In article ,
Marc 182 wrote:
you've just got to keep your radio, computer, electronics, and batteries
warm, which I suspect the RHUs were positioned to do anyway.

The trick is keeping them adequately warm in a dense atmosphere at LOX
temperatures, while not frying them in space beforehand. Just good
insulation almost certainly is not enough; the atmosphere is likely to
increase heat transfer enough that you'll need to either add electric
heat, or have some sort of variable heat leak which switches off during
descent. It's feasible but it adds mass and complexity.

(While there are insulation types whose effectiveness is different in
atmosphere than in vacuum, unfortunately, the change goes the wrong way:
good in vacuum and bad in atmosphere rather than vice-versa.)

But, of course, they never expected it to live for any length of time on
the surface... or did they?

They weren't even sure it would survive impact (and on a really hard
surface, it probably wouldn't have). The primary mission lasted three
minutes after impact -- just long enough for a few pictures and some
readings from the simple little set of surface-material sensors.

I wonder what the thinking was when they slipped in the big batteries.

If memory serves, the requirement was to reliably complete the primary
mission with one battery cell failed. That meant having some safety
margin against worst-case conditions *after* taking one cell out of the
picture. The result, unsurprisingly, was that with all cells working and
conditions generally not too bad, there was a large reserve of energy.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |