MERs: what limits their lifetime on Mars surface?

"Keith Lynch" wrote in message ...

Yes and no. Pioneers 10 and 11, if I recall correctly, had things
like venetian blinds which opened or closed depending on temperature.
I believe they used no electronics, but just bimetallic strips.

Indeed - thermal control louvres. Wonderful gizmos, and used in both US and
USSR missions for many years.

Something like that ought to work even better on Mars than in vacuum.

Ah, no.
Or at least, not in the way intended. Louvres alter the emissivity/albedo
ratio of an object, and if that object is lit by sunlight and is in hard
vacuum, then altering that ratio radically changes the heat-balance of the
object, and thus one can control its temperature.

On Mars, you have this pervasive if rather thin atmosphere which tends to
even out the troughs and peaks of temperature that the spacecraft would
otherwise experience if it were in a vacuum.

-James Garry
(fighting a cooling problem in a vacuum chamber this very day - and probably
resorting to peltier coolers and stout copper rods)