Re: anti-space-nuke nuts rise again

In article <1160250671.243375.225320@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
Alex Terrell <alexterrell@xxxxxxxxx> wrote:
...To date has anyone used solar as far out as Jupiter?

No. NEAR was, I believe, the first to use it beyond Mars -- NEAR got out
to about 2_AU while in transit -- and observations during its Mathilde
flyby were severely hampered by shortage of power. If memory serves,
Rosetta will push it considerably farther, at the cost of needing very
large solar arrays, but still not out to Jupiter. (Cassini's canceled
sister ship, CRAF, which was to do essentially the Rosetta mission, would
have used RTGs.)

In the last two decades solar power has progressed much faster than
nuclear power. The rule of thumb was solar to Mars, RTG beyond Mars. At
the time of Cassini, solar power was not an option. If the mission were
designed again for launch in 2010, the power supply analysis might come
up with different answers.

No, quite likely the same. There have been occasional proposals to do
solar-powered outer-system missions, but the solar arrays get huge and
there are lingering uncertainties about operation of solar cells in dim
light and severe cold.

In future, it might also be desirable to deploy electric propulsion to
speed up mission times. The same 32 kg 50KW array could provide over
100KW for this purpose.

Unfortunately, the place where electric propulsion gives the greatest
leverage is at the far end -- for orbit insertion at the destination --
precisely where solar power is weakest. Outer-system electric propulsion
really needs nuclear power.

believe RTGs are used to keep certain parts of the spacecraft warm -
like batteries.

RTGs don't generally get used for that, although smaller plutonium heater
capsules see considerable use -- they show up in a lot of spacecraft, e.g.
Mars Pathfinder, but deliberately don't get much publicity.

If memory serves, CRAF was going to have a heat pipe from its RTGs to its
electronics, to permit use of RTG heat for warmth in extremely cold parts
of its mission.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. | henry@xxxxxxxxxxxxx
.

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