If the return delta-v is that high, the vehicle would only ever be fully fueled on Mars, as it doesn't need nearly as much delta-v to get to Mars.
Quote from: Vultur on 08/30/2015 06:47 amIf the return delta-v is that high, the vehicle would only ever be fully fueled on Mars, as it doesn't need nearly as much delta-v to get to Mars.It would likely be fully fueled in both directions. However the payload back to earth would be much lower to achieve the higher delta-v with the same amount of fuel.
Quote from: guckyfan on 08/30/2015 07:05 amQuote from: Vultur on 08/30/2015 06:47 amIf the return delta-v is that high, the vehicle would only ever be fully fueled on Mars, as it doesn't need nearly as much delta-v to get to Mars.It would likely be fully fuelled in both directions. However the payload back to earth would be much lower to achieve the higher delta-v with the same amount of fuel.Also you could utilize the extra delta-v to make the booster a little smaller and maybe make the trip to Mars take less time.It is the leg that requires most delta-v that steers the parameters of the rest.
Quote from: Vultur on 08/30/2015 06:47 amIf the return delta-v is that high, the vehicle would only ever be fully fueled on Mars, as it doesn't need nearly as much delta-v to get to Mars.It would likely be fully fuelled in both directions. However the payload back to earth would be much lower to achieve the higher delta-v with the same amount of fuel.
Quote from: guckyfan on 08/30/2015 07:05 amIt would likely be fully fueled in both directions. However the payload back to earth would be much lower to achieve the higher delta-v with the same amount of fuel.Maybe, but the return payload has to be large enough to accommodate people + life support according to Musk, and less fuel means fewer tanker launches needed to fuel up the vehicle going to Mars.
It would likely be fully fueled in both directions. However the payload back to earth would be much lower to achieve the higher delta-v with the same amount of fuel.
Quote from: symbios on 08/30/2015 09:12 amQuote from: guckyfan on 08/30/2015 07:05 amQuote from: Vultur on 08/30/2015 06:47 amIf the return delta-v is that high, the vehicle would only ever be fully fueled on Mars, as it doesn't need nearly as much delta-v to get to Mars.It would likely be fully fuelled in both directions. However the payload back to earth would be much lower to achieve the higher delta-v with the same amount of fuel.Also you could utilize the extra delta-v to make the booster a little smaller and maybe make the trip to Mars take less time.It is the leg that requires most delta-v that steers the parameters of the rest.Actually, the dry weight of the MCT (and total mass on a return flight) also is very important in this equation since the ΔV budget of a fully fuelled craft could be significantly different when it departs LEO from when it departs Mars surface.
This, the dry weight is too small and encloses too large of a volume (spreading it very thin) to be able to survive re-entry on Earth which is a minimum of 11 km/s. Even once we take into account for the 75% reduction in cargo on the Earth return leg.
Quote from: Impaler on 08/31/2015 05:25 amThis, the dry weight is too small and encloses too large of a volume (spreading it very thin) to be able to survive re-entry on Earth which is a minimum of 11 km/s. Even once we take into account for the 75% reduction in cargo on the Earth return leg.The volume would be pressurized so is stable when reentering head on. Only when it has slowed down a lot it would pivot over for flying engines first for landing. I have speculated before that they may pressurize for more than 1000 millibar for reentry.Going for good mass fraction prohibits massive walls like on capsules.And one of my standard arguments. The designers at SpaceX are certainly aware of that problem and have at least tentatively a solution. A Falcon 9 first stage cannot do it because it is too long and slender. A second stage or a MCT has different proportions.
This was proposed on one of these threads, but I have no data on its plausibility. Can you provide any references on the concept of superpressure as lighter-weight substitute for structural strength during reentry?
Internal pressure doesn't prevent you from burning up which is my main concern.
>How heavy is a Dragon heat shield? Googling I find 848 kg for Apollo heat shield, and PICA-X is supposed to be better than previous materials.>
Quote from: Impaler on 08/31/2015 08:30 amInternal pressure doesn't prevent you from burning up which is my main concern.That's what PicaX is for. At its size I think MCT would be lighter per volume and per surface than a Dragon capsule. Especially with a small cargo entering earth's atmosphere at high speed. The shield would be thick and strong on the tip but could be thin at the sides.
PICAX is nice stuff but no one even knows how to seal seems in it yet so it can only be used in monolithic pieces, assuming this limitation is over come their are other issues.
Quote from: Impaler on 09/01/2015 04:52 amPICAX is nice stuff but no one even knows how to seal seems in it yet so it can only be used in monolithic pieces, assuming this limitation is over come their are other issues. I guess these don't count as seams then? SpaceX figured out how to seal PICAX seams on their very first cargo dragon flight back in 2010.
Quote from: sublimemarsupial on 09/01/2015 06:02 amQuote from: Impaler on 09/01/2015 04:52 amPICAX is nice stuff but no one even knows how to seal seems in it yet so it can only be used in monolithic pieces, assuming this limitation is over come their are other issues. I guess these don't count as seams then? SpaceX figured out how to seal PICAX seams on their very first cargo dragon flight back in 2010.Yes, I'm not sure where this idea comes from. PICA-X does not have to be monolithic. Statements like this makes me question your other assertions, Impaler.