No, not remotely.First off, all sides of an object doing reentry need Thermal protection systems because hot air swirls around the back of a capsule shaped vehicle, so the habitat your placing on the top would need extensive TPS which then gets left on Mars. Likewise their would need to be yet more on the now exposed top of the propulsion stage to allow it to land on Earth. Lastly their is no way to send anyone or anything back to Earth which is required.The crane necessary to remove this habitat would be monstrous, and it would need to be mobile both before and AFTER picking up the habitat for it to do anything other then put it on the ground right next to the propulsion section which needs to blast off again, a very bad place to be. The crane would have a higher mass then what it is lifting and would be extremely dangerous.I'm proposing a habitat that is INSIDE the lander and deployed by WHEELS down a ramp, I can't see anything being simpler then that, and am perplexed why anyone feels this needs improving.
......I'm proposing a habitat that is INSIDE the lander and deployed by WHEELS down a ramp, I can't see anything being simpler then that, and am perplexed why anyone feels this needs improving.
Quote from: Impaler on 06/23/2015 02:41 am......I'm proposing a habitat that is INSIDE the lander and deployed by WHEELS down a ramp, I can't see anything being simpler then that, and am perplexed why anyone feels this needs improving.Your proposal is excellent and should be employed. I would add only this:After you have unloaded your habitat, now go back and unload the whole top section of the MCT as another habitat.Maximum cargo delivered in just one trip of the MCT. Win-win for SpaceX!###[Edit: A bonus -- we will be returning to Earth the absolute minimum mass that is physically possible.]
First off, all sides of an object doing reentry need Thermal protection systems because hot air swirls around the back of a capsule shaped vehicle, so the habitat your placing on the top would need extensive TPS which then gets left on Mars.
.........I have suggested before, that the whole cabin or cargo compartment may be removable and reused as habitat space on Mars. But that as an initial method. Not in a later stage when large numbers of colonists are transfered, that means the 100 people per flight are actually transported. At that stage the colony needs to be able to provide habitats and work places for all the arriving colonists.
I agree. And I bow to your earlier posting (reference?)
Quote from: Impaler on 06/23/2015 02:41 amNo, not remotely.First off, all sides of an object doing reentry need Thermal protection systems because hot air swirls around the back of a capsule shaped vehicle, so the habitat your placing on the top would need extensive TPS which then gets left on Mars. Likewise their would need to be yet more on the now exposed top of the propulsion stage to allow it to land on Earth. Lastly their is no way to send anyone or anything back to Earth which is required.The crane necessary to remove this habitat would be monstrous, and it would need to be mobile both before and AFTER picking up the habitat for it to do anything other then put it on the ground right next to the propulsion section which needs to blast off again, a very bad place to be. The crane would have a higher mass then what it is lifting and would be extremely dangerous.I'm proposing a habitat that is INSIDE the lander and deployed by WHEELS down a ramp, I can't see anything being simpler then that, and am perplexed why anyone feels this needs improving.I value your critique. You mentioned needing TPS on all sides of the MCT; I am only familiar with TPS on one side, where it serves as a leading edge during aerobraking on Mars,i.e. Design Reference Architecture 5A. Is the all-around TPS now a requirement for all Mars landers? Did your design include this? I have seen a suggested design for MCT that is an enlarged version of a Dragon V.2, which sports a 15 m shield on the bottom and heat-resistant metal or composite for the rest of the "capsule'". Is this approach now obsolete?The system I suggested could have TPS on all surfaces, but that would probably be expensive. If so, it would be less desirable to leave a whole section on Mars permanently. The large crane I suggested could be replaced by a different, low-mass system. But the first issue is TPS.
Your proposal is excellent and should be employed. I would add only this:After you have unloaded your habitat, now go back and unload the whole top section of the MCT as another habitat.Maximum cargo delivered in just one trip of the MCT. Win-win for SpaceX!###[Edit: A bonus -- we will be returning to Earth the absolute minimum mass that is physically possible.]
Except that the proposals are in headon conflict with two basic principles Elon Musk has stated over and over again.One is mass fraction. Best possible mass fraction is required for full reusability. Having an outer shell capable of withstanding atmospheric reentry at interplanetary speeds and the resultant heating plus an inner habitat capable of holding pressure for crew is extremely mass inefficient.The second is full reusability. I think it might be possible that some low value but heavy equipment not needed for a smaller return crew might be removed if necessary. Especially if they can be reused on Mars. But except early on as a special startup arrangement the complete MCT will go back to reach the cost goals.I have suggested before, that the whole cabin or cargo compartment may be removable and reused as habitat space on Mars. But that as an initial method. Not in a later stage when large numbers of colonists are transfered, that means the 100 people per flight are actually transported. At that stage the colony needs to be able to provide habitats and work places for all the arriving colonists.
Quote from: Robotbeat on 06/20/2015 08:45 pmWhy would MCT weigh that much dry, particularly in a cargo config (because you mentioned 100mt payload, and Musk keeps talking about cargo flights as separate from passenger flights) and without yet counting the heat shield?I would guess more like 30-35 tons.Just the propellant tank portion, 5 Raptor engines and possibly landing legs too would weight ~40mt. Now add the reentry shield and the cargo bay structure. Of course the cargo variant will not have as high a dry weight as the crew variant but where is the tradeoff in crew payload size and crew vehicle dry weight increase. If you could get the cargo variant to have a dry weight as low as 60mt then reduce the payload size of the crew variant (crew + supplies) to only 60mt on a crew variant that dry weight 100mt things will work out better in that the overall system becomes smaller. You shrink the size and maybe some savings on the propellant tank dry weight due to smaller tanks.My only problem with the estimates is that the more detail we go the heavier the MCT gets.
Why would MCT weigh that much dry, particularly in a cargo config (because you mentioned 100mt payload, and Musk keeps talking about cargo flights as separate from passenger flights) and without yet counting the heat shield?I would guess more like 30-35 tons.
F9 first stage has 8% of dry mass in the leg system, and this is designed for flat artificial surfaces and is not carry precious human cargo. The LEM had around 3% of touch down mass in legs, but that was a soft-touchdown with a deeply throttling engine, not the SpaceX 'hover-slam'.
And their would not be any kind of integral habitat in a 'crew' version. Their will just be a single version with an unpressurized cargo bay into which a habitat module would be placed.
Yes, the depot could be a specially equipped MCT for 0 boil-off since it would have large enough tanks to refuel 1+ MCT's for Earth departure. This would make it easy to orbit the depots since they are just another cargo specialized version of the MCT which are then manufactured in the 10's to 100's.
So it would take one MCT depot to refuel one MCT going to Mars. The Depot if emptied each time it goes up could come back to be refueled and checked out then. No need to worry about boil off. Launch the Fuel depot, launch the MCT to dock, refuel and head to Mars. Fuel depot returns, refuels, and relaunches with the next MCT. I too like the idea of a cylinder MCT. It could be stretched for a fuel depot without much expense.
Quote from: Impaler on 06/21/2015 06:06 pmQuote from: nadreck on 06/21/2015 05:32 pmMy visualization for the MCT version of the BFR upper stage is 4 raptors, but the hardware to cant them for Mars landing/take off. I think 60t works for the dry weight of a cargo only version, and I am not committed one way or the other yet as to whether the passenger ECLSS and quarters are just cargo 'modules' that fit on an otherwise standard MCT or a seperately designed and built MCT. What I do expect is that a passenger MCT is less loaded with payload than the cargo only one so that it has more ΔV partly for slighlty shorter transit time, partly for more safety margin.I don't believe integrated habitat and direct Earth-reutrn are compatible.An integrated hab for 6-10 people could probably mass less than 25 tonnes, so it seems possible for initial missions. Later missions with more would need a larger hab and that could not be integrated. So I believe you have made an important point, integrated habs have no long term future on the MCT, so will probably not be designed in the first place.
Quote from: nadreck on 06/21/2015 05:32 pmMy visualization for the MCT version of the BFR upper stage is 4 raptors, but the hardware to cant them for Mars landing/take off. I think 60t works for the dry weight of a cargo only version, and I am not committed one way or the other yet as to whether the passenger ECLSS and quarters are just cargo 'modules' that fit on an otherwise standard MCT or a seperately designed and built MCT. What I do expect is that a passenger MCT is less loaded with payload than the cargo only one so that it has more ΔV partly for slighlty shorter transit time, partly for more safety margin.I don't believe integrated habitat and direct Earth-reutrn are compatible.
My visualization for the MCT version of the BFR upper stage is 4 raptors, but the hardware to cant them for Mars landing/take off. I think 60t works for the dry weight of a cargo only version, and I am not committed one way or the other yet as to whether the passenger ECLSS and quarters are just cargo 'modules' that fit on an otherwise standard MCT or a seperately designed and built MCT. What I do expect is that a passenger MCT is less loaded with payload than the cargo only one so that it has more ΔV partly for slighlty shorter transit time, partly for more safety margin.
So it would take one MCT depot to refuel one MCT going to Mars. The Depot if emptied each time it goes up could come back to be refueled and checked out then. No need to worry about boil off. Launch the Fuel depot, launch the MCT to dock, refuel and head to Mars. Fuel depot returns, refuels, and relaunches with the next MCT.
I too like the idea of a cylinder MCT. It could be stretched for a fuel depot without much expense.
I see the depot as much larger than that. I would prefer to see passenger carrying MCT's launch in pairs as close to simultaneously as possible. Also because of the intensity of the black body radiation of the earth and its daytime reflection of heat, I see the depot needing far more active cooling than the MCT which will only need to keep its propellant from boiling off near Mars and between Mars and Earth but will not need to keep it cool for long in the 10 radii range of the Earth. I also see the depot with a hab as transit station, and a place where PicaX can be recoated on MCT's along with engine swaps (engines taken off BFR tanker stages)
If you have to have 10 flights of cargo with 1 passenger flight of 100 with say 4 crew, why not have a crew of 4 with 10 passengers on each flight. Have the rest as cargo. That way every MCT would be identical, and so it only carries about 80-90 tons of cargo. However, the cargo could be loaded in modules, that could be unloaded and when emptied can be used for habitat. No need for separate cargo and human flights. The 10 colonists could stay on Mars to work, build habitats, landing pads, solar power stations, and maintain ISRU equipment. 10 MCT's would get you 100 colonists.
If your saying that the Thermal protection can be integrated with the pressure hull then that's a non-starter for the simple reason that it provides a direct heat path into the interior and will COOK people. The pressure hull has to have a stand-off gap between it and the TPS, likewise for propellent tanks.Thus a removable habitat inside of an unpressurized bay is hardly any less efficient then an integrated one, the only extra mass is a little sheet metal wall for the payload bay and the system to secure the payload during launch and landing. The benefits are getting BIG habitats deployed on the surface for early missions and reducing the mass at launch from Mars surface to a minimum.What is inefficient is doing high speed entry from interplanetary speeds, I'm advocating for much much lower speeds which will tax the vehicle design far less, which should more then make up for mass costs of a removable hab. And it will also allow a single type of lander to do both crew and cargo flights, a key factor in making it cheaper to develop, manufacture and operate.