Henry Spencer wrote:

In article ,
McLean1382 wrote:
Even with LEO transit costs a couple of orders of magnitude less, you are still
going to have strong incentives to minimize mass. Getting from LEO to Mars and
back still requires a lot of delta v, even with aerobraking.

So? Fuel is cheap, especially if you don't insist on using liquid
hydrogen. Looked at carefully, almost always the way you minimize cost is
to throw mass at problems, rather than throwing engineering man-years at
them.

For example, it is almost certainly cheaper to use LOX/methane than to
solve the problems of long-term LH2 storage in space. (Slightly modified
RL10s have been run on LOX/methane.)

Could you define "slightly"? A reference detailing the changes would be
appreciated.

So what if it makes the vehicle
heavier? Almost all of the mass is either methane, which is cheap, or
LOX, which is almost free. If the cost of getting them into LEO is
reasonable, using them is better than inventing new LH2 technology.

And the need for
extreme reliability will drive up development costs in any case.

Not if you send along tools and spare parts (and guys who know how to use
them) instead, and provide enough redundancy and backups to give time for
them to be used. In highly-lethal Earth environments, like Antarctica, we
don't see anywhere near the same development costs. If you're going to
the trouble of sending people as part of the mission, you should exploit
their capabilities to the fullest to make the engineering easier.

Yes, this implies a somewhat larger expedition -- multiple ships,
substantial crews. That is actually cheaper than a cut-to-the-bone
minimal expedition where everything *has* to work perfectly because
there's no safety margin and no repair option.
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