Nuclear-Powered Spacecraft Is Proposed for Voyage to Jupiter Moons

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?
"Tony Sivori" wrote in message
news
And are you ready for this - it would be called the JIMO! :-)

The craft would be a radical departure in that it will be equipped with a
nuclear reactor, instead of nuclear batteries. Power output would be about
1000 times higher than the nuclear battery method.

This opens exciting new possibilities for both power hungry sensors like
ground penetrating radar, and the unprecedented possibility of orbiting
one moon and then moving to another of Jupiter's moons at will (orbital
mechanics permitting, of course). The reactor will power an ion drive that
would be about 10 times more powerful than Deep Space One's drive.

Full article at NY Times:
http://www.nytimes.com/2003/12/16/sc...UPI.html?8hpib

--
Tony Sivori

sharpthoughts wrote:

Why must JIMO be nuclear? What's wrong with hydrogen fuel cells?

Because you can't store cryogens long enough for the duration of the
mission; the mass penalty would be too high (you need oxygen for the fuel
cell, too); you end up with water as a by-product, which is useless for an
unmanned craft and must be vented/dumped overboard; and the power output
would probably be too low.

Alternatively, why not strap together 10 deep space ones and use the same
light collectors?

Because they don't use "light collectors" much out past Earth orbit; too
little solar energy for a realistic mass of photovoltaic arrays. RTGs (or
better, a thermal reactor) has a much better mass/energy ratio.

--
Herb Schaltegger, B.S., J.D.
Reformed Aerospace Engineer
Remove invalid nonsense for email.

sharpthoughts wrote:

Whatever We're getting for the money, $8 billion is more than half the
annual NASA budget. The armed forces have a few more pennies than that to
play with. BTW if we do build a nuclear reactor powered Jupiter boat,
should we be using MPD rather ion drives? They're supposed to be much
more efficient at higher powers than ion, and they could scoop hydrogen
from Jupiter to refuel.

Too much "fiction" and not enough "science" in this idea. You'd have to
store enough H2 to get to Jupiter in the first place, then try an untested,
science-fiction idea (scooping H2 from Jupiter's atmosphere) for the first
time ever and hope it works.

--
Herb Schaltegger, B.S., J.D.
Reformed Aerospace Engineer
Remove invalid nonsense for email.

What's RTG stand for?
"Herb Schaltegger" lid
wrote in message ...
sharpthoughts wrote:

Why must JIMO be nuclear? What's wrong with hydrogen fuel cells?

Because you can't store cryogens long enough for the duration of the
mission; the mass penalty would be too high (you need oxygen for the fuel
cell, too); you end up with water as a by-product, which is useless for an
unmanned craft and must be vented/dumped overboard; and the power output
would probably be too low.

Alternatively, why not strap together 10 deep space ones and use the
same
light collectors?

Because they don't use "light collectors" much out past Earth orbit; too
little solar energy for a realistic mass of photovoltaic arrays. RTGs (or
better, a thermal reactor) has a much better mass/energy ratio.

--
Herb Schaltegger, B.S., J.D.
Reformed Aerospace Engineer
Remove invalid nonsense for email.

sharpthoughts wrote:

What's RTG stand for?

Radioisotope Thermoelectric Generator- it uses a radioactive isotope to
generate heat, which in turn heats the "hot side" of a series
thermocouples (the "cold side" is attached to radiator fins) and these
produce electricity- RTGs are simple and reliable, and have been used to
provide electrical power for many space probes:
http://www.seds.org/spaceviews/cassini/rtg.html
two of them also powered each of the twin Viking Mars landers back in 1976.

Pat

"sharpthoughts" wrote:
Why must JIMO be nuclear? What's wrong with hydrogen fuel cells?

Capacity. Although you could probably deal with that by an EOR
strategy.

Alternatively, why not strap together 10 deep space ones and use the same
light collectors?

10x the light collectors might work, but would probably also require
EOR or heavylift. Light collectors (photovoltaics) are just okay for
MER, since Mars orbit still has enough light flux for reasonable size
collectors to work. Google on RTG in the sci.space.* groups for more
detailed comments on this.

/dps

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.

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.)

They could use the new Quantum Nucleonic Reactor which uses halfnium 174.
They use xrays to cause a burst of gamma ray plasma to spin a turbine.
That's the engine designed for the Global Explorer. A great way to genereate
power for probes. It could produce thrust in other ways

"sharpthoughts" 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?
"Tony Sivori" wrote in message
news
And are you ready for this - it would be called the JIMO! :-)

The craft would be a radical departure in that it will be equipped with
a
nuclear reactor, instead of nuclear batteries. Power output would be
about
1000 times higher than the nuclear battery method.

This opens exciting new possibilities for both power hungry sensors like
ground penetrating radar, and the unprecedented possibility of orbiting
one moon and then moving to another of Jupiter's moons at will (orbital
mechanics permitting, of course). The reactor will power an ion drive
that
would be about 10 times more powerful than Deep Space One's drive.

Full article at NY Times:
http://www.nytimes.com/2003/12/16/sc...UPI.html?8hpib

--
Tony Sivori




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I thought the Voyager missions had Plutonium batteries. They just keep going
and going and going.............

"sharpthoughts" 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?
"Tony Sivori" wrote in message
news
And are you ready for this - it would be called the JIMO! :-)

The craft would be a radical departure in that it will be equipped with
a
nuclear reactor, instead of nuclear batteries. Power output would be
about
1000 times higher than the nuclear battery method.

This opens exciting new possibilities for both power hungry sensors like
ground penetrating radar, and the unprecedented possibility of orbiting
one moon and then moving to another of Jupiter's moons at will (orbital
mechanics permitting, of course). The reactor will power an ion drive
that
would be about 10 times more powerful than Deep Space One's drive.

Full article at NY Times:
http://www.nytimes.com/2003/12/16/sc...UPI.html?8hpib

--
Tony Sivori




---
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