Author Topic: MCT Speculation and Discussion Thread 4  (Read 621484 times)

Offline MikeAtkinson

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Re: MCT Speculation and Discussion Thread 4
« Reply #1100 on: 11/04/2015 01:37 PM »
Given these, I'm going to ask for consensus from both sides of the debate:
Is it possible to conclude at this point that the *only way* to achieve 1 mission per synod per vehicle (given obvious assumptions like methalox + Raptor) is using high-velocity aerocapture as well as refueling from an already-prepared Mars surface fuel depot during a short (days-weeks) surface stay?

I know no other way to achieve 1 mission per synod per vehicle than using opposition class missions. This requires refuelling from a Mars surface depot.

The NASA Tracjectory Browser can give useful results. Earth re-entry speeds may be pretty high.




Offline guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #1101 on: 11/04/2015 01:40 PM »
1) was not explicitly mentioned by someone SpaceX, as far as I know but yes it is a necessary requirement. That is if aerocapture includes the possibility of direct EDL from interplanetary speeds.

2) and 3) were both mentioned as part of the plan, so yes.

Offline spacenut

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Re: MCT Speculation and Discussion Thread 4
« Reply #1102 on: 11/04/2015 03:11 PM »
So, a few robotic MCT's might have to land first to get fuel made before humans arrive.  SEP tugs might have to get fuel depots in place also.  I know a Martian GPS system and 24 hour communication system will have to be in place.  Why not fuel depots at either end as well as on the surface? 

Offline nadreck

Re: MCT Speculation and Discussion Thread 4
« Reply #1103 on: 11/04/2015 03:48 PM »
Given these, I'm going to ask for consensus from both sides of the debate:
Is it possible to conclude at this point that the *only way* to achieve 1 mission per synod per vehicle (given obvious assumptions like methalox + Raptor) is using high-velocity aerocapture as well as refueling from an already-prepared Mars surface fuel depot during a short (days-weeks) surface stay?

I know no other way to achieve 1 mission per synod per vehicle than using opposition class missions. This requires refuelling from a Mars surface depot.

The NASA Tracjectory Browser can give useful results. Earth re-entry speeds may be pretty high.

One other possibility involves LMO refuelling and cargo transfer to dedicated surface to LMO craft.

It is all well and good to quote those things that made it past your confirmation bias that other people wrote, but this is a discussion board damnit! Let us know what you think! And why!

Offline guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #1104 on: 11/04/2015 04:02 PM »
Why not fuel depots at either end as well as on the surface?

It would require dedicated launch vehicles to fill up the depot on Mars. Early in colony development there will be no capability to service them.

Offline slavvy

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Re: MCT Speculation and Discussion Thread 4
« Reply #1105 on: 11/04/2015 04:06 PM »
Don´t know if this fits in this thread. It is a speculation and it involves Mars and SpaceX...
Could they secretly plan and build a Mars bound payload for the next 2018 launch window?
Launch on a Falcon Heavy, a Mars communication satellite or even a small lander with, for example, an ISRU test payload?

Offline Jim_LAX

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Re: MCT Speculation and Discussion Thread 4
« Reply #1106 on: 11/04/2015 04:43 PM »
Schedule-wise this is at least conceivable, but I think they will be focusing on first stage reuse and working through their launch manifest.  I could see their first Falcon Heavy sending something around the moon, but Mars is much farther into the future!
"I don't go along with going to the Moon first in order to build a launch pad to go to Mars.  We should go to Mars from Earth orbit."

Offline Burninate

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Re: MCT Speculation and Discussion Thread 4
« Reply #1107 on: 11/04/2015 08:13 PM »
Given these, I'm going to ask for consensus from both sides of the debate:
Is it possible to conclude at this point that the *only way* to achieve 1 mission per synod per vehicle (given obvious assumptions like methalox + Raptor) is using high-velocity aerocapture as well as refueling from an already-prepared Mars surface fuel depot during a short (days-weeks) surface stay?

I know no other way to achieve 1 mission per synod per vehicle than using opposition class missions. This requires refuelling from a Mars surface depot.

The NASA Tracjectory Browser can give useful results. Earth re-entry speeds may be pretty high.

One other possibility involves LMO refuelling and cargo transfer to dedicated surface to LMO craft.

If you think this is a legit alternative, could you expand on it sufficient to understand what you're proposing?  It doesn't seem to mitigate the need for extreme aerocapture or a Mars surface depot or a short stay, and it sounds fairly difficult on top of that.

Still waiting to hear acknowledgements or challenges from several others on my point.

Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #1108 on: 11/05/2015 12:31 AM »
It should be noted that the direct-entry trajectory that MSL Curiosity did (using a PICA heatshield, by the way...) or especially Pathfinder--7km/s entry--did weren't much more "extreme" than the aerocapture we're talking about here. Aerocapture on the first pass would only need to bleed enough velocity off to allow capture (and can do so over a longer distance because you have both sides of periapsis plus ability to use negative lift), whereas those had to bleed all the velocity at once. I know that parts of MSL's entry peaked at like 15 gees, briefly. An aerocapture from even a fast transit would be much lower acceleration.


...btw, I'm waiting for c3planner.com to return. It sure is nice to calculate ~100 day transits to Mars to see the required c3 and entry c3 (although even c3planner.com doesn't give the TRUE minimum c3...).
« Last Edit: 11/05/2015 12:43 AM by Robotbeat »
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Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #1109 on: 11/05/2015 02:20 AM »
Given these, I'm going to ask for consensus from both sides of the debate:
Is it possible to conclude at this point that the *only way* to achieve 1 mission per synod per vehicle (given obvious assumptions like methalox + Raptor) is using high-velocity aerocapture as well as refueling from an already-prepared Mars surface fuel depot during a short (days-weeks) surface stay?

I know no other way to achieve 1 mission per synod per vehicle than using opposition class missions. This requires refuelling from a Mars surface depot.

The NASA Tracjectory Browser can give useful results. Earth re-entry speeds may be pretty high.

One other possibility involves LMO refuelling and cargo transfer to dedicated surface to LMO craft.

If you think this is a legit alternative, could you expand on it sufficient to understand what you're proposing?  It doesn't seem to mitigate the need for extreme aerocapture or a Mars surface depot or a short stay, and it sounds fairly difficult on top of that.

Still waiting to hear acknowledgements or challenges from several others on my point.

I would almost agree with this, if we were talking about a manned mission.  But if we relax the requirement to cargo and thus have nearly the entire snyod to spend in space we can take the slowest trajectories and arrive back at Earth just short of the next launch window.

Playing around with the NASA trajectory it looks like their is a class of trajectories that are longer then traditional opposition missions but just shy of a full synod.  The aerocapature on these trajectories is significantly easier particularly on Earth ( ~14 km/s most cases vs >16 for nearly all opposition returns), mars stay times are around 100 days (which still means having propellant ready on the surface before arrival), mars departure and capture DeltaV is lower too but the Earth entry velocity is always the going to be the more demanding one in any trajectory.  They generally consist of a slow outbound leg in which the spacecraft goes beyond mars orbit followed by a return in which the craft stay outside of Earth orbit rather then going through aphelion within the orbit of the Earth and often inside that of Venus on an opposition return.

I'm calling them "Syno-Max"  trajectories

NASA trajectory Browser

Earth Departure  Feb-20-2030  ->  Earth reentry Dec-24-2031      14.86 km/s reentry

Earth Departure Aug-02-2031  ->   Earth reentry Jul-22-2033      14.11 km/s reentry

Earth Departure  Sep-08-2033  ->  Earth reentry  Sep-14-2035     14 km/s reentry

Here are some examples that just about work though some departures are a few months from working, I think some additional tweaking could get these to dove-tail together as their is a lot of time on mars or outbound leg time that could be taken from.  At least a month on Earth seems a reasonable minimum to refurbish and relaunch.

To really find out what is possible we would need trajectory simulator that actually chains together the many back and forth legs and can find for minimizing both DeltaV, duration and entry velocity.  The optimum chain may actually consist of a mix of different trajectories from year to year.


Also if were talking SEP their may be 1 synod round trips their as well, but they would require a lot of power and would look mostly like classic opposition trajectories in which you do aphelion withing the orbit of Earth.  It requires some impressive DeltaV, 10 km/s outbound 22 inbound and this is just to go between High Earth orbit and mars obit with propulsive capture but the acceleration is fairly modest at only 0.40 mm/s outbound and 0.56 mm/s inbound.  If we were to do aerocapture (which would certainly require the magneto-plasma technique to brake a SEP vehicle) the DeltaV would drop considerably, and if we took on SEP propellants at Mars orbit (presumably from depots) we would be looking at very nearly 80% of the outbound mass being cargo.  I'm doubtful that it would be desirable for crew as the transit times are a year each way so this is best used a freight-hauling solution.

My solution would be to make a vehicle that splits in two, a large drive section and a simple freight section that is just a frame with cargo containers attached all over it's surface and propellant tanks.  Upon arrive at the destination the vehicles splits apart and changes out it's freight section and picks up a new one.  At Earth a freight section full of cargo and propellants is picked up, at mars this freight section is empty of propellant and is dropped off and a section full of return propellant is picked up.  With 3 freight sections per drive section you have one being loaded, one being unloaded and one in transit at all times, and the freight section acts as the propellant depot and the turn-around operation is simplified to a single docking and un-docking for the drive section.

https://engineering.purdue.edu/people/james.m.longuski.1/ConferencePapersPresentations/2005Low-ThrustRoundtripTrajectoriestoMarswithOne-Synodic-PeriodRepeatTime.pdf
« Last Edit: 11/05/2015 07:03 PM by Impaler »

Offline Sohl

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Re: MCT Speculation and Discussion Thread 4
« Reply #1110 on: 11/05/2015 04:57 PM »
My solution would be to make a vehicle that splits in two, a large drive section and a simple freight section that is just a frame with cargo containers attached all over it's surface and propellant tanks.  Upon arrive at the destination the vehicles splits apart and changes out it's freight section and picks up a new one.  At Earth a freight section full of cargo and propellants is picked up, at mars this freight section is empty of propellant and is dropped off and a section full of return propellant is picked up.  With 3 freight sections per drive section you have one being loaded, one being unloaded and one in transit at all times, and the freight section acts as the propellant depot and the turn-around operation is simplified to a single docking and un-docking for the drive section.

Something like this?  ;D


Offline Lars-J

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Re: MCT Speculation and Discussion Thread 4
« Reply #1111 on: 11/05/2015 05:43 PM »

Impaler, please shorten your URL, it is breaking the site layout. (using Chrome)

Use this syntax (without spaces): [ url = http://whatever ] link text [ url ]

Offline meekGee

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Re: MCT Speculation and Discussion Thread 4
« Reply #1112 on: 11/05/2015 06:59 PM »
Impaler's concept always made sense to me, but with VTVL.

I envisioned MCT as a fuel-and-propulsion central core, and then cargo/habitat all around it.

It lands, sheds the payload, and can fly back much lighter.

You automatically get the benefit of a large cross section for Mars EDL, and a smaller one when returning to Earth.

Basically, Mars needs enclosed volumes for habitation and storage.  It seems such a shame to haul back an empty cargo hold.

This configuration also solves the "how to get the payload to the ground" question.  It's already at ground level when you land.

Get back to earth, attach new "saddle bags", and lift off again.

IMO there won't be in-orbit refueling around Mars, and so it is important to minimize the empty mass of MCT on the flight back, so the same engine and tanks will give you more dV.

EDIT:  No SEP in my concept.  Just a rocket with about 5 km/sec outbound dV, and about 1.5 times that on the way back.
« Last Edit: 11/05/2015 10:05 PM by meekGee »
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Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #1113 on: 11/05/2015 09:47 PM »
My solution would be to make a vehicle that splits in two, a large drive section and a simple freight section that is just a frame with cargo containers attached all over it's surface and propellant tanks.  Upon arrive at the destination the vehicles splits apart and changes out it's freight section and picks up a new one.  At Earth a freight section full of cargo and propellants is picked up, at mars this freight section is empty of propellant and is dropped off and a section full of return propellant is picked up.  With 3 freight sections per drive section you have one being loaded, one being unloaded and one in transit at all times, and the freight section acts as the propellant depot and the turn-around operation is simplified to a single docking and un-docking for the drive section.

Something like this?  ;D

No nothing like that, it would look like this  8)



You see I'm not proposing a landing craft, I'm proposing a pure spacecraft (did I not mention it was SEP propulsion based).  The landers stay at mars and unload it over the whole synod as well as refill the fuel tanks.  At Earth we have the BFR launching constantly and a smaller type of SEP tug that moves cargo from LEO up the high orbit staging area.

This old Russian concept is what it would most resemble, but rather then a habitat and lander it moves pure cargo  http://www.energia.ru/en/history/mars/concept.html


Impaler's concept always made sense to me, but with VTVL.

I envisioned MCT as a fuel-and-propulsion central core, and then cargo/habitat all around it.

It lands, sheds the payload, and can fly back much lighter.

You automatically get the benefit of a large cross section for Mars EDL, and a smaller one when returning to Earth.

Basically, Mars needs enclosed volumes for habitation and storage.  It seems such a shame to haul back an empty cargo hold.

This configuration also solves the "how to get the payload to the ground" question.  It's already at ground level when you land.

Get back to earth, attach new "saddle bags", and lift off again.

IMO there won't be in-orbit refueling around Mars, and so it is important to minimize the empty mass of MCT on the flight back, so the same engine and tanks will give you more dV.

You have it backwards I'm not proposing a lander that comes apart, that is a bad idea it makes the vehicle much weaker and complicates it a lot.  I think the lander would have an internal cargo-bay which is simply emptied at mars for a cargo flight and carries a small return habitat for a crew flight.  Also their is no reason to reduce cross-section at Earth, more cross-section is always better for aerocapture.  And yes I'm in favor VTVL.

« Last Edit: 11/05/2015 09:50 PM by Impaler »

Online docmordrid

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Re: MCT Speculation and Discussion Thread 4
« Reply #1114 on: 11/05/2015 10:35 PM »
My solution would be to make a vehicle that splits in two, a large drive section and a simple freight section that is just a frame with cargo containers attached all over it's surface and propellant tanks.  Upon arrive at the destination the vehicles splits apart and changes out it's freight section and picks up a new one.  At Earth a freight section full of cargo and propellants is picked up, at mars this freight section is empty of propellant and is dropped off and a section full of return propellant is picked up.  With 3 freight sections per drive section you have one being loaded, one being unloaded and one in transit at all times, and the freight section acts as the propellant depot and the turn-around operation is simplified to a single docking and un-docking for the drive section.

Something like this?  ;D

No nothing like that, it would look like this  8)



You see I'm not proposing a landing craft, I'm proposing a pure spacecraft (did I not mention it was SEP propulsion based). 
>

Not to pick nits, but Enterprise saucer section could land. The entire Intrepid Class (ex: Voyager) could land.
DM

Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #1115 on: 11/06/2015 02:59 AM »
Impaler: So your spacecraft wouldn't land? Cool, so you're not actually describing Musk's MCT but something else. Musk pretty clearly said MCT would land.
« Last Edit: 11/06/2015 03:02 AM by Robotbeat »
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Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #1116 on: 11/06/2015 03:38 AM »
The BFR first stage won't even reach Earth orbit, dose that mean it's not part of the Mars Colonial Transport SYSTEM?  I have already clearly described a landing craft (which you railed against most vehemently).

In-space only vehicles are more efficient mass movers, but need landers to be of any use.  A lander could operate initially on it's own all be it less efficiently so the logical development is to do the lander firs and then augment it will a freight hauler.  This is how you would get into the huge numbers per year colonization effort as they would be requiring huge cargo imports that are time-insensitive.


Not to pick nits, but Enterprise saucer section could land. The entire Intrepid Class (ex: Voyager) could land.

More of a survivable crash-landing that left the vehicle a total loss.  And Intrepid class landing sequence really makes no sense the landing-gear-area is orders of magnitude too small, the legs would be driven strait into anything softer then solid rock.  Which brings us back to the prepared/unprepared landing site distinction, Intrepid depicts the landing-gear appropriate for the former but performs the later.
« Last Edit: 11/06/2015 03:54 AM by Impaler »

Offline GregA

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Re: MCT Speculation and Discussion Thread 4
« Reply #1117 on: 11/06/2015 10:28 AM »
The BFR first stage won't even reach Earth orbit, dose that mean it's not part of the Mars Colonial Transport SYSTEM?  I have already clearly described a landing craft (which you railed against most vehemently).
But.... "Land the whole thing", right?

Offline philw1776

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Re: MCT Speculation and Discussion Thread 4
« Reply #1118 on: 11/06/2015 12:02 PM »
I'm one of those who in this thread adheres to Musk quotes like "land the whole thing" for the purpose of coherent speculation.  However I'll bet that most here agree that SX's concepts for MCT have likely evolved considerably from the few sometimes off the cuff statements by Elon, many several years old.  I'll state further that I believe it probable the MCT that actually flies will again have notable differences from the MCT concept that Musk reveals later this year, if he even meets that schedule.
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Offline spacenut

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Re: MCT Speculation and Discussion Thread 4
« Reply #1119 on: 11/06/2015 04:25 PM »
Since a lot more freight would have to be hauled to Mars than people.  In space could be done by SEP tugs on a continuous bases.  LEO to LMO via one or more SEP tugs.  A specialty lander for use on Mars could indeed take freight from LMO to the surface.  The lander could have ISRU equipment/solar panels to manufacture it's fuel from Martian atmosphere when not in use or there could be a separate fuel farm nearby.  Once refueled, it could go pick up another load. 

Humans could travel at a much faster rate with the MCT. 

This plan would require the BFR.
It would require a reusable second stage.
It would require a fleet of large SEP tugs.
A cargo carrier that can be transferred from the second stage to the SEP tug.
A re-usable lander at Mars.
A fuel farm at Mars or a lander large enough to have it's on ISRU equipment. 

An MCT that could be refueled in LEO and fly to Mars.  It might not need to land on Mars, just transfer the human habitation module to the lander.  MCT would fly back to earth.  Lander would take people to Mars surface.  The habitation module could be or would be about the same size as a cargo module. 

This plan might be cheaper to operate overall, but would require a lot of building and development of specialty components.  It would also require a lot of in space dockings and transfers.   However, these specialty components could be built by other companies or countries to have a stake in the colonialization process. 

On the other hand, if everything Musk wants to build is big, then It might be more simple to go directly from Earth to Mars will a couple of refueling stops for both humans and cargo an have contributors supply fuel or Martian surface cargo to have a stake in colonialization. 
« Last Edit: 11/06/2015 04:27 PM by spacenut »

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