From: niklas.holsti@tidorum.invalid   
      
   On 2022-01-10 9:09, JF Mezei wrote:   
      
      
   > Wikipedia says it has 159 litres of hydrazine and 79.5l of oxydizer.   
   > That may make it the world's most fuel efficient vehicle if it can climb   
   > a hill 1.5m killometres long with only 159 litres of gasoline :-)  (and   
   > that includes fiueld for station keeping for roughly 10 years, so that   
   > is pretty amazing).   
      
      
   At the post-deployment press conference, it was reported that thanks to   
   the accurate performance of the Ariane 5, the JWST now has propellant   
   for about 20 years of operation. The "about" was emphasized, presumably   
   because it is hard to predict the actual rate of propellant expenditure   
   for station-keeping.   
      
   It seems to me that one issue in that prediction may be the solar-sail   
   effect of the sunshield. To observe a desired point on the sky, the   
   whole craft is tilted -- the telescope cannot be pointed separately from   
   the shield. When the sunshield tilts, the photon pressure force tilts   
   too, because the sail is reflective. Possibly the sequence of   
   observations, and thus the sequence of tilts, could be designed to   
   provide part of the station-keeping forces, saving propellant.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)