Newsgroups: sci.space.history
From: henry@spsystems.net (Henry Spencer)
Subject: Re: It's that time of year again...
Date: Wed, 20 Dec 2000 13:55:18 GMT

In article <ebi04t4p8b15c4i36ergs68nbph7rvk18a@4ax.com>,
OM  <om@RE_MOVE_THIS.ccsi.com> wrote:
>2) Regardless, this doesn't detract from the success that
>Pathfinder/Sojourner was, Beady. If only Jack Schmidt can get into the
>NASA director's chair quick enough to get the landing bag method
>restored for future landings, we'd see more of this.

Uh, the landing-bag method *has* been restored for future landings... but
whether that will last is unclear, given that it's generally an inferior
technique.  Rocket landing has a much longer history of successful use, is
more versatile, is not significantly more complex (the airbag system is
not nearly as simple as it looks), and lands a rather larger payload.

Don't throw the baby out with the bathwater.  Rocket landing has failed
*once*, due (probably) to a problem completely unrelated to the rockets,
after being used very successfully by Surveyor, Apollo, and Viking.

Airbag landing has only been tried once... and was generally considered a
high-risk approach.
--
When failure is not an option, success  |  Henry Spencer   henry@spsystems.net
can get expensive.   -- Peter Stibrany  |      (aka henry@zoo.toronto.edu)

Newsgroups: sci.space.history
From: henry@spsystems.net (Henry Spencer)
Subject: Re: It's that time of year again...
Date: Wed, 20 Dec 2000 18:51:58 GMT

In article <emt14tg2f932hfkqnucj9qqntfvfbdc6pb@4ax.com>,
OM  <om@RE_MOVE_THIS.ccsi.com> wrote:
>...No arguement there. However, the tetrahedral airbag method does
>have one advantage that the rocket method doesn't have: if the lander
>winds up perched on a rock precariously, the airbags can be deflated
>and inflated in sequences that could wobble the lander off the rock
>into a more stable position...

Except that with current hardware, the airbag inflation and deflation is
one-shot.  You don't get to inflate them a second time, and you don't have
any idea where you are or what the surroundings are like until after they
have deflated.

However, OM has put his finger on a key point, slightly indirectly.  The
one place where the airbag system (the real one, not the fantasy one that
some people seem to have in mind) does win is in its ability to land in
very rough terrain.  If it does land on a rock, or half on a rock, it just
bounces and rolls, with a good chance of stopping on a more or less flat
spot.
--
When failure is not an option, success  |  Henry Spencer   henry@spsystems.net
can get expensive.   -- Peter Stibrany  |      (aka henry@zoo.toronto.edu)

Newsgroups: sci.space.history
From: henry@spsystems.net (Henry Spencer)
Subject: Re: It's that time of year again...
Date: Thu, 21 Dec 2000 15:53:34 GMT

In article <f6134tkt01a6mmvd60as470j0kr6hgbuci@4ax.com>,
OM  <om@RE_MOVE_THIS.ccsi.com> wrote:
>>Except that with current hardware, the airbag inflation and deflation is
>>one-shot.  You don't get to inflate them a second time...
>
>...Now this is interesting. According to much of the JPL commentary
>from the Pathfinder landing, there were several statements to the
>effect that the bags could be reinflated if necessary. This especially
>came up during commentary related to what if Pathfinder landed on its
>side instead of on its bottom as it actually did, or if the deflated
>airbags were hung on a rock during retraction.

I've never heard of a re-inflation capability, and I wonder if this isn't
the result of confusion of some kind.  Side landing was a non-issue due to
the way Pathfinder unfolded -- as the sides ("petals") opened, if it was
lying on one of them, trying to open that petal would push the base up and
over and it would automatically right itself.  And I believe the tactic
for dealing with an airbag hung up on a rock involved fiddling with the
petal opening mechanism (which was reversible) and the retraction winches.

>>However, OM has put his finger on a key point, slightly indirectly.  The
>>one place where the airbag system ... does win is in its ability to land in
>>very rough terrain...
>
>...Oh no. Does this qualify me for an ICH T-Shirt, Henry, or was this
>merely just an assist and doesn't count as such? :-) :-)

Just an assist, since I never actually said anything to the contrary.
--
When failure is not an option, success  |  Henry Spencer   henry@spsystems.net
can get expensive.   -- Peter Stibrany  |      (aka henry@zoo.toronto.edu)