In article ,
says...
By looking at the MERs the solar panels have no future in robotic
exploration.

Sorry, but the MERs show quite the opposite. Those solar panels are
extremely cheap and lightweight compared to RTGs. They produce quite
respectable amounts of power and could obviously produce more if they had
been made to track on one or two axes. For that matter, a solar thermal
concentrator could be used to drive a direct heat engine during the day,
making solar an extremely efficient option.

They need to be faced towards the sun to produce anything

Well most all solar collectors and PV will produce around double the
power if they track. However, actually many systems including amorphous
PV and flat panel collectors can work quite well with diffuse light.

and
they require lots of space when deployed.

Perhaps. I'm not sure that this is a problem in most cases.


You also need heavy onboard
batteries to cover the blackouts.

Yes, for things like rovers perhaps. For normal probes they can rely on
sun virtually all the time. It is also worth noting that one could use a
small 1 or 2 kilo RTG as a backup power source, rather than a real
battery. It will provide plenty of waste heat in cold areas like mars
and as well as reasonable amounts of standby power. As you probably know
the MERs do have about 8 tiny radio-isotopic heaters on board.


I seriously doubt solar panels can come
anywhere near RTG in watts per kg comparison,

I gave the figures. RTGs standardly produce 500W thermal per kg of fuel.
That is standardly only converted at around 10% efficiency or less with
thermal diodes. OTOH, PV can easily get several KW electrical per pound
of solar panel, especially if the panels are equipped with tracking
capabilities. Even cutting this capacity factor by about 3 for 8 hours
of sunlight and assuming the lower insolation of mars means that PV and
other solar technologies come out ahead.

However, I think that a combination of solar and RTG could work quite
well. Things like amorphous PV can be coated onto many external surfaces
and provide basic DC power needs during the day. Like I said before,
you'd have to be very far from the sun, or in a very special environment,
before an RTG only approach would be the best one.

especially if they operate on
the planet with night/day cycles.

Of course there are appropriate technologies. It would be nice to have
an RTG so that a rover could keep operating at night. But I don't see
any fundamental technology breakthrough on the horizon that will make
RTGs substantially cheaper. OTOH, solar continues to improve in
efficiency and drop in cost virtually every five minutes.

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