XPost: sci.astro, sci.astro.amateur   
   From: volker.hetzer@gmx.de   
      
   hankman wrote:   
   > I still do not have a clear picture of exactly what was lost due to the   
   > glitches with the data channel on Huygens. Most reports just barely mention   
   > the glitch and most do not even mention it and none are clear on just what   
   > data was lost and what was recovered, and how it was recovered.   
   >   
   > Some seem to indicate that nearly nothing was lost due to the fact that the   
   > channels were redundant and the data was duplicated over both channels.   
   > Others seem to indicate that the "recovered" data was due to the   
   > "eavesdropping" of the earth-based radio telescopes. Yet other reports seem   
   > to indicate that half (some 350 of 700) the images were completely lost (and   
   > not recovered by some other means such as redundancy of channels or   
   > eavesdropping from earth).   
   >   
   > Can anyone shed some light on these issues and why the media seem shy to   
   > dwell more on these matters as well on the notable successes of the mission.   
      
   The data transmisssion of the huygens probe was to go over two channels   
   of the cassini probe. Accidentally, only one of these channels was   
   actually switched on, so all taba going over the dead channel was lost.   
   OTOH, every group with an experiment on huygens could choose how they   
   utilized those channels for their data. Many groups chose to send   
   essentially the same data (or enough redundancy) over both channels,   
   sacrifying data amount for safety. They were ok.   
      
   The images experiment didn't and instead chose to send half of the   
   images over each channel, so half the images are lost. IMHO they   
   couldn't have done any better since any redundancy would have cost them   
   images anyway.   
      
   The doppler wind experiment chose to use one channel only, unfortunately   
   the dead one. So all of that data is lost too. Incidentally, a lot of   
   radio telescopes were able to track the probes descent with a precision   
   of 1km and from that trajectory much information about the winds could   
   still be gained so that the guy wanting to know about winds on titan   
   has some data nevertheless by analyzing how the probe got bounced around   
   during descend.   
      
   Hope this helps.   
   Volker   
      
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