XPost: rec.radio.shortwave   
   From: bit_bucket@gmx.com   
      
   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   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)