ion engine was RE: [extropy-chat] Saving the Hubble

[Robert J. Bradbury]

On Tue, 20 Jan 2004, Jeff Davis wrote:

> That new SMART-1 ion engine seems to be working well.
> How much does one of them cost.  The first was pricey
> naturally, but now the price should go down, right?

The mission cost was $110m Euros ($126M).  But the launch
costs were defrayed due to it piggy backing on an
Ariane 5 with 2 large communications satellites.

The U.S. also had a ion engine in Deep Space 1 and I
believe has 1-2 teams at NASA Glenn and the JPL working
on versions with increased thrust.

I could see 3 problems with an ion engine rescue --
a) Possibly surrounding the Hubble in a cloud of ions
   (though one presumably has a problem with the exhaust
    of chemical trusters as well);
b) the low thrust disrupting telescope operations for a
   longer period (remember the Hubble is *heavy*);
c) the need for the ion engine to take up its own solar
   panels for power (I doubt the designers thought far
   enough ahead to include a power outlet on the outside
   of the Hubble itself...).

> And by the way, this business of using xenon as the
> reaction mass, can't we go with something a mite less
> exotic, like, say, iron?  (I'm looking ahead to those
> asteroids...)  What's the story?

Spike may correct me but I believe its because Xenon provides
the greatest thrust for the amount of electric power you
put into the engine.  It may also include the fact that
ionizing a gas, particularly a heavy element, is easier
(requires less power invested).  I'm sure ionizing solids
is a bit trickier because you have to probably have to
vaporize them (perhaps with something like a high power
electric are or high power lasers???).  That would make
the engine more complex and probably shorten its lifetime.
The choice for asteroids might be oxygen and for comets
might be neon as both would be fairly abundant.

Robert