[ExI] Mars rover on its way

[spike]

>... On Behalf Of Kelly Anderson
Subject: Re: [ExI] Mars rover on its way

>> The launch sequence isn't what scares me on this mission, it's that
landing sequence...

>Indeed. Aren't only about half of the missions to Mars successful to date?
Seems like everyone who goes there gets something wrong a lot of the time.
It would be nice for this one to work though! -Kelly


Mars landing missions are the controls engineer's playground.  This is JPL,
so you can be sure they would come up with something crazy complicated, but
before we discount their design, note that JPL influenced the Gravity Probe
B design, which was even more complicated than this mission, and it worked.
Yes I know PGB was primarily Stanford (go Cards!) but we used JPL assistance
for some of the controls stuff. 

Another way to think about it: assume the Curiosity mission's requirements,
then try to imagine the design alternatives.  Since you will be in transit
for over 8 months, you don't have the option of LOX/H2 retro-propellant, so
that means hauling probably monomethyl hydrazine and nitrogen tet, with all
the scaries that go with that stuff, then you get to the really cool
problems of how to detect and control altitude, speed and orientation,
maintaining all that with four propulsion systems, which is quite a trick
all by itself considering how many feedback loops are needed, all of which
must work perfectly on the first and only try.  

Given all the stuff Curiosity plans to do, the broad mission pushes the
design weight waaay up.  Consequently that balloon landing they did with
Spirit and Opportunity probably wouldn't work for something this heavy
(would it?  I think not.)  So you end up with wacky complicated stuff like
Curiosity's aerobrake, parachute, four retro-rockets and a tether notion,
and please please, we beseech thee O Holy Evolution, let this crazy scheme
work.  We want to know what Curiosity can tell us, should it survive the
landing sequence.

spike