I don't think we will use fully propulsive Mars landers. Ever tried firing a rocket into a hypersonic jet stream coming at you?
Topic Summary Posted on: Today at 03:56 AMPosted by: mmeijeri Insert QuoteIt is unlikely heavy payloads can be landed without using propulsion for substantially more than final descent and landing. Of course that doesn't mean you don't want to use aerodynamic deceleration to the maximum degree possible.
I agree that other things being equal, you can save a lot of propellant by using aerobraking, but for heavy payloads, that's not trivial. There are faring issues as well. Meanwhile, a fully propulsive Mars lander could be had more or less off the shelf if it were a beefed up Lunar lander.
Quote from: Warren Platts on 09/25/2011 12:56 PMI agree that other things being equal, you can save a lot of propellant by using aerobraking, but for heavy payloads, that's not trivial. There are faring issues as well. Meanwhile, a fully propulsive Mars lander could be had more or less off the shelf if it were a beefed up Lunar lander.Hey, I'm all for that, in fact I've advocated just that. But eventually I think both propulsive braking and aerodynamic deceleration will play substantial roles. Large single-use heatshields that require huge fairings - not so much.
Mars' gravity and atmosphere is not as great as earth, like 35-40% I think.
Jim has shown that a 10m heat shield can be folded in half to fit a 5m EELV.
Quote from: spacenut on 09/26/2011 05:19 PMJim has shown that a 10m heat shield can be folded in half to fit a 5m EELV.Only if it's a disk. The DRM 5.0 aeroshells were biconics and 10 m across.
So air braking might be just as costly as propulsive braking or landing?
IMO, the cheapest and fastest way to Mars would be a simple (as in pretty much fully propulsive), reusable (cheaper since it can be used over and over again), all chemical (faster than SEP), architecture that was evolved from previous spacecraft a la the ULA Lunar plan. Zegler et al. say their DTAL lander could easily be evolved for use on Mars. My own BOTE calculations suggest that a stretched tank DTAL lander (i.e, an ACES-71) equipped with a heat resistant titanium hull (so it could withstand the full 1 W/cm2) could land fully propulsively--no ballutes, parachutes, or heat shields required.Then the ULA MTV has a crew capacity of 16 and a nominal delta v of 11 km/sec. If there was refueling capability in Mars orbit, the ULA MTV could cut the 1-way transit times by over half compared to the Hohman transfer; if refueling was deemed impractical (probably the case for the initial missions), it would have enough delta v to do a round trip taking Hohman transfers. Again, this would all be fully propulsive--no heat shields required. The 7 hundred tonnes of propellant would only cost about $350 million, if refueled at L2 (with Lunar derived LH2/LO2). See, so the whole thing would be faster and cheaper, since it would be a simple evolution from the ULA Lunar architecture, which is itself a simple evolution from the Centaur 3rd-stage architecture.