Henry:
Sorry, but time to call bullshit.
I was on the ESAS team and personally costed a dozen different depot and
reusable lander concepts.
The view through your knothole might be biased....
Bill
On Sun, Mar 4, 2018 at 1:51 PM Henry Vanderbilt <hvanderbilt@xxxxxxxxxxxxxx>
wrote:
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.
This all reminds me of the strong LEMcentricity of NASA on potential new
Lunar landers.
Ten-ish years ago when Constellation was still a thing and I was working
on a propulsion tech demo aimed at such landers, I was exposed to a fair
amount of the customer's thinking on the matter.
All of the concepts were scaled-up versions of the basic Apollo LEM
configuration, a tail-lander with long legs to provide ground clearance
for a big centrally-mounted engine. All.
There were amusing problems with the scale-ups. You'd see things like
thirty-foot vertical ladders for crew access, and in at least one
instance, a built-in crane (!) for lowering cargo from the
several-stories-up lander upper deck to the surface.
Side lander concepts, such as the Masten/ULA XEUS, apparently weren't
even thinkable.
There also was (is still?) an accompanying utter refusal to consider
reusable landers and the propellant depot system to support such - too
risky, too expensive. Likely so - if done by those usual suspects under
business-as-usual.
Henry V