Author Topic: MCT Speculation and Discussion Thread 4  (Read 569540 times)

Offline Chris Bergin

Re: MCT Speculation and Discussion Thread 4
« Reply #1900 on: 04/09/2016 04:50 PM »
Chris, and I'll report my own post so Chris reads it. You seem to know things about SpaceX's Mars plans. Is it true you've kept some of it to yourself or is it all in L2?

Yeah, I've had to keep a lot to myself, working to the guidelines provided when it was shown to me (that's totally natural on the process for a lot of things....in fact it's almost a set response of "what can I actually use" with most things). With L2, we already had an envisioning process going on (really cool work by clever folk, both in numbers and renders) and we mixed in, with permission, some of the planning phase into that to aid the accuracy of the envisioning. Naming no names, but we sent the rendering envisioning on a particular (you'd know the name) person at SpaceX I've chatted with and that got some thumbs up (probably because they look super cool, not making any claims here ;))

The notable caveats to everything include that they will be evolving their plans all the time (and getting "crazier" by the month apparently, which I'm sure Elon was alluding to yesterday) and only Elon will be the one to show off the actual plans - and that's only right.

Sometimes you have to remember you're a fan of rockets first and foremost and I prefer to watch history evolve with the rest of the community. That will apply in Mexico. Sh-ts about to get real folk.

Online WBY1984

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Re: MCT Speculation and Discussion Thread 4
« Reply #1901 on: 04/09/2016 05:04 PM »
I'm confused, what's going on on Mexico?

Offline Ben Hawes

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Re: MCT Speculation and Discussion Thread 4
« Reply #1902 on: 04/09/2016 05:15 PM »
Thanks Chris!

I'm confused, what's going on on Mexico?

Elon said he's going to give details at the IAC in Mexico this year.

Offline Bubbinski

Re: MCT Speculation and Discussion Thread 4
« Reply #1903 on: 04/09/2016 09:32 PM »
When is the IAC?!? I will be staying tuned!

Will I need to pick my jaw up off the floor after that unveiling Chris?
I'll even excitedly look forward to "flags and footprints" and suborbital missions. Just fly...somewhere.

Offline Retired Downrange

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Re: MCT Speculation and Discussion Thread 4
« Reply #1904 on: 04/09/2016 09:41 PM »
http://www.iac2016.org

Every year, the International Astronautical Federation together with the International Academy of Astronautics and the International Institute of Space Law (IISL), holds the International Astronautical Congress (IAC) which is hosted by one of the national society members of the IAF.

Offline kaoru

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Re: MCT Speculation and Discussion Thread 4
« Reply #1905 on: 04/12/2016 04:09 AM »
Here are some screen shots of my model.  The engineering/service module, which is the workhorse of the BFS, is coming along.  In the shots shows the major areas which would contain the following components (not shown but coming): ECLSS (closed loop O2/H2O generation & CO2 scrubbing) with removable H2O/air tanks, ISRU/Sabatier reactor, IVF(cyrogenic plant), mechanical/electrical power generation (solar/batteries & ICE), and thermal management.  Of course, these systems are within the deck's pressure vessel to allow service.  The removable tanks allows them to be off-loaded to the surface via the tunnel.  The service module has some permanent tanks for the trip back to earth (assuming less passengers/crew only); they're outside the engineering deck.

Other additions include the heat shield cover for the aft airlock door, which is a dynamic component (ie. it opens/closes with a click on the model).

What I have remaining is the landing legs, solar panels, radiators, Draco thrusters, control moment gyroscopes, communication array, and CBM rings.  This will complete the module.  Next up is to do the crew module & cargo/fuel module which is the payload; this would complete the upper stage.

What do you think?
Kaoru

Offline Oli

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Re: MCT Speculation and Discussion Thread 4
« Reply #1906 on: 04/12/2016 06:02 AM »
What do you think?
Kaoru

I'm not an expert on reentry, but this doesn't look like a viable reentry shape.

Online Cinder

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Re: MCT Speculation and Discussion Thread 4
« Reply #1907 on: 04/12/2016 06:05 AM »
Would an inflatable heat shield stowed in that hatch not be feasible either?
The pork must flow.

Offline Lars-J

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Re: MCT Speculation and Discussion Thread 4
« Reply #1908 on: 04/12/2016 06:53 AM »
This is just an over-complicated design IMO. There is no need for a hatch at the bottom like that. And all that around the engines - the exhaust deflector housing - is going to need some *SERIOUS* active cooling to not melt during Raptor burns. Simplify. Remove the bottom hatch/tunnel. Remove the tunnel in the middle of the tanks. Increase tank volume.

It looks like you decided on 4 raptors in such an arrangement early on (with engine cowlings - why?) and you don't want to let go of it. That shape doesn't make much sense.
« Last Edit: 04/12/2016 06:55 AM by Lars-J »

Offline kaoru

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Re: MCT Speculation and Discussion Thread 4
« Reply #1909 on: 04/12/2016 03:22 PM »
This is just an over-complicated design IMO. There is no need for a hatch at the bottom like that. And all that around the engines - the exhaust deflector housing - is going to need some *SERIOUS* active cooling to not melt during Raptor burns. Simplify. Remove the bottom hatch/tunnel. Remove the tunnel in the middle of the tanks. Increase tank volume.

It looks like you decided on 4 raptors in such an arrangement early on (with engine cowlings - why?) and you don't want to let go of it. That shape doesn't make much sense.
I value your feedback as it questions my design choices, which in turn, validates the reason why I made those design choices.  Of course, my design is still very much a thought exercise until I model it.  Until then, my design choices are obviously unclear so I'll make a mental note to show why I decided that way (or clarify the choice).

In regards to the hatch, tunnel, and associated placement of the engines, this choice is born out of the idea of a "space train".  Having done some calculations on mass, I concluded that's it borderline impractical mass wise, even assuming refueling, for a full up BFS holding 100 passengers/crew, cargo, and consumables for the following modes: ascent, trans-Mars-injection, long term flight, Mars EDL, long term surface ops, and return to Earth.  Of course, the base assumption that everything is to be reused and play a role in the entire mission.  My idea for a "space train" is a cool way to address the requirements hence I chose to break up the dry mass into modules.  This choice requires a means to "link" the modules together (link a train) and this is where the aft hatch, tunnel, etc. come into play.

To visualize this, I envision four separate modules: service (the current model), cargo/consumables, fuel, and crew.  A single crew module will hold 48-52 people with life support supplied by the service module.  Given this, I envision that 4 launches (4 BFR with RTLS; upper stages are 2 x service + crew, 1 x service + cargo, 1 x service + fuel) would occur for a single Mars mission.  All the modules would link up like a train, aka 2 x crew, 1 x cargo, 1 x fuel, and 4 x service modules.  The tunnel and forward/aft CBM/hatches allows traversal (consumables/fuel/cargo) across all the modules on orbit/in-flight and servicing of all critical systems.  Prior to arriving at Mars, the train would break up into 3 or 4 landing units (1 service + module each) depending if fuel will remain orbiting Mars or land if needed (aka ISRU failed).

The engines can cant 15 degrees to do retro-propulsion (EDL) and for trans-Mars injection.  The exhaust deflector is essentially PICAX (no regenerative cooling required) and is primarily for retro-propulsion to maximize the plasma plume/atmosphere interface.  The aft CBM/hatch heat shield is obvious but has to open as not to impede the "train" link up.  Once on Mars surface, the hatch and tunnel is how cargo will be lowered to the surface; that's why the airlock has a large diameter.  Water tanks, air tanks, BEAM-like habitats, etc. is capable of fitting through the tunnel/airlock.  The engineering deck has ISRU, water/air generators to support on surface ops x 4 for redundancy.  The crew modules provide habitat while the base is being built.

As you can see, that's a lot of detail I put thought into when I made my design choices.  Of course, this is all speculation on my part but it does confirm in my mind that Elon's MCT is quite doable and at a fairly low cost (as costs go for Mars; at least lower than the wild projections being posted).

Food for thought,
Kaoru 

Offline biosehnsucht

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Re: MCT Speculation and Discussion Thread 4
« Reply #1910 on: 04/12/2016 11:49 PM »
With regards to canting the engines within the engine nacelles / fairings / whatever they are, for EDL purposes, I recall reading that in order to benefit you need them to be operating from behind the shock front during EDL, not in the middle of it, so they would need to be further up the body (sort of Super Draco style).

As I understand it, with them at the shockfront, running the engines will _reduce_ the aerodynamic deceleration and  require greater thrust from the engines to make up for the loss of aerodynmic deceleration (which, if you can afford more propellant than heat shielding might be useful) and not go splat.

The obvious downsides of course with placing the engines higher so that they can operate behind the shockfront is that you are probably stuck with sizable cosine losses, and potentially more complicated plumbing (if the tanks are at the bottom, must pump up), etc ...

Offline Oersted

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Re: MCT Speculation and Discussion Thread 4
« Reply #1911 on: 04/13/2016 03:38 PM »
I have a hard time envisioning a Mars base constructed with elements limited in size by having to pass through a tunnel such as the one in your plans.

Offline kaoru

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Re: MCT Speculation and Discussion Thread 4
« Reply #1912 on: 04/13/2016 04:40 PM »
I have a hard time envisioning a Mars base constructed with elements limited in size by having to pass through a tunnel such as the one in your plans.
If you look at the dimensions of BEAM, it's not small by any standard (once expanded) but small enough to pass thru my modeled tunnel.  My thoughts stem from the requirement in building any habitat, either here on Earth or Mars, is that your materials have to be transported to your job site.  Here on Earth we have the luxury of heavy machinery.  On Mars, you're not going to have that luxury thus moving building materials is going to be manual labour which in turn means the size/weight will have to be limited.  Using BEAM like components is like using IKEA flat packs, some assembly required...  :D  Since a BEAM like component will fit thru the tunnel with a simple lift/pulley (or magnetic lift) system, you eliminate heavy equipment (like a crane, cargo doors, ramps).  With a small motorized dolly, building a habitat from small modules is more practical but time consuming.

Since your going to be on Mars for awhile, time to move and assemble a lot of small modules/components is not an issue... You'll have plenty of time.  This is why my model speculates that it (the service module/lander) will be a temporary habitat while on surface.

Kaoru
« Last Edit: 04/13/2016 04:41 PM by kaoru »

Offline Lars-J

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Re: MCT Speculation and Discussion Thread 4
« Reply #1913 on: 04/13/2016 06:40 PM »
The train idea is interesting, and you've obviously quite a attached to it. But I don't think the added complexity and compromises is worth it.

Offline kaoru

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Re: MCT Speculation and Discussion Thread 4
« Reply #1914 on: 04/13/2016 08:37 PM »
The train idea is interesting, and you've obviously quite a attached to it. But I don't think the added complexity and compromises is worth it.
Thank you for finding the "space train" idea interesting, but I'm not attached to it.  It's only choices which I made that, IMHO, is a possible and plausible MCT architecture.

Of course, I don't disagree that there is added complexity to my speculative design.  It's easy to fall into the trap of solving a problem for the sake of the model and not necessarily the requirements of the assumed mission (aka 100 people to Mars).

However, the underlying point of doing a speculative model is to test all the possibilities, assuming some set conditions.  It's the set conditions (which are speculative too but assumed to be correct) that pre-determine the model.  For example, what's needed for the ascent after BFR MECO?  How MCT will prep for trans-Mars injection?  The journey there and Mars EDL?  How surface ops/building a habitat occur?  Finally, how to ascend from Mars surface, do trans-Earth injection, and finally complete Earth EDL?

When asking these questions or pondering them in relation to the other speculative designs, I seem to come up short on the design being a plausible implementation.  My design and the choices are all founded on *existing* implementations that are modified/interpreted (aka speculated) by myself to answer the above questions.  Things being equal, you may find aspects of my design not plausible and that's feedback that I value.  It's the peer review of speculation.  ;D

Offline spacenut

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Re: MCT Speculation and Discussion Thread 4
« Reply #1915 on: 04/13/2016 09:39 PM »
If an inflatable unit can fit the tunnel, is the lander going to be high enough for it to turn 90 degrees after exiting the spacecraft to get out?  If some items can't make the 90 degree turn, they would have to be offloaded from the top via a crane.  Then weight and balance can become a problem.  Maybe if the fuel is placed higher, payload at the bottom, with people at the top, and they can come down the tunnel. 
« Last Edit: 04/14/2016 01:23 AM by spacenut »

Offline kaoru

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Re: MCT Speculation and Discussion Thread 4
« Reply #1916 on: 04/14/2016 02:31 AM »
If an inflatable unit can fit the tunnel, is the lander going to be high enough for it to turn 90 degrees after exiting the spacecraft to get out?  If some items can't make the 90 degree turn, they would have to be offloaded from the top via a crane.  Then weight and balance can become a problem.  Maybe if the fuel is placed higher, payload at the bottom, with people at the top, and they can come down the tunnel.
Great insight!  I'm glad you mentioned it because I've already put some thought into the two necessary components to handle this.  The first component is the tunnel and the lift system which I believe can be made as a electromagnetic rails/lift system with a special platform.  This I already mentioned.  What I didn't mention is my design for the legs.  All the designs I've seen use the same style of SpaceX landing legs.  The reality is that they would have to be completely redesigned to work on Mars.  First they have to extend and then retract on demand.  Secondly, and more germane to your insight, the legs will have to auto-level lifting the weight of the lander (in Earth gravity).  Obviously, to aid in the unloading of items on Mars the legs would have the strength to jack up the ship and/or there is a height restriction on the cargo matched to the clearance the legs provide.  In either case the legs will require an interesting design due to these requirements.  My yet-to-be-modeled legs will be pure speculation but founded in the above realization.

Kaoru
« Last Edit: 04/14/2016 02:42 AM by kaoru »

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #1917 on: 04/14/2016 07:32 AM »
I have a hard time envisioning a Mars base constructed with elements limited in size by having to pass through a tunnel such as the one in your plans.
If you look at the dimensions of BEAM, it's not small by any standard (once expanded) but small enough to pass thru my modeled tunnel.  My thoughts stem from the requirement in building any habitat, either here on Earth or Mars, is that your materials have to be transported to your job site.  Here on Earth we have the luxury of heavy machinery.  On Mars, you're not going to have that luxury thus moving building materials is going to be manual labour which in turn means the size/weight will have to be limited.  Using BEAM like components is like using IKEA flat packs, some assembly required...  :D  Since a BEAM like component will fit thru the tunnel with a simple lift/pulley (or magnetic lift) system, you eliminate heavy equipment (like a crane, cargo doors, ramps).  With a small motorized dolly, building a habitat from small modules is more practical but time consuming.

Since your going to be on Mars for awhile, time to move and assemble a lot of small modules/components is not an issue... You'll have plenty of time.  This is why my model speculates that it (the service module/lander) will be a temporary habitat while on surface.

Kaoru

While your right that standardized cargo modules that can be linked together to form habitats, your size is much too small.  The BEAM module is a mere 2.36 m in diameter and 1.7 tall when compressed for a volume of ~7.5 m^3.  ISS cargo has a fairly low average density so your looking at many dozens of such modules needing to be unloaded from each ship and then linked together.  As these modules are already too large to be moved by anything other then cranes their is every incentive to go bigger as the usefulness of the modules increases as well as the speed of unloading.

I favor a module size comparable to a TEU shipping container which is  6.1 m x 2.44 m x 2.59 m totaling 38.5 m^3 roughly 5 times larger then BEAM when compressed and about twice as large as BEAM when expanded.  If a module this size expanded with the same ratio as BEAM the resulting interior space would be 80 m^3 a very generous and spacious habitat indeed.

Containers this size will necessitate a side door and a cargo bay of around 500 m^3 in which containers can be stacked and secured by bolting them to structural hard-points as in modern containerized cargo on ships, planes, trains etc etc.  This is very similar to the Space Shuttle which had 300 m^3 internal cargo bay and similar hard-point mountings.  Cargo would be loaded/unloaded by a gantry crane in the roof of the cargo bay and extends out to clear the edge of the vehicle.  First a flat bed truck is unloaded, then modules are unloaded onto the truck which take them away.

Remember we need to think about the entire SYSTEM in MCT including logistics of ground transportation on Mars, we can't just dump stuff right at the landing site, we need the habitat a safe distance of a few miles away.

Offline Burninate

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Re: MCT Speculation and Discussion Thread 4
« Reply #1918 on: 04/14/2016 03:37 PM »
I have a hard time envisioning a Mars base constructed with elements limited in size by having to pass through a tunnel such as the one in your plans.
If you look at the dimensions of BEAM, it's not small by any standard (once expanded) but small enough to pass thru my modeled tunnel.  My thoughts stem from the requirement in building any habitat, either here on Earth or Mars, is that your materials have to be transported to your job site.  Here on Earth we have the luxury of heavy machinery.  On Mars, you're not going to have that luxury thus moving building materials is going to be manual labour which in turn means the size/weight will have to be limited.  Using BEAM like components is like using IKEA flat packs, some assembly required...  :D  Since a BEAM like component will fit thru the tunnel with a simple lift/pulley (or magnetic lift) system, you eliminate heavy equipment (like a crane, cargo doors, ramps).  With a small motorized dolly, building a habitat from small modules is more practical but time consuming.

Since your going to be on Mars for awhile, time to move and assemble a lot of small modules/components is not an issue... You'll have plenty of time.  This is why my model speculates that it (the service module/lander) will be a temporary habitat while on surface.

Kaoru

While your right that standardized cargo modules that can be linked together to form habitats, your size is much too small.  The BEAM module is a mere 2.36 m in diameter and 1.7 tall when compressed for a volume of ~7.5 m^3.  ISS cargo has a fairly low average density so your looking at many dozens of such modules needing to be unloaded from each ship and then linked together.  As these modules are already too large to be moved by anything other then cranes their is every incentive to go bigger as the usefulness of the modules increases as well as the speed of unloading.

I favor a module size comparable to a TEU shipping container which is  6.1 m x 2.44 m x 2.59 m totaling 38.5 m^3 roughly 5 times larger then BEAM when compressed and about twice as large as BEAM when expanded.  If a module this size expanded with the same ratio as BEAM the resulting interior space would be 80 m^3 a very generous and spacious habitat indeed.

Containers this size will necessitate a side door and a cargo bay of around 500 m^3 in which containers can be stacked and secured by bolting them to structural hard-points as in modern containerized cargo on ships, planes, trains etc etc.  This is very similar to the Space Shuttle which had 300 m^3 internal cargo bay and similar hard-point mountings.  Cargo would be loaded/unloaded by a gantry crane in the roof of the cargo bay and extends out to clear the edge of the vehicle.  First a flat bed truck is unloaded, then modules are unloaded onto the truck which take them away.

Remember we need to think about the entire SYSTEM in MCT including logistics of ground transportation on Mars, we can't just dump stuff right at the landing site, we need the habitat a safe distance of a few miles away.
We have some evidence/conjecture for the notion that BFR is going to be 15m diameter.  MCT is going to require lots of space for vacuum bell nozzles to achieve high Isp with enough engines for redundancy, so it will probably be about the same 15m diameter.  A side-loading cargo dispenser at 15m overall diameter might have six <=5m diameter cargo pods arrayed along the outer edge, of indefinite length, around a central structural core + crane system.  We know that ISS modules have already been designed at 4.1 to 4.5m diameter for 10 to 20 tons of mass, and that MCT is targeting 100 tons 'useful cargo'  to the Martian surface.  This provides a cargo footprint that is usefully similar to the Shuttle's payloads.

Lower these standard cargo pods to the ground, and you can have vehicles drive out of their ends, just like a new automobile might drive out of an ISO container coming off the shipyard stacks in Baltimore.  ISO containers are built of the cheapest materials that will take the load of intermodal shipping, and weigh about 10% of their rated maximum load.
« Last Edit: 04/14/2016 03:45 PM by Burninate »

Offline RanulfC

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Re: MCT Speculation and Discussion Thread 4
« Reply #1919 on: 04/14/2016 04:27 PM »
Unless the Raptor engines consist of combustors around a plug-nozzle which doubles as a heat shield :)

Added: ROMBUS style lander for the win:
http://www.fantastic-plastic.com/IthacusSSTOCatalogPage.htm
http://www.pmview.com/spaceodysseytwo/spacelvs/sld008.htmhttp://www.spacefuture.com/archive/single_stage_to_orbit_vertical_takeoff_and_landing_concept_technology_challenges.shtml
http://www.spacefuture.com/archive/history_of_the_phoenix_vtol_ssto_and_recent_developments_in_single_stage_launch_systems.shtml

Randy
Note in Project Selene using ROMBUS the drop tanks were replaced by hab modules that were lowered onto wheels and driven into place for use. Just saying :)
« Last Edit: 04/14/2016 04:33 PM by RanulfC »
From The Amazing Catstronaut on the Black Arrow LV:
British physics, old chap. It's undignified to belch flames and effluvia all over the pad, what. A true gentlemen's orbital conveyance lifts itself into the air unostentatiously, with the minimum of spectacle and a modicum of grace. Not like our American cousins' launch vehicles, eh?

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