XPost: sci.space.science   
   From: henry@spsystems.net   
      
   In article ,   
   th   wrote:   
   >> LEO satellites don't really need anything beyond error-correcting memory...   
   >> and in an equatorial orbit, probably not even that.  (Almost all of the   
   >> bit-flips in memory occur during passage through either the South Atlantic   
   >> Anomaly or one of the auroral ovals, and an equatorial orbit encounters   
   >> neither.)   
   >   
   >This is a very optimistic statement! Bit flips may occur in memories   
   >already when you are flying in a passenger aircraft across the poles.   
   >IIRC the shuttle computers get a couple of hundred bit flips per mission   
   >at 28 degrees inclination, even more at ISS orbit inclination.   
      
   Please read what I wrote:  the auroral ovals (around the magnetic poles)   
   and the South Atlantic Anomaly (which both a 28deg orbit and the ISS orbit   
   pass through) are the big hot spots for radiation effects.  If you plot   
   memory errors vs. location on a map, they're very obvious.  An equatorial   
   orbit *doesn't pass through those hot spots*.   
      
   Now, if I were building a satellite for an equatorial LEO, I probably   
   *would* put error-correcting memory in it, just on general principles.   
   But one might well be able to get away without it.   
      
   The severity of the radiation problem in space is much exaggerated.  The   
   MOST astronomy satellite, in about the worst possible LEO -- relatively   
   high and polar -- has error-correcting memory, and some care was taken in   
   the design of its electronics, but it has no rad-hard parts.  (The project   
   couldn't afford them.)  It's coming up on two years in orbit, and the only   
   radiation effect yet visible is some drift in the calibration of some   
   sensors.   
   --   
   "Think outside the box -- the box isn't our friend."    |   Henry Spencer   
                                   -- George Herbert       | henry@spsystems.net   
      
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