QUESTION:
Is there enough water and solar energy in the Jovian system of moons to
eventually serve as a refueling stop for a future craft? By this I mean could
electrolysis be used to create hydrogen/oxygen for fuel by using solar energy
and Jovian system water? Is this likely to ever be feasible?

ANSWER from Todd Barber on March 5, 1997:
Thanks for the very intriguing question!  You bring up a very 
"forward-thinking" concept!  You asked about the availability of water 
and solar energy.  Water availibility is actually not the problem.  
Europa, one of Jupiter's interesting moons currently being explored in 
great detail by Galileo, is covered GLOBALLY by water ice (it may even 
have a liquid water ocean underneath!).  Therefore, finding enough 
water to perform electrolysis would not be a problem at all.
     
Solar power is tougher question.  Jupiter is five times further from 
the sun than the Earth is.  This actually means that Jupiter only gets 
1/25th of the amount of sunlight the Earth does (this is called the 
"inverse square" law).  So solar energy is rather feeble at Jupiter.  
This is precisely why Galileo has nuclear power sources on board to 
provide spacecraft power.
     
However, with big enough solar panels on Europa (or perhaps better, 
nuclear power plants), you could generate enough electricity to 
electrolyze water into hydrogen and oxygen.  Then you would have a 
great refueling station on Europa!
     
I think this is feasible, but not for some years.  Perhaps when you as 
6th graders one day graduate from college, you could be the first ones 
to design such a system!  Thanks for the great question....