On 3/3/2018 8:37 PM, Henry Spencer wrote:
On Sat, 3 Mar 2018, Lars Osborne wrote:
The discussion about LITVC reminded me of some of the studies that have been
performed on making an ascent vehicle for Mars sample return...
I was a bit surprised that they throught a hybrid would be the best choice, but that must have been strongly driven by the desirement to be storable at low temperatures. I am surprised they found it to be the lightest option as well. A paraffin wax hybrid no less.
The key question to ask is something that is often skipped over even in papers, never mind presentations: what were the assumptions used in the analysis? It's all too common to choose the assumptions carefully so they stack the deck in favor of the pre-chosen winner. It's interesting that the two studies shown in this slide deck ranked the different approaches in quite different orders.
About twenty years ago, when LLNL was in the rocket business for a little while, John Whitehead (LLNL) and Carl Guernsey (JPL) came up with a rough design sketch of a biprop SSTO Mars ascent vehicle that was lighter than any of these concepts and had about twice the payload. The key features were pump feed using LLNL's miniature piston pumps, and propellants stored in tanks aboard the mothership and loaded into the ascent-vehicle tanks only just before ascent -- the combination permitted *very* lightweight ascent-vehicle tanks, since they didn't have to carry significant pressure loads or Earth-launch/Mars-landing loads. (Oh, and the design wasn't constrained to fit into a narrow cylinder, as the ones in this latest study seem to be.) W&G might have been too optimistic in spots, but it was an interesting approach and looked promising.
