(Gary W. Swearingen) wrote in message ...
"Ool" writes:

I'd be surprised if an airbag system would do a lot of good. Since
there's no air you can't use any aero-braking methods to slow down,
so, unlike the Mars probes, Moon probes would have to stand on top of
a descent stage rocket anyway, rather than hang from a parachute. If
such a rocket can slow the probe down enough for airbags to work, it
could slow it down enough for a simple soft touchdown, too, I bet.

I may be wrong, but I don't think airbags would be practical on the
Moon. They'd be much heavier than the extra fuel for a soft landing.

Maybe, but I don't buy your reasoning. The purpose of the bags is not
to slow the craft down for landing. However that is done, it is
supposed to leave the bagged craft at near-zero velocity, just above
the surface. They can save money by building a lousy system that
can't be trusted to leave it very close, so they design it to stop
many meters above the surface and hope it stops somewhere between the
surface and too high for the bags to work. The main reason for the
bags is so the craft doesn't have to be capable (and expensive) enough
to guide itself to a good landing and settle down on its legs on
good-enough ground. Bag landers don't have to worry about moving
sideways to avoid hills, cliffs, big rocks, etc.

But many missions can't put up with the limitations of bags even now,
despite the cost savings. And as rocket landing systems get more
modular and mass-produced, the cost difference will decrease.

This asks the question - if you took the MERA configuration and made
a few adjustments (perhaps an improved retro in place of the parachute)
could you land it on the moon? If we can standardize our delivery
system for these rovers, it should make it a bit more affordable and
reliable.

Also, is it better to have one lander per launch, or a "MIRV"?