From: kozelsm@comcast.net   
      
   "Glenn Mulno"  wrote:   
   >   
   > "richard schumacher"  wrote:   
   > >   
   > > > I am a bit puzzled why they only made the probe last the few short   
   > > > hours after it detached from cassini. They could of built a better   
   > > > battery when Voyager I is like 28 year and still going. I know it is   
   > > > like -300F and mechanical things won't operate long in that harsh   
   > > > environment. Assuming the probe could survive the environment it would   
   > > > of been nice to be able to tap it for everything possible.   
   > >   
   > > The issue is how long the orbiter is in range to relay data from Huygens   
   > > to Earth.  It's only a few hours, so a longer-life battery for Huygens   
   > > would have been pointless.   
   >   
   > If that were the "only" reason then I would disagree.  Cassini will be   
   > passing by Titan again in a few weeks.  I would think they could have held   
   > data and then blasted it at the satellite each time it passed.   
   >   
   > However, as I understand it that is not really why they kept the life to   
   > only a few hours.  I think it had more to do with just getting it down   
   > safely, the weight of the probe on Cassini, cost, and probably just the   
   > general expectation that  conditions were not favorable to the life of the   
   > unit being long.   
      
   The Voyagers and Cassini itself receive electrical power from a   
   Radioisotope Thermoelectric Generator (RTG).  An RTG can provide   
   electrical power to a robust suite of spacecraft systems for 20 years or   
   more, but an RTG would have been way too heavy to install on the Huygens   
   spacecraft.   
      
   The Mars lander spacecrafts utilize solar cell panels to create   
   electrical power which is stored in rechargable batteries, and Mars has   
   very little cloud cover that would interfere with that system, and Mars'   
   night is similar in length to Earth's; so that system is workable on   
   Mars.   
      
   Titan has a dense, hazy atmosphere, and even in the clear, the Saturn   
   system is way too far from the Sun, making a solar power system to be   
   infeasible (the solar panel system would have to be gargantuan).   
      
   The Huygens spacecraft could not utilize an RTG or solar power, so it   
   was limited to un-rechargable batteries, and given the number of   
   instruments on board, battery capacity was limited to a matter of hours.   
      
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