Jim Kingdon wrote in message ...
Why must JIMO be nuclear? What's wrong with hydrogen fuel cells?
Alternatively, why not strap together 10 deep space ones and use the same
light collectors?

Nuclear does give you additional capacity, as others have noted.

But if I'm reading the JIMO situation correctly, making it nuclear is
the whole point. In other words, the main motive for doing JIMO is to
demonstrate the nuclear power. It would be paid for out of the
exploration budget, not the science budget.

Not exactly. It's a good example of a decent "full up"
technology demonstration missions. More along the lines
of an "inaugural launch" than a test. Like NEAR or
Deep Space 1 (more like NEAR though). JIMO is a science
packed mission no matter how you look at it. Similar
in concept to Dawn, JIMO represents the new class of
"multi-rendezvous" (my word) missions enabled by electric
propulsion. Dawn, for example, will rendezvous with
asteroids Vesta then Ceres, performing a detailed, year
long study of each. The Jupiter Icy Moons Orbiter (JIMO)
will perform a similar multi-rendezvous with Callisto,
Ganymede, and Europa, spending several months at each
(and the longest time at Europa, the final target).

Certainly it's a demonstration of the technology, but
the very design of the mission can't help but to produce
mountains of science.


(For the JIMO targets at least there is really no way
to do the mission without nuclear power. It might be
feasible with RTGs and might not require a reactor,
but it would not work with Solar power. Otherwise
you're going to have to bring along several percent of
a hectare in PV arrays in order just to have the
power to run the propulsion system and nothing else.
And that doesn't even begin to go into how in the hell
you'd keep the PV arrays pointed at the Sun, the
HGA pointed at Earth, the camera pointed at the Moon,
and the thruster pointed opposite of where you want to
go.)