In Early exploration any abort to surface is fatal because their is zero rescue infrastructure on the surface and no conceivable capsule could carry sufficient supplies to see them through more then a few days. So I consider this a pointless abort. By the time you have an infrastructure to do surface rescue your passenger count is much too high for the small capsule your proposing, it would need to be a large vehicle comprising a significant portion of the whole mass of the vehicle and would present great difficulty in landing as you going to be falling on a ballistic trajectory from a high altitude and need massive retro-propulsion to not impact the surface, it in no way resembles the kind of un-powered capsule landing that can be done on Earth.
I don't know if you saw it earlier but I did a mass brake down of my MCT concept. I'd like to see what the IBMCT comes out at.Thermal protection at 5 kg/ m^2 over an area of 650 m^2: 5 mTTanks and Plumbing 5% of 300 mT propellant mass: 15 mTLanding legs, 10% of touch down mass: 18 mT4 Raptor Engines at 150:1 T:W ratio: 6 mTVernier Engines that can hover on landing at 100:1 T:W ratio: 1 mTSolar, Radiator and computer systems: 5 mTStructural skeleton, 1/3rd of dry mass: 25 mTTotal 75 mT dry mass
Quote from: Impaler on 10/07/2015 02:33 amIn Early exploration any abort to surface is fatal because their is zero rescue infrastructure on the surface and no conceivable capsule could carry sufficient supplies to see them through more then a few days. So I consider this a pointless abort. By the time you have an infrastructure to do surface rescue your passenger count is much too high for the small capsule your proposing, it would need to be a large vehicle comprising a significant portion of the whole mass of the vehicle and would present great difficulty in landing as you going to be falling on a ballistic trajectory from a high altitude and need massive retro-propulsion to not impact the surface, it in no way resembles the kind of un-powered capsule landing that can be done on Earth.This. You put it better than I could have. This is why IMO the way to increase safety for the MCT is to make he whole thing abort capable, through added redundancies in propulsion and systems. If a MCT has to abort during a Mars ascent and land far down-range, the crew can survive for an *extended* period in the MCT. Not in a small capsule where everyone is squeezed into. Designing in a pointless separable abort capsule leads you down the path of terrible engineering trade-offs.
Isn't LOX heavier than Liquid methane? Also it will take twice the lox to burn the methane. So shouldn't the Lox tank be on bottom with the Methane on top?
I've said all along that an elongated 2nd stage would do tanker duty, and depots are in my opinion unnecessary, the MCT will act as it's own depot taking on propellants from visiting 2nd stages until it is full. As MCT must depart Earth with some propellant for EDL at mars and must then hold significant amounts while on the martian surface (which while cold is still warmer then cryogenic LOX), so the MCT will have to have significant long-term cryo-storage capabilities likely through a combination of insulation and cryo-coolers, thus it makes an excellent depot. These cryo-systems along with radiators and solar arrays are the only systems that I would integrated into the vehicle. Human habitats placed into the MCT are simply plugged into these utilities much like an RV.
One significant factor that needs to be taken into account for a biconic vehicle (which I advocate) is a the mass distribution. It needs to be have the proper balance when almost empty (normal atmospheric entry & landing), and it needs to be able to also have the proper balance for a near full propellant load. (Earth or Mars abort) Also, when near empty of propellant the vehicle must also be properly balanced for a full cargo load vs empty.To handle this range, the layout that makes most sense (IMO) is to put the cargo/crew in the middle of the vehicle - with the LOX tank above, and Methane tank below. This would allow a balanced biconic sideways reentry with ANY cargo load, and ANY propellant load.EDIT: See image below for how that might look, in this DC-Y(?) drawing:
Again, this a concept in reaction to some who feel strongly the LAS is necessary. (I argued against an LAS, but was out voted, heh) It could very easily be left off, with no Mars ascent abort option (for an explosive event, you can abort to orbit with just an engine out), and a separate LEO-taxi with LAS for Earth ascent. For those that favor that, I think that's viable too.
Quote from: Lars-J on 10/06/2015 11:38 pmOne significant factor that needs to be taken into account for a biconic vehicle (which I advocate) is a the mass distribution. It needs to be have the proper balance when almost empty (normal atmospheric entry & landing), and it needs to be able to also have the proper balance for a near full propellant load. (Earth or Mars abort) Also, when near empty of propellant the vehicle must also be properly balanced for a full cargo load vs empty.To handle this range, the layout that makes most sense (IMO) is to put the cargo/crew in the middle of the vehicle - with the LOX tank above, and Methane tank below. This would allow a balanced biconic sideways reentry with ANY cargo load, and ANY propellant load. Or to balance cargo above and below propellant tanks.EDIT: See image below for how that might look, in this DC-Y(?) drawing:The IBMCT would have most of the dry mass in the nose and MPS as the aft (Engines, thrust structure, etc). Between the two would empty main propellant tanks, a cargo deck, and volumous, but relatively light Hab area. The cargo deck would be between the hab volume and the tanks, and may have a fairly heavy mass when loaded with surface cargo. So for Mars EDL, that would be about in the middle. So you have your greatest mass areas in the nose, in the tail, and [roughly] in the middle. So it shouldn't be too bad. There will be some residuals in the tanks to power Raptor from terminal velocity to hover.I don't know you need two separate tanks top and bottom like in this concept.
One significant factor that needs to be taken into account for a biconic vehicle (which I advocate) is a the mass distribution. It needs to be have the proper balance when almost empty (normal atmospheric entry & landing), and it needs to be able to also have the proper balance for a near full propellant load. (Earth or Mars abort) Also, when near empty of propellant the vehicle must also be properly balanced for a full cargo load vs empty.To handle this range, the layout that makes most sense (IMO) is to put the cargo/crew in the middle of the vehicle - with the LOX tank above, and Methane tank below. This would allow a balanced biconic sideways reentry with ANY cargo load, and ANY propellant load. Or to balance cargo above and below propellant tanks.EDIT: See image below for how that might look, in this DC-Y(?) drawing:
Except, what do you want loitering in LEO while it's being filled up? A reusable unmanned depot, or your crewed MCT? I think the preference would be to not have MCT floating around up there any longer than necessary. Even if you sent the crew up later once it was tanked up, it's just that much more time in LEO to get struck by MMOD.
Quote from: Lobo on 10/07/2015 04:52 pm Except, what do you want loitering in LEO while it's being filled up? A reusable unmanned depot, or your crewed MCT? I think the preference would be to not have MCT floating around up there any longer than necessary. Even if you sent the crew up later once it was tanked up, it's just that much more time in LEO to get struck by MMOD.There will have to be plenty of loiter time in LEO for MCTs. Why? Because of launch windows to Mars. You will likely want to launch a fleet of them in very close succession, and this will require lots of loitering to place, refuel, & prepare the MCT's in orbit. Having a couple of weeks system checkouts in the relative safety of LEO is also advantageous.
No. If you are truly scaling this to be able to deliver 100t of cargo, you really need to have it in the middle. Not up front with the hab volume. When you do atmospheric entry, the propellant tanks will be mostly empty, so then by placing the cargo up top you are now forcing yourself to have to have a substantial minimum cargo load or the thing won't fly right.Think about it. 100t. And it could be there, or it could be empty. If you do a sideways re-entry, that DOES constrain you to a center placement of cargo. OR you need to split the cargo into two balanced areas, one below and one above propellant tanks.
A SEP transit vehicle that takes you to high earth orbit followed by a perigee burn near Earth to send you to Mars, the SEP vehicle flies independently to mars and you rendevoue with it on low mars orbit to return to a high Earth orbit where crew disembark on a Dragon capsule. The bi-conic just dose mars assent with a 25 mT habitat inside pluss a modest landing propellent reserve. The intent is to ultimatly be able to do a rapid cycle between mars surface and low orbit, loading cargo and orbit and unloading on the surface.
Quote from: Lars-J on 10/03/2015 12:57 amI'm rather surprised that you aren't aware of the Pendulum FallacyBut I don't know that my stated bit about inherent stability is incorrect. Just not exactly as I stated.In that, would it not be similar to a helicopter? Why is a helicopter more stable
I'm rather surprised that you aren't aware of the Pendulum Fallacy
than something like the LLRV?
And in this way I think they'd act more like the F9 core grid fins, which are placed up high to provide force (via air resistance rather than a jet of thrust) to help stabilize the core for landing.
The lifeboat would be [....] A flight deck in the nose with a bulkhead and hatch between it and the rest of the hab. Not much more to it that that. Not quite like a separate spacecraft.
For early exploration missions Dragon 2 would be sufficient, no separate system needed as crews will only be maybe 6-7.
Others thought it needed it, as later during colonization they'd want to launch all 100 people on the MCT rather than have a separate ferry.
I argued against an LAS, but was out voted, heh
10 or 100 people per flight.10 people means 10 times the number of manned flights. Which means 10 times the likelihood of a flight with crew loss. Will people say, oh well, it is only 10 people, not 100, that's OK? I doubt it.
Quote from: guckyfan on 10/06/2015 09:18 am10 or 100 people per flight.10 people means 10 times the number of manned flights. Which means 10 times the likelihood of a flight with crew loss. Will people say, oh well, it is only 10 people, not 100, that's OK? I doubt it.However, with extra crew ships on the same route, if there is a failure of a major system on one of the ships, those 10 people can be spread amongst the remaining 9 ships. Additionally, during the emergency, they'd have nearby external help operating out of safe, fully functional ships, rather than trying to save themselves from within the failing ship using failing systems (with the nearest advice operating behind several minutes comms lag.)With a single crew, no chance of rescue, any major failure means LOM/LOC.The advantage of that 9-fold backup, IMO, is worth its weight in diamonds.
I assume you mean that the early crews would ferry up to an MCT in LEO using D2? (Since D2 can't launch back off the surface of Mars. It will never be used for human missions to Mars.)In which case, you are proposing an entirely different kind of MCT just for the first few missions. Your escape vehicle can't be retro-fitted to an existing MCT design. You can't just cut through a few joins connecting the flight-deck to the rest of the MCT and add some pyro-bolts. You have the design the entire MCT around the separation mechanism. That's not going to be an afterthought or upgrade.
You are still not getting what I'm trying to say. Let me try again.The MCT must be able to launch, fly, and land with full cargo/crew. But ALSO when no cargo/crew is present.The MCT must be able to launch, fly, and land with full propellant load. But ALSO with tanks nearly empty.That places severe constraints on the placement of these elements on a biconic entry vehicle, and you can't just hand-wave that away by a "100t payload vs 100t cargo" semantic discussion. It doesn't matter.
I'm not sure I agree with that.Ok, so let's say you have a 12.5m wide IBMCT (our working diameter for it and the booster). A separable nose would be 12.5m wide at the base, tapering down. So you'd have quite a lot of volume there for a small crew returning from Mars if they had to abort and land down range. For 100 people, yea, it's not going to keep them for very long, but for a crew of 5-7? Should be just fine. In fact, that may be the only hab space they need/have for exploration missions, with everything below for surface cargo. That's a volume twice as wide as Skylab op the base, and probably about the same height as the Skylab pressurized volume. There's no squeezing involved.They would have provisions and supplies sufficient for the 4-6 month transit back to Earth, so they should be ok for quite awhile.Then you have the question of what sort of contingency plan do you want to have in place to deal with them at that point. That's really a separate discussion. Maybe a remote operated large pressurized rover that could drive itself over to the lifeboat, to give them transportation to a supply cache somewhere pre-positioned for such a contingency?In a situation where they are transporting 100 people to Mars, obviously 100 people won't be coming back home, so there will be far fewer people on it. Probably just some SpaceX employees or NASA personnel returning home after a tour of serving at the colony, and a few people who have either become more ill than can be treated on Mars, or have changed their minds and want to go home. But even if it were more people, with a colony on Mars, rescue could be dispatched anywhere on the globe, it's just a matter of how long it would take to get there, so the lifeboat would need to be set up to support X number of people of Y length of time needed to get rescue there.As far as whole vehicle abort goes, there really is no such thing for Mars ascent. If the MCT MPS explodes, a separable lifeboat can save the crew. Whole vehicle abort would only work for Earth ascent. If there's a non explosive failure, like an engine out, that's when having a redundant engine comes in. So it's really all or nothing if you don't have a separable design. And that's ok, the LAS lifeboat is mainly for Earth ascent so the crew can get away from an exploding booster where you cannot abort the whole fueled stage. But with that comes the ability to abort on Mars if necessary. But there would need to be contingency plans to for the marooned crew obviously.Quote from: Impaler on 10/07/2015 02:33 amIn Early exploration any abort to surface is fatal because their is zero rescue infrastructure on the surface and no conceivable capsule could carry sufficient supplies to see them through more then a few days. So I consider this a pointless abort. By the time you have an infrastructure to do surface rescue your passenger count is much too high for the small capsule your proposing, it would need to be a large vehicle comprising a significant portion of the whole mass of the vehicle and would present great difficulty in landing as you going to be falling on a ballistic trajectory from a high altitude and need massive retro-propulsion to not impact the surface, it in no way resembles the kind of un-powered capsule landing that can be done on Earth.Not necessarily. It would only be a smaller portion of the whole weight of the vehicle (Maybe 1/3 total dry mass or so?...but more importantly is it leaves all the propellant mass behind with just the LAS/landing propellant on board). It would leave behind the main tanks, engines, most of the TPS covering, etc. It wouldn't be insignificant, but it would be certainly less than the whole vehicle. The LAS engines and tanks would need to be sized not only for abort, but for propulsive landing.Also it would be a biconic shape. So it can do a biconic EDL rather than ballistic. It would still need a large retro propulsion as any vehicle would, but again, that would have to be designed into the LAS system if you wanted it.Again, this a concept in reaction to some who feel strongly the LAS is necessary. (I argued against an LAS, but was out voted, heh) It could very easily be left off, with no Mars ascent abort option (for an explosive event, you can abort to orbit with just an engine out), and a separate LEO-taxi with LAS for Earth ascent. For those that favor that, I think that's viable too.It would probably still need landing thrusters of some sort to land on Earth, which would likely be pressure fed for fast reaction control and reliability. Otherwise a means of landing on Earth with a vacuum Raptor nozzle would need to be figured out. Something like a retractable nozzle extension, or a jettisonable nozzle extension, so that the Raptor thrust isn't too over expanded for sea level. I'm not an engine expert, but have been told by several that vacuum engines with large vacuum nozzles like M1D-Vac and RL-10B cannot operate at sea level due to their large high efficiency nozzles.But Raptor would still have to be capable of quickly responsive throttle in order to be able to land, which it may not be being a big pump fed staged combustion main propulsion engine. Otherwise you are back to landing thrusters.