From: henry@spsystems.net   
      
   In article <1108334314.696467.114070@z14g2000cwz.googlegroups.com>,   
   Allen Thomson  wrote:   
   >It would be interesting to know if there is currently   
   >any propulsion approach available that would allow   
   >significantly faster than Hohmann trips for humans   
   >to other planets/moons/major asteroids... "Currently available"   
   >can be interpreted to mean "available by 2025 at a development   
   >+ procurement cost of no more than $10G in 2004 dollars   
   >per year between now and then."   
      
   Yes:  orbital assembly/fueling will let you do faster-than-Hohmann trips   
   for small expeditions with chemical propulsion.  You need an orbital fuel   
   depot, and lots of fuel launches, but the former is fairly straightforward   
   if you don't insist on using LH2, and the latter provides high flight   
   rates for RLVs and a large competitive market for launchers of all sorts.   
      
   Double yes:  if you're willing to spend a bunch on R&D to reduce launch   
   rates -- which is probably a bad deal, but is undeniably attractive to   
   organizations that specialize in R&D -- solid-core nuclear rockets can   
   considerably improve the picture, speeding things up further or permitting   
   larger expeditions or both.  Rover/NERVA solved most of the major   
   technical problems of a first-cut version in the 60s, and demonstrated   
   that a fast-paced program could improve the state of the art remarkably   
   quickly in this area.  You can start with NERVA derivatives, and pursue   
   more ambitious designs in parallel with the first expeditions.  The one   
   big hassle is low-emissions test facilities, and it's one that should   
   yield quickly to substantial amounts of money -- no breakthroughs are   
   required.   
      
   Liquid-core or nuclear-lightbulb is substantially better, and gas-core   
   is much better, although they are longer-term options with significant   
   development issues.   
      
   >Equally intresting would be to know about the technology   
   >for life support systems that would reasonably reliably   
   >sustain a half-dozen people for two or more years in   
   >space without help from Earth.   
      
   Adequate water recycling -- the big issue -- has been demonstrated, on   
   a modest scale.  (Air is a minor side issue by comparison.)  The simplest   
   way to address the food loop is not to try, given that freeze-dried food   
   weighs less than half a ton per man-year.  Generally, much the simplest   
   and most reliable way to tackle a lot of the smaller recycling/repair   
   issues is brute force:  more mass, and more fuel to push it, is cheaper   
   than major engineering R&D.   
      
   Of course, trying to sell that approach to R&D-oriented organizations is a   
   bit of a challenge.  "Anything which they do not wish to do is always   
   lacking in technology.  Whether single stage to orbit or Mars missions,   
   the technology is never quite ready..." (Jim French)   
      
   --   
   "Think outside the box -- the box isn't our friend."    |   Henry Spencer   
                                   -- George Herbert       | henry@spsystems.net   
      
   --- SoupGate-Win32 v1.05   
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