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Old February 4th 05, 06:37 AM
John Schilling
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"Allen Thomson" writes:

Probably such things have been hashed out before, but allow me to
solicit the opinion of the readership on this question that has
come up in some off-line discussions:


Supposing you wanted a reactive propulsion system -- say a
nuclear rocket, electrical thruster, mass driver or other
throw-mass-out-the-back widget that had continuous thrust =
1 kN, ISP = 10,000 sec (= 100 km/sec Ve) and a total run
time = 1 megasecond or greater, preferably getting toward
10 Ms.


If it needs a reactor or other power supply, plumbing,
radiators to get rid of excess heat, etc., ignore that and
concentrate on the thrust-producing part.



Oh, in that case, no problem. Ion thrusters can do that quite
easily, just a matter of scaling. Possibly some sorts of plasma
thrusters as well, but if you talk to whomever winds up owning
Boeing's ion thruster shop after the current round of mergers
and selloffs, convince them you are serious, they can make you
up a cluster of high-power ion thrusters that deliver the sort
of performance you are looking for, without even stretching the
state of the art.

The hundred or so megawatts of electric power it will take to
run the thing, most of us would consider a showstopper, but you've
told us to ignore that part of the problem. And yes, the ion
thruster array will be heavy (kiloton) and expensive (gigabuck),
but unless you're invoking magic the power supply will be heavier
and more expensive, so no worries there. If it really matters,
I suspect the second gigabuck could shrink the mass down to a
hundred tons, but anything beyond that is going to be *really*
expensive.


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