Quote from: Zannanza on 12/03/2013 03:17 pmMay I ask is the PICA-X heat shield of Dragon designed and expected to survive a high-speed reentry of the Martian atmosphere?That's a key question, and yes it is.There's a lot of information upthread, and places like http://en.wikipedia.org/wiki/Red_Dragon_(spacecraft)For those that don't know, Red Dragon EDL was evaluated by NASA Ames who added some insight from MSL. Their concerns were not mass or heatshield, but things like backshell heating, firing the engines while supersonic, and landing leg strength. (Aspects I addressed in my cartoon design above.)
May I ask is the PICA-X heat shield of Dragon designed and expected to survive a high-speed reentry of the Martian atmosphere?
It will be the the manned Dragon without full ECLSS. That will be capable of landing through the earth atmosphere. It will have landing legs that support the landing in earth gravity. It has a pressure cabin, so what backshell? Why additional batteries? It may need better, not bigger solar panels if even that. So except the com equipment for interplanetary distances what else would add weight?
Quote from: guckyfan on 12/03/2013 07:02 pmIt will be the the manned Dragon without full ECLSS. That will be capable of landing through the earth atmosphere. It will have landing legs that support the landing in earth gravity. It has a pressure cabin, so what backshell? Why additional batteries? It may need better, not bigger solar panels if even that. So except the com equipment for interplanetary distances what else would add weight?I just listed this. I think if you do some research on the items I mentioned it will be helpful.
Lobo, I think the heat shield would still need to be beefy. It isn't just total heat. Duration of heating is an important factor. I don't have anything to back that up, but read something along those lines somewhere years ago. Feel free anyone if you can shed light or add a link.
I do remember the discussion of the reentry of the Inspiration Mars capsule. It was said NASA did extensive studies because the reentry speed is extreme. So they checked skip reentry against direct reentry and came to the conclusion that the hard direct reentry is more suited to the characteristics of PicaX (or ablative heatshields in general?).In any case with the thin atmosphere and the low reentry speed on Mars a Red Dragon should be fine. Unless newpylong can point us to studies that show otherwise. He did not yet do that above his claims there would be problems.
Quote from: guckyfan on 12/04/2013 05:58 pmI do remember the discussion of the reentry of the Inspiration Mars capsule. It was said NASA did extensive studies because the reentry speed is extreme. So they checked skip reentry against direct reentry and came to the conclusion that the hard direct reentry is more suited to the characteristics of PicaX (or ablative heatshields in general?).In any case with the thin atmosphere and the low reentry speed on Mars a Red Dragon should be fine. Unless newpylong can point us to studies that show otherwise. He did not yet do that above his claims there would be problems.Why does there need to be a study?
My point was a group of people at Ames did research with SpaceX 3 years ago on this. Much has changed since then. It is a theoretical idea and it would not work with an off the shelf Dragon. Every modification would add mass. If you are not accepting of my opinion, that is fine.
What about supersonic chutes to start with? They aren't light...
I believe the plan was to have no chutes at all.FWIW, I have been very sceptical of the Red Dragon idea all along. Seems to be right at the margin of what is technically possible within the mass limits. We don't know enough about the super-dracos to really say, either way, but IMHO it's very close.
Further, they are canted significantly from vertical and will suffer large cosine losses.
Quote from: Kaputnik on 12/08/2013 07:00 pmFurther, they are canted significantly from vertical and will suffer large cosine losses.Are you sure about that? I don't think the losses are very significant, maybe 5-10%.
SpaceX is being very tight lipped about the SuperDracos. The last time I had anyone tell me anything about them, they said the on-orbit specific impulse was going to be at least 320 seconds, which suggests some sort of adjustable nozzle. There's been no public statements to the same effect, and we've seen no pictures to suggest this is true. Everything we have seen suggests over-expansion.Dragon version 2 was supposed to be revealed this year, but it didn't happen. Presumably it has to happen before the abort test next year.
Quote from: QuantumG on 12/08/2013 11:33 pmSpaceX is being very tight lipped about the SuperDracos. The last time I had anyone tell me anything about them, they said the on-orbit specific impulse was going to be at least 320 seconds, which suggests some sort of adjustable nozzle. There's been no public statements to the same effect, and we've seen no pictures to suggest this is true. Everything we have seen suggests over-expansion.Dragon version 2 was supposed to be revealed this year, but it didn't happen. Presumably it has to happen before the abort test next year.Huh, it's already 2014?