Safer Martian landings

Hard landings on Mars are easy; soft landings are very hard indeed.

I've been doing some scaling estimations for Martian descent models, and it
looks like the maximum risk benefit against descent failure comes with the
lowest-mass vehicles. This matches only roughly aginst the actual track
record for Martian descents, but we don't have really good information about
the failures to judge them all that well.

Still, I wonder how far one can carry this, especially for human
exploration. Should we try to develop a descent system for one person at a
time? The basic analysis shows that the best descent system for humans
might be incredibly minimal -- just a space suit, a personal heat shield, a
braking parachute and a jet pack. This might mass out to something like
half a fully-laden Mercury capsule.

Things like this have been considered for emergency descent from Earth
orbit, but a descent to Mars is actually hairier, what with the thin
atmosphere and a significanly greater-than-Luna gravity well.

I'm still working on the Gs that would be pulled in a personal descent
system that has a high aerodynamic cross section and low mass -- the
deceleration force is pretty scary -- but this model may be the most
reliable for any manned descent, and as a bonus, it's also probably the
least expensive. Reducing the entry velocity appears to offer the greatest
benefit, so I wonder if it might be safest and sanest to drop one-person
descent units off the bottom of a tether from Phobos.

Of course, this does not speak to the problem of ascent :-) but I think we'd
better figure out how to get people onto the surface in one piece first.
Has anyone done any work on stuff like this?


Jim McCauley

Jim McCauley wrote:

I'm still working on the Gs that would be pulled in a personal descent
system that has a high aerodynamic cross section and low mass -- the
deceleration force is pretty scary -- but this model may be the most
reliable for any manned descent, and as a bonus, it's also probably the
least expensive.

The Gs aren't scarier in a system with high aerodynamic cross section and
low mass. Such a system will decelerate higher where the atmosphere is
thinner. Typically the deceleration will be softer than with denser systems.

I have done some BOE engineering for such systems. One interesting
possibility is to have a mesh shield. You have a heat shield to protect
what you want to bring to the ground and you extend the shield out
further to increase the drag. But the part of the shield that doesn't
protect the payload from heat and is there only to increase the drag
can be a mesh. The gaps in it lets the heat flow through it and it can
have high drag for a low mass. The details of the implementation are
left as an exercise to the reader :-)


Alain Fournier

On Aug 28, 6:56 pm, Alain Fournier wrote:
Jim McCauley wrote:
I'm still working on the Gs that would be pulled in a personal descent
system that has a high aerodynamic cross section and low mass -- the
deceleration force is pretty scary -- but this model may be the most
reliable for any manned descent, and as a bonus, it's also probably the
least expensive.

The Gs aren't scarier in a system with high aerodynamic cross section and
low mass. Such a system will decelerate higher where the atmosphere is
thinner. Typically the deceleration will be softer than with denser systems.

I have done some BOE engineering for such systems. One interesting
possibility is to have a mesh shield. You have a heat shield to protect
what you want to bring to the ground and you extend the shield out
further to increase the drag. But the part of the shield that doesn't
protect the payload from heat and is there only to increase the drag
can be a mesh. The gaps in it lets the heat flow through it and it can
have high drag for a low mass. The details of the implementation are
left as an exercise to the reader :-)

Alain Fournier

Properly shielded humans are not ever going to be "low mass", and as a
species we tend to avoid bad situations where folks like yourself do
not understand the risk to our frail DNA, not to mention our frail
bones and everything else.

Even a soft landing on Mars is essentially a mission death wish, and
much quicker yet for those accomplishing our moon (especially by
day).
- Brad Guth