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.
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.
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.
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.
Quote from: Robotbeat on 04/21/2015 12:34 pmYou 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....
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.
...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?
...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). ...
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.
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.
Quote from: spacenut on 04/22/2015 12:32 amEarth'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.
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.
Quote from: Hyperion5 on 04/22/2015 03:16 am2) 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),
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.
Quote from: Hyperion5 on 04/22/2015 03:16 am2) 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.
Quote from: Semmel on 04/21/2015 09:45 pm3. 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.
Quote from: Semmel on 04/21/2015 09:45 pm2. 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.