It would work even better with additional depots at L1, SEL2 / ISRU and SEP
How much easier do things become if you 1) enter from orbit instead of directly, 2) slow down more than is necessary to enter the atmosphere, 3) use the biggest possible EELV fairing (6.5m) and 4) use a lifting body? I'm thinking of entering the atmosphere at a mere 2km/s.
May I ask, why would you want to use rocket propulsion for hypersonic/supersonic braking manouevres when you can just resort to larger shroud diameters?Perhaps that's why we should get a HLV. It certainly makes things a lot easier for Mars. For the Moon it's not necessary, but for Mars, I certainly think so.
Well then deal with the reality of not going to Mars.Something like Direct's Jupiter or Atlas Phase 2 is certainly necessary for Mars missions.
A problem? I thought flying a 30t lander on a lifting trajectory with a 15m heatshield would get you below Mach 0.8 at sufficient altitude to start retropropulsion.The last approach is just plain nuts, no offense.
The vehicle would mass hundreds of tonnes and would only be able to land tens of tonnes.
I think if you want to do some propulsive deceleration it is best to do it as late as possible: let the atmosphere do the work of decelerating you to about 1km/s, and then do the rest propulsively.
Coming in from orbit will reduce the heat load of the heat shield, but it will not significantly reduce the required delta-v. And designing a heat shield for 6km/s hyperbolic entry is not that challenging compared to an earth entry. So if your mission architecture requires hyperbolic entry (e.g. mars direct) you can do it.
A lifting body or any kind of high L/D shape would be very useful to reduce the required propulsive delta-v. But then a non-axially symmetric vehicle might be much harder to design. It might be easier to just accept the 0.2 PMF required for semi-propulsive braking.
Injecting some "exotic engineering" here, I wonder if anyone ever considered using buoyancy as a way to descent to Mars. The question is of course, whether an airship similar in design as the one proposed by JP Aerospace for Earth, could achieve enough uplift through the Martian atmosphere earlier enough to not crash, but to achieve a slow and controlled descent.
Quote from: rklaehn on 09/02/2009 12:05 pmI think if you want to do some propulsive deceleration it is best to do it as late as possible: let the atmosphere do the work of decelerating you to about 1km/s, and then do the rest propulsively.Sure, but the problem is that that is very difficult with EELV fairings, unless you come up with something like foldable or inflatable heatshields. By the time you get to just above the surface you would be going too fast and the atmospheric density would be too high to fire your thrusters.
QuoteComing in from orbit will reduce the heat load of the heat shield, but it will not significantly reduce the required delta-v. And designing a heat shield for 6km/s hyperbolic entry is not that challenging compared to an earth entry. So if your mission architecture requires hyperbolic entry (e.g. mars direct) you can do it.From orbit it is something like 3.5 km/s, which is quite a bit less than 6 km/s.
But when you slow down from orbit and at the sime time attempt to maitain your altitude above the surface you're incurring huge gravity losses.
Quote from: simon-th on 09/02/2009 12:22 pmInjecting some "exotic engineering" here, I wonder if anyone ever considered using buoyancy as a way to descent to Mars. The question is of course, whether an airship similar in design as the one proposed by JP Aerospace for Earth, could achieve enough uplift through the Martian atmosphere earlier enough to not crash, but to achieve a slow and controlled descent.I think the airship to orbit idea of JP aerospace is completely unworkable. But the idea of using large inflatable structures for reentry is quite workable.Here is a very interesting project of the german mars society about mars reentry using a balloon that is inflated in space. It is made from somewhat heat-resistant material, and due to the large surface area per mass unit (low ballistic coefficient), the heating is gentle enough for the balloon to survive reentry. http://www.archimedes-ballon.de/index.php?id=EN