Quote from: philw1776 on 01/08/2016 06:12 pmHow does the MCT escape module land on Mars w/o killing everyone as it slams into the regolith? Chutes ain't gonna git 'er done there.......they will if you add a retro-rocket to them, like this:
How does the MCT escape module land on Mars w/o killing everyone as it slams into the regolith? Chutes ain't gonna git 'er done there....
This is my idea of MCT, focusing on survival on all critical parts of Mars Journey, since there will multiple MCT on the way and they will not probably use 100 people before base is build and they could help each others.
Quote from: raketa on 01/07/2016 10:17 pmThis is my idea of MCT, focusing on survival on all critical parts of Mars Journey, since there will multiple MCT on the way and they will not probably use 100 people before base is build and they could help each others.That reminds me of the idea which was to fly a F9 reusable 2nd stage together with a dragon 2 as one spaceship.How does the crew transfer between the escape pod and the hab module through the heat shield?Is the heat shield necessary for an aerobreak?
Quote from: Robotbeat on 01/08/2016 11:34 pm...they will if you add a retro-rocket to them, like this...That chute will help some after the heat shield reaches terminal velocity, but in an atmosphere that's 0.0059 X the density of Earth's atmosphere at the surface, you're still going to have a lot more velocity to overcome with retrorockets than that pallet has. Your gravity losses will be less, but you still have the inertia to kill off.
...they will if you add a retro-rocket to them, like this...
Can it really not do Mars entry engines first? Rocket engines already deal with pretty intense heat...
Quote from: Vultur on 01/14/2016 03:22 amCan it really not do Mars entry engines first? Rocket engines already deal with pretty intense heat...If it was feasible to do so, why did we ever invent ablative heatshields? Rocket engines deal with heat either ablatively or with regenerative cooling - heating up the propellant - in which case you need to expend the propellant steadily.The guidance from the SSTO guys is that for Mars, direct retro burns basically overwhelm any drag benefit of the rest of the spacecraft; You're left with a mass-intensive propulsive descent, as if Mars had no atmosphere.
Randy, Speaking of the SSTO designs of the past, has it occured to anyone that the current design for the Dragon V2 could easily be the same basic design, externally, for the MCT?
If SpaceX were to use a asymetrical aerospike system for each of the quads, the design would be very similar to many of the SSTO designs of the 1960's and 70's. I meantion this idea as what most people know is that exhaust effeciency at various altitudes changes as you get higher, resulting in the need for a radically different exhaust bell than you'd have at sea level. (Part of the reason we stage rockets). Aerospikes don't suffer this issue and asymetric aerospikes, using mostly Raptor components, should prove most effecient for Landings on both earth and Mars and launches from Mars.
From what I've heard, it seems that the Raptor engines are primarily for the BFR first stage, while the same plumbing could be used for the MCT. This should also give the advantage of less debris being kicked up under the MCT, as the exhaust would be spread and off to the sides, rather than concentrated underneith the craft, and having to make holes in the TPS. Making holes in the TPS adds mass for the hing and closing systems, (which would also have to be shielded against teh exhaust of engines cutting through the TPS) plus it complicates the landing sequence more than needed.
I have further thoughts on the MCT design that I'll post later.
Quote from: Burninate on 01/14/2016 03:43 amQuote from: Vultur on 01/14/2016 03:22 amCan it really not do Mars entry engines first? Rocket engines already deal with pretty intense heat...If it was feasible to do so, why did we ever invent ablative heatshields? Rocket engines deal with heat either ablatively or with regenerative cooling - heating up the propellant - in which case you need to expend the propellant steadily.The guidance from the SSTO guys is that for Mars, direct retro burns basically overwhelm any drag benefit of the rest of the spacecraft; You're left with a mass-intensive propulsive descent, as if Mars had no atmosphere.That's because the exhaust creates a virtual "aerospike" which reduces the drag on the vehicle, but has nothing to do with the question. He didn't ask about using the engines but if they could stand the reentry temperatures and therefore have an "engines-forward" entry.
Engineers working on the SERV concept originally estimated that they would need TPS doors to cover the engine nozzles during reentry but subsequent testing showed that especially in SERVs case the overall base diameter was sufficient to reduce the heating load so that no TPS doors or special insulation was required. That's Earth though and Mars is a bit different but you should be able to, if the base is wide enough, to enter engines first as long as they are designed properly and integrated into the base of the vehicle. At worst you can probably cold-flow some propellant through the engine system during the period of highest heating, dumping it through the nozzle and overboard.The benefit is once you're down far enough you only have to add in the other propellant to the engine and ignite it for the powered landing.Randy
Quote from: Vultur on 01/14/2016 03:22 amCan it really not do Mars entry engines first? Rocket engines already deal with pretty intense heat...If it was feasible to do so, why did we ever invent ablative heatshields?
Rocket engines deal with heat either ablatively or with regenerative cooling
- heating up the propellant - in which case you need to expend the propellant steadily.
Quote from: RanulfC on 01/14/2016 05:40 pmQuote from: Burninate on 01/14/2016 03:43 amQuote from: Vultur on 01/14/2016 03:22 amCan it really not do Mars entry engines first? Rocket engines already deal with pretty intense heat...If it was feasible to do so, why did we ever invent ablative heatshields? Rocket engines deal with heat either ablatively or with regenerative cooling - heating up the propellant - in which case you need to expend the propellant steadily.The guidance from the SSTO guys is that for Mars, direct retro burns basically overwhelm any drag benefit of the rest of the spacecraft; You're left with a mass-intensive propulsive descent, as if Mars had no atmosphere.That's because the exhaust creates a virtual "aerospike" which reduces the drag on the vehicle, but has nothing to do with the question. He didn't ask about using the engines but if they could stand the reentry temperatures and therefore have an "engines-forward" entry.I'm pointing out that the cooling mechanism on a regeneratively cooled engine, the thing that keeps it from melting during normal operation, is cold propellant flowing through it rapidly on the way to combustion. You can't do that without having the engine turned on. Having the engines directly in the flow poses perhaps the worst aerothermodynamic problem: a parachute-shaped facing surface with sharp frontal edges.
Quote from: Burninate on 01/14/2016 11:52 pmQuote from: RanulfC on 01/14/2016 05:40 pmQuote from: Burninate on 01/14/2016 03:43 amQuote from: Vultur on 01/14/2016 03:22 amCan it really not do Mars entry engines first? Rocket engines already deal with pretty intense heat...If it was feasible to do so, why did we ever invent ablative heatshields? Rocket engines deal with heat either ablatively or with regenerative cooling - heating up the propellant - in which case you need to expend the propellant steadily.The guidance from the SSTO guys is that for Mars, direct retro burns basically overwhelm any drag benefit of the rest of the spacecraft; You're left with a mass-intensive propulsive descent, as if Mars had no atmosphere.That's because the exhaust creates a virtual "aerospike" which reduces the drag on the vehicle, but has nothing to do with the question. He didn't ask about using the engines but if they could stand the reentry temperatures and therefore have an "engines-forward" entry.I'm pointing out that the cooling mechanism on a regeneratively cooled engine, the thing that keeps it from melting during normal operation, is cold propellant flowing through it rapidly on the way to combustion. You can't do that without having the engine turned on. Having the engines directly in the flow poses perhaps the worst aerothermodynamic problem: a parachute-shaped facing surface with sharp frontal edges.I know it's probably been mentioned many, many times now but it's something which SpaceX have already accomplished, several times now?https://www.nasa.gov/press/2014/october/new-commercial-rocket-descent-data-may-help-nasa-with-future-mars-landings/
Quote from: dror on 01/13/2016 05:18 pmQuote from: raketa on 01/07/2016 10:17 pmThis is my idea of MCT, focusing on survival on all critical parts of Mars Journey, since there will multiple MCT on the way and they will not probably use 100 people before base is build and they could help each others.That reminds me of the idea which was to fly a F9 reusable 2nd stage together with a dragon 2 as one spaceship.How does the crew transfer between the escape pod and the hab module through the heat shield?Is the heat shield necessary for an aerobreak?Gemini-B would have had a hatch in the heat shield.
I'm a bit confused guys...When did SpaceX say that the MCT was going to be two sections, a main ship and an escape module?