XPost: rec.radio.shortwave   
   From: detritus@ix.netcom.com   
      
   John Smith wrote:   
      
   > On 11/13/2011 10:25 AM, Lord Valve wrote:   
   > > Don Pearce wrote:   
   > >   
   > >> On Sun, 13 Nov 2011 08:38:28 -0700, Lord Valve   
   > >>   wrote:   
   > >>   
   > >>> dave wrote:   
   > >>>   
   > >>>> On Sun, 13 Nov 2011 11:39:03 +0000, Geoffrey S. Mendelson wrote:   
   > >>>>   
   > >>>>>> It is much more important to know exactly how long and how well your   
   > >>>>>> satellite is going to work than to hope to get longer by using a   
   > >>>>>> technology that might last longer, but will more probably die   
   > >>>>>> unexpectedly when struck by a cosmic ray burst.   
   > >>>>>   
   > >>>>> Sometimes you can not predict how long a satellite will be used. A   
   > >>>>> friend of mine worked on a civilian satellite for a defense contractor   
   > >>>>> and just before the division was sold off, cleaned out any old   
   documents   
   > >>>>> and files they had on it.   
   > >>>>>   
   > >>>>> Since the satellite he had worked on was way past its expected life   
   (but   
   > >>>>> still in use), the contracts had long expired, the work was not   
   > >>>>> classified and a new improved one was due to be launched in a few days,   
   > >>>>> he was told to dump it all.   
   > >>>>>   
   > >>>>> A few days later, the booster exploded on the pad, and the replacement   
   > >>>>> was destroyed.   
   > >>>>>   
   > >>>>> The sattelite was kept running for many years, although there were no   
   > >>>>> documents on what to do or how it was built.   
   > >>>>>   
   > >>>>> Geoff.   
   > >>>>   
   > >>>> What good is a diagram if the unit is 24,000 miles in the air?   
   > >>>   
   > >>> It had better *not* be in the air...  ;-)   
   > >>>   
   > >>> Besides - I saw mention upthread of using the ambient   
   > >>> vacuum with just the tube elements, rather than a typical   
   > >>> evacuated glass (or other material) enclosure...is the   
   > >>> vacuum in geosynchronous orbit really hard enough?   
   > >>> It would seem to me that there are probably plenty of   
   > >>> gas molecules floating around at that height, even if   
   > >>> it would still qualify as a "soft" vacuum.  Anybody?   
   > >>>   
   > >>> Lord Valve   
   > >>>   
   > >>>   
   > >>   
   > >> For all sorts of other reasons, standard enclosed tubes are used. Main   
   > >> reasons are first to contain the electrons so other metalwork doesn't   
   > >> get involved, and second to maintain the correct physical positioning.   
   > >> The helix is of very fine tolerance in both pitch and positioning.   
   > >> Space is certainly hard enough, but the environment around a satellite   
   > >> is frequently not space, but a diffuse cloud of exhaust gas which   
   > >> would extinguish a TWT immediately.   
   > >>   
   > >> d   
   > >   
   > > Ah. Good point!   
   > >   
   > > Satellites do indeed need to use propellant of some sort   
   > > to keep in position; I didn't think of that at all.  And it   
   > > would seem that even if the ambient vacuum were   
   > > hard enough, conventional construction of the TWT   
   > > would be needed to keep contaminants out of it during   
   > > the satellite assembly process down on Terra firma.   
   > > But I must admit, the idea of using ambient vacuum   
   > > tickles my fancy a bit.  ;-)   
   > >   
   > > Lord Valve   
   > >   
   > >   
   > >   
   >   
   > I don't recall anyone ever claiming there was no enclose on the devices   
   > ... just the reasons for enclosing them the way we do on earth is now   
   > gone ...   
   >   
   > Regards,   
   > JS   
      
   Do you actually read this shit, or have you been into the medicine cabinet?   
      
      
   Lord Valve   
      
      
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