In article , Sander Vesik wrote:

A test program including both subscale tests and then sending an
unmanned return vehicle 2 years ahead of the crew, to manufacture
its return fuel before the crew leave Earth, are both planned.
If the first return vehicle fails to successfully manufacture its
return fuel for any reason, you don't send the crew until the
second ERV has landed and manufactured *its* fuel, etc.

Note that earlier in the thread, a sample return mission was mooted
(not by me) as going to cost more or less as much as the manned
mission anyways and thus not worth it... Which at least appears to
rule that scenario out.

Not precisely. The MD plan runs like this:

2010: send return vehicle. RV lands, makes fuel
2012: send crew, in hab vehicle. Send second RV next month.
Crew lands near first RV, with the ability to use that
to go home. Second RV lands nearby (as backup) or at new
site (for next mission). Crew flies home in RV1.
2014: send second crew, in HV2, send RV3, second crew returns
in RV2 (or RV3 as backup)...

The first return mission isn't a sample return one; it's just the first
mission spread over a few years for safety. If an earlier step fails,
you know it's failed before it can kill you, is the logic. (There are
still critical steps, but this removes some).

Indeed, it's arguable that the first mission to get to Mars will be the
flight hardware for "Mars Direct I".

[I do suspect that some form of automatic sample return mission will
take place, previously or concurrently, but I don't think it'll be part
of that program... remember, the US managed six lunar landings without
ever doing that critical technological sample-return ;-)]

Since we now definitely know that Mars is basically a frozen muddy glacial
ice ball just a few meters below the surface (to a depth of several
kilometers), and that Mars is only dry and desiccated in the top few meters
of soil, then the whole in situ fuel manufacturing scenario suddenly becomes
considerably more plausible.

Nope. We don't know that - its hydrogen you are talking about (unless
there is new data i have missed) and does not need to be ice at all. Not
all of the hydrogen need even be in water molecules.

Indeed. We've reduced the number of possible interpretations of the
Martian hydrosphere from what they used to be, but those still-supported
ones are still intensely debated...

(I mean, it doesn't have canals everywhere and occasional oases. But
that doesn't mean the Global Acatama and the Occasional Aquifer sides
(or whatever you want to call them) agree g)

--
-Andrew Gray