From: Technotranscendence (neptune@mars.superlink.net)
Date: Mon Sep 23 2002 - 17:28:10 MDT
The Beagle 2 lander currently under development
by the European Space Agency as part of its
Mars Express program is going to use airbags
for landing, much as the earlier, successful
NASA Pathfinder mission. However, unlike
Pathfinder, Beagle 2 will have only a parachute
to slow down its descent before deploying
airbags to bring it to a stop. Pathfinder used
a parachute then rockets near the final stage of
descent to slow it even more. The ESA is, of
course, trying to save money -- a strange thing
for a tax-funded agency to do, though laudable since
it's not its money.:)
The problem is none of the airbags tested so far
seem to be able to withstand the estimate 150 kph
impact. Thus far the effort has been to make the
airbags tougher or to make the parachute better
at slowly down the lander.
Perhaps another solution would be to have layered
airbags with each layer designed to give, absorbing
some of the energy of impact while preserving the
overall integrity of the whole system. Think of
this as a kind of bubble wrap design, where the
failure of one or more layers doesn't make the
whole system fail. In fact, it will enhance the
system's durability by making failures only local.
A problem with this approach is, of course, complexity.
A few airbags can be managed far easier than many more.
It's far easier to check, inflate, deploy, and deflate
a few than many airbags. Still, the idea is worth
considering -- if not for Beagle 2 then for future
missions.
Still another idea would be akin to other packaging
methods, such as peanut packing materials. These
are small peanut shaped foam units made specifically
to absorb shock for transporting items such as
computer parts. To my knowledge, the stuff hasn't
been tested in space, but imagine a lander packed partly
in this stuff with the idea that it would cushion impact
by both allowing for absorbing some of the force,
slipping to absorbing still more, and even breaking
apart to absorb the rest.
This kind of break apart system could be packed outside
(or inside?) airbags, making for a composite system.
What are the problems with this system? The lander
would have to be much larger, though this might not
increase weight. Why? The packing is not inflatable.
Traveling through space might aversely affect the
material, making it stiffer or otherwise less
effective. The material might contaminate the landing
site. If the goal is not to contaminate the site, the
material would have to made so that it didn't harbor
any life. This would increase manufacturing costs.
(This applies to airbags too, though it would seem
foam packing would be harder to manage in this
respect.)
Some of these methods could be applied to landing on
other planets or asteroids. E.g., sticky lander could be
designed to land on asteroids. It might have airbags
that stick to the surface -- to avoid bouncing which
for many asteroids would mean the lander bouncing off
and never returning given their low gravity.
Anyhow, I just wanted to share these ideas in hopes
that they might find application here or elsewhere
and that they might stoke more imaginative approaches.
Cheers!
Dan
http://uweb.superlink.net/neptune/
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