From: someguy@somewhere.se.retro.com   
      
   Henry Spencer wrote:   
   > In article <1104968476.664619.36540@c13g2000cwb.googlegroups.com>,   
   > thomsona@flash.net  wrote:   
   >   
   >>>Civilian receivers have limits on speed and altitude to prevent   
   >>>people from using them to make ICBM guidance systems, for example.   
   >>   
   >>True, but even in the mid-1990s, when a red team looked at this, it   
   >>turned out that many GPS vendors implemented the limits in ways that   
   >>were readily circumventable.  At least one, in Canada IIRC, just put   
   >>the limitation in the display driver.   
   >   
   >   
   > Unfortunately, there is more to building a satellite GPS receiver than   
   > just taking the limits off.  Consumer receivers are unlikely to be able to   
   > cope with the high Doppler shifts, rapid motion, and fast changes of   
   > satellite visibility.   
   >   
   > (And there are known problems with consumer receivers in high-vibration   
   > environments, which don't matter to a satellite but are significant for   
   > rocketry.  Things like crystal oscillators and SAW filters can malfunction   
   > when vibration gets excessive.)   
      
   Well, it partly matters also to a satellite since the receiver has to   
   survive the vibrations during launch. Vibration can induce permanent   
   mechanical damages to solderings and component pins. Such errors might   
   be recovered from when the environment becomes more stable but they can   
   also come back when the device experiences thermal cycling in orbit.   
      
   --   
   th   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)