Re: RE: RE: [Fwd: starship-design: HIGHLY OPTIMIZED TOLERANCE]

[Steve VanDevender <stevev@efn.org>]

KellySt@aol.com writes:
 > >I don't have the figures to back this up, but I would think even at the
 > >orbit of Mars there would still be enough solar radiation for solar power,
 > >perhaps not much beyond that. 
 > 
 > I remember it was geting to be a serious problem with the recent Mars probes. 
 >  Thats why the Rovers and such died so rapidly.  The old nuclear Mars probes 
 > kept going for years.  The new ones only lasted a couple weeks.

The Sojourner rover was still operating when the lander stopped
communicating after 80-some days of operation.  The original mission
plan assumed that the lander would operate for only 30 days and the
rover only 7.  Both used solar power to recharge batteries to allow some
overnight operations; while there's no definitive evidence to say
exactly why the lander failed, electronics failure due to thermal
cycling or battery failure after so many daily charge/discharge cycles
are possibilities.  However, it was possible to operate both the lander
and the rover from solar power alone without any battery support at all,
and I believe the rover operated that way later in the mission.

The Pathfinder mission was intentionally built cheap; its limitations
were not the result of using solar power instead of nuclear.  Mars
Global Surveyor is completely solar-powered and has been operating in
Mars orbit for two and a half years, and should operate for quite a
while more.

The Cassini web site has a pretty nice presentation on why they couldn't
use solar power for Cassini (to answer the anti-nuclear activists who
spread untenable scare scenarios about a Cassini launch failure or Earth
impact during its swingby):

http://www.jpl.nasa.gov/cassini/rtg/solar.htm