earth and Mars.  If necessary you could even trim back to landing only on 4 throttled Raptors for the final stage of descent.  To help the Raptors out during landing, you would likely rely upon faster-firing RCS engines (powered either by methane-oxygen or a propellant mixture found on Mars).  To launch off Mars you would simply open up those doors to allow the vacuum-optimized Raptors behind the doors to fire.  These would only fire during the TMI burn, the launch to LMO, and the TEI burn. 

Now I know SC methalox engines aren't ideal for aborts, but last I looked Mars won't have a ready supply of monomethyl hydrazine needed for SuperDraco engines.  That would seem like it would rule out using epic numbers of SuperDracos for landings and aborts.  Since we know that Spacex is only developing one engine for now, that suggests that if they're landing on Mars or aborting during Earth launch, it will have to be done with Raptor engines.  Fortunately for Spacex, many aborts do not require instantaneous engine spin-up.  I'm thinking of at least 2 different incidents.  The much more recent incident is when an Antares rocket blew up in late October 2014.  Given it took several seconds for the rocket to fully be consumed, I believe that SC methalox engines would have had the time required to perform the abort burn.  The other incident was the abort performed in 1983 by the crew of Soyuz T-10: https://www.youtube.com/watch?v=UyFF4cpMVag.  In both cases I think it is reasonable to believe that SC methalox engines could have saved the crew. 

I know I'm going to catch some flack for this, but having some abort ability is better than none.  If you believe there is a way to source propellants for SuperDracos on Mars, I'm all ears.  Failing that, I'd like to hear how you would improve this situation.  Currently the most plausible alternative I've heard is relying upon an expendable LAS tower during Earth launches and using the Raptors to land on Mars and Earth. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: spacenut on 04/22/2015 09:31 PM
The LAS tower would be heavy, especially if it is solid fueled.  Someone mentioned having a small amount of pressure to kick start the metholox engines until the turbines kicked in for LAS. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: RanulfC on 04/22/2015 09:45 PM
Landing could be done downwind of a space colony location and use electric space trucks to haul items to the colony location.  The trucks could use Tesla batteries and could be recharged at a solar panel location.  Every item could be designed to be towed or hauled by a space truck.  Once initial colony is in place the trucks could be used as battery banks for nighttime use at the colony, and only a few trucks used to haul ice for the water and hydrogen processing ISRU unit.  Hopefully ice can be found below the surface and extracted out of the soil around the colony.  Smooth landing areas could be made in the process or smooth areas for future colony construction and or solar panel layouts.

If you read the paper I quoted, one of the primary dangers is damage to the craft itself from blow back, another is destabilizing the surface beneath the craft for relaunch, and the blow out that could damage existing installations could throw for several kilometers. ...
I am certain the "several kilometers" part would only be relevant on the Moon. Mars' atmosphere and higher gravity prevents debris from a landing from traveling anywhere near that far.

You'd be surprised :) The main worry is low-angle, high velocity debris which could be handled for the most part with a berm built up between the landing area and the colony. It would be a good idea if you have multiple landings and take offs (surge in the middle of the cycle) to move landed vehicles behind berms or have berms around the take off site to prevent debris from other take offs or landings from damaging the vehicle. Probably not going to stop it from happening though unless the landing and take off sites are far apart (which brings up logistics issues) so a robust structure is pretty much a must.

RAndy
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Elmar Moelzer on 04/22/2015 10:10 PM
Just build a nice, big and most of all solid landing pad with a shield for the debris, towards the colony?
Title: Re: MCT Speculation and Discussion Thread 3
Post by: RanulfC on 04/22/2015 10:28 PM
Just build a nice, big and most of all solid landing pad with a shield for the debris, towards the colony?

Eventually you "build" a stabilized soil/additive (concrete) pad IF you can guarantee every vehicle will land on it exactly, more normally you'd build a long berm (that's your shield) between the colony (and everyone else) and the landing/take off field and be done with it. It only has to be long enough to shield the outlying sections (and work areas) from the majority of flying debris. You're going to be moving soil for the colony anyway so it's not a major project.

Randy
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/22/2015 11:51 PM

Note that Lobo's earlier 5 engine configuration in which a central engine penetrates the heat-shield and is used for landing isn't viable because that central engine can't gimble, which is absolutely necessary for controlling the hover-slam.  The engine-through heat-shield concept is only viable for high altitude deceleration and even then it's though that the engines will need to be angled to the side so the vehicles remains stable and doesn't 'wobble' on it's own plume, when landing you simply must have a gimbling engine or multiple engines with adjustable thrust.


???
Huh?  I never proposed that to be with a bottom heat shield.  That's for a biconic aeroshell shape with the engines on the aft.  So there is no need for consideration of engines going through a heat shield.  Did you not see the various pictures I posted?  Where did you get the idea I meant the engines would go through the heat shield?

For the record, I feel [personally] about 90% sure a biconic aeroshell will be the same of MCT, not these various ovoid giant capsule shapes where there will be the engine/heatshield issue.

Again....that's 90% is 100% my opinion.  :-)
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Elmar Moelzer on 04/23/2015 12:04 AM
Just build a nice, big and most of all solid landing pad with a shield for the debris, towards the colony?

Eventually you "build" a stabilized soil/additive (concrete) pad IF you can guarantee every vehicle will land on it exactly, more normally you'd build a long berm (that's your shield) between the colony (and everyone else) and the landing/take off field and be done with it. It only has to be long enough to shield the outlying sections (and work areas) from the majority of flying debris. You're going to be moving soil for the colony anyway so it's not a major project.

Randy
Its not just about protecting the colony though, but also the spacecraft.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: nadreck on 04/23/2015 12:30 AM
Just build a nice, big and most of all solid landing pad with a shield for the debris, towards the colony?

Eventually you "build" a stabilized soil/additive (concrete) pad IF you can guarantee every vehicle will land on it exactly, more normally you'd build a long berm (that's your shield) between the colony (and everyone else) and the landing/take off field and be done with it. It only has to be long enough to shield the outlying sections (and work areas) from the majority of flying debris. You're going to be moving soil for the colony anyway so it's not a major project.

Randy
Its not just about protecting the colony though, but also the spacecraft.
and making sure that you can set up more than one "camp" before you are building permanent berms, pads etc. to explore you need to land many places.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 04/23/2015 01:20 AM
To explore, you need a truck (battery powered) and a way to recharge (large deployable solar arrays). Way better than using a rocket.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: sanman on 04/23/2015 01:57 AM
Could a cargo version of MCT haul large pieces of equipment like ground vehicles to the surface of Mars?
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 04/23/2015 02:12 AM
Could a cargo version of MCT haul large pieces of equipment like ground vehicles to the surface of Mars?
Yes.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lars-J on 04/23/2015 02:24 AM

Could a cargo version of MCT haul large pieces of equipment like ground vehicles to the surface of Mars?

Why would you bother to have a cargo MCT if it could not? Ground rovers/excavators/haulers would be the primary payloads for early missions.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Impaler on 04/23/2015 02:42 AM

???
Huh?  I never proposed that to be with a bottom heat shield.  That's for a biconic aeroshell shape with the engines on the aft.  So there is no need for consideration of engines going through a heat shield.  Did you not see the various pictures I posted?  Where did you get the idea I meant the engines would go through the heat shield?

For the record, I feel [personally] about 90% sure a biconic aeroshell will be the same of MCT, not these various ovoid giant capsule shapes where there will be the engine/heatshield issue.

Again....that's 90% is 100% my opinion.  :-)

Sorry about that, thought you were describing a alternative vehicle from the one in your sketches, a bi-conic that lands vertically on it's tail indeed has no heat-shield penetration issues (other then landing legs). 

Note though that the capsule configuration would almost certainly use the Dragon configuration of side wall mounted engines so again a monolithic heat-shield except for landing legs.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 04/23/2015 02:49 AM

Could a cargo version of MCT haul large pieces of equipment like ground vehicles to the surface of Mars?

Why would you bother to have a cargo MCT if it could not? Ground rovers/excavators/haulers would be the primary payloads for early missions.
Indeed. The very first payloads, in fact. They need some sort of mining vehicle to extract water for ISRU of the propellant needed to send the MCT back to Earth.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: nadreck on 04/23/2015 03:31 AM
To explore, you need a truck (battery powered) and a way to recharge (large deployable solar arrays). Way better than using a rocket.

ground vehicles may be good for a few hundred kilometers, however you will want to have, in the first few years a dozen or more different sites where you can explore by ground vehicle. There will not just be one landing site, but many, hopefully before final decisions are made on where permanent installations will be made. Though I imagine the first site will be selected carefully enough to be worth building up and setting up landing pads, berms etc.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: spacenut on 04/23/2015 05:11 AM
I could see an earth grader to make a level building site or landing site, by pushing soil in a berm between the building site and the landing site. 

I could see a hauler or dump truck type vehicle to carry soil with ice frozen inside for water processing and fuel making.

I could see a backhoe type vehicle for digging trenches for building semi-underground or underground.

I could see all of these using the same type frame and electrical drive based on Tesla technology.  I could also see them being coupled together like train engines to haul either ice or some type of Mars mineral like basalt, or other type of ore back to a processing center pulling connected cars.  Mining companies use these type trackless trains in Australia carrying ore to coastal towns for shipments. 

If each vehicle weighs 2-3 tons that adds up to a lot of vehicles and weight on an MCT. 

I could see a small crane used to lift and load items onto trucks or even underground cylinder type units to be buried underground for shelters/homes. 

I could also see two of everything for the sake of if one is broken down, or while one is charging during the daylight, the other one is being used.  Then the charged one is used the next day and rotated. 

I could also see the vehicles used as battery banks for night power after being charged during the day, especially during the 18 months that no shipments are sent to Mars. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lars-J on 04/23/2015 05:25 AM
I could see an earth grader to make a level building site or landing site, by pushing soil in a berm between the building site and the landing site. 

I could see a hauler or dump truck type vehicle to carry soil with ice frozen inside for water processing and fuel making.

I could see a backhoe type vehicle for digging trenches for building semi-underground or underground.

I could see all of these using the same type frame and electrical drive based on Tesla technology.  I could also see them being coupled together like train engines to haul either ice or some type of Mars mineral like basalt, or other type of ore back to a processing center pulling connected cars.  Mining companies use these type trackless trains in Australia carrying ore to coastal towns for shipments. 

If each vehicle weighs 2-3 tons that adds up to a lot of vehicles and weight on an MCT. 

I could see a small crane used to lift and load items onto trucks or even underground cylinder type units to be buried underground for shelters/homes. 

I could also see two of everything for the sake of if one is broken down, or while one is charging during the daylight, the other one is being used.  Then the charged one is used the next day and rotated. 

I could also see the vehicles used as battery banks for night power after being charged during the day, especially during the 18 months that no shipments are sent to Mars.

To reduce single point of failure, it would make sense to deploy several robotic vehicles that can do several of these tasks. More than sharing a common frame, have them be multi-purpose. Time is not of the essence, as long as they may slow progress there can be lots done between the launch windows.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: spacenut on 04/23/2015 01:14 PM
I was thinking that making the vehicles have common frame, motors, batteries and such, modular if you will, would allow for quick repairs if necessary.  Also since their batteries are fairly powerful, they can dub as power at night for the living and working units.  Solar can recharge them during the day and having double can be rotated out for power supply and working.  Robotics can do a lot, maybe with lots of cameras and be operated remotely by someone to extract water soil for processing. 

With vehicles, there probably should be a shop unit that a vehicle can be brought in to be worked on in a shirtsleeve environment.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 04/23/2015 01:24 PM
Ground vehicles are off-topic.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: RanulfC on 04/23/2015 06:00 PM
Its not just about protecting the colony though, but also the spacecraft.

No it's MOSTLY about protecting the colony :)

I've already mentioned already landed and not readying for take off vehicles would be "sheltered" in individual revetment/berm structures.

I don't know if I mentioned it or not but the BEST practice is in fact to tow a launching MCT onto a launch pad surrounded by a berm to protect everything from debris of the blast off. You could do without the individual berms that way. You probably would need a large area that with a blocking berm for landing after which he MCT would be towed to the other side of the berm for unloading/loading and maintenance. Then its towed to the launch pad, fueled any crew passengers board and launch. Repeat with the next outgoing launch.

and making sure that you can set up more than one "camp" before you are building permanent berms, pads etc. to explore you need to land many places.

You all know a "berm" is simply a built up dirt wall right? "Revetments" are usually faced with something and reinforced but berms can be loose soil covered by a tarp. All your looking for is something to absorb and/or deflect debris from a take-off or landing rocket blast.

Randy
Title: Re: MCT Speculation and Discussion Thread 3
Post by: nadreck on 04/23/2015 06:13 PM
Its not just about protecting the colony though, but also the spacecraft.

No it's MOSTLY about protecting the colony :)
We (ok at least me) are/is talking about protecting the craft that is landing from damage to it's engine/heathshield from impacts with 1cm sized gravel moving as much as 1.2km/s - one of the reasons why engines might be mounted on the outside and have a gimbal range from 0° from the vertical to 30° from the vertical (pointing out). That angling, and the fact that the engines are on the outer radius, also protects the landing site from being destabilized under the landing craft so that it can't take off without major earth moving, hoisting, etc.




and making sure that you can set up more than one "camp" before you are building permanent berms, pads etc. to explore you need to land many places.

You all know a "berm" is simply a built up dirt wall right? "Revetments" are usually faced with something and reinforced but berms can be loose soil covered by a tarp. All your looking for is something to absorb and/or deflect debris from a take-off or landing rocket blast.

Randy

Yes, but that will only be done if more traffic is going there, so it will probably be the 2nd or later MCT to that site location that caries the earth moving equipment to do that. 

My point is that I think the MCT has to be designed (and operated) to minimize the risks to the MCT and to anything already on the ground. Angling the engines outward, having them outside of the radius of the craft, and ensuring that landing orientation of engines puts already landed equipment at the least risk is needed before landing pads are built up at a site that will experience significant future traffic.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: JasonAW3 on 04/23/2015 07:09 PM
Its not just about protecting the colony though, but also the spacecraft.

No it's MOSTLY about protecting the colony :)

I've already mentioned already landed and not readying for take off vehicles would be "sheltered" in individual revetment/berm structures.

I don't know if I mentioned it or not but the BEST practice is in fact to tow a launching MCT onto a launch pad surrounded by a berm to protect everything from debris of the blast off. You could do without the individual berms that way. You probably would need a large area that with a blocking berm for landing after which he MCT would be towed to the other side of the berm for unloading/loading and maintenance. Then its towed to the launch pad, fueled any crew passengers board and launch. Repeat with the next outgoing launch.

and making sure that you can set up more than one "camp" before you are building permanent berms, pads etc. to explore you need to land many places.

You all know a "berm" is simply a built up dirt wall right? "Revetments" are usually faced with something and reinforced but berms can be loose soil covered by a tarp. All your looking for is something to absorb and/or deflect debris from a take-off or landing rocket blast.


I would seem that a small, deep crater with the center peak flattened out would likely be the best choice for this sort of launch pit.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: JasonAW3 on 04/23/2015 07:17 PM
Amusing thoughts here;

     First, I would not be at ALL suprised if the MCT lander turned out to resemble the Aries 1B from 2001.  It's a simple design that lends itself fairly well to atmospheric deceleration, with an appreciable payload capibility.

     Also; it occures to me that Clarke and Kubrick may have been more prescient than anyone suspected.  Remember that the lunar landing facility for the Aries was built underground, in what appeared to be a large tunnel!  Can we say a spaceport and colony in a lava tube?  I thought we could...
Title: Re: MCT Speculation and Discussion Thread 3
Post by: sheltonjr on 04/23/2015 07:23 PM
I don't know if I mentioned it or not but the BEST practice is in fact to tow a launching MCT onto a launch pad surrounded by a berm to protect everything from debris of the blast off. You could do without the individual berms that way. You probably would need a large area that with a blocking berm for landing after which he MCT would be towed to the other side of the berm for unloading/loading and maintenance. Then its towed to the launch pad, fueled any crew passengers board and launch. Repeat with the next outgoing launch.

I have put some thought into this, and I do not think the MCT will be towable. The general consensus is the MCT will mass around 60-75MT. On Mars it will weigh 20-25MT empty.

I find it hard to conceive of light weight landing pads or legs being able to stand up to the lateral loads that towing would put on them. And some type of wheels that could castor would also need be added. After landing and unloading, perhaps the MCT could be jacked up and wheels placed under the landing pad or legs.

The tow truck would be light weight due to being transferred there by the MCT and would have very little traction. It could be ballasted by Mars dirt or all the iron meteorites laying around.

It will definitely make the logistics easier if the MCT can be towed around and reduce the need for pin-point landing accuracy. This adds another difficult requirement to the design of the MCT. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: TripD on 04/23/2015 09:41 PM
Not sure that I agree with the notion of towing an MCT.  In lieu of this approach, perhaps a 'take them as you find them' plan might be better.  Essentially, you could jack up the MCT where it landed and either place blocks underneath, or just use some process to harden the ground at least temporarily for the next launch.  You would avoid any complications like getting stuck while being towed.

Later when landing accuracy is dependable, perhaps prefabbed landing pads with all the applicable infrastructure would be the norm.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Jcc on 04/23/2015 11:30 PM
If it has some residual fuel, perhaps MCT could "hop" to a new location by Raptor power.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: spacenut on 04/24/2015 12:02 AM
Once landed, the first MCT could have some type of steel plating that could laid out on the ground for future landers to keep from kicking up dust and or earth moving vehicles to build berms around the lander.  Maybe just having the engines higher on the sides might be all that is needed. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Impaler on 04/24/2015 12:39 AM
I have put some thought into this, and I do not think the MCT will be towable. The general consensus is the MCT will mass around 60-75MT. On Mars it will weigh 20-25MT empty.

I find it hard to conceive of light weight landing pads or legs being able to stand up to the lateral loads that towing would put on them. And some type of wheels that could castor would also need be added. After landing and unloading, perhaps the MCT could be jacked up and wheels placed under the landing pad or legs.

The tow truck would be light weight due to being transferred there by the MCT and would have very little traction. It could be ballasted by Mars dirt or all the iron meteorites laying around.

It will definitely make the logistics easier if the MCT can be towed around and reduce the need for pin-point landing accuracy. This adds another difficult requirement to the design of the MCT.

I think you could just have a few small tow vehicles which each individually clamp too and jack up one landing leg.  Then they simply drive in unison, connected by steel rods if need be to prevent any chance of wrenching the landing legs with lateral loads.

I agree that simply having wheels on the landing legs and trying to tow the whole MC from one towing point is bad, it adds unnecessary mass and requires the vehicle to be stiffed and able to take loads from yet another direction which would add to the mass of its frame.  As much as possible the movement on the ground should be offloaded to specialized ground vehicles, just as we do with rockets on the Earths surface.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Ben the Space Brit on 04/24/2015 09:21 AM
Personally, I'd have electromechanical wheels in the landing pads so that MCT could taxi itself should it be necessary (say, roll over to the base to mate to a pressurised crew transfer 'sky space bridge'). Think of them as massively scaled-up versions of the propulsion system on MSL and the MERs.

In fact, I'd make that a standard part of any large scale crewed base establishment and support effort. Instead of precision landing, land them just nearby and roll over to a convenient location. Then, when they're empty, roll away to their final storage location or back to the aluminium grid launch pad.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lars-J on 04/24/2015 08:29 PM
Wheels are harder than it seems on Mars - or any near vacuum body. I don't think it is realistic that massive landers massing 100+ tonnes can be supported by wheels. Just look at how the MSL wheels are surviving. The lander will also be VERY heavy when fully loaded with propellants for departure.

No, IMO you need to plan on landing them where you need them. If you can't do precision landing yet, you probably should not start a colony.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: spacenut on 04/24/2015 08:34 PM
This is why a vehicle or vehicles of some sort should be landed on the first lander to take people and supplies over to wherever robotic equipment has landed to set up housing.  That being said, a 100 ton lander on Mars would weigh 40 tons, but that is still quite heavy.  I think some type of flat plains area should be used for landers. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: llanitedave on 04/24/2015 10:28 PM
Wheels are harder than it seems on Mars - or any near vacuum body. I don't think it is realistic that massive landers massing 100+ tonnes can be supported by wheels. Just look at how the MSL wheels are surviving. The lander will also be VERY heavy when fully loaded with propellants for departure.

No, IMO you need to plan on landing them where you need them. If you can't do precision landing yet, you probably should not start a colony.


Regardless, Mars wheels are going to have to be mastered if the colony is going to work.  But I agree, the landers shouldn't have to be pulled around.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/24/2015 11:58 PM


Agreed.  So you resolve this by not having the engines in the heat shield at all.  That gets back to the biconic aeroshell with engines at the aft.  Essentially a wingless Spaceshuttle that lands on it's SSME's.

Given the number of designs with engines embedded behind deployable heat shield doors, I would think the "wingless" Space Shuttle design is far from given.  The simplicity of landing with a Dragon-style vertical lander on Mars is not something to be given up lightly.

Well, we can't say anything is a given or not given until SpaceX announces something official.  ;-)

But some of these designed you posted pictures of are comparing apples to Oranges, or are some artist's fiction.  None of the addresses both Issues MCT will have to. 
1)  To be fully reusable, rather than 1-shot.
2)  To get itself back off the surface after it lands. which introduces a lot of issues like a large high performance engine needed, rather than just some low ISP landing thrusters.  All Mars Landers to date had those in one form or another, but none of them had to get back up and back through TEI.  Heck Dragon could land on Mars and it's a capsule.  It just can't get itself back to Earth.  So that's a very different issue that makes capsule designs much more problematic.

Image #1:  I can't see where the heat shield is on this.  The whole bottom is shaded, and I can't see the other side.  But this almost looks like the heat shield is on the other side, given the odd shape of it's bottom.  This looke more like a "wingless shuttle" than a capsule.

Image #2:  Again, where's the heat shield.  Is it on the other side?  Is this a wingless shuttle too?  Or did it have a jettisonable heatshield on the bottom.  If so, then it's not reusable like MCT will be.  MCT won't [likely] be jettisoning it's heat shield.  Otherwise it couldn't land back on earth.  If it were to some how be able to brake itself into LEO (how?) it would need a new heatshield brought up and attached in LEO.  Which seems...unnecessarily complex.

Image #3:  Ok...so what was protecting thos engines during entry?  Did it have a portion of the heat sheild jettison?  And if so, see my comments about that on Image #2.

Image #4:  That image is from "Voyage" by Stephen Baxter.  Great book!  I highly recommend it.  That is the Mars lander Baxter put in his novel.  But that is an expendable two-stage lander like the LEM.  It had a conventional capsule shaped descent module (described by Baxter that it was chosen over other more advanced bionic designs because of it's heritage and that they "know" it would survive, where biconics hadn't been tried before....and if they are going to risk Humans on the very first trip (there was only funding for just one manned trip to Mars) they wanted to go with a proven and stable design. 
It's top and central core were the ascent module.  It blasted off from the capsule bottom back to LMO for rendezvous with the MTV.  It was really an Apollo redux, but with a lander descent module that could withstand atmospheric entery.  Again, this lander can't get itself off the surface whole, only the ascent module portion could get back to LMO, just like the Apollo LEM.  The ascent module engines were protected within the MEV like the LEM AM engine was, and the descent module portion was destoyed when the ascent module blasted off.    The whole lander couldn't take back off again with it's landing thrusters (even if it could have been refueled) and it wasn't reusable.  A good safe one shot design but it would share little in common with what MCT is supposed to do.

A biconic has a lot of advantage over a capsule.  It has a large surface area, so it's TPS doesn't have to be quite as thick and it's terminal velocity is slower.  The engines are in the afte and not exposed to the atmospheric entry, or the supersonic terminal velocity slip stream like those of a capsule.  Although it's not impossible to have doors in your heat shield...the shuttle, X-37B, and Dreamchaser do after all for their landing gear...having a large main engine with a large nozzle which gimbals is more problematic than landing gear.  Assuming such a capsule design would have Superdraco like landing thrusters, and then one or more Raptors tucked behind the heat shield, then you have to retract those doors (that can be done on the ground if there are separate side wall landing thrusters) but then you need enough room for those main engines to gimbal, so the doors need to be much wider than the nozzles.  and then those doors need to close again prior to Earth EDL or else you have the Columbia all over again. 
That's on top of landing gear which will need to come through the heat shield as well.  So there will need to be several doors in the heat shield. 

I'm sure it -could- be made to work.  But why force it when you don't have to?  A biconic "wingless shuttle" design solves all of that.  You can even get around needing to have legs extend through the heat shield on its' side in various ways, include just having jackstand like legs come straight down from the MPS (if the diameter is wide enogh to be stable, similar to your pictures #2)  or you could have blisters around the MPS housing the legs.  With a shape not unlike your image 1.  The legs could fold out from those blisters to give MCT a wider stance on the surface. 
Because while there are vehicles which have had doors in their TPS, there's never been one that's had to close those doors again prior to anther reentry.  They open once after atmospheric entry and that's it.  They're closed on the ground an checked out before sent back up.  So avoiding that dynamic portion of the heat shield and making it all static/passive increases mission safety.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/25/2015 12:03 AM
I also think SpaceX should develop their Raptor engine like the BE-3 that can throttle from 30% to 110%.  That would make for easier landing on earth or Mars.

I believe the RD-180 could throttle down to around 30%.  As Raptor will be staged combustion like the RD-180, I would -assume- that 30% is not too big of an issue for Raptor.  If they do which to land with Raptor, rather than just use it for 2nd stage/in-space/Mars ascent propulsion, then they may be able to design it with a little lower throttle point.  Even if Raptor is inefficient at that low throttle point it's immaterial.  All it's needing to do is get MCT on the surface.  Superdraco thrusters will be inefficient too, but they don't need to have a high ISP, so a low ISP deeply throttle Raptor might not be a major problem.

Again, if they want to try to land on Raptor rather than have some dedicated landing thrusters.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/25/2015 12:11 AM
Sorry about that, thought you were describing a alternative vehicle from the one in your sketches, a bi-conic that lands vertically on it's tail indeed has no heat-shield penetration issues (other then landing legs). 


Ahhh...no problem.

The legs don't necessarily have to protrude through the side heat shield.  I did post one image showing that, but as I said in my reply to Hyperion, there's other ways around it.  In fact, Hyperion posted a couple of pics illustrating those alternatives.

Pic 1:  shows legs deploying through the side TPS.

Pic 2:  Extendable jack-stand like legs that come pretty much straight down.  The H/W ratio of MCT would be a factor in that to make sure it's stance was wide enough.

Pic 3:  blisters or nacels on the sides which legs could exend out and even more of an angle, for a wider stance.  (Again, I almost think this picture is a biconid with the TPS on the other side.  The dorsal side is shown to us.  That MPS on the bottom just doesn't look set of for atmospheric entry that way.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: BobHk on 04/25/2015 02:34 AM
This is why a vehicle or vehicles of some sort should be landed on the first lander to take people and supplies over to wherever robotic equipment has landed to set up housing.  That being said, a 100 ton lander on Mars would weigh 40 tons, but that is still quite heavy.  I think some type of flat plains area should be used for landers.

Isn't MCT supposed to deliver 100 tons (at least the later versions)?  Assuming 5 or more raptors, remaining fuel on Mars landing and dry mass of the lander plus 100 tons of cargo/people... even more unlikely to work on wheels of any kind that would be effective on unprepared terrain.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Impaler on 04/25/2015 05:14 AM
Lets try to do some volume estimates for MCT and think about how much propellent that would hold.

I'm imagining a 15 m diameter Dragon v2 shaped capsule.  That is almost exactly 4 times the diameter of Dragon meaning that the MCT would have 66x the volume of Dv2.  Dragon v2 I estimate to be 24 m^3 in its EXTERIOR dimensions by calculating it as a simple truncated cone 3.7 m in diameter, 4.7 m high and with a 15 degree wall slope.  This means the capsule style MCT is ~1500 m^3

Dry mass of Dragon v1 was 3180 kg (according to some VERY old numbers so take it with a grain of salt).  Assuming mass directly scaling with volume that would mean a ~200 MT vehicle before any payload or propellents.  But many parts of the vehicle will not scale cubically, such as the heat-shield which while 16x larger in area would not need to become 4x thicker.  I'm thinking 100-150 MT is a reasonable dry mass range.

Allocation of volume, lets go with 100 m^3 for integrated crew space, 500 m^3 for cargo-hold inside which additional passenger accommodation modules can be carried and connected with the integral space.  Take another 100 m^3 for miscellaneous uses and that leaves 800 m^3 in propellent tanks.  LOX/Methane propellent averages out to right around 1 MT per m^3 so we would be looking at take off propellent of up too 800 MT.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: symbios on 04/25/2015 09:06 AM
I like your reasoning Impaler, you at least try to use logic and not a pet theory of how it should be done. As Musk would say; use the first principles.

You are missing that the MCT will probably be a two stage system.

Booster and transfer stage. Where the transfer stage is both upper stage and payload in one. So when you calculate you have to include the US mass.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: symbios on 04/25/2015 09:43 AM
I’m fairly new at this. And for you people here that work with this will see any flaws in my logic straight away, please comment so I can adjust my thinking.

Mass is everything in space. It is the limiting factor for everything. We do not know the mass.

I divide the mass of the transfer stage of the MCT into three parts - vehicle, cargo and tankage (fuel).

We know the cargo mass that we want to get to Mars; 100 mt.
If we knew the vehicles mass we could calculate the fuel.
We do not know the vehicle mass.

We could set some limits on the unknown mass of the vehicle by making some assumptions:

-   The shorter the trip the lower the fuel needed (less mass), so assume we are only going to LEO to refuel.
   We can have more capacity for tankage than we have fuel in them. This is only about vehicle mass.
-   The booster that takes us part way to LEO are assumed to be 12-15 M lbs. and we are fairly good guess
   about the ISP of the engines.
-   We have a fairly good guess about the ISP of the transfer stage (US) of the MCT.

So using these assumptions can we calculate the max allowed mass of the MCT transfer stage vehicle AND is this mass reasonable? Could this be calculated both using 12 Mlbs and 15Mlbs on the booster?
Title: Re: MCT Speculation and Discussion Thread 3
Post by: fast on 04/25/2015 10:25 AM
Sorry about that, thought you were describing a alternative vehicle from the one in your sketches, a bi-conic that lands vertically on it's tail indeed has no heat-shield penetration issues (other then landing legs). 


Ahhh...no problem.

The legs don't necessarily have to protrude through the side heat shield.  I did post one image showing that, but as I said in my reply to Hyperion, there's other ways around it.  In fact, Hyperion posted a couple of pics illustrating those alternatives.

Pic 1:  shows legs deploying through the side TPS.

Pic 2:  Extendable jack-stand like legs that come pretty much straight down.  The H/W ratio of MCT would be a factor in that to make sure it's stance was wide enough.

Pic 3:  blisters or nacels on the sides which legs could exend out and even more of an angle, for a wider stance.  (Again, I almost think this picture is a biconid with the TPS on the other side.  The dorsal side is shown to us.  That MPS on the bottom just doesn't look set of for atmospheric entry that way.

biconic looks good. You are correct, legs not a problem. Just wrong rendering: TPS must be on the opposite side from ramp.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Impaler on 04/25/2015 04:47 PM
You are missing that the MCT will probably be a two stage system.

I didn't miss that, I simply disagree.  I believe the traditional 2 stages + capsule will be the way SpaceX goes, same configuration as Falcon9 + Dragon.

The logic behind combining MCT with 2nd stage was to provide huge propellent tanks for both TMI and direct Earth return from Mars surface.  But both these things can be done with just the smaller more conservative capsule base MCT if your smart about it.

For TMI you simply keep the 2nd stage that launched the MCT attached, load the propellent into it rather then the MCT and do a TMI burn with that 2nd stage.  The stage can even do a boost-back and return to Earth surface.

To do Earth return we fill both the integral tanks of the MCT capsule AND inflatable tanks that have been brought along in a deflated state.  These inflatables fill the now empty cargo hold.  If 300 MT can be held in this way (note that on Mars this is the same load on the payload-bay floor that the 100MT of cargo exerted on Earth), then the combined propellent load would reach 1100 MT.  A direct Earth return DeltaV would be ~6.8 km/s which at Raptor ISP of 360 will mean a dry mass of no more then 15%.  With 1100 MT of propellent a dry mass of 200 MT can be sent which covers the MCT and a small return payload.

If internal volume is traded between the integral tanks and the payload bay and larger inflatable tanks are used then an even larger payload bays should be possible without harming return DeltaV.  An higher volume payload bay is very desirable for transporting low density cargoes.

If we wish to just go to Low Mars orbit (for example to meet a dedicated in-space vehicle, visit Phobos, or just do a suborbital hop) then integral tanks alone should be able to do this, allowing the cargo hold to once again carry cargo up to it's full load while retaining propellent for landing.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: sheltonjr on 04/25/2015 07:46 PM
Here is my hypothetical MCT design based on the constraint of a 225 MT Fully Reusable BFR.

I also disagree about the two stage system. Inflatable tanks in the cargo hold are also not required.

Tanks above cargo gives the best layout and CG for landing. So I have chosen it believing the plumbing problem will be solved. If the engines are side mounted, It may even be easier.

A crew MCT will not be able to get 100 MT of cargo to Mars. Crew support equipment and systems will subtract from the available 100 MT.

Dragon derived 15 m capsule with 15 degree side-walls. Capsule is 25 m tall not including the heat shield hemisphere. Top diameter dome 1.6 m across.

The MCT is divided into 6 Floors from bottom to top with the following characteristics:

| Floor                        | Height (m) | Usable Pct (%) |Volume (m3) | Area (m2),(ft2) | Fuel (MT) |
|-----------------------|-------------|------------------|--------------|------------------|-----------|
| Upressurized Cargo   | 2.5            | 95                    | 383              | 177, 1902         |                |
| Habitat                     | 2               | 95                    | 257              | 146, 1577         |                |
| Pressurized Cargo     | 2               | 95                    | 216              | 124, 1339         |                |
| Systems                   | 1.5            | 95                    | 138              | 104, 1121         |                |
| LOX                          | 4.6            | 97                    | 309              | N/A                  | 361         |
| CH4                          | 12.4          | 97                    | 258              | N/A                  | 112         |

MCT Empty Mass = 65 MT
Cargo <= 100 MT
Total Fuel = 473 MT

MCT Launches with cargo and crew and 60 MT of fuel to awaiting BFR Depot to fully fuel with additional 400 MT of fuel. Performs TMI and EDL at Mars with a DV of 5036 m/s. Each Mars MCT will only require 2 BFR Tankers.

MCT Refuels on Mars utilizing 473 MT of ISRU fuel and returns to Earth with up to 10 MT of crew/cargo with a DV 7405 m/s.

Distributed MCT engines require a minimum thrust around 50 MT and 250 MT Maximum.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Impaler on 04/25/2015 09:00 PM
Tanks above cargo gives the best layout and CG for landing. So I have chosen it believing the plumbing problem will be solved. If the engines are side mounted, It may even be easier.

I agree that tanks above cargo/habitats is the logical arrangement.  In a side mounted engine configuration the propellent lines should be quite short.  The radius of the bottom heat-shield may prove unusable for cargo though so some splitting up of propellents may be necessary.

A crew MCT will not be able to get 100 MT of cargo to Mars. Crew support equipment and systems will subtract from the available 100 MT.

Again I agree that when transporting passengers the MCT dose not also deliver 100 MT of cargo, in essence the 100 MT figure is the relevant number only when flying unmanned.  I believe that passenger will be transported by placing special pressurized passenger-accommodation modules inside the cargo bay.  These modules will be permanently left on the Martian surface as living quarters.  This allows a bare bones integral habitat, it is really more like the 'galley' at the front of an airliner and has the external airlock, docking ports and other infrequent systems, the accommodation modules are like railway sleeper cars and are most of the bulk, they are also loaded with all the outbound food and consumables and air handlers so these scale directly with the number of passengers being transported.  I'm assuming 300 m^3 in module volume if the whole cargo hold is used, plus the 100 of the integral giving us 400 total for passenger transport configuration.  At full passenger loading their is no other cargo going to Mars other then the passengers and modules.  To bring people back from Mars the integral habitat can hold a handful which should be sufficient if people are really 'colonizing', if not then we simply retain the necessary number of passenger modules to handle the return rate.

Dragon derived 15 m capsule with 15 degree side-walls. Capsule is 25 m tall not including the heat shield hemisphere. Top diameter dome 1.6 m across.

The MCT is divided into 6 Floors from bottom to top with the following characteristics:

| Floor                        | Height (m) | Usable Pct (%) |Volume (m3) | Area (m2),(ft2) | Fuel (MT) |
|-----------------------|-------------|------------------|--------------|------------------|-----------|
| Upressurized Cargo   | 2.5            | 95                    | 383              | 177, 1902         |                |
| Habitat                     | 2               | 95                    | 257              | 146, 1577         |                |
| Pressurized Cargo     | 2               | 95                    | 216              | 124, 1339         |                |
| Systems                   | 1.5            | 95                    | 138              | 104, 1121         |                |
| LOX                          | 4.6            | 97                    | 309              | N/A                  | 361         |
| CH4                          | 12.4          | 97                    | 258              | N/A                  | 112         |

MCT Empty Mass = 65 MT
Cargo <= 100 MT
Total Fuel = 473 MT

Your total volume estimate matches my own at ~1500 m^3 though your going with a taller cone height my own math showed their was hardly any volume in the last few meters.  Comparatively your using a smaller unpressurized cargo-hold (383 vs 500), a considerably larger Habitat (257 vs 100), smaller integral tanks (567 vs 800) and a pressurized cargo area of 216 which I did not have.

But the factor that is most out of synch is the dry mass estimate for the vehicle, 65 MT is nearly half of my estimated upper range (100-150).  This seems too optimistic as it is about 33% of the direct Dragon scaling, rather then my own 50-75% estimate.  Whats your mass estimation method?


MCT Launches with cargo and crew and 60 MT of fuel to awaiting BFR Depot to fully fuel with additional 400 MT of fuel. Performs TMI and EDL at Mars with a DV of 5036 m/s. Each Mars MCT will only require 2 BFR Tankers.

MCT Refuels on Mars utilizing 473 MT of ISRU fuel and returns to Earth with up to 10 MT of crew/cargo with a DV 7405 m/s.

Distributed MCT engines require a minimum thrust around 50 MT and 250 MT Maximum.

The basic mission profile is good, my only real difference are less propellent in the MCT at launch primarily because of higher dry mass estimates.  And then a corresponding increase in Tanker delivered propellents and ISRU propellents.  It is clear that making the MCT dry mass as low as possible will have huge operational payoffs, but these crude extrapolations from Dragon mass are all I can manage.


It would be interesting if Lobo or others could do the same volume/mass estimate on the combined 2nd-stage style MCT concept.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: BobHk on 04/26/2015 07:01 PM
Here is my hypothetical MCT design based on the constraint of a 225 MT Fully Reusable BFR.

I also disagree about the two stage system. Inflatable tanks in the cargo hold are also not required.

Tanks above cargo gives the best layout and CG for landing. So I have chosen it believing the plumbing problem will be solved. If the engines are side mounted, It may even be easier.

A crew MCT will not be able to get 100 MT of cargo to Mars. Crew support equipment and systems will subtract from the available 100 MT.

Dragon derived 15 m capsule with 15 degree side-walls. Capsule is 25 m tall not including the heat shield hemisphere. Top diameter dome 1.6 m across.

The MCT is divided into 6 Floors from bottom to top with the following characteristics:

| Floor                        | Height (m) | Usable Pct (%) |Volume (m3) | Area (m2),(ft2) | Fuel (MT) |
|-----------------------|-------------|------------------|--------------|------------------|-----------|
| Upressurized Cargo   | 2.5            | 95                    | 383              | 177, 1902         |                |
| Habitat                     | 2               | 95                    | 257              | 146, 1577         |                |
| Pressurized Cargo     | 2               | 95                    | 216              | 124, 1339         |                |
| Systems                   | 1.5            | 95                    | 138              | 104, 1121         |                |
| LOX                          | 4.6            | 97                    | 309              | N/A                  | 361         |
| CH4                          | 12.4          | 97                    | 258              | N/A                  | 112         |

MCT Empty Mass = 65 MT
Cargo <= 100 MT
Total Fuel = 473 MT

MCT Launches with cargo and crew and 60 MT of fuel to awaiting BFR Depot to fully fuel with additional 400 MT of fuel. Performs TMI and EDL at Mars with a DV of 5036 m/s. Each Mars MCT will only require 2 BFR Tankers.

MCT Refuels on Mars utilizing 473 MT of ISRU fuel and returns to Earth with up to 10 MT of crew/cargo with a DV 7405 m/s.

Distributed MCT engines require a minimum thrust around 50 MT and 250 MT Maximum.

What amount did you set aside for ship power generation?  Waste recycling for 100.  Is this amount your 'systems' set aside? 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Hyperion5 on 04/27/2015 02:17 AM


Agreed.  So you resolve this by not having the engines in the heat shield at all.  That gets back to the biconic aeroshell with engines at the aft.  Essentially a wingless Spaceshuttle that lands on it's SSME's.

Given the number of designs with engines embedded behind deployable heat shield doors, I would think the "wingless" Space Shuttle design is far from given.  The simplicity of landing with a Dragon-style vertical lander on Mars is not something to be given up lightly.

Well, we can't say anything is a given or not given until SpaceX announces something official.  ;-)

But some of these designed you posted pictures of are comparing apples to Oranges, or are some artist's fiction.  None of the addresses both Issues MCT will have to. 
1)  To be fully reusable, rather than 1-shot.
2)  To get itself back off the surface after it lands. which introduces a lot of issues like a large high performance engine needed, rather than just some low ISP landing thrusters.  All Mars Landers to date had those in one form or another, but none of them had to get back up and back through TEI.  Heck Dragon could land on Mars and it's a capsule.  It just can't get itself back to Earth.  So that's a very different issue that makes capsule designs much more problematic.

It's almost like dear Lobo did not glance at the thread-related materials found in that level of NSF that must not be named. ;)  No doubt he'll go back over there and look at them again before, right? :)  There are ways of going fully reusable with a capsule design that has heat shield doors, Lobo.  You use 8 Raptors on the sides (which would produce about 350 seconds of Isp on Mars) that you would use to land on Mars or Earth.  Then, when you need to launch off Mars, you open up the doors.  Multiple vacuum-optimized Raptor engines would then blast you into LMO and later perform the TEI burn.  So long as you refuel on Mars, an MCT will be large enough to make it all the way back to Earth on only one stage.  Full reuse is just as possible via a capsule design as your preferred design. 


Image #1:  I can't see where the heat shield is on this.  The whole bottom is shaded, and I can't see the other side.  But this almost looks like the heat shield is on the other side, given the odd shape of it's bottom.  This looke more like a "wingless shuttle" than a capsule.

Image #2:  Again, where's the heat shield.  Is it on the other side?  Is this a wingless shuttle too?  Or did it have a jettisonable heatshield on the bottom.  If so, then it's not reusable like MCT will be.  MCT won't [likely] be jettisoning it's heat shield.  Otherwise it couldn't land back on earth.  If it were to some how be able to brake itself into LEO (how?) it would need a new heatshield brought up and attached in LEO.  Which seems...unnecessarily complex.

Image #3:  Ok...so what was protecting thos engines during entry?  Did it have a portion of the heat sheild jettison?  And if so, see my comments about that on Image #2.

Image #4:  That image is from "Voyage" by Stephen Baxter.  Great book!  I highly recommend it.  That is the Mars lander Baxter put in his novel.  But that is an expendable two-stage lander like the LEM.  It had a conventional capsule shaped descent module (described by Baxter that it was chosen over other more advanced bionic designs because of it's heritage and that they "know" it would survive, where biconics hadn't been tried before....and if they are going to risk Humans on the very first trip (there was only funding for just one manned trip to Mars) they wanted to go with a proven and stable design. 

It's top and central core were the ascent module.  It blasted off from the capsule bottom back to LMO for rendezvous with the MTV.  It was really an Apollo redux, but with a lander descent module that could withstand atmospheric entery.  Again, this lander can't get itself off the surface whole, only the ascent module portion could get back to LMO, just like the Apollo LEM.  The ascent module engines were protected within the MEV like the LEM AM engine was, and the descent module portion was destoyed when the ascent module blasted off.    The whole lander couldn't take back off again with it's landing thrusters (even if it could have been refueled) and it wasn't reusable.  A good safe one shot design but it would share little in common with what MCT is supposed to do.

With regards to where the heat shields went, they either were retracted back into the vehicle or were deployed and disposed during Martian atmospheric entry.  Obviously they're not perfect analogies for an MCT design, but they should prove that capsule designs are a very plausible MCT design option.  Alterations can be made after all!

A biconic has a lot of advantage over a capsule.  It has a large surface area, so it's TPS doesn't have to be quite as thick and it's terminal velocity is slower.  The engines are in the afte and not exposed to the atmospheric entry, or the supersonic terminal velocity slip stream like those of a capsule.  Although it's not impossible to have doors in your heat shield...the shuttle, X-37B, and Dreamchaser do after all for their landing gear...having a large main engine with a large nozzle which gimbals is more problematic than landing gear.  Assuming such a capsule design would have Superdraco like landing thrusters, and then one or more Raptors tucked behind the heat shield, then you have to retract those doors (that can be done on the ground if there are separate side wall landing thrusters) but then you need enough room for those main engines to gimbal, so the doors need to be much wider than the nozzles.  and then those doors need to close again prior to Earth EDL or else you have the Columbia all over again.

That's on top of landing gear which will need to come through the heat shield as well.  So there will need to be several doors in the heat shield. 

Heat shield doors (successfully) protecting spacecraft reentering Earth's atmosphere is nothing new, as they have never failed to protect the Shuttles from harm.  This is why Dragon 2 is going to use them for its landing gear.  What did in Columbia was foam detaching from the external tank and striking the orbiter's wing, damaging some of the heat shielding found there.  I'm surprised Jim didn't beat me to pointing that out.  If heat shield doors can protect landing gear through over 133 reentries, then why not engines? 

I'm sure it -could- be made to work.  But why force it when you don't have to?  A biconic "wingless shuttle" design solves all of that.  You can even get around needing to have legs extend through the heat shield on its' side in various ways, include just having jackstand like legs come straight down from the MPS (if the diameter is wide enogh to be stable, similar to your pictures #2)  or you could have blisters around the MPS housing the legs.  With a shape not unlike your image 1.  The legs could fold out from those blisters to give MCT a wider stance on the surface. 

The one alternative to legs coming through the heat shield is to have them extend out from the sides of the MCT.  They might be embedded in the side or more exposed (and protected by heat shielding). 

Because while there are vehicles which have had doors in their TPS, there's never been one that's had to close those doors again prior to anther reentry.  They open once after atmospheric entry and that's it.  They're closed on the ground an checked out before sent back up.  So avoiding that dynamic portion of the heat shield and making it all static/passive increases mission safety.

Never been one?  Why exactly are we not counting a Shuttle orbiter?  That craft opened its heat shield doors after a reentry in order to land, and those doors were closed again for the next mission's reentry.  If I were to survey our experts, how many of them would say that opening and closing the Orbiter's landing gear doors once in space would likely result in a loss of mission?  My guess is the chance is quite slim, and in any case you would have time to get them retracted back in via a crew repair if absolutely necessary.  An MCT is not going to be opening and closing heat shield doors much more than a Shuttle did.  It will need to open and close them once on the way to Mars, and once on the way back.  For landing on both Mars and Earth you don't need to open heat shield doors whatsoever, as you can use the side-mounted Raptors and landing legs to touch down safely. 

Is there some additional risk?  Yes, but it's a manageable kind of risk, with the Shuttle's flight experience and the Dragon 2's design being the best evidence. 

Title: Re: MCT Speculation and Discussion Thread 3
Post by: CyclerPilot on 04/27/2015 04:16 AM
It would be interesting if Lobo or others could do the same volume/mass estimate on the combined 2nd-stage style MCT concept.

Regarding MCT dry mass.  I did a rough speculative design way back in Thread 2 (http://forum.nasaspaceflight.com/index.php?topic=35424.msg1288500.msg#1288500), so I thought I would share how I estimated that MCT dry mass.

I did a combined S2+MCT with separate pressure fed LAS/landing thrusters.

All masses in kg:
Raptors8,402
Main Prop tanks5,303
Landing legs   3,000
Heat shield2,213
pressure vessel26,460
8 Metholox Draco's3,200
Pressurized insulated tanks1,200
Radiators2,000
Solar panels3,841
Other misc mass4,926
Total Mass60,545

Obviously ultra optimistic, but I think the MCT has to be or it doesn't work.

Raptor.  I used a 100:1 t/w.  This was the old raptor (8.2 MN), so equivalent to 3 of the new, lower thrust raptors.

Prop Tanks.  Used Al-Li alloy.  12m dia. Common bulkhead.  Enough volume to store 1,000 tons of metholox prop.  40% margin gives 3mm walls.

Pressure vessel. I scaled up from Dragon.  So it does include a lot of misc systems.

Solar panels.  ZTJ Space solar panels.  8.4 kg/m^3.  457 m^3.  175kw Earth, 80kw Mars.  Shared structure with radiators.

Heat shield. pica X.  290 kg/m^3.  30mm thick.  Looking back at my old math, probably unrealisticly optimistic.

Misc mass covered a lot of structures and systems not covered elsewhere.

Everything else is a total guess, mainly based on scale up of similar systems in Falcon or Dragon.

Anyways there's some numbers to poke some holes in / get the conversation moving.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: RanulfC on 04/27/2015 05:46 PM
We (ok at least me) are/is talking about protecting the craft that is landing from damage to it's engine/heathshield from impacts with 1cm sized gravel moving as much as 1.2km/s - one of the reasons why engines might be mounted on the outside and have a gimbal range from 0° from the vertical to 30° from the vertical (pointing out). That angling, and the fact that the engines are on the outer radius, also protects the landing site from being destabilized under the landing craft so that it can't take off without major earth moving, hoisting, etc.

Pretty sure the majority of the "early" MCT fights are simply going to have to "risk" it until something more "permanent" gets built. The main problem with lot of "gimbal" is that you have to have flexible connections and hoses and those increase your possible failure points.

Quote
Yes, but that will only be done if more traffic is going there, so it will probably be the 2nd or later MCT to that site location that caries the earth moving equipment to do that. 

My point is that I think the MCT has to be designed (and operated) to minimize the risks to the MCT and to anything already on the ground. Angling the engines outward, having them outside of the radius of the craft, and ensuring that landing orientation of engines puts already landed equipment at the least risk is needed before landing pads are built up at a site that will experience significant future traffic.

Unless the FIRST MCT flight goes directly to the "colony" site I suspect it will be MUCH later than the second flight :)
However, once it IS decided that MCT flights will be going to a designated colony site then you MUST assume a higher flight rate in and out and therefore prepare for mitigation. Then the "first" colony MCT is going to carry what amounts bulldozer and other construction equipment.
Let me address/point out this:
I would seem that a small, deep crater with the center peak flattened out would likely be the best choice for this sort of launch pit.

Probably the best idea. It actually doesn't have to be very deep as once the MCT is a couple of meters up the "blast" out angle gets shallower and shallower and the blast itself dissipates rapidly with distance.

Figure one of the "main" criteria for a colony site is an already existing "port" area for MCT landings and take offs and find a convenient crater to use. Put the colony on the "surface" above the crater wall and you will have almost no issues with flying debris getting to it. Now you concentrate on protecting landed MCTs from landing or taking off MCTs. (I should probably point out that the MCT would benefit greatly from an outer layer of TransHab material as a buffer layer and a "skin" layer of flexible TPS blankets)

Towing versus "hopping" or using the MCT rockets: Even empty the rockets are going to throw rocks and debris so you want to avoid using them as much as possible in proximity to other MCTs or structures. So unless you're going to land far enough away to avoid any possible problems, (which brings up logistical concerns about getting cargo and passengers back and forth to the colony in a timely manner) you need to arrange and design the "port" to handle the problem within itself.

I'd not assume that the "legs" of the MCTs will be used at all OTHER than for landing and holding it upright for take off. It's going to be attached to the BFR stage so we can assume it will have "hard-points" that can be used on Mars as points where it can be lifted and supported. Light weight "dollies' or individual "jack" wheel sets can lift the MCT so that it can be towed into a "take-off" berm, (the image used to be quite popular, imagine a circular, low angled "wall" with a section MCT wide cut out facing away from any structures or MCT landing area) where it waits for loading, propellant and crew.

Wheels are harder than it seems on Mars - or any near vacuum body. I don't think it is realistic that massive landers massing 100+ tonnes can be supported by wheels. Just look at how the MSL wheels are surviving. The lander will also be VERY heavy when fully loaded with propellants for departure.

No, IMO you need to plan on landing them where you need them. If you can't do precision landing yet, you probably should not start a colony.

Nobody jacks up a fully loaded aircraft why would you assume they do so for an MCT? :) At landing it will be almost empty of propellants so its FAR from as heavy as you seem to be thinking.

"Landed where you need them?" Nice idea but how ACCURATE does that have to be? You "need" not to put the colony structure in danger, nor other already landed MCTs. 2km? 5km?

This is why a vehicle or vehicles of some sort should be landed on the first lander to take people and supplies over to wherever robotic equipment has landed to set up housing.  That being said, a 100 ton lander on Mars would weigh 40 tons, but that is still quite heavy.  I think some type of flat plains area should be used for landers. 

You'll have to have some sort of vehicles to move passengers and cargo from the landed MCT to the colony site, but if you're on 'flat-plains' then the MCTs have to landed far enough away to NOT be a danger to the colony. Even on Mars that's going to be several kilometers. Now add in separation from other MCTs...

A berm is simpler and safer and berms between the MCTs even more so but if your landing accuracy is "only" 1km that means each and every MCT landing "site" has to be a kilometer in diameter... ("Assuming" that the MCT hits dead center EVER time, otherwise you have to include that into your calculations)

Nothing impossible but its some basic considerations for operations.

Randy
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lars-J on 04/27/2015 05:58 PM
Wheels are harder than it seems on Mars - or any near vacuum body. I don't think it is realistic that massive landers massing 100+ tonnes can be supported by wheels. Just look at how the MSL wheels are surviving. The lander will also be VERY heavy when fully loaded with propellants for departure.

No, IMO you need to plan on landing them where you need them. If you can't do precision landing yet, you probably should not start a colony.

Nobody jacks up a fully loaded aircraft why would you assume they do so for an MCT? :) At landing it will be almost empty of propellants so its FAR from as heavy as you seem to be thinking.

"Landed where you need them?" Nice idea but how ACCURATE does that have to be? You "need" not to put the colony structure in danger, nor other already landed MCTs. 2km? 5km?

If you have a colony you will need a LOT more accuracy, why else prepare pads? I imaging the requirement that you need to have pin-point accuracy. +/- just a few meters.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: RanulfC on 04/27/2015 06:08 PM
Heat shield doors (successfully) protecting spacecraft reentering Earth's atmosphere is nothing new, as they have never failed to protect the Shuttles from harm.  This is why Dragon 2 is going to use them for its landing gear.  What did in Columbia was foam detaching from the external tank and striking the orbiter's wing, damaging some of the heat shielding found there.  I'm surprised Jim didn't beat me to pointing that out.  If heat shield doors can protect landing gear through over 133 reentries, then why not engines?

This must be L2 information because the DV2 was shown that the legs extend FROM the heat-shield and there ARE no doors.
Quote
I'm sure it -could- be made to work.  But why force it when you don't have to?  A biconic "wingless shuttle" design solves all of that.  You can even get around needing to have legs extend through the heat shield on its' side in various ways, include just having jackstand like legs come straight down from the MPS (if the diameter is wide enogh to be stable, similar to your pictures #2)  or you could have blisters around the MPS housing the legs.  With a shape not unlike your image 1.  The legs could fold out from those blisters to give MCT a wider stance on the surface. 

The one alternative to legs coming through the heat shield is to have them extend out from the sides of the MCT.  They might be embedded in the side or more exposed (and protected by heat shielding). 

Or like the Stage-1 legs they could fold up 'inside' the heat shadow of the shield or TPS :)
Quote
Because while there are vehicles which have had doors in their TPS, there's never been one that's had to close those doors again prior to anther reentry.  They open once after atmospheric entry and that's it.  They're closed on the ground an checked out before sent back up.  So avoiding that dynamic portion of the heat shield and making it all static/passive increases mission safety.

Never been one?  Why exactly are we not counting a Shuttle orbiter?  That craft opened its heat shield doors after a reentry in order to land, and those doors were closed again for the next mission's reentry.  If I were to survey our experts, how many of them would say that opening and closing the Orbiter's landing gear doors once in space would likely result in a loss of mission?  My guess is the chance is quite slim, and in any case you would have time to get them retracted back in via a crew repair if absolutely necessary.  An MCT is not going to be opening and closing heat shield doors much more than a Shuttle did.  It will need to open and close them once on the way to Mars, and once on the way back.  For landing on both Mars and Earth you don't need to open heat shield doors whatsoever, as you can use the side-mounted Raptors and landing legs to touch down safely.

Uhm, the Shuttle orbiter NEVER opened its gear doors in space. They were REFURBISHED after landing and SEALED so they would provide continuous TPS coverage. If they opened prior to reentry and closed the danger that they could have a burn through was SIGNIFICANT from everything I've read. TPS "doors" that can be opened and closed have in fact NOT been demonstrated as far as I've been able to find. Engine protective doors were found be superfluous on the SERV design ONLY because the vehicle was wide enough and base heating low enough (due to a VERY light loading on landing) that they were not needed.

You COULD avoid the issue completely and use the landing engines to take off again. Then use the entire TPS base as a landing gear :)

Randy
Title: Re: MCT Speculation and Discussion Thread 3
Post by: RonM on 04/27/2015 06:09 PM
Wheels are harder than it seems on Mars - or any near vacuum body. I don't think it is realistic that massive landers massing 100+ tonnes can be supported by wheels. Just look at how the MSL wheels are surviving. The lander will also be VERY heavy when fully loaded with propellants for departure.

No, IMO you need to plan on landing them where you need them. If you can't do precision landing yet, you probably should not start a colony.

Nobody jacks up a fully loaded aircraft why would you assume they do so for an MCT? :) At landing it will be almost empty of propellants so its FAR from as heavy as you seem to be thinking.

"Landed where you need them?" Nice idea but how ACCURATE does that have to be? You "need" not to put the colony structure in danger, nor other already landed MCTs. 2km? 5km?

If you have a colony you will need a LOT more accuracy, why else prepare pads? I imaging the requirement that you need to have pin-point accuracy. +/- just a few meters.

Yes, accuracy will be required to support a colony. Pin-point accuracy won't be difficult using radio beacons at the pad.

To minimize danger to the colony, the pads might be some distance away with berms between the pads and the colony. No need to move the MCT. Vehicles can be used to move cargo, fuel, and personnel.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: RanulfC on 04/27/2015 06:11 PM
If you have a colony you will need a LOT more accuracy, why else prepare pads? I imaging the requirement that you need to have pin-point accuracy. +/- just a few meters.

Part of the point was you actually don't NEED pads in the fist place :) But even with that amount of accuracy it would be preferable to have the landing and take off areas surrounded by berms to avoid the issue. THAT amount of accuracy and the main criteria will be noise not debris anyway :)

Randy
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lars-J on 04/27/2015 06:14 PM
If you have a colony you will need a LOT more accuracy, why else prepare pads? I imaging the requirement that you need to have pin-point accuracy. +/- just a few meters.

Part of the point was you actually don't NEED pads in the fist place :) But even with that amount of accuracy it would be preferable to have the landing and take off areas surrounded by berms to avoid the issue. THAT amount of accuracy and the main criteria will be noise not debris anyway :)

Randy

Of course there will be berms... That's part of the need for pinpoint accuracy. You can't build berms *everywhere*. There will need to be a number of dedicated prepared pads with berms to direct exhaust away from the colony and other pads. Hardening the surface will also reduce the debris that is ejected.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Impaler on 04/27/2015 06:59 PM
I think it's more likely the berm will be OVER the colony, aka structures burried under a few meters of regolith.  You could littarlly land right next to that if need be and throw all kinds of rock at it without doing a thing.

The stuff that we should worry about are solar-panels, scientific instruments, surface vehicles not inside garages, thermal radiators etc etc.  These things might be protected by individual berms or placed at a distance from the colony.  As we would expect their to be a fairly consistent ground-track approach path and departure path from the MCT in an east-2-west arrangement we would want the bulk of the colony either north or south of that line to minimize the chance for a crashed vehicle hitting anything.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: TomH on 04/27/2015 07:42 PM
THAT amount of accuracy and the main criteria will be noise not debris anyway :)

The atmospheric density on the surface of Mars is 0.59% that of Earth. There is almost no medium through which to transmit sound waves.

Electromagnetic waves travel through the vacuum of space/time with no other medium necessary. They all travel at 186kmi/sec. Acoustic waves must travel through physical matter. Density is a factor of the velocity and intensity at which acoustic waves travel through a physical medium. CO2 would make the pitch lower, and scarcity of gasseous atoms/molecules would mean almost no sound through the Martian atmosphere.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: JasonAW3 on 04/27/2015 08:25 PM

Uhm, the Shuttle orbiter NEVER opened its gear doors in space. They were REFURBISHED after landing and SEALED so they would provide continuous TPS coverage. If they opened prior to reentry and closed the danger that they could have a burn through was SIGNIFICANT from everything I've read. TPS "doors" that can be opened and closed have in fact NOT been demonstrated as far as I've been able to find. Engine protective doors were found be superfluous on the SERV design ONLY because the vehicle was wide enough and base heating low enough (due to a VERY light loading on landing) that they were not needed.

You COULD avoid the issue completely and use the landing engines to take off again. Then use the entire TPS base as a landing gear :)

Randy

True enough, or have the gear fold down from the spacecraft sides...  Gee, wonder where THAT came from...?

However; Setting up landing gear bays that could be opened and resealed in space really doesn't strike me as that difficult.  Simply use a system similar to how the cabin doors on a jet work.  Shouldn't need to much pressure behind the gear doors to hold them shut in orbit.

     On the other hand, the TIRES on the landing gear were designed as very high pressure tires, (I heard someplace 150 PSI, but that could be 747 tires I'm thinking about) but ONLY in an atmosphere with a pressure around 14 PSI.  Exposing the tires to the vacume of space and either the direct heat of the sun, or the cold of the dark would almost assure explosive failure!  And THIS would be very, VERY bad for the space craft!  in fact, It'd probably make Apollo 13 look like a spring picnic in comparison.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: JasonAW3 on 04/27/2015 09:18 PM
Interesting note here;

     It occures to me that, if the MCT lander is supposed to be able to land on Earth, assuming a propulsive landing, then at .38 Gees, (Mars Gravity) it should be possible to propulsivly land about double the total mass of the MCT crew and passengers and their personal effects on Mars.  (This is also assuming a parachute assist, if needed).

     That said, and again, assuming a similar arrangement of landing thrusters as on the Dragon V2.0, it should be sufficent to land a fairly large cargo module under it.  (Note; as this cargto module is essentially on a one way trip, it would only require sudfficent TPS to handle one Mars atmospheric entry.  Plus, should the TPS be thick enough, it could also be used as insulation against the martian surface, leeching heat out of the module.)

     So, assuming the return mass of the MCT is about 60 tons, including any returning personnell, equipment and samples, that would mean that the Launch Vehicle lofting the MCT and cargo module would have to loft approximately 120 tons each launch, to hook up with the carrier vehicle already in orbit and refurbed there as well.

As this is considered already within the launch capibilities of the BFR, then to mount the first Mars expedtion, it would likely take five to six launches.

  First launch is to put the MCT Carrier into orbit.  It could be automated to unfold and prepair for the next launch.

  Second launch, about 100 tons fuel in 20 ton fuel tank, mounted on MCT carrier.

     Third launch, First MCT and cargo Module.  Links to MCT carrier and launches on automated flight to Mars.
     Upon arrival, MCT and cargo module detach and begin landing sequence.  Just above landing site, cargo module is detached and lowered on teathers from sides of MCT lander.  Once on ground, MCT detatches, flys to nearby spot and lands.  Rover robots reploy solar panels snd set up IRSU refueling rig, while cargo module deploys two manned rover vehicles, both pressurized.  All rovers begin site preperation while the MCT begins making fuel for return trip.  MCT returns to Earth.

     Fourth launch; Refurbishment equipment for MCT Carrier and Workshack station for MCT Carrier operations.

     Fifth launch; fuel for MCT Carrier.  Fuel tanks swapped out. Empty returns to Earth on upper stage for refurbishment and reuse.  (This assumes a TPS shroudto protect said tankage upon reentry of upper stage).

     Sixth launch; First Mars team Launched to Mars. Between 16 to 30 people for first team, (Psychological reasoning based upon early 20th century polar expeditions) Upon arrival, Mars atmospheric entry after MCT Carrier detachment.  At site, hover and drop cargo module. Land MCT lander nearby but not too close to either first MCT lander or cargo modules.  Cargo Modules placed in close proximity and linked and sealed for habitat and growing space.  Areas bermed around MCT landers as blast debris suppression pits.  Second MCT deploys solar panels and begins IRSU refuelling operations.

     Once first mission complete, some personnel may stay behind while the rest launch back to Earth on first MCT lander when the MCT Carrier arrives.  Upon Earth return, MCT lander's fuel tanks are topped off and MCT returns to Earth after 3 or 4 week quarentine in orbit.  (During this, time active excercising will be done to prepare returning personnel for Earth Gravity.  This is assuming that artificial gravity was not generated on the trip out and back)

     After return, MCT Carrier is outfitted to carry 2 MCT landers and cargo modules, wich includes increased fuel loads.  At this point second MCT Carrier already outfitted for dual MCT lander carriage is launched and outfitted.  Unless MCT carriers are outfitted with advanced high powered drives, (Assuming Vasmier or NERVA) at least 1 MCT carrier would be launched from Earth while the other is homebound from Mars.  Likely there may be some overlap in missions assuming at least 3 or more MCT carriers on continious round trips as circumstances allow.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: TomH on 04/27/2015 09:30 PM
On the other hand, the TIRES on the landing gear were designed as very high pressure tires, (I heard someplace 150 PSI, but that could be 747 tires I'm thinking about) but ONLY in an atmosphere with a pressure around 14 PSI.  Exposing the tires to the vacume of space and either the direct heat of the sun, or the cold of the dark would almost assure explosive failure!  And THIS would be very, VERY bad for the space craft!  in fact, It'd probably make Apollo 13 look like a spring picnic in comparison.

What matters is the pressure differential. 150 PSI on the interior is offset by that 14 PSI on the exterior for a difference of 136. A tire that has internal pressure of 136 with a vacuum pressure of 0 on the exterior is experiencing the same situation as the 150 PSI tire at 1 earth atmosphere pressure on the outside. It's not going to explode. Expose it to unfiltered UV and the polymers will break down quickly, so the polymers must be protected from that. Heat and cold can take a toll as well, but by itself, that pressure is not a problem. Do you see any astronaut EVA suits exploding?
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Joffan on 04/27/2015 09:45 PM
What matters is the pressure differential.
Yes indeed. This is not well understood and it's a common mistake to think that a pressure differential in a "hard" vacuum is somehow more powerful than the same pressure differential from normal conditions. Especially when comparing containing 1 bar in vacuum to, say, containing 2 bar in 1 bar ambient. As in, a rather deflated car tire, reading 15psig.

Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/27/2015 09:54 PM
I don't know if I mentioned it or not but the BEST practice is in fact to tow a launching MCT onto a launch pad surrounded by a berm to protect everything from debris of the blast off. You could do without the individual berms that way. You probably would need a large area that with a blocking berm for landing after which he MCT would be towed to the other side of the berm for unloading/loading and maintenance. Then its towed to the launch pad, fueled any crew passengers board and launch. Repeat with the next outgoing launch.

I have put some thought into this, and I do not think the MCT will be towable. The general consensus is the MCT will mass around 60-75MT. On Mars it will weigh 20-25MT empty.

I find it hard to conceive of light weight landing pads or legs being able to stand up to the lateral loads that towing would put on them. And some type of wheels that could castor would also need be added. After landing and unloading, perhaps the MCT could be jacked up and wheels placed under the landing pad or legs.

The tow truck would be light weight due to being transferred there by the MCT and would have very little traction. It could be ballasted by Mars dirt or all the iron meteorites laying around.

It will definitely make the logistics easier if the MCT can be towed around and reduce the need for pin-point landing accuracy. This adds another difficult requirement to the design of the MCT.

There's been concept with towable landers before.  It wouldn't necessarily be too hard to do unto itself. See below.

However, as I was pointing out to Hyperion, MCT will be different than these various other landers, shaped like these or shaped like capsules, etc, because MCT will be a)  reusable, and B) need to get itself back off the ground.  Which doesn't apply to almost all Mars lander concepts.

That makes capsule shapes problematic, and heat-shield-less and horizontal landers pretty much impossible.  What's really left is the biconic aeroshell vertical lander, which is why I keep coming back to that shape as the most logical until I see some info from SpaceX showing otherwise.  (They may have some clever concept that none of us are picturing). 

But I agree, I don't think a biconic aeroshell vertical lander can be feasibly towed once on the ground any more than F9 will be.  I'm sure they'll crane the F9 core onto some transporter to move it from the landing area back to the launch facility.  They won't be able to to that with MCT, so MCT will sit where it lands. 

But I don't really see that as a big deal.  YOu just land them a few km's from the colony, or however far they observe debris beign kicked up by the landing and lift off engines.  Landing will be a lot less thrust so that's the less important I'd imagine.  MCT's going to be much heavier at lift off, and would kick up far more debris.  But as long as the legs are designed to withstand that blast, I don't know it'll be any issue.  Once there were some sort of real colony going, they may assembly some sort of vehicle which can go under an empty MCT, jack it up off the ground, and then slowly move it to a new position prior to launch.  That's be a substantial vehicle which would need to be brough to Mars in pieces and assembled there probably though.  I'm guessing they'll just land them away from the colony, and land them away from each other.  One critia in selecting a location for a colony would be to have a nice flat area for several km's next to it.  The MCT's can refuel themselves with on board equipment, and people and equipment can be transported from MCT to the colony and back again via rovers.  Some sort of large soloar array would be deployed next to the MCT to power it to make the methane for the return trip.  Another MCT coming down would land somewhere far enough away that it won't kick up debris on landing or on take off. 

And here's the thing.  Once a location has had an MCT land and/or take off from it, most of the small dusty regolith will probably be blasted away from it.  After that, it'll be rock or hard packed regolith and will kick up much less debris on subsequent landings and launches.  So that location would then be a nice, excavated location to make a regular landing spot. 

Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/27/2015 10:14 PM
Lets try to do some volume estimates for MCT and think about how much propellent that would hold.

I'm imagining a 15 m diameter Dragon v2 shaped capsule.  That is almost exactly 4 times the diameter of Dragon meaning that the MCT would have 66x the volume of Dv2.  Dragon v2 I estimate to be 24 m^3 in its EXTERIOR dimensions by calculating it as a simple truncated cone 3.7 m in diameter, 4.7 m high and with a 15 degree wall slope.  This means the capsule style MCT is ~1500 m^3

Dry mass of Dragon v1 was 3180 kg (according to some VERY old numbers so take it with a grain of salt).  Assuming mass directly scaling with volume that would mean a ~200 MT vehicle before any payload or propellents.  But many parts of the vehicle will not scale cubically, such as the heat-shield which while 16x larger in area would not need to become 4x thicker.  I'm thinking 100-150 MT is a reasonable dry mass range.

Allocation of volume, lets go with 100 m^3 for integrated crew space, 500 m^3 for cargo-hold inside which additional passenger accommodation modules can be carried and connected with the integral space.  Take another 100 m^3 for miscellaneous uses and that leaves 800 m^3 in propellent tanks.  LOX/Methane propellent averages out to right around 1 MT per m^3 so we would be looking at take off propellent of up too 800 MT.

I'm imaging a Saturn S-II stage with integrated crew and cargo on it, and legs on the bottom.

The S-II was 24.8m long and 10m wide.  Deducting 1.8m for the engines, that would give a cylindrical volume of about 1800m^3.  It'll actually be a bit less than that because there will be domes on the top and bottom rather than flat ends, but you get the idea. 
So MCT does't necessarily need to be 15m wide or whatever.  It can hold quite a bit being 10m wide.  If less than the 1700-ish m^3 volume is needed, then it'd be shorter.

Maybe MCT will be a couple meters wider and a bit shorter, to make it more stable.  SpaceX can figure out those things.  But this is a pretty reasonable starting point.  And upthread I already estimated (roughly) that if the S-II were fully fueled in LEO, it should be able to push over 200mt through TMI.  derate for the lower ISP Raptors vs. J2 (only 40s impulse) and you might be in the 180-190mt range for MCT with a similar -mass- of propellant.  But as the LCH4 is quite a bit more dense than the LH2 in the S-II, there's a pretty reasonable change that an MCT with S-II range performance would be smaller than the S-II.
Add a crew deck and cargo deck to that, and you are back to about the size of the S-II (roughly).

So again, picture the S-II, with a TPS on one side and legs on the bottom, and I think you have a ball park approximately of MCT.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/27/2015 10:20 PM
biconic looks good. You are correct, legs not a problem. Just wrong rendering: TPS must be on the opposite side from ramp.

I didn't draw it, I just borrowed it.  But yea, if thee's a ramp, it'd make no sense to have it open through the TPS on the ventral side.   It'd open out of the dorsal side.

Same with any sort of solar arrays that they may use for power in space.  That saves having to have doors in the TPS system all together.  Same with the docking hatching.  It'd be on the ventral size, like it was on the shuttle.  They opted not to have a docking hatch in the nose of the Shuttle for a reason I think...
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/27/2015 10:45 PM
It's almost like dear Lobo did not glance at the thread-related materials found in that level of NSF that must not be named. ;)  No doubt he'll go back over there and look at them again before, right? :)  There are ways of going fully reusable with a capsule design that has heat shield doors, Lobo.  You use 8 Raptors on the sides (which would produce about 350 seconds of Isp on Mars) that you would use to land on Mars or Earth.  Then, when you need to launch off Mars, you open up the doors.  Multiple vacuum-optimized Raptor engines would then blast you into LMO and later perform the TEI burn.  So long as you refuel on Mars, an MCT will be large enough to make it all the way back to Earth on only one stage.  Full reuse is just as possible via a capsule design as your preferred design. 

I haven't poked around there recently, no.  I'll go see if there's something there that blows my hypothosis all to heck.  Heheheh.


With regards to where the heat shields went, they either were retracted back into the vehicle or were deployed and disposed during Martian atmospheric entry.  Obviously they're not perfect analogies for an MCT design, but they should prove that capsule designs are a very plausible MCT design option.  Alterations can be made after all!


Plausible?  Yes, of course.  I've said that.  You could have the thing transform into a giant robot too if you wanted it bad enough.  But I'll ask the question, "why?".  Why have all of those doors in your heat shield when you don't have to?  Unless for some reason a biconic is impossible to make safely stable during EDL...as by design it won't be as stable as a capsule...why not go with a biconic?
Also, a biconic can share the same tanking and tooling used to make the MCT booster.  A giant DRagon shaped MCT would need  very separate type of manufacuring to make.  Just like Dragon doesn't share anything with F9 or F9US. 
A biconic also has more surface area, and the atmosphere will slow it down more....which is why biconics have often been favored in the various design reference missions over the years.


Heat shield doors (successfully) protecting spacecraft reentering Earth's atmosphere is nothing new, as they have never failed to protect the Shuttles from harm.  This is why Dragon 2 is going to use them for its landing gear.  What did in Columbia was foam detaching from the external tank and striking the orbiter's wing, damaging some of the heat shielding found there.  I'm surprised Jim didn't beat me to pointing that out.  If heat shield doors can protect landing gear through over 133 reentries, then why not engines? 

.......

Never been one?  Why exactly are we not counting a Shuttle orbiter?  That craft opened its heat shield doors after a reentry in order to land, and those doors were closed again for the next mission's reentry.  If I were to survey our experts, how many of them would say that opening and closing the Orbiter's landing gear doors once in space would likely result in a loss of mission?  My guess is the chance is quite slim, and in any case you would have time to get them retracted back in via a crew repair if absolutely necessary.  An MCT is not going to be opening and closing heat shield doors much more than a Shuttle did.  It will need to open and close them once on the way to Mars, and once on the way back.  For landing on both Mars and Earth you don't need to open heat shield doors whatsoever, as you can use the side-mounted Raptors and landing legs to touch down safely. 


I -am- counting the shuttle orbiter!  Have those landing gear doors ever been opened in space?  Not that I'm aware of.  (someone correct me if that's wrong)
Morever, the question should be asked if the Shuttle can even retract it's gear on it's own?  Do they close again like an aircraft's?  Or deploy only?  Why make them retract automatically if they'll never have to?  They'll be closed in the VAB manually prior to integration with the ET, and reset and checked prior to the next mission.  Maybe they are passively spring loaded with a latch?, as that'd be a more reliable system than hydraulic or electric actuators that deploy and then retract them.  Wasn't Dreamchasers supposed to be like that?

But certainly a landing gear deployment in space would cause of LOC if they couldn't retract.

But regardless, I'm not aware that they ever have, even if they can.  Not saying they -couldn't- be made to.  They made the payload bay doors open and retract reliably.  Same with X-37B.  I'm just saying to my knowledge, there's never been a door open through the TPS in space and then close again.  Maybe because there's no reason to.  Maybe because they try to avoid having any hatches that do need to open in space open through the TPS for safety.

But as you say, if there's sidewall mounted landing thrusters, then any heat shield door don't need to be opened during the stressfull EDL.  But they will need to close again properly on the ride home prior to Earth EDL. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: TomH on 04/27/2015 10:48 PM
What matters is the pressure differential.
Yes indeed. This is not well understood and it's a common mistake to think that a pressure differential in a "hard" vacuum is somehow more powerful than the same pressure differential from normal conditions. Especially when comparing containing 1 bar in vacuum to, say, containing 2 bar in 1 bar ambient. As in, a rather deflated car tire, reading 15psig.

Yes, many almost think of it like a negative number, or of the ratio rising toward infinity and thus somehow inducing material rupture/explosion.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/27/2015 10:49 PM
Uhm, the Shuttle orbiter NEVER opened its gear doors in space. They were REFURBISHED after landing and SEALED so they would provide continuous TPS coverage. If they opened prior to reentry and closed the danger that they could have a burn through was SIGNIFICANT from everything I've read. TPS "doors" that can be opened and closed have in fact NOT been demonstrated as far as I've been able to find. Engine protective doors were found be superfluous on the SERV design ONLY because the vehicle was wide enough and base heating low enough (due to a VERY light loading on landing) that they were not needed.


Ahhh...I posted my last before I read this.  Thanks for the input Randy.  That's what I'd thought, but didn't know for sure.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/27/2015 10:51 PM
Wheels are harder than it seems on Mars - or any near vacuum body. I don't think it is realistic that massive landers massing 100+ tonnes can be supported by wheels. Just look at how the MSL wheels are surviving. The lander will also be VERY heavy when fully loaded with propellants for departure.

No, IMO you need to plan on landing them where you need them. If you can't do precision landing yet, you probably should not start a colony.

Nobody jacks up a fully loaded aircraft why would you assume they do so for an MCT? :) At landing it will be almost empty of propellants so its FAR from as heavy as you seem to be thinking.

"Landed where you need them?" Nice idea but how ACCURATE does that have to be? You "need" not to put the colony structure in danger, nor other already landed MCTs. 2km? 5km?

If you have a colony you will need a LOT more accuracy, why else prepare pads? I imaging the requirement that you need to have pin-point accuracy. +/- just a few meters.

Yes, accuracy will be required to support a colony. Pin-point accuracy won't be difficult using radio beacons at the pad.

To minimize danger to the colony, the pads might be some distance away with berms between the pads and the colony. No need to move the MCT. Vehicles can be used to move cargo, fuel, and personnel.

I imagine lessons learned from landing both Dv2 and the F9 booster over the next several years will play a big part in their approach to landing MCT.  They've already gotten very close to target, just need to work out some stability/horizontal vector issues.
I think pinpoint accuracy on Mars should be pretty easy once they have beacons and/or GPS sats in place.  And time will allow them to work out the stability and approach.

If they can get Dv2 down safely reliably, I don't think MCT will be a problem.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/27/2015 10:57 PM

     On the other hand, the TIRES on the landing gear were designed as very high pressure tires, (I heard someplace 150 PSI, but that could be 747 tires I'm thinking about) but ONLY in an atmosphere with a pressure around 14 PSI.  Exposing the tires to the vacume of space and either the direct heat of the sun, or the cold of the dark would almost assure explosive failure!  And THIS would be very, VERY bad for the space craft!  in fact, It'd probably make Apollo 13 look like a spring picnic in comparison.

I think there's ways around that.

And as a few mention just up thread, there's no reason you can't have a pressurized tire in a vacuum.  The tire doesn't know there's a vacuum on the outside, it just knows what the pressure differential is from outside to inside.  Below modules would be inflatable in a hard vacuum after all.  You just need less pressure in the tires.

However, I think the risk of bad things happening if there's a tire leak is far greater than it is for your car.  I think that's more the issue.  If MCT were to have tires on it's landing gear....presumably so it could be towed around on the surface or something? (can't think of any other reason we're even talking about it otherwise).  And one were to pop during the trip out, or just go flat, that could cause various issues, not the least of which is being unstable on a flat tire ont he surface and risking tipping over. 

So if there are any need for wheels on Mars, something like this can be used.  Just probably with lighter and more UV and temp resistant elastomers than we use for typical tires.  You can afford $20,000 tires on a rover that can better withstand the low temps and UV radiation on Mars than regular tire rubber, and are half the weight or something...when you are paying for a Mars mission.



Title: Re: MCT Speculation and Discussion Thread 3
Post by: Impaler on 04/28/2015 01:17 AM
I'm imaging a Saturn S-II stage with integrated crew and cargo on it, and legs on the bottom.

The S-II was 24.8m long and 10m wide.  Deducting 1.8m for the engines, that would give a cylindrical volume of about 1800m^3.  It'll actually be a bit less than that because there will be domes on the top and bottom rather than flat ends, but you get the idea. 
So MCT does't necessarily need to be 15m wide or whatever.  It can hold quite a bit being 10m wide.  If less than the 1700-ish m^3 volume is needed, then it'd be shorter.

Maybe MCT will be a couple meters wider and a bit shorter, to make it more stable.  SpaceX can figure out those things.  But this is a pretty reasonable starting point.  And upthread I already estimated (roughly) that if the S-II were fully fueled in LEO, it should be able to push over 200mt through TMI.  derate for the lower ISP Raptors vs. J2 (only 40s impulse) and you might be in the 180-190mt range for MCT with a similar -mass- of propellant.  But as the LCH4 is quite a bit more dense than the LH2 in the S-II, there's a pretty reasonable change that an MCT with S-II range performance would be smaller than the S-II.
Add a crew deck and cargo deck to that, and you are back to about the size of the S-II (roughly).

So again, picture the S-II, with a TPS on one side and legs on the bottom, and I think you have a ball park approximately of MCT.

We are very close on volume estimates 1500 vs 1700.  The surface areas are 176 vs 230 so your bi-conic has a lower basaltic-coefficient (assuming the same mass), that paired with the superior lift-2-drag ratio of a biconic over a capsule would make for a considerably improve EDL, and reduced retro-propulsion needs.

I'm wondering how such a vehicle serves as a 2nd-stage for launch from Earth though.  If you have similar volume for cargo, habitat and systems as I estimate (700 m^3 total) your left with only 1000 MT of propellents.  We know all stages under the MCt will be reusable and if the F9 reusables staging is a reliable indicator then the first stage will only do about 2 km/s (staging at Mach 6), leaving a whopping 7-8 km/s for this 2nd stage vehicle to do.  Full to the brim with propellents it would only be able to do ~140 MT to LEO, minus the 100 MT payload that leaves an impossibly small 40 MT for the dry mass of the MCT.  It seems that a normal 2nd stage is going to be necessary in the stack to deliver 3-4 km/s before the MCT separates and acts as the 3rd stage.

This is my central argument that given the reasonable mass/volume of the MCT as a lander on Mars, it can't do the whole job of being a second stage during Earth launch when it is loaded with cargo.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 04/28/2015 03:24 PM
Heat shield doors (successfully) protecting spacecraft reentering Earth's atmosphere is nothing new, as they have never failed to protect the Shuttles from harm.  This is why Dragon 2 is going to use them for its landing gear.  What did in Columbia was foam detaching from the external tank and striking the orbiter's wing, damaging some of the heat shielding found there.  I'm surprised Jim didn't beat me to pointing that out.  If heat shield doors can protect landing gear through over 133 reentries, then why not engines?

This must be L2 information because the DV2 was shown that the legs extend FROM the heat-shield and there ARE no doors.
Quote
I'm sure it -could- be made to work.  But why force it when you don't have to?  A biconic "wingless shuttle" design solves all of that.  You can even get around needing to have legs extend through the heat shield on its' side in various ways, include just having jackstand like legs come straight down from the MPS (if the diameter is wide enogh to be stable, similar to your pictures #2)  or you could have blisters around the MPS housing the legs.  With a shape not unlike your image 1.  The legs could fold out from those blisters to give MCT a wider stance on the surface. 

The one alternative to legs coming through the heat shield is to have them extend out from the sides of the MCT.  They might be embedded in the side or more exposed (and protected by heat shielding). 

Or like the Stage-1 legs they could fold up 'inside' the heat shadow of the shield or TPS :)
Quote
Because while there are vehicles which have had doors in their TPS, there's never been one that's had to close those doors again prior to anther reentry.  They open once after atmospheric entry and that's it.  They're closed on the ground an checked out before sent back up.  So avoiding that dynamic portion of the heat shield and making it all static/passive increases mission safety.

Never been one?  Why exactly are we not counting a Shuttle orbiter?  That craft opened its heat shield doors after a reentry in order to land, and those doors were closed again for the next mission's reentry.  If I were to survey our experts, how many of them would say that opening and closing the Orbiter's landing gear doors once in space would likely result in a loss of mission?  My guess is the chance is quite slim, and in any case you would have time to get them retracted back in via a crew repair if absolutely necessary.  An MCT is not going to be opening and closing heat shield doors much more than a Shuttle did.  It will need to open and close them once on the way to Mars, and once on the way back.  For landing on both Mars and Earth you don't need to open heat shield doors whatsoever, as you can use the side-mounted Raptors and landing legs to touch down safely.

Uhm, the Shuttle orbiter NEVER opened its gear doors in space. They were REFURBISHED after landing and SEALED so they would provide continuous TPS coverage. If they opened prior to reentry and closed the danger that they could have a burn through was SIGNIFICANT from everything I've read. TPS "doors" that can be opened and closed have in fact NOT been demonstrated as far as I've been able to find. Engine protective doors were found be superfluous on the SERV design ONLY because the vehicle was wide enough and base heating low enough (due to a VERY light loading on landing) that they were not needed.

You COULD avoid the issue completely and use the landing engines to take off again. Then use the entire TPS base as a landing gear :)

Randy
Pray tell, how did the SSMEs get propellant from the External Tank, if not from an interface of some sort that closed in space? :)
Title: Re: MCT Speculation and Discussion Thread 3
Post by: sheltonjr on 04/28/2015 04:27 PM
Here is my hypothetical MCT design based on the constraint of a 225 MT Fully Reusable BFR.

I also disagree about the two stage system. Inflatable tanks in the cargo hold are also not required.

Tanks above cargo gives the best layout and CG for landing. So I have chosen it believing the plumbing problem will be solved. If the engines are side mounted, It may even be easier.

A crew MCT will not be able to get 100 MT of cargo to Mars. Crew support equipment and systems will subtract from the available 100 MT.

Dragon derived 15 m capsule with 15 degree side-walls. Capsule is 25 m tall not including the heat shield hemisphere. Top diameter dome 1.6 m across.

The MCT is divided into 6 Floors from bottom to top with the following characteristics:

| Floor                        | Height (m) | Usable Pct (%) |Volume (m3) | Area (m2),(ft2) | Fuel (MT) |
|--------------------------|-------------|------------------|--------------|------------------|-----------|
| Upressurized Cargo   | 2.5            | 95                    | 383              | 177, 1902         |                |
| Habitat                     | 2               | 95                    | 257              | 146, 1577         |                |
| Pressurized Cargo     | 2               | 95                    | 216              | 124, 1339         |                |
| Systems                   | 1.5            | 95                    | 138              | 104, 1121         |                |
| LOX                          | 4.6            | 97                    | 309              | N/A                  | 361         |
| CH4                          | 12.4          | 97                    | 258              | N/A                  | 112         |

MCT Empty Mass = 65 MT
Cargo <= 100 MT
Total Fuel = 473 MT

MCT Launches with cargo and crew and 60 MT of fuel to awaiting BFR Depot to fully fuel with additional 400 MT of fuel. Performs TMI and EDL at Mars with a DV of 5036 m/s. Each Mars MCT will only require 2 BFR Tankers.

MCT Refuels on Mars utilizing 473 MT of ISRU fuel and returns to Earth with up to 10 MT of crew/cargo with a DV 7405 m/s.

Distributed MCT engines require a minimum thrust around 50 MT and 250 MT Maximum.

What amount did you set aside for ship power generation?  Waste recycling for 100.  Is this amount your 'systems' set aside? 

My concept for power generation is solar panels that would fold up like the petals of a flower from the bottom of the MCT towards the top. The actuator at the bottom would be similar to the ones used by the grid fins, being able to pitch and roll. This would require a stiff composite panel for the solar panels to mount too and perhaps a thin layer of Pica-X to protect it from the heat.  While this does add weight to the MCT, These fold down solar panels would work both in space and on Mars. Being able to roll the panel towards the Sun will increase their performance.

If approximately %50 of the MCT surface area can be covered by these solar panel "petals", They would generate 92KW in Earth orbit and 40KW on Mars. Calculations are based on these solar panels: http://www.azurspace.com/index.php/en/products/products-space/space-solar-cells

The systems level would contain all the systems used on the MCT for ship operations; Flight control computers, cryo-coolers, Communications and telemetry; For Crewed MCTs it would also include all the systems for life support and entertainment including water and air recycling, etc..  They Systems floor would provide hallways to allow easy access to all equipment and spares so the MCT can be maintained by the crew in Space and on Mars. 

I do not think a MCT this size can support 100 people. I would not want to be on it with that many people. The first three floors if only used for crew would be the size of a large house at around 4000 ft2. And Zero gravity will make utilization of that space more efficient. That would be very packed house for 5-6 months.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/28/2015 04:50 PM
We are very close on volume estimates 1500 vs 1700.  The surface areas are 176 vs 230 so your bi-conic has a lower basaltic-coefficient (assuming the same mass), that paired with the superior lift-2-drag ratio of a biconic over a capsule would make for a considerably improve EDL, and reduced retro-propulsion needs.


Which I'm sure is why the biconic shape has been a favorite in many concepts for a Mars lander in many concepts over the years.  Although the traditional capsule shape is what it is becuase it's inherrently self orienting during EDL.  which is why it's been used so often over the years....even on most Mars landers to date.  But a really large lander on Mars has needs that make alternative shapes with other benefits in consideration.


I'm wondering how such a vehicle serves as a 2nd-stage for launch from Earth though.  If you have similar volume for cargo, habitat and systems as I estimate (700 m^3 total) your left with only 1000 MT of propellents.  We know all stages under the MCt will be reusable and if the F9 reusables staging is a reliable indicator then the first stage will only do about 2 km/s (staging at Mach 6), leaving a whopping 7-8 km/s for this 2nd stage vehicle to do.  Full to the brim with propellents it would only be able to do ~140 MT to LEO, minus the 100 MT payload that leaves an impossibly small 40 MT for the dry mass of the MCT.  It seems that a normal 2nd stage is going to be necessary in the stack to deliver 3-4 km/s before the MCT separates and acts as the 3rd stage.

This is my central argument that given the reasonable mass/volume of the MCT as a lander on Mars, it can't do the whole job of being a second stage during Earth launch when it is loaded with cargo.

I agree that 40mt seems a bit lean for dry mass of MCT.  The dry mass of the S-II was 45mt.  And while that's 1960's tech, it was still a fairly well designed/light stage of it's size.  Today they could probably make such a stage a little lighter, but I'd have a hard time thinkign MCT could be less than the mass of the S-II at a minmum.  I'm thinking at least 50-60 for some reason.

I also agree that the booster would stage pretty early, so as to be "low and slow" for RTLS.  That's why I very much like the Saturn INT-21 as an analog here.  The S-1C was a large booster that also staged low and slow.  The S-II was a very large 2nd stage which provided all of the rest of the dV needed to get the payload to LEO.   If INT-21 had every flown as INT-21 anyway.  It essentially did when putting Skylab in orbit.
It was estimated that INT-21 could have put almost 120mt into LEO.  Plus the dry mass of the S-II at 45mt plus (I'm assuming) a couple of tonnes of residuals at SECO.  We'll call that 160mt to LEO in total roughly.
That's be 100mt of cargo plus a 60mt MCT.  Which may be a little skinny still, but now we're at a very plausible point.
J2 had 40s better ISP than Raptor, so MCT would need a little more propellant to get that same 160mt gross to LEO.  But LCH4 is a lot more dense than LH2. 

So you calculated 140mt to LEO.  The good news is we're actually pretty close to 160mt (minimum) with that.  We just need to get another 20mt or 30mt to LEO.  So as an integrated spacecraft/upper stage, how large does it need to be to get there?  Play with MCT/S-II analog's size until you get say 160mt to LEO, or 170mt.  What size is that stage now?  If it's too tall to be a stable lander, we can make it 11m instead of 10m wide, or even 12m.  Again, just using the S-II as an analog to demonstrate that MCT might not need to be some 15+m wide spacecraft.  10m may work, or just a bit wider.
The booster's width and height then would just be set to match MCT once MCT's dimensions are established.

Keep in mind that until we hear something to the contrary, I think we have to assume that MCT will take itself from the surface of Mars all the way back to the surface of Earth itself.  So we're talking a big stage regardless.  Even if there were 2 stages under the MCT spacecraft, it would still need to be very large in order to do that.  Perhaps a bright bulb could calculate the volume and mass of methalox needed to get say 60mt of dry mass directly from the surface of Mars to the surface of Earth.  Let's see what we are talking about there, and then compare it with our methalox mass and volume needs to get 160mt gross from "low and slow" staging (2 km/s?) to LEO.  Assuming an integrated 2nd stage/MCT, MCT would need enough propellant capacity to do both of those functions, so whichever one is the greater propellant needed would be the driver in the size of MCT's tanks.



Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/28/2015 06:09 PM

With regards to where the heat shields went, they either were retracted back into the vehicle or were deployed and disposed during Martian atmospheric entry.  Obviously they're not perfect analogies for an MCT design, but they should prove that capsule designs are a very plausible MCT design option.  Alterations can be made after all!


Here is my hypothetical MCT design based on the constraint of a 225 MT Fully Reusable BFR.
I also disagree about the two stage system. Inflatable tanks in the cargo hold are also not required.
Tanks above cargo gives the best layout and CG for landing. So I have chosen it believing the plumbing problem will be solved. If the engines are side mounted, It may even be easier.
A crew MCT will not be able to get 100 MT of cargo to Mars. Crew support equipment and systems will subtract from the available 100 MT.
Dragon derived 15 m capsule with 15 degree side-walls. Capsule is 25 m tall not including the heat shield hemisphere. Top diameter dome 1.6 m across.


I want to point out another reason I don't think MCT will be a capsule shape.

Unlike every other capsule that's been designed in the history of space flight intended to enter into a planet with an atmosphere...MCT will have to get itself back off the ground.  Apollo didn't have to.  Dragon doesn't have to, CST-100 won't have to, Viking and the MER's and MSR didn't have to, etc.  So the capsule shape didn't have to house really large propellant tanks.  Just some small RCS thruster propellant tanks that can be stuffed into the spare geometric volume of the shape. 

But MCT will need a LOT of propellant to get itself back to Earth.  It'll in fact, be mainly a big fuel tank with a crew cabin bolted on, as opposed to most capsules to date which have been crew cabins (or cago volume) with a heat shield bolted on.  What's the most geometrically efficient shape to have large volumes of two propellants?  Cylinders....which is why almost all rocket stages have always been cylinders (with a few exceptions).   It'll be mainly a rocket stage...with a crew cabin bolted on.  Which is also why I think it'll do double duty as MCT's 2nd stage for ascent to LEO as well as get itself to Mars and back to Earth.  It'll already be essentailly a rocket stage by necessity.  Why pay to develop a separate dedicated 2nd stage for MCT.
A biconic aeroshell shape is also a cylinder.   Thus...logic would lean towards MCT being a cylindrical shape with a biconic EDL profile, as opposed to a capsule with a blunt body EDL profile.

So it's not just because you don't have to have doors in your heatshield for the engines with a cylindrical biconic shape....that's just a bonus.  It's not just that the biconinc has more surface area and better L/D ratio so it can milk more dV out of the atmosphere with more mild deceleration...that's just another bonus.  It's not just that you don't have to risk lighting your Raptor main engines on the Mars sruface and risk debris being blown up into your bottom heat shield damaging it....that's just another bonus with the TPS on the side. etc.

It's that MCT will be a big fuel tank with a crew cabin bolted on (top or bottom), and a cylinder is the most efficient geometry for a bi-propellant tank....and fortunately that happns to make a biconic shape.
With a giant capsule, you either have tanks with very odd/inefficient/difficult geometries to utilize that internal volume, or you have cylindrical tanks wrapped by a capsule shell...which then leaves a lot of inefficient internal volume around the tanks.  And as we know, in a space craft, no cubic inch of internal volume is desired to be wasted.

So let's not get too distracted with the concept of doors in the heat shield for the engines.  I don't think that's a show stopper given sufficient time and money during development.  But I also think it'd be desriable to avoid if possible, for the various reasons discussed.

NOTE:  I understand that this is not a true biconic shape.  I'm just using it as a reference term.  It'd be technically a "biconic nosed cylinder" I suppose.  Or a "blunt nosed cylinder", depending on what's determined to be better.

So, although the better L/D ratio of the biconic over the capsule is a bonus, not the driving factor in my opinion, I did find this bit interesting from wikipedia.

Quote
Biconic:  The biconic is a sphere-cone with an additional frustum attached. The biconic offers a significantly improved L/D ratio. A biconic designed for Mars aerocapture typically has an L/D of approximately 1.0 compared to an L/D of 0.368 for the Apollo-CM. The higher L/D makes a biconic shape better suited for transporting people to Mars due to the lower peak deceleration.
Arguably, the most significant biconic ever flown was the Advanced Maneuverable Reentry Vehicle (AMaRV). Four AMaRVs were made by the McDonnell-Douglas Corp. and represented a significant leap in RV sophistication. Three of the AMaRVs were launched by Minuteman-1 ICBMs on 20 December 1979, 8 October 1980 and 4 October 1981. AMaRV had an entry mass of approximately 470 kg, a nose radius of 2.34 cm, a forward frustum half-angle of 10.4°, an inter-frustum radius of 14.6 cm, aft frustum half angle of 6°, and an axial length of 2.079 meters. No accurate diagram or picture of AMaRV has ever appeared in the open literature. However, a schematic sketch of an AMaRV-like vehicle along with trajectory plots showing hairpin turns has been published.[12]
 
The DC-X, shown during its first flight, was a prototype single stage to orbit vehicle, and used a biconic shape similar to AMaRV.
Opportunity rover's heat shield lying inverted on the surface of Mars.AMaRV's attitude was controlled through a split body flap (also called a "split-windward flap") along with two yaw flaps mounted on the vehicle's sides. Hydraulic actuation was used for controlling the flaps. AMaRV was guided by a fully autonomous navigation system designed for evading anti-ballistic missile (ABM) interception. The McDonnell Douglas DC-X (also a biconic) was essentially a scaled up version of AMaRV. AMaRV and the DC-X also served as the basis for an unsuccessful proposal for what eventually became the Lockheed Martin X-33.

Another interesting bit from there was how apparently the AMaRV was able to make hairpin turns.  That indicates a pretty high level of aerodynamic steerability is possible with the shape. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: TomH on 04/28/2015 07:43 PM
| Floor                        | Height (m) | Usable Pct (%) |Volume (m3) | Area (m2),(ft2) | Fuel (MT) |
|-----------------------|-------------|------------------|--------------|------------------|-----------|
| Upressurized Cargo   | 2.5            | 95                    | 383              | 177, 1902         |                |
| Habitat                     | 2               | 95                    | 257              | 146, 1577         |                |
| Pressurized Cargo     | 2               | 95                    | 216              | 124, 1339         |                |
| Systems                   | 1.5            | 95                    | 138              | 104, 1121         |                |
| LOX                          | 4.6            | 97                    | 309              | N/A                  | 361         |
| CH4                          | 12.4          | 97                    | 258              | N/A                  | 112         |

MCT Empty Mass = 65 MT
Cargo <= 100 MT
Total Fuel = 473 MT

MCT Launches with cargo and crew and 60 MT of fuel to awaiting BFR Depot to fully fuel with additional 400 MT of fuel. Performs TMI and EDL at Mars with a DV of 5036 m/s. Each Mars MCT will only require 2 BFR Tankers.

MCT Refuels on Mars utilizing 473 MT of ISRU fuel and returns to Earth with up to 10 MT of crew/cargo with a DV 7405 m/s.

The CH4 is the fuel. You are using that word to mean the fuel and the oxidizer, which together are known as the propellant. You will be taken seriously by no one if you don't distinguish correctly between fuel and propellant.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: BobHk on 04/28/2015 09:37 PM
Here is my hypothetical MCT design based on the constraint of a 225 MT Fully Reusable BFR.

I also disagree about the two stage system. Inflatable tanks in the cargo hold are also not required.

Tanks above cargo gives the best layout and CG for landing. So I have chosen it believing the plumbing problem will be solved. If the engines are side mounted, It may even be easier.

A crew MCT will not be able to get 100 MT of cargo to Mars. Crew support equipment and systems will subtract from the available 100 MT.

Dragon derived 15 m capsule with 15 degree side-walls. Capsule is 25 m tall not including the heat shield hemisphere. Top diameter dome 1.6 m across.

The MCT is divided into 6 Floors from bottom to top with the following characteristics:

| Floor                        | Height (m) | Usable Pct (%) |Volume (m3) | Area (m2),(ft2) | Fuel (MT) |
|--------------------------|-------------|------------------|--------------|------------------|-----------|
| Upressurized Cargo   | 2.5            | 95                    | 383              | 177, 1902         |                |
| Habitat                     | 2               | 95                    | 257              | 146, 1577         |                |
| Pressurized Cargo     | 2               | 95                    | 216              | 124, 1339         |                |
| Systems                   | 1.5            | 95                    | 138              | 104, 1121         |                |
| LOX                          | 4.6            | 97                    | 309              | N/A                  | 361         |
| CH4                          | 12.4          | 97                    | 258              | N/A                  | 112         |

MCT Empty Mass = 65 MT
Cargo <= 100 MT
Total Fuel = 473 MT

MCT Launches with cargo and crew and 60 MT of fuel to awaiting BFR Depot to fully fuel with additional 400 MT of fuel. Performs TMI and EDL at Mars with a DV of 5036 m/s. Each Mars MCT will only require 2 BFR Tankers.

MCT Refuels on Mars utilizing 473 MT of ISRU fuel and returns to Earth with up to 10 MT of crew/cargo with a DV 7405 m/s.

Distributed MCT engines require a minimum thrust around 50 MT and 250 MT Maximum.

What amount did you set aside for ship power generation?  Waste recycling for 100.  Is this amount your 'systems' set aside? 

My concept for power generation is solar panels that would fold up like the petals of a flower from the bottom of the MCT towards the top. The actuator at the bottom would be similar to the ones used by the grid fins, being able to pitch and roll. This would require a stiff composite panel for the solar panels to mount too and perhaps a thin layer of Pica-X to protect it from the heat.  While this does add weight to the MCT, These fold down solar panels would work both in space and on Mars. Being able to roll the panel towards the Sun will increase their performance.

If approximately %50 of the MCT surface area can be covered by these solar panel "petals", They would generate 92KW in Earth orbit and 40KW on Mars. Calculations are based on these solar panels: http://www.azurspace.com/index.php/en/products/products-space/space-solar-cells

The systems level would contain all the systems used on the MCT for ship operations; Flight control computers, cryo-coolers, Communications and telemetry; For Crewed MCTs it would also include all the systems for life support and entertainment including water and air recycling, etc..  They Systems floor would provide hallways to allow easy access to all equipment and spares so the MCT can be maintained by the crew in Space and on Mars. 

I do not think a MCT this size can support 100 people. I would not want to be on it with that many people. The first three floors if only used for crew would be the size of a large house at around 4000 ft2. And Zero gravity will make utilization of that space more efficient. That would be very packed house for 5-6 months.

Thanks for your response.  Have you considered reduced solar generation on Mars due to location/weather (seasonally longer periods of darkness depending on location, sand storms lasting longer than a day) and what they're storing the energy in when the sun isn't present, like battery systems and their mass/volume?  What would you consider a reasonable core temperature for MCT and what amount of power generation on planet would be needed to keep the ship livable and functional with power generation left over for other uses? 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 04/29/2015 02:43 AM

With regards to where the heat shields went, they either were retracted back into the vehicle or were deployed and disposed during Martian atmospheric entry.  Obviously they're not perfect analogies for an MCT design, but they should prove that capsule designs are a very plausible MCT design option.  Alterations can be made after all!


Here is my hypothetical MCT design based on the constraint of a 225 MT Fully Reusable BFR.
I also disagree about the two stage system. Inflatable tanks in the cargo hold are also not required.
Tanks above cargo gives the best layout and CG for landing. So I have chosen it believing the plumbing problem will be solved. If the engines are side mounted, It may even be easier.
A crew MCT will not be able to get 100 MT of cargo to Mars. Crew support equipment and systems will subtract from the available 100 MT.
Dragon derived 15 m capsule with 15 degree side-walls. Capsule is 25 m tall not including the heat shield hemisphere. Top diameter dome 1.6 m across.


I want to point out another reason I don't think MCT will be a capsule shape.

Unlike every other capsule that's been designed in the history of space flight intended to enter into a planet with an atmosphere...MCT will have to get itself back off the ground.  Apollo didn't have to.  Dragon doesn't have to, CST-100 won't have to, Viking and the MER's and MSR didn't have to, etc.  So the capsule shape didn't have to house really large propellant tanks.  Just some small RCS thruster propellant tanks that can be stuffed into the spare geometric volume of the shape. 

But MCT will need a LOT of propellant to get itself back to Earth.  It'll in fact, be mainly a big fuel tank with a crew cabin bolted on, as opposed to most capsules to date which have been crew cabins (or cago volume) with a heat shield bolted on.  What's the most geometrically efficient shape to have large volumes of two propellants?  Cylinders....which is why almost all rocket stages have always been cylinders (with a few exceptions).   It'll be mainly a rocket stage...with a crew cabin bolted on.  Which is also why I think it'll do double duty as MCT's 2nd stage for ascent to LEO as well as get itself to Mars and back to Earth.  It'll already be essentailly a rocket stage by necessity.  Why pay to develop a separate dedicated 2nd stage for MCT.
A biconic aeroshell shape is also a cylinder.   Thus...logic would lean towards MCT being a cylindrical shape with a biconic EDL profile, as opposed to a capsule with a blunt body EDL profile.

So it's not just because you don't have to have doors in your heatshield for the engines with a cylindrical biconic shape....that's just a bonus.  It's not just that the biconinc has more surface area and better L/D ratio so it can milk more dV out of the atmosphere with more mild deceleration...that's just another bonus.  It's not just that you don't have to risk lighting your Raptor main engines on the Mars sruface and risk debris being blown up into your bottom heat shield damaging it....that's just another bonus with the TPS on the side. etc.

It's that MCT will be a big fuel tank with a crew cabin bolted on (top or bottom), and a cylinder is the most efficient geometry for a bi-propellant tank....and fortunately that happns to make a biconic shape.
With a giant capsule, you either have tanks with very odd/inefficient/difficult geometries to utilize that internal volume, or you have cylindrical tanks wrapped by a capsule shell...which then leaves a lot of inefficient internal volume around the tanks.  And as we know, in a space craft, no cubic inch of internal volume is desired to be wasted.

So let's not get too distracted with the concept of doors in the heat shield for the engines.  I don't think that's a show stopper given sufficient time and money during development.  But I also think it'd be desriable to avoid if possible, for the various reasons discussed.

NOTE:  I understand that this is not a true biconic shape.  I'm just using it as a reference term.  It'd be technically a "biconic nosed cylinder" I suppose.  Or a "blunt nosed cylinder", depending on what's determined to be better.

So, although the better L/D ratio of the biconic over the capsule is a bonus, not the driving factor in my opinion, I did find this bit interesting from wikipedia.

Quote
Biconic:  The biconic is a sphere-cone with an additional frustum attached. The biconic offers a significantly improved L/D ratio. A biconic designed for Mars aerocapture typically has an L/D of approximately 1.0 compared to an L/D of 0.368 for the Apollo-CM. The higher L/D makes a biconic shape better suited for transporting people to Mars due to the lower peak deceleration.
Arguably, the most significant biconic ever flown was the Advanced Maneuverable Reentry Vehicle (AMaRV). Four AMaRVs were made by the McDonnell-Douglas Corp. and represented a significant leap in RV sophistication. Three of the AMaRVs were launched by Minuteman-1 ICBMs on 20 December 1979, 8 October 1980 and 4 October 1981. AMaRV had an entry mass of approximately 470 kg, a nose radius of 2.34 cm, a forward frustum half-angle of 10.4°, an inter-frustum radius of 14.6 cm, aft frustum half angle of 6°, and an axial length of 2.079 meters. No accurate diagram or picture of AMaRV has ever appeared in the open literature. However, a schematic sketch of an AMaRV-like vehicle along with trajectory plots showing hairpin turns has been published.[12]
 
The DC-X, shown during its first flight, was a prototype single stage to orbit vehicle, and used a biconic shape similar to AMaRV.
Opportunity rover's heat shield lying inverted on the surface of Mars.AMaRV's attitude was controlled through a split body flap (also called a "split-windward flap") along with two yaw flaps mounted on the vehicle's sides. Hydraulic actuation was used for controlling the flaps. AMaRV was guided by a fully autonomous navigation system designed for evading anti-ballistic missile (ABM) interception. The McDonnell Douglas DC-X (also a biconic) was essentially a scaled up version of AMaRV. AMaRV and the DC-X also served as the basis for an unsuccessful proposal for what eventually became the Lockheed Martin X-33.

Another interesting bit from there was how apparently the AMaRV was able to make hairpin turns.  That indicates a pretty high level of aerodynamic steerability is possible with the shape.
I generally agree, however Mars has really thin atmosphere. A capsule shape may not be a problem.


But yes, I agree that we should be thinking of MCT mostly as what a reusable upper stage might look like (with a crew cabin bolted on--or likely integrated somewhat).
Title: Re: MCT Speculation and Discussion Thread 3
Post by: CyclerPilot on 04/29/2015 04:27 AM
Someone asked up thread how big the tanks have to be to return a 60 ton dry mass MCT to Earth's surface.

Assuming 8.2 km/s dv (4.4 km/s Mars launch, 3.8 km/s TEI).  I am assuming a non-optimum launch window because the MCT needs to return in the same synod.  I also assume a 380 ISP vac-optimised Raptor.

There needs to be prop reserved for EDL on Earth, likely not done with a vac-optimised 380 ISP raptor, but less effiecent thrusters.  I used 15 tons (providing 700 m/s to an empty MCT at 320 s ISP) for a total of 75 tons through TEI.

Mass of prop required?  603 tons.  Add 8 tons of prop for every ton of cargo you want to bring back. 

This huge prop requirement has several effects on the architecture.  The ISRU infrastructure on Mars needs to be massive.  Also you can see how critcal minimizing dry mass will be.   The MCT will be stripped on mars not only to supply the martians, but to reduce return trip dry mass.  I personally think the crew MCT will have a modular/removable hab .
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Impaler on 04/29/2015 04:55 AM
Lobo makes a good case for a bi-conic shape, and really when were debating between a Dragon style capsule with a 15 degree wall slope and a bi-conic with perhaps 10 degrees the difference is really small.  It's more a debate between the orientation of the vehicle during entry, either bottom-forward or side-forward.  Given the similar volumes discussed the final diameter and shape of the MCT is really splitting hairs.

I think the disagreement is more centered on what the vehicle will be CAPABLE of largely due to disagreements over the dry mass estimate.  I simply don't find dry masses under 100 mT credible given what MCT needs to do and the volume it will have.  Comparisons to Staurn V stages don't seem credible when these were expendable rocket stages that are hold nothing but propellents and are not capable of EDL on Mars.  I feel that only extrapolations from manned craft that carry cargo and perform atmospheric re-entry are logical (Dragon, Orion, Shuttle Orbiter all of these would make more sense), simply saying that MCT will do the ADDITIONAL task of being a second stage doesn't make it have the mass/volume ratio of a traditional 2nd stage, it just makes it a harder vehicle to engineer as it has more demands put upon it.

Also I find some flaws in the extrapolations from the Saturn 2nd Stage.  Lobo states this stage completes the delivery to LEO, it dose not, at 2nd stage engine cut off the vehicle is only going 7 km/s and a burn of the 3rd stage is necessary to actually reach LEO, though it is a modest one of just under 1 km/s.  In addition the first stage of the Saturn V stages at mach 8 rather then the expected BFR staging at mach 6 due to reusability constraints, while this is still 'lower and slower' then F9 current staging it is not a match for BFR.  Together this means the S-II had 1.5 km/s less Delta-V to achieve then the proposed 2nd-stage MCT would need to do to get to orbit.  Lastly Lobo states the INT-21 would have delivered 140 mT to orbit, but it was actually rated at 115 mT.

All together this just seems a bridge too far for me to believe the MCT can be combined with it's 2nd stage, though I think it could do considerable 3rd-stage duty and thus significantly reduce the ultimate Delta-V burden on the 2nd stage.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: symbios on 04/29/2015 08:52 AM
Someone asked up thread how big the tanks have to be to return a 60 ton dry mass MCT to Earth's surface.

Assuming 8.2 km/s dv (4.4 km/s Mars launch, 3.8 km/s TEI).  I am assuming a non-optimum launch window because the MCT needs to return in the same synod.  I also assume a 380 ISP vac-optimised Raptor.

There needs to be prop reserved for EDL on Earth, likely not done with a vac-optimised 380 ISP raptor, but less effiecent thrusters.  I used 15 tons (providing 700 m/s to an empty MCT at 320 s ISP) for a total of 75 tons through TEI.

Mass of prop required?  603 tons.  Add 8 tons of prop for every ton of cargo you want to bring back. 

This huge prop requirement has several effects on the architecture.  The ISRU infrastructure on Mars needs to be massive.  Also you can see how critcal minimizing dry mass will be.   The MCT will be stripped on mars not only to supply the martians, but to reduce return trip dry mass.  I personally think the crew MCT will have a modular/removable hab .

Size wise on a vehicle with a diameter of 10 m you get about ~700 m2 of volume out of a 10 m high section depending on the angle of the walls. So is this a reasonable volume out of the MCT?
Title: Re: MCT Speculation and Discussion Thread 3
Post by: GORDAP on 04/29/2015 11:18 AM
Someone asked up thread how big the tanks have to be to return a 60 ton dry mass MCT to Earth's surface.

Assuming 8.2 km/s dv (4.4 km/s Mars launch, 3.8 km/s TEI).  I am assuming a non-optimum launch window because the MCT needs to return in the same synod.  I also assume a 380 ISP vac-optimised Raptor.

There needs to be prop reserved for EDL on Earth, likely not done with a vac-optimised 380 ISP raptor, but less effiecent thrusters.  I used 15 tons (providing 700 m/s to an empty MCT at 320 s ISP) for a total of 75 tons through TEI.

Mass of prop required?  603 tons.  Add 8 tons of prop for every ton of cargo you want to bring back. 

This huge prop requirement has several effects on the architecture.  The ISRU infrastructure on Mars needs to be massive.  Also you can see how critcal minimizing dry mass will be.   The MCT will be stripped on mars not only to supply the martians, but to reduce return trip dry mass.  I personally think the crew MCT will have a modular/removable hab .

Nit, why does everyone insist the MCT will go into Mars orbit and then do a TEI burn?  I think there is a significant savings (10-20%?) in DV by going directly from Mars surface to Earth.  And with the exponential nature of the rocket equation, doesn't this translate into even bigger savings in fuel?  It just seems to me that there is absolutely no reason to loiter in Mars orbit before returning to Earth.  Sorta like me taking off on a cross country trip, but first circling my city a few times :-) 

CyberPilot, how much better do your numbers look if they do a direct launch from Mars to Earth?
Title: Re: MCT Speculation and Discussion Thread 3
Post by: sheltonjr on 04/29/2015 11:43 AM
| Floor                        | Height (m) | Usable Pct (%) |Volume (m3) | Area (m2),(ft2) | Fuel (MT) |
|-----------------------|-------------|------------------|--------------|------------------|-----------|
| Upressurized Cargo   | 2.5            | 95                    | 383              | 177, 1902         |                |
| Habitat                     | 2               | 95                    | 257              | 146, 1577         |                |
| Pressurized Cargo     | 2               | 95                    | 216              | 124, 1339         |                |
| Systems                   | 1.5            | 95                    | 138              | 104, 1121         |                |
| LOX                          | 4.6            | 97                    | 309              | N/A                  | 361         |
| CH4                          | 12.4          | 97                    | 258              | N/A                  | 112         |

MCT Empty Mass = 65 MT
Cargo <= 100 MT
Total Fuel = 473 MT

MCT Launches with cargo and crew and 60 MT of fuel to awaiting BFR Depot to fully fuel with additional 400 MT of fuel. Performs TMI and EDL at Mars with a DV of 5036 m/s. Each Mars MCT will only require 2 BFR Tankers.

MCT Refuels on Mars utilizing 473 MT of ISRU fuel and returns to Earth with up to 10 MT of crew/cargo with a DV 7405 m/s.

The CH4 is the fuel. You are using that word to mean the fuel and the oxidizer, which together are known as the propellant. You will be taken seriously by no one if you don't distinguish correctly between fuel and propellant.

Ok, Are you a Lawyer?  :D  CH4 & LOX are a Bi-propellant, And I usually consider a propellant to be used for SEP (Argon, Xenon) or NEP systems (Hydrogen).  Fuel is a lot shorter and I believe understood. You saw how many times I used it.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: sheltonjr on 04/29/2015 12:17 PM
My concept for power generation is solar panels that would fold up like the petals of a flower from the bottom of the MCT towards the top. The actuator at the bottom would be similar to the ones used by the grid fins, being able to pitch and roll. This would require a stiff composite panel for the solar panels to mount too and perhaps a thin layer of Pica-X to protect it from the heat.  While this does add weight to the MCT, These fold down solar panels would work both in space and on Mars. Being able to roll the panel towards the Sun will increase their performance.

If approximately %50 of the MCT surface area can be covered by these solar panel "petals", They would generate 92KW in Earth orbit and 40KW on Mars. Calculations are based on these solar panels: http://www.azurspace.com/index.php/en/products/products-space/space-solar-cells

The systems level would contain all the systems used on the MCT for ship operations; Flight control computers, cryo-coolers, Communications and telemetry; For Crewed MCTs it would also include all the systems for life support and entertainment including water and air recycling, etc..  They Systems floor would provide hallways to allow easy access to all equipment and spares so the MCT can be maintained by the crew in Space and on Mars. 

I do not think a MCT this size can support 100 people. I would not want to be on it with that many people. The first three floors if only used for crew would be the size of a large house at around 4000 ft2. And Zero gravity will make utilization of that space more efficient. That would be very packed house for 5-6 months.

Thanks for your response.  Have you considered reduced solar generation on Mars due to location/weather (seasonally longer periods of darkness depending on location, sand storms lasting longer than a day) and what they're storing the energy in when the sun isn't present, like battery systems and their mass/volume?  What would you consider a reasonable core temperature for MCT and what amount of power generation on planet would be needed to keep the ship livable and functional with power generation left over for other uses? 

I have only done scratch the surface type of engineering to see what is feasible. From my analysis I believe that Elon and SpaceX may get the MCT solution to close. Though it will be close. 165MT MCT & Payload will take 3 BFR launches to mount an expedition to Mars. 1 MCT & 2 for Fuel.  If MCT mass grows then payload may need to decrease. Adding a third refueling BFR and increasing the size of the the already huge MCT, And it should be doable, At increased cost.

As for solar energy on Mars, Having fold-down petals on the outside of the MCT can be quickly used for both in space and on Mars. If SpaceX does what I am proposing they would need to figure out all the details that you mentioned. They may need to also add ground solar. 

The question I was trying to answer for myself for solar power, is it enough for a unmanned ISRU MCT to generate 470MT of CH4 & LOX in 25 months fully autonomously.  Peak solar power of 40KW and working with the daily temperature variations on Mars may be enough, but I do not have the time or the knowledge to know that with any certainty.

ISRU of propellant on Mars is the pivotal technology to make the MCT system work. My guess is the first MCT to land on Mars will be a ISRU MCT.  With about 1000 m3 of volume to utilize. The first MCT will have 2-3 Sabatier reactors and possibly 4 sources of hydrogen to experiment with. 1) High pressure Hydrogen brought from Earth, 2) Water brought from Earth, 3) Water from the atmosphere, 4) Water dug from the surface.

1-2 Rovers with back-hoes will also be included for scouting the area and digging trenches to look for water to deposit in the MCT.

If all goes to plan, the first MCT will have enough fuel for the second MCT to land to return to Earth and validate the MCT for the Earth return part of the mission.

Autonomously refueling between the two MCT should be a fun. A long hose, precision landing and reliable and capable rovers.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: spacenut on 04/29/2015 01:21 PM
Why couldn't the MCT actually be a two piece lander, that the bottom half stays on Mars as habitat and/or water, methane, or oxygen storage?  Either engines could be mounted on the sides or in the center that would stay with the upper half returning to earth.  The bottom half could be around the returning center.  It could be sealed over after returning ship detaches for internal living quarters.  Outside previous methane and oxygen tanks could be refilled with ISRU made fuel and oxygen which would offer some radiation protection.  If the lander is high enough off the ground, it could also be sealed around the outside bottom for underneath living areas, vehicle storage and compression/decompression chamber for EVA's on the surface to mine for water.  Why not just bring the center or top half of the spacecraft back to earth to be reused?  Less building would be required, just modification of the bottom or outer ring of the spacecraft.  Less fuel needed for return. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: FishInferno on 04/29/2015 01:46 PM
Why couldn't the MCT actually be a two piece lander, that the bottom half stays on Mars as habitat and/or water, methane, or oxygen storage?  Either engines could be mounted on the sides or in the center that would stay with the upper half returning to earth.  The bottom half could be around the returning center.  It could be sealed over after returning ship detaches for internal living quarters.  Outside previous methane and oxygen tanks could be refilled with ISRU made fuel and oxygen which would offer some radiation protection.  If the lander is high enough off the ground, it could also be sealed around the outside bottom for underneath living areas, vehicle storage and compression/decompression chamber for EVA's on the surface to mine for water.  Why not just bring the center or top half of the spacecraft back to earth to be reused?  Less building would be required, just modification of the bottom or outer ring of the spacecraft.  Less fuel needed for return.

MCT is supposed to be completely reusable, and a 2-stage lander prohibits that.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 04/29/2015 02:29 PM
It could be possible that a large hab or something fills the payload bay for trips that are full (100 passengers) and is left on the surface to grow the colony, but that for return trips, people have to be satisfied with smaller quarters.

I mean, we know that MCT also has to have very significant payload capabilities, so that should be a possibility even if MCT were designed with enough room for 100 passengers all by itself.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: spacenut on 04/29/2015 02:32 PM
I know the MCT is supposed to be completely reusable.  However I was thinking hauling all the extra empty weight from Mars could be a waste of fuel, energy and time to make fuel.  A lot of tonnage of living space and fuel storage will be needed.  Why not used part of what was brought.  For instance, if say 50% of the fuel in LEO is used for TMI, 30% for landing on Mars, and 20% to return to Earth, 80% of the vehicle volume is empty and unused after landing on Mars.  One vehicle could make fuel and oxygen to store in the empty tanks.  One vehicle could used vented and dried out tanks for habitat, food storage, water storage (they are going to need a lot of water), growing plants, etc.  No engines would stay on Mars as they would be attached to the return vehicle.

 A lot of methane might be needed for melting Mars regolith for glass, aluminum, soft metals, to make objects and parts needed for colony construction.  So a lot of storage would be needed.  Methane could also be used in very hot melting ovens for harder metals such as iron and steel manufacturing.  More carbon and hydrogen could be added to methane for heavier fuels, butane, propane, even kerosene and diesel for hotter burning fuels needed for manufacturing. 

All this fuel and manufacturing will need storage tanks that could be provided by a two piece MCT. 

In my thinking, the MCT would have to be wide, 12-15m at least for this.  With the top portion or center portion a 5m diameter cylinder type unit return craft. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: guckyfan on 04/29/2015 03:24 PM
It could be possible that a large hab or something fills the payload bay for trips that are full (100 passengers) and is left on the surface to grow the colony, but that for return trips, people have to be satisfied with smaller quarters.

I mean, we know that MCT also has to have very significant payload capabilities, so that should be a possibility even if MCT were designed with enough room for 100 passengers all by itself.

I think they will not design MCT with 100 passengers going back to earth in mind. Early missions where everybody returns at some time will have a much smaller number of passengers. 100 person flights will be for colonists with mostly no intention to return.

Once the population rises above 1000 or several thousand it may no longer be possible to return everybody to earth at all. But that would be at a time where mostly selfsustenance is established.

Title: Re: MCT Speculation and Discussion Thread 3
Post by: Ben the Space Brit on 04/29/2015 03:32 PM
My feeling is that MCT will be a LEO-to-Mars Surface architecture that will be customised with mission modules and extra fuel tanks for various different missions. For example, a 100-passenger flight may literally be a flying barrack block that will just land at the destination site, roll over, hook up to the rest of the colony and stay there. Engineers would come along later, remove the Raptor/Methane Merlin propulsion module and move it off for recycling elsewhere.

I think they will not design MCT with 100 passengers going back to earth in mind. Early missions where everybody returns at some time will have a much smaller number of passengers. 100 person flights will be for colonists with mostly no intention to return.

Once the population rises above 1000 or several thousand it may no longer be possible to return everybody to earth at all. But that would be at a time where mostly self-sustenance is established

Agreed; early missions may have as little as six crew (exploration/survey with the majority of the payload made up with things like a pressurised long-haul rover and sensors) with early colonial missions being around 20 personnel, mostly engineers. Some will remain on Mars for multiple MCT visits but the majority would return back to Earth every flight.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 04/29/2015 04:11 PM
If MCT doesn't launch with people from Earth, then you're talking about doubling the development cost and probably also the per ticket price.

Refueling in Earth orbit, absolutely.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: TomH on 04/29/2015 04:18 PM
I usually consider a propellant to be used for SEP (Argon, Xenon) or NEP systems (Hydrogen).  Fuel is a lot shorter and I believe understood. You saw how many times I used it.

Those gasses are the propellant in SEP, however regarding chemical propulsion, you are incorrect. The fuel and oxidizer are not together called fuel. They are propellant. The CH4 is the fuel and the LOx is the oxidizer. It's just that plain and simple. You do not get to redefine these things just because you feel like it. And again, if you insist on using terminology incorrectly, you will not be taken seriously. Rather than being defensive, wouldn't it be easier just to say, You are right; thanks for the correction? Fuel is shorter, however prop, the accepted abbreviation for propellant, is the same length.

See Robotbeat's closing tag line one post above.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/29/2015 04:23 PM
Lobo makes a good case for a bi-conic shape,

Thanks!  :-)

and really when were debating between a Dragon style capsule with a 15 degree wall slope and a bi-conic with perhaps 10 degrees the difference is really small.  It's more a debate between the orientation of the vehicle during entry, either bottom-forward or side-forward.  Given the similar volumes discussed the final diameter and shape of the MCT is really splitting hairs.

Agreed.  If MCT were a minimally sloped capsule shape, it would look more like a traditional biconic, rather than a biconic nosed cylinder.  Certainly a lot of side entry biconics that actually do look like that (see below).
However, I go with the biconic nosed cylinder becuase it's easier to make big tanks in a cylindrical shape, than it is to make biconic shaped fuel tanks.  That's why rocket stages are cylinders and not biconic or some other shape.  I don't think a true biconic or capsule shape really has much advantage vs. a biconic nosed cylinder during EDL (maybe someone in the know could confirm or refute that) so I'm just thinking keep it simple.  NASA's DRM 5.0 aeroshells were basically biconic nosed cylinders rather than true biconics.  They were payload only though, without having large tanks themselves, and just meant to get lander through the Martian atmosphere.  Still, I think NASA's use of the shape is a good endorsement of it's viability.


I think the disagreement is more centered on what the vehicle will be CAPABLE of largely due to disagreements over the dry mass estimate.  I simply don't find dry masses under 100 mT credible given what MCT needs to do and the volume it will have.  Comparisons to Staurn V stages don't seem credible when these were expendable rocket stages that are hold nothing but propellents and are not capable of EDL on Mars. 


I have no idea what the dry mass of MCT might really be like.  I'm using the Saturn S-II as a reference that would be an upper stage in the ball part of what I think the MCT spacrcraft/upper stage might be like.  And to show that MCT itself doesn't necessarily have to be some ginormous BFR putting near 300mt inot LEO and have 15Mlbs of thrust and 30+ Raptor engine.

So, let's say today, we could make an S-II stage that's say 35mt dry, rather than 45mt dry, with modern manufacturing techniques and materials...for example.  To that we need to add:
1)  crew cabin
2)  landing legs
3)  TPS system on the side
4)  ECLSS
5)  Sabatier reactor
6)  LH2 fed stock or equipment that can mine water vapor out of the air and then electrolyze it for H2 feed stock.  (there's some interesting research into that).
7)  Cago bay  (this is basically empty space, but the alloy housing it would add a bit of overall mass.  It could be unpressurized to reduce the housing mass required.
8  )  Deployable/retractable solar array(s) for power during transit)
9)  Anything else I can't think of right now).

If we start with 35mt base for the "stage", how much extra mass will all of this add?  I have no idea.  If about 30mt, then MCT would dry mass around 65mt, and be in our ballpark.
I don't think the ECLSS system or sabatier reactor would be all that heavy.  Ditto for a cargo area.  The crew cabin would essentially be empty space too and not mass much itself.  The crew accomodations like bathrooms, seats, controls, computers, etc would be where the mass for that comes from. 
That leaves landing legs, TPS, and the solar array.
Given the much larger surface area, I think they could use a TPS that's lighter per square ft than the Pica-X they use on Dragon.  The fragile ceramic tiles of the Shuttle should probably be avoided in favor of something a little more robust that needs less maintenance to turn around after a round trip.
What are some options that are out there to consider?  Anyone know what NASA would have used for their Aeroshells in DRM 5.0?
Can we keep this down to around 65mt, give or take?  There's the question.


I feel that only extrapolations from manned craft that carry cargo and perform atmospheric re-entry are logical (Dragon, Orion, Shuttle Orbiter all of these would make more sense), simply saying that MCT will do the ADDITIONAL task of being a second stage doesn't make it have the mass/volume ratio of a traditional 2nd stage, it just makes it a harder vehicle to engineer as it has more demands put upon it.


The problem with using those for analogs, is they are just crew (or payload) housings.  They aren't rocket ships.  MCT will need to be a rocket stage/ship.  Even if it's lofted to LEO by a 2-stage booster, it still has considerable dV requirements to provide itself that no other spacecraft has.
I think a better analog would be Rocketplane Kistler's K-1.  That's probably about as close to this as has been legitimately designed.  But it did a ballistic nose entry rather than a biconic side entry, and it landed on airbags on it's side.  So it's not a great analog, but one of the closest I think.  See below.


Also I find some flaws in the extrapolations from the Saturn 2nd Stage. 

Of course there are flaws.  It's just a rough analog to help picture what a 2-stage MCT might look like with an integrated 2nd stage/spacecraft.

Lobo states this stage completes the delivery to LEO, it dose not, at 2nd stage engine cut off the vehicle is only going 7 km/s and a burn of the 3rd stage is necessary to actually reach LEO, though it is a modest one of just under 1 km/s. 

So how did Skylab get into it's orbit?  There was no 3rd stage on it.
This is why I've been using Saturn INT-21 as my reference, not actually Saturn V, as that was a 3 stage LV and INT-21 was a 2-stage LV, like my MCT concept.


Lastly Lobo states the INT-21 would have delivered 140 mT to orbit, but it was actually rated at 115 mT.


No, I've said Saturn INT-21 would do almost 120mt.  115.8mt to be exact.
http://www.astronautix.com/lvs/satint21.htm

I've actually seem some people run estimates that the LEO of INT-21 would have actually been over 120mt (I believe Hyperion5 did actually, maybe I'll check back with him), but we'll stick with 116mt for now.

With the dry mass of the S-II itself which would also be in that same LEO (like it was after delivering Skylab) of 45mt, that's means about 161mt to LEO.  I would assume there was at least a couple tonnes of residual propellants in the S-II after SECO, so the total mass to LEO would probably be closer to 165mt or so.


All together this just seems a bridge too far for me to believe the MCT can be combined with it's 2nd stage, though I think it could do considerable 3rd-stage duty and thus significantly reduce the ultimate Delta-V burden on the 2nd stage.

You certainly could be right.  There might be a 2-stage booster under the MCT vehicle.  But I still think there are more advantages to having MCT as the 2nd stage.  One being you only pay the mass penalty for the upper stage(s) once, not twice.  Otherwise you are pushing the dry mass of the 2nd stage along with the dry mass of MCT to LEO.  A dedicated 2nd stage would be resuable, so you'd pay for the additional dry mass of it's reusability hardware twice.  The mass of a TPS on both the 2nd stage and MCT, landing legs on both, etc.  With just one stage, you only "pay" for all of that once.  So there's advantages to it.  And if you are refueling in LEO anyway, why not?
Not to mention it's one less development to pay for, and one less piece to have to remotely deorbit and land.  This way, you only are bringing back the actual MCT (which can be a LEO taxi configuration, or tanker configuration) back from orbit.  Rather than both an MCT and a dedicated 2nd stage.

Of course, this is all predicated on the assumption that an integrated upper stage/MCT -can- be made to work feasible.  If not, then there will be a dedicated 2nd stage. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/29/2015 04:28 PM
Someone asked up thread how big the tanks have to be to return a 60 ton dry mass MCT to Earth's surface.


That was me.  Thanks!

603mt doesn't seem too prohibative.

And 603mt will weigh about 200mt on the Mars surface.  A 500klb Raptor is 226mt of thrust.  If MCT was 60mt dry, that makes a surface mass of about 220mt (equivalent).  Which would mean a single Raptor could about do the job by itself.

Not saying they'd only have a single Raptor, but we're right in this ballpark area.

And you are right, the methalox generation will have to be substantial.  I'll leave that to SpaceX to engineer.  That's above my pay grade.  ;-)

Title: Re: MCT Speculation and Discussion Thread 3
Post by: hkultala on 04/29/2015 04:48 PM
Someone asked up thread how big the tanks have to be to return a 60 ton dry mass MCT to Earth's surface.


That was me.  Thanks!

603mt doesn't seem too prohibative.

And 603mt will weigh about 200mt on the Mars surface.

mars gravity is 3.711 m/s^2 , not ~3.3.

So it weights about 2238 MN.

Quote
  A 500klb Raptor is 226mt of thrust.  If MCT was 60mt dry, that makes a surface mass of about 220mt (equivalent).  Which would mean a single Raptor could about do the job by itself.

correct weight would be  ~2460 MN. So that's more than the ~2256 MN stated by elon as the raptor thrust.

So it has to weight something like <50 tonnes instead of 60 tonnes to use only one raptor for liftoff, or raptor thrust has to be greater than elon's last comment about it.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/29/2015 05:52 PM
Nit, why does everyone insist the MCT will go into Mars orbit and then do a TEI burn?  I think there is a significant savings (10-20%?) in DV by going directly from Mars surface to Earth.  And with the exponential nature of the rocket equation, doesn't this translate into even bigger savings in fuel?  It just seems to me that there is absolutely no reason to loiter in Mars orbit before returning to Earth.  Sorta like me taking off on a cross country trip, but first circling my city a few times :-) 

CyberPilot, how much better do your numbers look if they do a direct launch from Mars to Earth?

Myself, I agree.  I can only see MOI if SpaceX has a plan to somehow refuel in Mars Orbit.  That seems unnecessarily complicated if there's any way MCT can do a Direct ascent to Earth.  I don't know the physics behind it, if I think SpaceX won't mess with Mars orbit fueling if they don't have to.  In which case there's not need for MOI, and keep the return propellant requitements for MCT as low as possible. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/29/2015 06:02 PM

As for solar energy on Mars, Having fold-down petals on the outside of the MCT can be quickly used for both in space and on Mars. If SpaceX does what I am proposing they would need to figure out all the details that you mentioned. They may need to also add ground solar. 


I would expect the in-space solar array to be different than the on-surface one.  The in-space one will be designed to deploy and retract in zero-g vacuum.  And it will have to be done automatically, unless want a series of EVA's in space to be requried to unfurl and refurl them.  X-37B has showin that a solar array can be remotely deployed and retracted again reliably, so I think that would be the case for MCT.
On the surface it's a different story.  You'll have a whole crew unloading cargo and setting up equipment.  They can simply have soft-backed sollar cell sheets that they unroll on the surface like giant tarps.  Or they could have rigid arrays that can be set up on bases to track the sun, or whatever.  But you have time and bodies on the surface to set all of that up. 

You could also have radio isotope generators.  Those would expecially be handy if you wanted to send an MCT ahead of a crew to fuel up and be waiting as a lifeboat in case there's an issue with fueling up the MCT they come in.  Deploying solar arrays and the surface remotely of the size needed seems like it'd be a pretty difficult thing to do.   So they might want a method of power generation that doesn't need to be remotely deployed. 
A full nuclear reactor is unlikely for various political reasons, but lots of isotope powered sats have been launched over the years.

Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/29/2015 06:27 PM
Why couldn't the MCT actually be a two piece lander, that the bottom half stays on Mars as habitat and/or water, methane, or oxygen storage?  Either engines could be mounted on the sides or in the center that would stay with the upper half returning to earth.  The bottom half could be around the returning center.  It could be sealed over after returning ship detaches for internal living quarters.  Outside previous methane and oxygen tanks could be refilled with ISRU made fuel and oxygen which would offer some radiation protection.  If the lander is high enough off the ground, it could also be sealed around the outside bottom for underneath living areas, vehicle storage and compression/decompression chamber for EVA's on the surface to mine for water.  Why not just bring the center or top half of the spacecraft back to earth to be reused?  Less building would be required, just modification of the bottom or outer ring of the spacecraft.  Less fuel needed for return.

It's an interesting concept, but I think it would have a few problems. 

First, if you leave the lower part of the lander back on Mars, how do you do EDL on Earth?  You'd have left your landing legs at least.
Plus, if you've seen the video of the last couple of Apollo missions, the DM of the LEM looked pretty thrashed after the AM lifted off.  I would predict at least one Raptor firing down into a lower stage to be left on Mars getting similarly thrashed.

As RobotBeat mentioned, there could be some sort of cargo module or something that could be unloaded to the surface and then moved a safe distance away and then used as a habitat, or storage shed, or whatever.  I could see that somehow being implimented.  Still, there are difficulties with any large pod.  If it's on top, how do you get it down?  If it's on the bottom, how do you get it out?  There'd be plumbing between the tanks and engines to negotiate so you'd have size constraints to it's size and shape.
But I could see something along those lines being implimented.  Maybe just multiple smaller cargo pods the size of those Pods containers you use when you move.  Or a small cargo container size, that can be pulled off the bottom of MCT with a ramp or cables, and then towed away with a rover to where they can be unloaded.  Once loaded, they could be pressurized and used as surface habs.  They could be stacked together like "apartments", and have soil pushed up around them and over them to help protect against radation.  Some sort of universal cargo/hab pod with wheels so it can be moved around.  Once unloaded, they could be interlocked together.

A company very near where I work does something kind of similar with cargo containers.  They make mobile living quarters out of them for the military.  They are shipped to wherever the Army needs them, and then power is run to them and they are instant small houses.  For Mars, they'd just be empty vessels that are sealed to hold an atmosphere.  They are loaded up on Earth with equipment and supplies, and then plugged into MCT's cargo container hold.   On Mars they are pulled off, towed away, unloaded, and then plugged into a common ECLSS with the other containers and all uses as surface habs. 

That way every MCT will bring a certain number of pre-fab surface habs with it to be left there for future use.  Perhaps they could be designed to be interlocked together and opend up to create larger hab structures, like building blocks?
Not quite like leaving part of the MCT on the surface to use, but a more feasible way to impliment that idea.

Something akin to this, but set up to hold cargo on the trip out, and then be used for habs.

http://www.dropboxinc.com/products/photo-gallery
http://www.energistx.com/spaces/Hurricane%20Relief%20Units.html

Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/29/2015 06:32 PM

correct weight would be  ~2460 MN. So that's more than the ~2256 MN stated by elon as the raptor thrust.

So it has to weight something like <50 tonnes instead of 60 tonnes to use only one raptor for liftoff, or raptor thrust has to be greater than elon's last comment about it.

Ahhh. thanks for the accuracy.  I was just going 1/3 for estimation.

I doubt MCT would have just one Raptor.  If it's an integrated 2nd stage, it'd need probably 3-4 to get to LEO after booster staging.  So if we're assuming that, it'd have multiple Raptors.  only 2 would be needed to get off the surface.  A cluster of 4 or 5 would result in MCT being multi-engine out scenario fault tolerant.  So I think it likely MCT will have 4-5 Raptors.  So pleanty of thrust to get 600mt of fuel and a >50mt MCT off the surface.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 04/29/2015 06:56 PM
Musk mentioned multiple Raptors for the MCT in the AMA. This would allow much lower gravity losses and thus less propellant needed.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Impaler on 04/30/2015 12:54 AM


Agreed.  If MCT were a minimally sloped capsule shape, it would look more like a traditional biconic, rather than a biconic nosed cylinder.  Certainly a lot of side entry biconics that actually do look like that (see below).
However, I go with the biconic nosed cylinder becuase it's easier to make big tanks in a cylindrical shape, than it is to make biconic shaped fuel tanks.

If the biconic has a reasonably low slope to the side wall then a cylindrical tank (or 2) can fit inside of a conic without wasting much room.  The outer form of the vehicle don't have to be the shape of the tanks inside unless it is like a rocket stage in which these are one in the same, but the thermal protection systems necessary for reentry dictates that the outer surface can't be the tank anyways.

I have no idea what the dry mass of MCT might really be like.  I'm using the Saturn S-II as a reference that would be an upper stage in the ball part of what I think the MCT spacrcraft/upper stage might be like.  And to show that MCT itself doesn't necessarily have to be some ginormous BFR putting near 300mt inot LEO and have 15Mlbs of thrust and 30+ Raptor engine.

So, let's say today, we could make an S-II stage that's say 35mt dry, rather than 45mt dry, with modern manufacturing techniques and materials...for example.  To that we need to add:
1)  crew cabin
2)  landing legs
3)  TPS system on the side
4)  ECLSS
5)  Sabatier reactor
6)  LH2 fed stock or equipment that can mine water vapor out of the air and then electrolyze it for H2 feed stock.  (there's some interesting research into that).
7)  Cago bay  (this is basically empty space, but the alloy housing it would add a bit of overall mass.  It could be unpressurized to reduce the housing mass required.
8  )  Deployable/retractable solar array(s) for power during transit)
9)  Anything else I can't think of right now).

I think we need to minimizing integration of superfluous systems into the vehicle to get as low a mass as possible.  I'd drop the Sabatier reactor and H2 equipments (atmospheric moisture extractors most likely) immediately, that is a system that makes absolutely ZERO sense to bring back to Earth as its ONLY usable on the surface of Mars and we desperately want to get as high a volume of propellent production going as possible so every bit of ISRU equipment sent to Mars needs to stay to build up production capacity.





If we start with 35mt base for the "stage", how much extra mass will all of this add?  I have no idea.  If about 30mt, then MCT would dry mass around 65mt, and be in our ballpark.
I don't think the ECLSS system or sabatier reactor would be all that heavy.  Ditto for a cargo area.  The crew cabin would essentially be empty space too and not mass much itself.  The crew accomodations like bathrooms, seats, controls, computers, etc would be where the mass for that comes from. 
That leaves landing legs, TPS, and the solar array.
Given the much larger surface area, I think they could use a TPS that's lighter per square ft than the Pica-X they use on Dragon.  The fragile ceramic tiles of the Shuttle should probably be avoided in favor of something a little more robust that needs less maintenance to turn around after a round trip.
What are some options that are out there to consider?  Anyone know what NASA would have used for their Aeroshells in DRM 5.0?
Can we keep this down to around 65mt, give or take?  There's the question.

The problem with using those for analogs, is they are just crew (or payload) housings.  They aren't rocket ships.  MCT will need to be a rocket stage/ship.  Even if it's lofted to LEO by a 2-stage booster, it still has considerable dV requirements to provide itself that no other spacecraft has.
I think a better analog would be Rocketplane Kistler's K-1.  That's probably about as close to this as has been legitimately designed.  But it did a ballistic nose entry rather than a biconic side entry, and it landed on airbags on it's side.  So it's not a great analog, but one of the closest I think.  See below.


How about we try this strategy, start with your basic rocket-stage mass and fractions (and I'd recommend using F9 upper stage as an analog rather then Saturn V hardware, it's hydrocarbon based an much more modern), and then for the 'other' stuff try to derive that extra mass from vehicle that had thouse things like capsules or the shuttle orbiter, taking into account the target volumes devoted to these purposes.   That splits the difference between considering the vehicle as 'all stage' or 'all capsule'.


So how did Skylab get into it's orbit?  There was no 3rd stage on it.

According to what I've read Skylab had a mass of only 75 mT, so their was plenty of performance in the first 2 stages to reach LEO without the 3rd stage, or so I presume.


You certainly could be right.  There might be a 2-stage booster under the MCT vehicle.  But I still think there are more advantages to having MCT as the 2nd stage.  One being you only pay the mass penalty for the upper stage(s) once, not twice.  Otherwise you are pushing the dry mass of the 2nd stage along with the dry mass of MCT to LEO.  A dedicated 2nd stage would be resuable, so you'd pay for the additional dry mass of it's reusability hardware twice.  The mass of a TPS on both the 2nd stage and MCT, landing legs on both, etc.  With just one stage, you only "pay" for all of that once.  So there's advantages to it.  And if you are refueling in LEO anyway, why not?
Not to mention it's one less development to pay for, and one less piece to have to remotely deorbit and land.  This way, you only are bringing back the actual MCT (which can be a LEO taxi configuration, or tanker configuration) back from orbit.  Rather than both an MCT and a dedicated 2nd stage.

Of course, this is all predicated on the assumption that an integrated upper stage/MCT -can- be made to work feasible.  If not, then there will be a dedicated 2nd stage. 

Staging is ALWAYS going to give performance, not take it away.  Having a 2nd stage that did the full Delta-V to LEO and simply dropped the MCT there would indeed be inefficient in the sense that the empty stage mass is mass that could have been vehicle, but I'm expecting the MCT to have some propellent at launch allowing it to do 1-2 km/s after separating from the second stage, that 2nd stage has not in fact been brought to LEO.  A 2nd stage like this that is short of orbital speed like this might still go around the Earth once to allow a RTLS, otherwise downrange recovery may be needed.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Impaler on 04/30/2015 01:41 AM
If someone has a more accurate calculation of DeltaV from Mars surface to Earth return trajectory thous would be very useful.  Their may be some saving, but I suspect it will be minimal because a planetary surface and Low orbit are basically the same with regard to the gravity well and Oberth effect.

Of particular interest would be transit times in a direct return, how low can you go and how much dose it cost?
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Impaler on 04/30/2015 02:06 AM

The question I was trying to answer for myself for solar power, is it enough for a unmanned ISRU MCT to generate 470MT of CH4 & LOX in 25 months fully autonomously.  Peak solar power of 40KW and working with the daily temperature variations on Mars may be enough, but I do not have the time or the knowledge to know that with any certainty.

ISRU of propellant on Mars is the pivotal technology to make the MCT system work. My guess is the first MCT to land on Mars will be a ISRU MCT.  With about 1000 m3 of volume to utilize. The first MCT will have 2-3 Sabatier reactors and possibly 4 sources of hydrogen to experiment with. 1) High pressure Hydrogen brought from Earth, 2) Water brought from Earth, 3) Water from the atmosphere, 4) Water dug from the surface.

1-2 Rovers with back-hoes will also be included for scouting the area and digging trenches to look for water to deposit in the MCT.

If all goes to plan, the first MCT will have enough fuel for the second MCT to land to return to Earth and validate the MCT for the Earth return part of the mission.

Autonomously refueling between the two MCT should be a fun. A long hose, precision landing and reliable and capable rovers.

No this would not be adequate as the chemical synthesis of hydrocarbon fuel/oxidizer mix from water and CO2 feedstock needs around 5 kW/h per kg of propellents.  In addition collection of water necessary to make this 1 kg of propellents (NOT 1 kg or water) would require an additional 5-7 kW/h if collected from the atmosphere, the most reliable means we know of (I can not even begin to estimate mass and power costs for mining ice or regolith).  Production from H2 feed stocks greatly lowers energy needs but has all kinds of other problems as I'm sure you know.

40 kW (which I assume is peak power in daylight) is only going to yield ~240 kW/h per day and produce 24 kg of propellents per day, which is about 18 mT over a Martian synod.  You need several hundred kW power systems to get the kinds of propellent mass needed for the MCTs were speculating about here even back into orbit let alone back to Earth.

Thus I conclude that a separate surface-only power system is an absolute necessity, and that it should NOT be integrated into the vehicle.  It would simply another part of the propellent production equipment that will be carried as part of the 100 mT cargo load.  Thin film solar is up to the task from all the material I have read, but if you prefer some other source such as nuclear so be it, it would still be a surface only power source.

That said the in-space solar panels are certainly needed, 40 kW sounds like a reasonable amount, though I could see arguments for it to be higher.  If it is also deployable on the surface then it would be a nice supplemental power source and a good gap-filler before the surface power system is deployed.  I favor a disk deploying radially from under neath the nose-cone of the MCT, as this would shade the rest of the vehicle in space and on the Martian surface, use an otherwise inconvenient volume of the MCT and give maximum protection of the solar panels during EDL.

Title: Re: MCT Speculation and Discussion Thread 3
Post by: BobHk on 04/30/2015 02:31 AM
MCT could go light on the power systems if a separate ship landed nearby to provide power, like a Red Dragon launched before main mission.  If the Red Dragon is essentially a solar station + nuclear pile, rtg, artg or whatever, you could land dozens before the first MCT arrives, reducing mass/volume needs for power generation on the MCT itself.

Land them in a cluster, then run a kilometer of power cable to them when the MCT lands.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Semmel on 04/30/2015 05:38 AM
If someone has a more accurate calculation of DeltaV from Mars surface to Earth return trajectory thous would be very useful.  Their may be some saving, but I suspect it will be minimal because a planetary surface and Low orbit are basically the same with regard to the gravity well and Oberth effect.

Of particular interest would be transit times in a direct return, how low can you go and how much dose it cost?

It is a bit more to it since you dont have to raise the periapsis of the escape trajectory above the horizon. Still, the spacecraft needs to achieve escape velocity. So the savings are the "shortcut" that the spacecraft takes in a velocity triangle. However, the escape trajectory from surface has to be more "up" than "sideways", indicating higher gravity losses. I cant imagine that the savings will be significant. I can be totally wrong on this one though, its just my personal, feeling based opinion. As is btw. the opinion of other NSF members that the direct return trajectory saves a lot of fuel.

Unless someone can show me the math, I dont believe that a direct return trajectory is better than going to orbit first.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: GORDAP on 04/30/2015 09:53 AM
If someone has a more accurate calculation of DeltaV from Mars surface to Earth return trajectory thous would be very useful.  Their may be some saving, but I suspect it will be minimal because a planetary surface and Low orbit are basically the same with regard to the gravity well and Oberth effect.

Of particular interest would be transit times in a direct return, how low can you go and how much dose it cost?

It is a bit more to it since you dont have to raise the periapsis of the escape trajectory above the horizon. Still, the spacecraft needs to achieve escape velocity. So the savings are the "shortcut" that the spacecraft takes in a velocity triangle. However, the escape trajectory from surface has to be more "up" than "sideways", indicating higher gravity losses. I cant imagine that the savings will be significant. I can be totally wrong on this one though, its just my personal, feeling based opinion. As is btw. the opinion of other NSF members that the direct return trajectory saves a lot of fuel.

Unless someone can show me the math, I dont believe that a direct return trajectory is better than going to orbit first.

But even if the savings is 2% (and I think it's quite a bit more), what purpose is served by going to orbit first?
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Ben the Space Brit on 04/30/2015 09:54 AM
IMO, with regard to shape, I think that maximum utilisable volume will be a key. To me, that means a cylinder for the outer mould line with a biconic or even smoother aerodynamic nose fairing (either disposable or a key part of the vehicle itself).
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Semmel on 04/30/2015 11:18 AM
But even if the savings is 2% (and I think it's quite a bit more), what purpose is served by going to orbit first?

There are several reasons. It makes targeting the correct escape trajectory easier. I assume that the colony will not be directly at the equator of Mars, so when launching, launch time and the rotation of mars will determine the orbital plane of the MCT. For TEI, the MCT orbital plane must intersect the Ecliptic plane at the correct line (two planes intersection is a line). The TEI burn must happen in the correct direction of the MCT orbit. So there are two parameters that need to be controlled, both are time dependent. With a direct launch to TEI, both time dependent parameters (1: orbital intersection of the launch orbit and the ecliptic; 2: TEI burn direction) must line up. This is very very unlikely to ever happen.

Mars equator plane is 1.8 degrees off of the ecliptic. So if the colony is exactly at the equator, the error might be small enough so that a direct TEI is physically possible. I dont know what it takes to correct for up to ~2 degrees orbital plane misalignment on a TEI. I guess a larger correction burn during the transition would be necessary. The whole operation would be more error prone.

But as I said, its my personal opinion until convinced otherwise.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 04/30/2015 08:10 PM

If the biconic has a reasonably low slope to the side wall then a cylindrical tank (or 2) can fit inside of a conic without wasting much room.  The outer form of the vehicle don't have to be the shape of the tanks inside unless it is like a rocket stage in which these are one in the same, but the thermal protection systems necessary for reentry dictates that the outer surface can't be the tank anyways.


And actual biconic shape and/or capsule shape, would be inefficient for tanks.  Again, on a spacecraft volume (and mass) are at a premium.  So I don't think you'd want to have a big cylindrical central tank with a tapered shell around it.  It'd have a lot of empty space in it that would be difficult to use for anything.  At least not habitat.  Maybe cargo around the bottom, if there were doors that folded out or something.  A series of equipment storage compartments or something?
If you had multiple cylinderical tanks, you'd have something more akin to the S-1B stage.  Although Boeing Methalox concept Mars and Lunar lander did have clustered skinny tanks.
So it's not that you couldn't make it work, but is the capsule shape such an advantage that you'd want too?  Seems that a cylindrical rocket tank with cargo or crew decks on the top or bottom would be much more volume efficient.

And I don't know that the outer surface can't be the tanks.  It can be the tanks with TPS segments affixed to it.  You can't have significant heat get through the TPS system anyway or else it'll burn whatever is behind it, a tank or empty shell or otherwise. 


I think we need to minimizing integration of superfluous systems into the vehicle to get as low a mass as possible.  I'd drop the Sabatier reactor and H2 equipments (atmospheric moisture extractors most likely) immediately, that is a system that makes absolutely ZERO sense to bring back to Earth as its ONLY usable on the surface of Mars and we desperately want to get as high a volume of propellent production going as possible so every bit of ISRU equipment sent to Mars needs to stay to build up production capacity.


You can drop the Sabatier and H2 equipment on Mars, but you have to account for them on the outbound trip.  And it doesn't necessarily make sense to drop them, depending on how much they weigh.  A tank of LH2 would be empty for the trip back obviously, and the Sabatier reactor might not weigh that much.
Depends if you want to keep the MCT vehicle "whole", and how integrated those systems are. 
If you drive somewhere in your car on a hot day and use your A/C, you don't rip it out of your car if you are driving home on a cool day, just because you don't need it and you'll get a little better fuel efficiency without it.  Because the next time you drive your car you don't want to have to put another A/C system back in.
So it depends if those things are "cargo" to be dropped, or intragral parts of MCT's systems and structure.


How about we try this strategy, start with your basic rocket-stage mass and fractions (and I'd recommend using F9 upper stage as an analog rather then Saturn V hardware, it's hydrocarbon based an much more modern), and then for the 'other' stuff try to derive that extra mass from vehicle that had thouse things like capsules or the shuttle orbiter, taking into account the target volumes devoted to these purposes.   That splits the difference between considering the vehicle as 'all stage' or 'all capsule'.


The F9US is a more modern stage, but it's still a "small" upper stage in relation to the booster.  Typical of EELV class rockets.  The S-II was a very large upper stage in relation to it's booster, and much closer to the size range we'd be looking at for MCT.  The mass fractions, etc. of the F9US may not scale up to an S-II sized stage, like MCT (or larger).  The S-II is already about the size we're talking about for MCT, and we can perhaps assume a modern version of it would be may 10-20% lighter?
But for the rest of it, yea.  I think if we had a mass for the ISS ECLSS, that might be an approximate analogue for MCT.  The Shuttle's was really only designed for up to 7 people for two weeks.  Not sure if it'd be a real accurate analog. 

So how did Skylab get into it's orbit?  There was no 3rd stage on it.

According to what I've read Skylab had a mass of only 75 mT, so their was plenty of performance in the first 2 stages to reach LEO without the 3rd stage, or so I presume.

That's right.  INT-21 was calculated to have about 116mt to LEO by itself.  More like 120mt if you use the safety fuel reserve, I believe).  That's pleanty to get a 75mt Skylab into not only LEO, but the 50 deg X ~250mi orbit it was on, as opposed to at typical parking orbit.

When Saturn V was lofting Apollo, that means there was much more than 120mt on top of the S-II.
The S-IVB was 120mt gross by itself.  And the Apollo CSM/LEM stack was 45mt.  Then there's the LAS tower carried part way up.  So there was over 165mt on top of the S-II.  So the S-II couldn't get to LEO without the help of the S-IVB. 


Staging is ALWAYS going to give performance, not take it away.  Having a 2nd stage that did the full Delta-V to LEO and simply dropped the MCT there would indeed be inefficient in the sense that the empty stage mass is mass that could have been vehicle, but I'm expecting the MCT to have some propellent at launch allowing it to do 1-2 km/s after separating from the second stage, that 2nd stage has not in fact been brought to LEO.  A 2nd stage like this that is short of orbital speed like this might still go around the Earth once to allow a RTLS, otherwise downrange recovery may be needed.

I think staging helps performance...for traditional rockets with stages not refueled in orbit.  I think that's the new twist that is changing things.  Because staging helps by kicking off empty mass when the fuel has been burnt out of it.  However, every stage on the stack means there's duplicate tanks, plumbing and engines.  HAving just one upper stage means a heavy stage is going to LEO, but it can then be it's own 3rd stage, so it's mass isn't duplicated.
If you put MCT on a two stage rocket, then you have the dry mass of MCT and the dry mass of the 2nd stage. 

And look historically.  Most LV's that are only going to LEO are two stage.  Saturn 1B, Titan II, INT-21, Energia, STS, SLS (less DCSS or EUS), J-130 (if ever built), etc.  Some of those are 1.5 stage LV's but essentially 2-stage.  So you really don't need 3 stages to get to LEO.  You need 3 stages to get to Mars or the Moon.  And MCT would be it's own 2nd stage going to LEO, refuel, and then be it's own 3rd stage to TMI.
In that way, it can actually plausibly be more mass efficient than if it were launched on top of a 2-stage LV with a partially fueled MCT to be it's own kick stage.  Because then you are pushing up the dry mass of two stages instead of just one.

And it gets even better.  The Saturn V/Apollo stack was essentially a 6 stage LV. 
S-IC, S-II, S-IVB, LEM DM, LEM AM, and SM.  Each of those stages had it's own tanks, engines, plumbing, and electronics, etc.  With the CM essentally being the "Payload" that's returned....although it had it's own tanks, plumbing, RCS engines, electronics and systems.  Almost a 7th stage rather than a payload.
An integrated 2nd stage/MCT means you can do all of that with just two stages.  Refueling once in LEO, and refueling again on the Mars surface.  That's just two sets of tanks, engines, and systems, rather than 7.  One set of RCS thrusters rather than 4.  (The S-IVB had a type of attitude control as I understand?)
One crew area and one ECLSS rather than 3 (CM, SM, and LEM)
Etc.

And -that- is really the beauty of it, even if it were just a bit less than optimal efficient to LEO.  That irrelevant anyway, as any extra fuel burnt up to get to LEO can be replenished there.  IT doesn't have to be particularly fuel efficient to LEO.


EDIT:  Spelling

Title: Re: MCT Speculation and Discussion Thread 3
Post by: TomH on 04/30/2015 10:35 PM
...even if the savings is 2% (and I think it's quite a bit more), what purpose is served by going to orbit first?

Consumables cached in parking orbit for the return journey: food, batteries, medicine, clothing, spare parts, water, anything and everything that you need for the return but that you don't want to expend the ΔV/impulse for downmass/upmass. You'd need to do a trade to measure taking all that to the surface and back up again as opposed to leaving it in parking orbit and picking it back up on the return.  Even if you've recycled or made water on the surface, its heavy to bring up from the surface; leave your water there and pick up this water going uphill. Leave old worn out clothes on the surface (except for what you're wearing); pick up fresh ones from parking orbit. Maybe the trades would say better just to take it all to the surface and back on direct return. Maybe they's show better to park that in orbit and pick it up on the way back. I dunno, but examining the trades is the best way to decide.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Semmel on 05/01/2015 12:00 AM
Consumables cached in parking orbit for the return journey: food, batteries, medicine, clothing, spare parts, water, anything and everything that you need for the return but that you don't want to expend the ΔV/impulse for downmass/upmass. You'd need to do a trade to measure taking all that to the surface and back up again as opposed to leaving it in parking orbit and picking it back up on the return.  Even if you've recycled or made water on the surface, its heavy to bring up from the surface; leave your water there and pick up this water going uphill. Leave old worn out clothes on the surface (except for what you're wearing); pick up fresh ones from parking orbit. Maybe the trades would say better just to take it all to the surface and back on direct return. Maybe they's show better to park that in orbit and pick it up on the way back. I dunno, but examining the trades is the best way to decide.

Except that it is probably much more fuel effective to land and use the atmosphere for most of the breaking instead of using fuel to enter an orbit. Also the departure orbit inclination will probably be totally different than the arrival orbit inclination. Additionally, making rendezvous is much more complicated than making none. Keep it simple guys. The whole operation is complicated enough. Adding more operational hurtles like this will just increase the failure probability.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: TomH on 05/01/2015 01:50 AM
Except that it is probably much more fuel effective to land and use the atmosphere for most of the breaking instead of using fuel to enter an orbit.
This could be put into orbit ahead of time via aerobraking on a separate launch. That allows you to know its safely in place before the humans even leave Earth. I see the merit in your other points.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: guckyfan on 05/01/2015 06:29 AM
Consumables cached in parking orbit for the return journey: food, batteries, medicine, clothing, spare parts, water, anything and everything that you need for the return but that you don't want to expend the ΔV/impulse for downmass/upmass. You'd need to do a trade to measure taking all that to the surface and back up again as opposed to leaving it in parking orbit and picking it back up on the return.  Even if you've recycled or made water on the surface, its heavy to bring up from the surface; leave your water there and pick up this water going uphill. Leave old worn out clothes on the surface (except for what you're wearing); pick up fresh ones from parking orbit. Maybe the trades would say better just to take it all to the surface and back on direct return. Maybe they's show better to park that in orbit and pick it up on the way back. I dunno, but examining the trades is the best way to decide.

Doing the trade you need to take into consideration that the vehicle is designed for up to 100 people and early missions where they all return will have 10 or 12 people max. IMO placing consumables for return in orbit for so few is not worth the operational complexity. And especially not the development efforts needed to do it.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Impaler on 05/01/2015 06:45 AM

You can drop the Sabatier and H2 equipment on Mars, but you have to account for them on the outbound trip.  And it doesn't necessarily make sense to drop them, depending on how much they weigh.  A tank of LH2 would be empty for the trip back obviously, and the Sabatier reactor might not weigh that much.
Depends if you want to keep the MCT vehicle "whole", and how integrated those systems are. 
If you drive somewhere in your car on a hot day and use your A/C, you don't rip it out of your car if you are driving home on a cool day, just because you don't need it and you'll get a little better fuel efficiency without it.  Because the next time you drive your car you don't want to have to put another A/C system back in.
So it depends if those things are "cargo" to be dropped, or intragral parts of MCT's systems and structure.

Anything which is not integral to the vehicle is part of the 100 mT outbound cargo so it is fully accounted for.  The AC analogy is poor, think of it more like "Eskimo in Arctic puts freezer and solar panel in back of pick-up truck and drives to Desert, plugs freezer into solar panels, fills truck with enough ice to get back"  Now dose it makes sense to haul either the freezer or solar panel back to the Arctic?  Once deployed your golden cause you can now leave from the arctic or the desert with ice and ice will even be ready on arrival in the desert rather then having to redeploy the equipment and wait.

Also while the physical Sabatier equipment might have a mass of only a ton, the associated power system (solar or nuclear) is going to be MUCH larger, plus the water collection equipment is even heavier.  The whole Propellent production SYSTEM is HUGE.  I've crunched the numbers that show it is likely going to take the whole 100 mT cargo allocation to provide for the refilling of the size of MCT were talking about over an entire synod.  This is by no means a small bit of fuel efficiency were talking about here.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Semmel on 05/01/2015 10:02 AM
This could be put into orbit ahead of time via aerobraking on a separate launch. That allows you to know its safely in place before the humans even leave Earth. I see the merit in your other points.

Why not put it on the ground ahead of times? I agree, there should not be an MCT with people on board leaving earth before there is sufficient fuel and consumables stockpiled on Mars. But it is not necessary to put into orbit. Aero-breaking is not a viable concept outside of KSP. All missions (Venus, Mars, Jupiter and Saturn orbiters) that considered it decided against it so far.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 05/04/2015 08:39 PM

You can drop the Sabatier and H2 equipment on Mars, but you have to account for them on the outbound trip.  And it doesn't necessarily make sense to drop them, depending on how much they weigh.  A tank of LH2 would be empty for the trip back obviously, and the Sabatier reactor might not weigh that much.
Depends if you want to keep the MCT vehicle "whole", and how integrated those systems are. 
If you drive somewhere in your car on a hot day and use your A/C, you don't rip it out of your car if you are driving home on a cool day, just because you don't need it and you'll get a little better fuel efficiency without it.  Because the next time you drive your car you don't want to have to put another A/C system back in.
So it depends if those things are "cargo" to be dropped, or intragral parts of MCT's systems and structure.

Anything which is not integral to the vehicle is part of the 100 mT outbound cargo so it is fully accounted for.  The AC analogy is poor, think of it more like "Eskimo in Arctic puts freezer and solar panel in back of pick-up truck and drives to Desert, plugs freezer into solar panels, fills truck with enough ice to get back"  Now dose it makes sense to haul either the freezer or solar panel back to the Arctic?  Once deployed your golden cause you can now leave from the arctic or the desert with ice and ice will even be ready on arrival in the desert rather then having to redeploy the equipment and wait.

Also while the physical Sabatier equipment might have a mass of only a ton, the associated power system (solar or nuclear) is going to be MUCH larger, plus the water collection equipment is even heavier.  The whole Propellent production SYSTEM is HUGE.  I've crunched the numbers that show it is likely going to take the whole 100 mT cargo allocation to provide for the refilling of the size of MCT were talking about over an entire synod.  This is by no means a small bit of fuel efficiency were talking about here.

Making the propellant for the return trip may very well take up a large amount of the available cargo, particularly if they bring the LH2 feedstock with them....but as I understand, if using LH2 feed stock, after some intial heat to start the reaction, the reaction is exothermic and self sustaining.  At least the first phase of it.  Then the water produced needs to be cracked to get the O2 (and GH2 feed back into the reaction), and then the O2 and CH4 chilled and liquified.  So there's the energy requirement.  But it's less so than it would be if cracking atmospheric water vapor or mined ground water ice. 

So it uses up part of your cargo capacity, but requires less power.  And I think it produces the propellant much faster than mining water out of the air out out of the ground.  What I don't know is if it's more mass efficient to bring up all the extra solar panels or isotope reactors needed to crack water there for everything, or to bring LH2 feedstock from Earth.
I'm sure the plan at some point down the road is to have continuous propellant manufacturing on the Martian surface to refuel MCT's landing, so they can land will 100mt of other cargo.  Once everything is on the surface, there's no need to haul it back and forth.

However, I was more talking about the first wave of missions.  Which I feel confident will have small crews and which won't have the benefit of established gas stations already there.  Also, they will likely need to explore several interesting loctations across the surface while exploring and scouting for a good locataion to start a base...which would then become a colony.  These early missions would be much more like the Apollo lunar missions than the latter colonization missions.  They won't be leaving anyone on the surface, and if they were to leave a propellant depot, it might not be of use later as the next MCT would be landing at a new location to scout it.  Rovers will help exploration range, but they can only go so far.  At some distance you'll want a new MCT in the area to support the exploration crew.

However, what I sort of expect, would be something along the lines of a modified Mars Direct.  Where an MCT lands on the planet uncrewed with perhaps a tank of LH2 and some isotope generators for power.  (solar arrays would be difficult to deploy on the surface remotely I think, at least in sufficient size)  And then it fills itself up with propellant ahead of a crew. 
Then the crew lands near the first MCT.  Close enough that hoses from the first can be run to the 2nd.  Once landed, the crew MCT is filled up during the surface stay.  At that time large surface solar arrays can be deployed a distance away with power running to the tanker-MCT, as well as atmospheric water vapor extractors.  Now the plant will have the additional power to make propellant fully in-situ without needing more LH2 brough, so each MCT arriving in that location can carry more cargo.   It may take a few crew missions in that area to fully explore and scout it.  At which time the process will be repeated in another location on the planet.  If they had a way to remotely cut the wires to the tanker MCT, it could reuturn itself to Earth once it filled itself back up after the last departing crew has left, for repair and refit, and then be redeployed to a new location.
That would then get around the cargo penalty for each new MCT having to bring it's own propellant manufacturing equipment.  And if there was every a major malfuction with the crewed MCT, the tanker MCT could be used as a lifeboat if it had a crew cabin and ECLSS (which should be integral into all MCT's.  At least space for them would be)  Return trip provisions could be transferred from the crewed MCT to the tanker MCT and the crew can depart on it instead.

As a thought anyway. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: spacenut on 05/04/2015 09:06 PM
I could see a lander only or landers only to set up to begin to make O2 and CH4.   It will take a lot of power and time to process.  I could see a large SEP tug carrying the equipment several months prior to MCT to robotically set up ISRU fuel processing, as well as water and oxygen for humans coming.  Either large solar panels or a small nuclear power plant to make the fuel. 

I also don't really see a need for first landers to return to earth empty.  They could be salvaged for living quarters, fuel storage, water storage, etc.  Engines could be made detachable to return if/when the reusable landers can take the engines back for reprocessing. 

I've thought Falcon heavies could launch large SEP tugs, then 50 ton landers with equipment to be towed to Mars to set up ISRU.  Tugs could return to earth or an "L" location to pick up more equipment and landers.  Robot rovers could haul fuel hoses between the landers to connect for fuel transfers and storage.  Lots of preliminary work could be done with 50 ton units to LEO and SEP tugs. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: TomH on 05/04/2015 10:13 PM
And it gets even better.  The Saturn V/Apollo stack was essentially a 6 stage LV. 
S-IC, S-II, S-IVB, LEM DM, LEM AM, and SM.  Each of those stages had it's own tanks, engines, plumbing, and electronics, etc.  With the CM essentally being the "Payload" that's returned....although it had it's own tanks, plumbing, RCS engines, electronics and systems.  Almost a 7th stage rather than a payload.
An integrated 2nd stage/MCT means you can do all of that with just two stages.  Refueling once in LEO, and refueling again on the Mars surface.  That's just two sets of tanks, engines, and systems, rather than 7.  One set of RCS thrusters rather than 4.  (The S-IVB had a type of attitude control as I understand?)
One crew area and one ECLSS rather than 3 (CM, SM, and LEM)
Etc.

And -that- is really the beauty of it, even if it were just a bit less than optimal efficient to LEO.  That irrelevant anyway, as any extra fuel burnt up to get to LEO can be replenished there.  IT doesn't have to be particularly fuel efficient to LEO.


EDIT:  Spelling

In addition to all that, the BFR booster and the MCT are both supposed to be reusable. Any stages you stick between them are likely to be disposable. Either staging toward LEO is at such high V that reentry will burn it up, or it would be abandoned after TLI, on Mars, or in cis-Martian space. Also, even if the other stages could survive Earth reentry, you couldn't afford the prop for those burns. As it is, the thing is designed with a booster that can land and a return spaceship that can land. Both parts reusable, otherwise this thing would be way too expensive.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: TomH on 05/04/2015 10:21 PM
I've thought Falcon heavies could launch large SEP tugs, then 50 ton landers with equipment to be towed to Mars to set up ISRU.

FH or FHR? Use of Falcon may prove more expensive than BFR/MCT due to the latter's complete reusability and the high efficiency of the Raptor engine. Once the better LV exists, perhaps it's better to use that exclusively, although FH might be utilized to put things in place while BFR/MCT is still being developed. Don't know, just a thought.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 05/04/2015 11:06 PM
If you posit some lander that isn't Dragon or MCT (or smaller than either) you're talking about a development effort likely to be multiple billions of dollars. You then must justify why you're developing a new lander versus just using that funding to expedite MCT.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 05/04/2015 11:53 PM
And it gets even better.  The Saturn V/Apollo stack was essentially a 6 stage LV. 
S-IC, S-II, S-IVB, LEM DM, LEM AM, and SM.  Each of those stages had it's own tanks, engines, plumbing, and electronics, etc.  With the CM essentally being the "Payload" that's returned....although it had it's own tanks, plumbing, RCS engines, electronics and systems.  Almost a 7th stage rather than a payload.
An integrated 2nd stage/MCT means you can do all of that with just two stages.  Refueling once in LEO, and refueling again on the Mars surface.  That's just two sets of tanks, engines, and systems, rather than 7.  One set of RCS thrusters rather than 4.  (The S-IVB had a type of attitude control as I understand?)
One crew area and one ECLSS rather than 3 (CM, SM, and LEM)
Etc.

And -that- is really the beauty of it, even if it were just a bit less than optimal efficient to LEO.  That irrelevant anyway, as any extra fuel burnt up to get to LEO can be replenished there.  IT doesn't have to be particularly fuel efficient to LEO.


EDIT:  Spelling

In addition to all that, the BFR booster and the MCT are both supposed to be reusable. Any stages you stick between them are likely to be disposable. Either staging toward LEO is at such high V that reentry will burn it up, or it would be abandoned after TLI, on Mars, or in cis-Martian space. Also, even if the other stages could survive Earth reentry, you couldn't afford the prop for those burns. As it is, the thing is designed with a booster that can land and a return spaceship that can land. Both parts reusable, otherwise this thing would be way too expensive.

Well said Tom.  This is what I keep coming back to and why.  You hit it on the head.  With just two pieces, you have a RTLS booster, and a spacecraft that comes back. 

You pretty much -cannot- get more simple than that.  And I just don't see the need for that middle stage if you have LEO refueling.   It also means for the refueling, provisioning, and crew launches to LEO, there are just the two pieces to worry about.  The booster RTLS, and a spacecraft that orbit, docks, undocks, and returns just like Dragon does now.   And will land pretty much the same as Dv2 will. 

If the MCT is just these two pices, that's simple, and as Tom says, you don't have an expendable middle stage.  If it were to be made reusable, it'd need to go to Oribt, and then deorbit itself and land.  It could do that of course, but then you have a 3rd piece, and you beg the question, "why?"  Why have that extra piece to worry about?  Why not have MCT spacecraft get itself to LEO, and it just be refueled there?  Once fueled it would be the same as if it were delivered by a 2-stage booster anyway. 
MCT is it's own 2nd stage to orbit, then it's own 3rd stage to TMI.  Then it's own lander.  Then it's own single-stage direct return stage.   And finally it's it's own Earth reentry vehicle. 

To LEO, it wouldn't really be any different than Rocketplane Kistler's K-1, or if Dragon and F9US were integrated into one piece....it would just look like the F9US-R concept, rather than a capsule like Dragon.  But then that's why I believe MCT will also look like that, instead of being a capsule shape.  And why the K-1 looked like that.  Which is why I'm curious why the conventional wisdom seems to keep pushing the capsule shape.

If it were a capsule shape, it'd probably more most like the SERV.  Which would be a much more unconventional design than than a biconic.  That'd be quite a surprise of SpaceX tried to go with something like that, IMO.  Not to mention they've already entertained a biconic with the F9US-R concept.  Although they were building a capsule, F9US-R wasn't a capsule shape with bottom heat shield with engine doors on it.

 

 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 05/05/2015 12:25 AM
To tug on this MCT spacecraft shape issue a little more.   Even if there was a stage between MCT spacecraft and booster, MCT would -still- most likely look like K-1 or NASA DRM 5.0 biconic, because MCT Spacecraft will -still- need to be it's own rocket stage to get off the ground and get home, as well as doing TMI.  I think most people agree that regardless of how many stages the MCT stack turns out to be, the spacecraft will do it's own TMI, and then have to get itself help.  So it will -still- be a rocket stage.  And logic dictates it would look similar to the other such reusable spacecraft/stages.  Although those have been rare, that's what they look like.  It can't look like the Lockheed-Martin winning X-33 concept because that's a horizontal lander and can't get itself off the ground again without significant ground support equipment which MCT won't have for some time.

However, there were two other competing X-33 concepts.  Both look more like a rocket stage than the LM one.  The X-33 project was SSTO to orbit rather tahn TSTO, but it would still be it's own rocket stage.
See here and attached.

http://fas.org/spp/eprint/rampino.htm

The Rockwell one in particular, but as they had it landing horizontally on a runway too, it's only a good reference for it's overall shape...which is a rocket stage with airplane wings.

Then there's the McDonnell Douglas Concept.  Now THAT was is what I really think the MCT spacecraft will take it's lead from, although it shape would be more like the NASA DRM 5.0 biconic aeroshell than this more conical shape.   And I think that so that MCT spacecraft's hull can have commonality with the booster, where MD's X-33 concept was SSTO and there was really no need to have it have any commonality with anything else.
Unlike the Rockwell and LM concepts, the MD concept landed vertically as well as took off vertically, based on it's DC-X research (I'm assuming).  So that's why the MD concept is so interesting, becuase MCT will have to do that too.

Another interesting thing about it is it's leg/fin design.  Think about it, if you have extendable/retractable legs, what happens if one doesn't deploy properly during Mars or Earth EDL?  What happens if one doesn't retract properly during Mars ascent?  The Mars atmosphere is thin, but here will be drag on just one side which will destablize flight at least to some degree.  What happens if it can't be retracted before Earth EDL?  Your're looking at a large safety risk to the crew during Earth EDL and landing, if not a guaranteed  LOC. 
But what if you have fixed legs/fins, like the MD design?  Then you remove that risk entirely.  Just as the biconic shape removes the risk of heat shield door malfunctions.  A page or two ago we looked at a shape that had blisters on the outside resumably for landing legs to fold out of.  But why do that?  Just land on fixed tail fins/legs.  Nothing to fail.  Nothing to extend or retract.  No moving parts.  (Although there could be leveling jacks in them to to level MCT after landing.)  And then you avoid the need to have the legs somehow fold out of the TPS system, like that MCT-like sketch I've posted a few times.  (posted again below for reference...just picture the MD X-33 fin/legs where the extendable legs are).   

Additionally the fins would help provide stability during Mars ascent (the Martian atmosphere is much thinner, but much taller than Earth's, so you are plowing through it for longer), or in case of an emergency booster separation during Earth ascent.  (Think the fins on Dv2).   
I'm guessing that's why the MD X-33 concept had fixed leg/fins, rather than retractable legs.  Stability during early Earth ascent, and fixed landing pads for landing....as well as perhaps housing some control surfaces for "flying" during EDL?  Which would be beneficial for the same reason for MCT during both Mars and Earth EDL.  As I posted before, the AMaRV test vehicle was able to fly itself with some control surfaces using a split body flap.  The MD X-33 seems to have something similar under it to protect the engines, and perhaps steer too?

Again, just my opinion, but it just seemed so obvious once I saw this concept. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: spacenut on 05/05/2015 12:32 AM
I was thinking reusable Falcon heavy with 50 ton payloads to LEO.  It would take the development of a large SEP tug.  However, it can do double duty.  It could take large satelites to GSO launched from a Falcon 9 or a Falcon heavy.  Or tow something to the moon.  Or as a large SEP tug, just a cheap thrown together used once and discard lander kind of like the LEM to drop off the equipment on Mars. 

I'm thinking since Falcon heavy is to be launched this fall, and it will already be working, and if they get the first stage to begin landing and being reused, then use it to launch non perishable things to Mars as a preliminary to the BFR and MCT.  Maybe even a Mini MCT towed to Mars, land, unload, launch back to the tug, and bring it home to reuse.  This could test a lot of reusability for the MCT.  This also might require building fuel depots to refuel mini MCT's and the MCT when it becomes available. 

How far out do you thing BFR and MCT is?  5 years, 10 years? 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: FishInferno on 05/05/2015 12:38 AM
How far out do you thing BFR and MCT is?  5 years, 10 years?

5 years before fist flight, 10 years before Mars landing is my guess
Title: Re: MCT Speculation and Discussion Thread 3
Post by: spacenut on 05/05/2015 12:42 AM
I was just thinking about leveraging Falcon heavy + large SEP tug to haul things to Mars or at least build a fuel depot for the MCT to dock and refuel on it's way to Mars.  Falcon heavy could also carry a 50 ton payload that could be loaded into a large MCT for transport to Mars, or two payloads.  That might be a way to keep from having to land an MCT back on earth to be relaunched every time. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: FishInferno on 05/05/2015 12:49 AM
What if once the MCT arrived back to LEO it was inspected via EVA and if there were any problems that could not be fixed in orbit then it would land, but if everything is normal then it stays in LEO and is resupplied by Falcon Heavies.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 05/05/2015 12:53 AM
I was thinking reusable Falcon heavy with 50 ton payloads to LEO.  It would take the development of a large SEP tug.  However, it can do double duty.  It could take large satelites to GSO launched from a Falcon 9 or a Falcon heavy.  Or tow something to the moon.  Or as a large SEP tug, just a cheap thrown together used once and discard lander kind of like the LEM to drop off the equipment on Mars. 

I'm thinking since Falcon heavy is to be launched this fall, and it will already be working, and if they get the first stage to begin landing and being reused, then use it to launch non perishable things to Mars as a preliminary to the BFR and MCT.  Maybe even a Mini MCT towed to Mars, land, unload, launch back to the tug, and bring it home to reuse.  This could test a lot of reusability for the MCT.  This also might require building fuel depots to refuel mini MCT's and the MCT when it becomes available. 

How far out do you thing BFR and MCT is?  5 years, 10 years?
Mini MCT requires a whole different development that will soon be obsolete but still would be super expensive. Not really worth it. BFR/MCT are supposed to start test flights in ~5 years. Optimistic no doubt, but largely because SpaceX doesn't have the cash, a fact that developing mini-MCT won't help.

I can see maybe a Dragon-based lander for robotic ISRU work, though. Maybe launched (on F9 or FH, perhaps with the help of a SEP stage using their Hall-thrustered constellation satellites as a base for) concurrently with the BFR/MCT test flights.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Oli on 05/05/2015 01:10 AM
MCT is it's own 2nd stage to orbit, then it's own 3rd stage to TMI.  Then it's own lander.  Then it's own single-stage direct return stage.   And finally it's it's own Earth reentry vehicle. 

That's quite ambitious. Let's say propulsive landing from direct reentry costs you 1440m/s of delta v (see here (http://www.ssdl.gatech.edu/papers/conferencePapers/IEEE-2009-1219.pdf)). Add 4300m/s for LEO to Mars transfer gives 5740m/s. Now to the propellant mass fraction. The total MCT mass will be highly sensitive to that. I'd say 85% is extremely ambitious for a vehicle that does EDL on Mars, comes back and does the same on Earth, so let's take that value. Engine isp of 370s.

For bringing 100t to the Martian surface you're looking at an in-LEO mass of 1426t and a dry mass of 214t (without 100t payload).

Ok, that may work. But if you assume a PMF of 80% it's 14k tons in-LEO mass.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: TomH on 05/05/2015 01:14 AM
@Lobo, Also there is the issue of space junk. Look how many strikes the TPS on Orion EFT-1 was just reported to have. More stages means more fairings, more explosive bolts, just more dangerous junk in LEO. A massive two part system lessens the quantity of the junk.

@spacenut, 50 tons via FHR? No, even with another stretch, supercooling the RP-1, increasing the thrust on Merlin 1D again, cross feed, and fully disposable, it's still questionable that FH could reach that advertised 53 tons. FHR? Never.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 05/05/2015 01:29 AM
MCT is it's own 2nd stage to orbit, then it's own 3rd stage to TMI.  Then it's own lander.  Then it's own single-stage direct return stage.   And finally it's it's own Earth reentry vehicle. 

That's quite ambitious. Let's say propulsive landing from direct reentry costs you 1440m/s of delta v (see here (http://www.ssdl.gatech.edu/papers/conferencePapers/IEEE-2009-1219.pdf)).
WAY too high. More like 440m/s.
Quote
Add 4300m/s for LEO to Mars transfer gives 5740m/s.
You can split that in half by also refueling at a high orbit, like an elliptical orbit or EML1/2.

Title: Re: MCT Speculation and Discussion Thread 3
Post by: Oli on 05/05/2015 01:37 AM
MCT is it's own 2nd stage to orbit, then it's own 3rd stage to TMI.  Then it's own lander.  Then it's own single-stage direct return stage.   And finally it's it's own Earth reentry vehicle. 

That's quite ambitious. Let's say propulsive landing from direct reentry costs you 1440m/s of delta v (see here (http://www.ssdl.gatech.edu/papers/conferencePapers/IEEE-2009-1219.pdf)).
WAY too high. More like 440m/s.
Quote
Add 4300m/s for LEO to Mars transfer gives 5740m/s.
You can split that in half by also refueling at a high orbit, like an elliptical orbit or EML1/2.

- It's from the paper I linked to, page 6. Remember no HIAD. Also peak g-Load must be limited. Do you have a better source?

Edit: Found another source here (http://www.nss.org/settlement/mars/AccessToMars.pdf). Page 91. They assume 1/4 of the velocity in the retropropulsion phase is eliminated by drag. Either way, with reserve delta-v (hover/translate) they still at arrive at >1000m/s of propulsive delta-v.

- Yes that could be done, although then Mars to Earth delta v could be the "limiting" factor. In fact it might already be when you depart from LEO. In general though I was only addressing the "LEO to Mars surface and back to Earth surface" case.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Impaler on 05/05/2015 03:14 AM


Making the propellant for the return trip may very well take up a large amount of the available cargo, particularly if they bring the LH2 feedstock with them....but as I understand, if using LH2 feed stock, after some intial heat to start the reaction, the reaction is exothermic and self sustaining.  At least the first phase of it. 

Yes an exothermic H2 based reaction drops the energy cost by around an order of magnitude (cause your H2 IS stored energy), though you now need to get some supplemental oxygen cause your otherwise fuel rich.  While this would drop the mass of equipment needed it would require a huge amount of hydrogen for the size of vehicle being discussed, not only would need nearly the entire 100 mT outbound cargo mass be hydrogen, but you would need a tank so large that it would be bigger then the tank that holds the finished propellents.


I'm sure the plan at some point down the road is to have continuous propellant manufacturing on the Martian surface to refuel MCT's landing, so they can land will 100mt of other cargo.  Once everything is on the surface, there's no need to haul it back and forth.

Yes, Musk has been fairly explicit that water will be sourced on Mars meaning that with CO2 the entire propellent mass is sourced on Mars.  If they are going to establish that infrastructure to do this then why engineer a completely different system which is only used for bootstrapping initial missions and doesn't establish any of the future infrastructure.


However, I was more talking about the first wave of missions.  Which I feel confident will have small crews and which won't have the benefit of established gas stations already there. 

Your clearly familiar with Mars Direct as you quote it so you know that pre-deploying an autonomous lander to do propellent production is a standard way to in fact have a gas station already their, the question is will it be a singe gas can with no refill or will it be a propellent plant with long term production potential.  The only argument against a full blown plant your offering is that you think the power-source (solar) will not be deploy able autonomously.  Deployment is likely to be less of an engineering challenge then sending hydrogen, and even with hydrogen the vehicle needs a deploy able power system anyways, refrigeration of propellents and electrolysis of water that is an unavoidable byproduct of Sabatier, just like like in Mars Direct.  Their is no avoiding that power source, so might as well make it BIG and run a full propellent production plant.


Then the crew lands near the first MCT.  Close enough that hoses from the first can be run to the 2nd. 


Unnecessary, simply ride back in the vehicle that is already full of propellent.


Well said Tom.  This is what I keep coming back to and why.  You hit it on the head.  With just two pieces, you have a RTLS booster, and a spacecraft that comes back. 

You pretty much -cannot- get more simple than that.  And I just don't see the need for that middle stage if you have LEO refueling.   It also means for the refueling, provisioning, and crew launches to LEO, there are just the two pieces to worry about.  The booster RTLS, and a spacecraft that orbit, docks, undocks, and returns just like Dragon does now.   And will land pretty much the same as Dv2 will. 

If the MCT is just these two pices, that's simple, and as Tom says, you don't have an expendable middle stage.  If it were to be made reusable, it'd need to go to Oribt, and then deorbit itself and land.  It could do that of course, but then you have a 3rd piece, and you beg the question, "why?"  Why have that extra piece to worry about?

No it can get simpler, SINGLE STAGE TO EVERYWHERE!  But this nasty thing called the rocket equation prevents that, which is the same thing which I believe makes the only-2-pieces idea not work.  Talking about how cool and simple the idea is doesn't convince me that DeltaV budget works out when combined with a realistic dry mass or that this is a cheaper option then having the 3 piece system employed in F9.  Remember SpaceX uses common diameters, common tooling and common engines between it's first and second stages so they hardly count as extra vehicles to develop.  The only thing we don't know is how they would recover that 2nd stage but we know that they think that will be doable.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Hyperion5 on 05/05/2015 03:46 AM
I've thought Falcon heavies could launch large SEP tugs, then 50 ton landers with equipment to be towed to Mars to set up ISRU.

FH or FHR? Use of Falcon may prove more expensive than BFR/MCT due to the latter's complete reusability and the high efficiency of the Raptor engine. Once the better LV exists, perhaps it's better to use that exclusively, although FH might be utilized to put things in place while BFR/MCT is still being developed. Don't know, just a thought.

BFR is still drastically over-sized for many payloads, so they'll need to launch quite a few FHRs for more conventional payloads.  It is very unlikely Intelsat or Iridium will pay for an enormous launch rocket unless it's dirt cheap, and the fixed costs associated with the BFR means it would need many conventional payloads to pay the bills.  Multiple payloads mean complications, and the BFR's scale itself means rapid reuse is harder.  Economically it's much better suited to putting up massive, heretofore unimaginable spy satellites, space stations, MCTs and the like. 


@spacenut, 50 tons via FHR? No, even with another stretch, supercooling the RP-1, increasing the thrust on Merlin 1D again, cross feed, and fully disposable, it's still questionable that FH could reach that advertised 53 tons. FHR? Never.

Tom, I've got some good and bad news for you with regards to your speculation.  Dmitry_V_home and I just ran the numbers on the Falcon Heavy.  The good news?  The FHR is very unlikely to lift 50 tonnes to LEO.  The bad news?  A Falcon Heavy can definitely lift 53 tonnes to LEO.  I'd share more but a lot of the results rely upon L2 sources.  Let's just say that the FH gives the Saturn V a run-for-the-money to LEO, efficiency-wise.

Interested in knowing more?  Join L2 and go to this post: http://forum.nasaspaceflight.com/index.php?topic=35419.msg1368700#msg1368700. 
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Owlon on 05/05/2015 03:59 AM
No it can get simpler, SINGLE STAGE TO EVERYWHERE!  But this nasty thing called the rocket equation prevents that, which is the same thing which I believe makes the only-2-pieces idea not work.  Talking about how cool and simple the idea is doesn't convince me that DeltaV budget works out when combined with a realistic dry mass or that this is a cheaper option then having the 3 piece system employed in F9.  Remember SpaceX uses common diameters, common tooling and common engines between it's first and second stages so they hardly count as extra vehicles to develop.  The only thing we don't know is how they would recover that 2nd stage but we know that they think that will be doable.

The thing is, the two stage architecture is totally compatible with the rocket equation. The delta-V needed for an empty MCT to return to Earth from the surface of Mars results in a loaded MCT having enough delta-V to act as the second stage, fully refuel in LEO, and perform TMI. Nobody is realistically saying the MCT should act as the second stage through TMI without refueling--that would involve total disregard for the rocket equation, as you're saying. We already have confirmation from SpaceX that MCT will refuel in LEO, though, and we know the whole things needs to come back from the surface of Mars. The dry mass will necessarily have to be aggressive in order to return from Mars.

Knowing that LEO refueling is already in the plans, why would you use a second stage when the payload is a spacecraft with engines and an empty fuel tank of roughly the same size as the second stage? Why not just cut the mass of the second stage out and put that fuel in the MCT's empty tanks instead?
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Impaler on 05/05/2015 04:47 AM
I know Lobo expects to refuel in orbit, everyone knows that's necessary and SpaceX has said that is their plan.  I was clearly mocking his comment about simplicity when talking about a single stage, so making any argument about not refueling off of that is completely bizarre.

Simply stating 'the MCT WILL have X amount of DeltaV' therefore the rocket equation gods have been appeased is not remotely adequate.  You need to actually run the rocket equation and figure out the dry mass fraction that implies, and it's around 15% which is far in excess of what any craft that has done EDL has ever done.  The reusable Falcon 9 has a 6% dry mass so you have virtually no room to work with.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Owlon on 05/05/2015 06:55 AM
I know Lobo expects to refuel in orbit, everyone knows that's necessary and SpaceX has said that is their plan.  I was clearly mocking his comment about simplicity when talking about a single stage, so making any argument about not refueling off of that is completely bizarre.

Simply stating 'the MCT WILL have X amount of DeltaV' therefore the rocket equation gods have been appeased is not remotely adequate.  You need to actually run the rocket equation and figure out the dry mass fraction that implies, and it's around 15% which is far in excess of what any craft that has done EDL has ever done.  The reusable Falcon 9 has a 6% dry mass so you have virtually no room to work with.

By virtue of the fact that the MCT needs to return from Mars' surface, it will necessarily need a boundary-pushing dry mass fraction. SpaceX is extremely good at building lightweight rockets. The F9 upper stage is supposed to have a mass ratio between 1:27 and 1:30 after the F9v1.2 upgrades are implemented.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Semmel on 05/05/2015 07:41 AM
WRT the weight ratio.. I wouldn't be surprised if the dry mass scales with the diameter^2 and the wet mass scales with diameter^3, simply because the volume is linear to d^3 and surface area is scaled with d^2. So I wouldn’t be surprised to find a better dry mass to wet mass ratio with increasing diameter.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: The Amazing Catstronaut on 05/05/2015 07:53 AM

By virtue of the fact that the MCT needs to return from Mars' surface, it will necessarily need a boundary-pushing dry mass fraction. SpaceX is extremely good at building lightweight rockets. The F9 upper stage is supposed to have a mass ratio between 1:27 and 1:30 after the F9v1.2 upgrades are implemented.

True, and I agree with you, but I'll momentarily advocate the diabolical:

A lot of that dry mass will come from areas that they have no experience with to date, such as living areas, food, water, waste, life support, exercise machines, human beings, cargo, sleep compartments, along with just about anything else. It's a bit more than a stage/lander/return craft, it's also a flying apartment building.

Edit: fixed an error.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Krevsin on 05/05/2015 10:17 AM
The idea of a combined Dragon and F9 upper stage as a model for the MCT intrigued me, so for the sake of fun I combined the F9 upper stage and the Dragon V2 into a single vehicle (a mini MCT, if you will) to get a rough estimate of whether or not the mass ratios for an MCT are even possible.

So here's the numbers.

Falcon 9 upper stage wet mass: 96,57 tonnes (source (http://www.spaceflight101.com/falcon-9-v11.html))
Dragon V2 mass: 10,9 tonnes (source (http://forum.nasaspaceflight.com/index.php?topic=33423.msg1367977#msg1367977), I combined the launch weight and fuel. Correct me if this is wrong.)
Combined wet mass:107,47 tonnes

Falcon 9 upper stage dry mass: 3,9 tonnes (source (http://www.spaceflight101.com/falcon-9-v11.html))
Dragon V2 mass: 10,9 tonnes (source (http://forum.nasaspaceflight.com/index.php?topic=33423.msg1367977#msg1367977), the fuel mass was kept into the account intentionally)
Combined dry mass: 14,8 tonnes

The mass ratio, as calculated by combined wet mass divided by combined dry mass comes to 7,261, or 13,771% so it would seem that SpaceX can in fact do some pretty impressive mass ratios.

Assuming this ratio scales perfectly to the MCT, you get 7059,805 m/sec of delta V by plugging it into the rocket equation with an ISP of 363 sec (which I've seen tossed around for the Raptor on this forum somewhere),


Granted, this is by no means an exact model, as it doesn't take into account the heat shielding required for reentry or the landing gear required for the "mini MCT" to land, it assumes that the F9 2nd stage can land without any additional reinforcement, and (probably fatally) assumes that the mini MCT mass ratio would scale exactly to the proper MCT (which it doesn't, most likely), but it proves that high mass ratios for a combined US+Capsule vehicle are in fact achievable by current SpaceX tech.

edit: Let's be cheeky and plug in the values for the heat shield, landing gear and whatever is needed to make a 2nd stage landable into the "mini MCT" model above. Let's say it adds 5 more tonnes to the dry mass, more than a third of its original dry mass.

combined wet mass: 112,47 tonnes
combined dry mass: 18,2 tonnes


Mass ratio: 6,179 or 16,182%.

Delta V, if ratio scales perfectly to MCT proper: 6485,193 m/s
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 05/05/2015 02:55 PM
MCT is it's own 2nd stage to orbit, then it's own 3rd stage to TMI.  Then it's own lander.  Then it's own single-stage direct return stage.   And finally it's it's own Earth reentry vehicle. 

That's quite ambitious. Let's say propulsive landing from direct reentry costs you 1440m/s of delta v (see here (http://www.ssdl.gatech.edu/papers/conferencePapers/IEEE-2009-1219.pdf)).
WAY too high. More like 440m/s.
Quote
Add 4300m/s for LEO to Mars transfer gives 5740m/s.
You can split that in half by also refueling at a high orbit, like an elliptical orbit or EML1/2.

- It's from the paper I linked to, page 6. Remember no HIAD.
No HIAD but it's going to be mostly empty. It's a giant tank, and isn't limited to just 5m in diameter or whatever. It seems likely they may have deployable surfaces like legs which significantly increase the effective cross-section without using an inflatable (which would be expendable).
Quote
Also peak g-Load must be limited.
What's the ultimate limit? Humans can take a huge amount of g-load if for short periods. Also, a skip reentry followed by a lifting reentry and picking a low altitude landing site gives you lots of options for shedding the vast majority of velocity using drag without exceeding the allowable loads, even if you have especially high incoming velocity.

Quote
Edit: Found another source here (http://www.nss.org/settlement/mars/AccessToMars.pdf). Page 91. They assume 1/4 of the velocity in the retropropulsion phase is eliminated by drag.
Just 1/4 is WAY too low.
Quote
Either way, with reserve delta-v (hover/translate) they still at arrive at >1000m/s of propulsive delta-v.
Hover/translate is super, super wasteful especially on Mars. No wonder they get so high delta-v. You'd be much better off putting an escape pod where you cram everyone in (in case the nominal landing starts being non-nominal). No way this will be landed by humans like for Apollo. Far too risky to do that with the much higher gravity of Mars.


The terminal velocity of something like MCT on its side with aerosurfaces deployed landing at low altitude is more like 400-500m/s. Do a hover-slam on that. If the hover-slam is going badly, press the red button.
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 05/05/2015 04:57 PM
No it can get simpler, SINGLE STAGE TO EVERYWHERE!  But this nasty thing called the rocket equation prevents that, which is the same thing which I believe makes the only-2-pieces idea not work.  Talking about how cool and simple the idea is doesn't convince me that DeltaV budget works out when combined with a realistic dry mass or that this is a cheaper option then having the 3 piece system employed in F9.  Remember SpaceX uses common diameters, common tooling and common engines between it's first and second stages so they hardly count as extra vehicles to develop.  The only thing we don't know is how they would recover that 2nd stage but we know that they think that will be doable.

The thing is, the two stage architecture is totally compatible with the rocket equation. The delta-V needed for an empty MCT to return to Earth from the surface of Mars results in a loaded MCT having enough delta-V to act as the second stage, fully refuel in LEO, and perform TMI. Nobody is realistically saying the MCT should act as the second stage through TMI without refueling--that would involve total disregard for the rocket equation, as you're saying. We already have confirmation from SpaceX that MCT will refuel in LEO, though, and we know the whole things needs to come back from the surface of Mars. The dry mass will necessarily have to be aggressive in order to return from Mars.

Knowing that LEO refueling is already in the plans, why would you use a second stage when the payload is a spacecraft with engines and an empty fuel tank of roughly the same size as the second stage? Why not just cut the mass of the second stage out and put that fuel in the MCT's empty tanks instead?

Yes, you beat me to it Owlon,

It's not that this is two stage to TMI.  This is actually 3 stage to TMI.  Is there any reason a Saturn V couldn't have gone to Mars?  Just with less mass than it could send to the moon?  No.  It was a 3 stage rocket, just like this MCT concept would be.  It just removes the S-IVB stage dry mass, and integrates the LEM and Apollo CSM onto the S-II stage, and gets rid of the dry mass of their separate propulsion and RCS systems.  It's fully refueled in LEO, and thus becomes it's own 3rd stage prior to the TMI burn....it is now a 3 stage rocket  No rocket equation issues.  It avoids completely the LOI burn by the Apollo service module (MOI in this case) by doing direct Mars EDL.  And then it uses it's large biconic surface area to supply a large portion of the dV that the Apollo  LEM descent module provided.  It then refuels to provide both the LEM ascent module dV, and the Service Module TEI dV to get back to Earth.  Finally, just like the Apollo CM, it uses the Earth's atmosphere to supply almost all of the dV to land, with just a very small dV needing to be provided by it's enignes to land on the ground instead of by parachutes and the ocean itself.

I was clearly mocking his comment about simplicity when talking about a single stage

Now that's not very nice.  ;-)

By virtue of the fact that the MCT needs to return from Mars' surface, it will necessarily need a boundary-pushing dry mass fraction. SpaceX is extremely good at building lightweight rockets. The F9 upper stage is supposed to have a mass ratio between 1:27 and 1:30 after the F9v1.2 upgrades are implemented.

Yes.  Well said Owlon.  And I've said similar in previous posts.  It's not really the requirement to get to LEO that will drive the MCT Spacecraft's design...it's the requirements to get itself off the surface of Mars and back to Earth.  Once those are satisfied, it should be plenty large enough to get itself to LEO regardless.

And I don't know that it was ever published, but I'm sure it was calculated internally by SpaceX while they were considering it, but what might the mass ratio of the F9US-R concept have been?  It'd have added a TPS system, landing legs, and [apparently] superdracos and hypergolic tanks to a standard F9US.  I can't even hazard a guess....but the mass fraction of this...as a basic platform...doesn't look -too- prohibitive.

Title: Re: MCT Speculation and Discussion Thread 3
Post by: Lobo on 05/05/2015 05:19 PM
The idea of a combined Dragon and F9 upper stage as a model for the MCT intrigued me, so for the sake of fun I combined the F9 upper stage and the Dragon V2 into a single vehicle (a mini MCT, if you will) to get a rough estimate of whether or not the mass ratios for an MCT are even possible.

So here's the numbers.

Falcon 9 upper stage wet mass: 96,57 tonnes (source (http://www.spaceflight101.com/falcon-9-v11.html))
Dragon V2 mass: 10,9 tonnes (source (http://forum.nasaspaceflight.com/index.php?topic=33423.msg1367977#msg1367977), I combined the launch weight and fuel. Correct me if this is wrong.)
Combined wet mass:107,47 tonnes

Falcon 9 upper stage dry mass: 3,9 tonnes (source (http://www.spaceflight101.com/falcon-9-v11.html))
Dragon V2 mass: 10,9 tonnes (source (http://forum.nasaspaceflight.com/index.php?topic=33423.msg1367977#msg1367977), the fuel mass was kept into the account intentionally)
Combined dry mass: 14,8 tonnes

The mass ratio, as calculated by combined wet mass divided by combined dry mass comes to 7,261, or 13,771% so it would seem that SpaceX can in fact do some pretty impressive mass ratios.

Assuming this ratio scales perfectly to the MCT, you get 7059,805 m/sec of delta V by plugging it into the rocket equation with an ISP of 363 sec (which I've seen tossed around for the Raptor on this forum somewhere),


Granted, this is by no means an exact model, as it doesn't take into account the heat shielding required for reentry or the landing gear required for the "mini MCT" to land, it assumes that the F9 2nd stage can land without any additional reinforcement, and (probably fatally) assumes that the mini MCT mass ratio would scale exactly to the proper MCT (which it doesn't, most likely), but it proves that high mass ratios for a combined US+Capsule vehicle are in fact achievable by current SpaceX tech.

edit: Let's be cheeky and plug in the values for the heat shield, landing gear and whatever is needed to make a 2nd stage landable into the "mini MCT" model above. Let's say it adds 5 more tonnes to the dry mass, more than a third of its original dry mass.

combined wet mass: 112,47 tonnes
combined dry mass: 18,2 tonnes


Mass ratio: 6,179 or 16,182%.

Delta V, if ratio scales perfectly to MCT proper: 6485,193 m/s

Very interesting Krevsin.  Thanks for running that. 

A couple of comments.

Quote
Granted, this is by no means an exact model, as it doesn't take into account the heat shielding required for reentry or the landing gear required for the "mini MCT" to land, it assumes that the F9 2nd stage can land without any additional reinforcement, and (probably fatally) assumes that the mini MCT mass ratio would scale exactly to the proper MCT (which it doesn't, most likely), but it proves that high mass ratios for a combined US+Capsule vehicle are in fact achievable by current SpaceX tech.


Heat Shield:  Dv2 will have a heat shield, so it's dry mass does account for it.  Of course, it's a much smaller heat shield that an integrated stage/capsule biconic shape would have.  But the biconic has a much greater surface area so it's "fluffier" and thus has a lower heat load per surface area.  So the TPS may not need to be as thick.  So Dragon's heat shield mass may not be a wholly inaccurate estimate of the larger but potentially thinner biconic heat shield

Landing Legs:  The F9US probably would not need to be reinforced to land, or at least not much.  During launch, an interstage adaptor that fits right under it's tanks support it's fully fueled mass during take off...not to mention the mass of the payload and PLF sitting on top of it.  So there's no reason to think that if legs are attached on that same area that it couldn't support it's mass dry when it touches down.  Granted, the legs can't attach to right where the interstage adaptor does, so some bracketing will need to be done, but you see the point. 
As for including their mass in your estimate, the dry mass of Dv2 does includes landing legs, although they would probably be a little smaller than an integrated F9US/Dv2 would need.  Still, Dv2's dry mass does in fact account for landing legs...of a type.

Mass Ratio:  AS Semmel states, the mass ratio should actually get better as you scale up.

WRT the weight ratio.. I wouldn't be surprised if the dry mass scales with the diameter^2 and the wet mass scales with diameter^3, simply because the volume is linear to d^3 and surface area is scaled with d^2. So I wouldn’t be surprised to find a better dry mass to wet mass ratio with increasing diameter.

Finally you mention a Raptor ISP of 363s.  Maybe others have heard differently, but I thought I'd heard Elon say that 380s was the impulse they are hoping for with Raptor?  If so, maybe you run the equation again with the higher ISP value?

Title: Re: MCT Speculation and Discussion Thread 3
Post by: Robotbeat on 05/05/2015 05:22 PM
Remember that pressure vessels don't scale with simple surface area, but their mass is proportional to volume.

Also remember that many structures (buckling-limited ones) actually scale up worse the larger they get, which is why there aren't any elephant-sized insects (on land, at least).
Title: Re: MCT Speculation and Discussion Thread 3
Post by: Oli on 05/05/2015 05:46 PM