From: schillin@spock.usc.edu   
      
   "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.   
      
      
   --   
   *John Schilling                    * "Anything worth doing,         *   
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