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Re: Longevity-sat proposal



At 03:54 AM 10/28/2003 -0800, Cathryn Mataga wrote:
>I had a thought, and that is what about a satellite with the
>following properties.
>
>1.  No batteries.  Design from the start to live off of power
>from the solar cells.  This means the satellite could live beyond the
>life of existing batteries

You really would need batteries if you want the satellite to work during 
eclipses.  You could run the transponder off the panels only but you should 
have minimal battery power to keep alive some critical systems.  Also, you 
may need some battery power to cushion the blow of high powered signals 
coming into the transponder.  If you listen to AO-7 you can tell when the 
solar panels are not providing adequate power because it will FM.  But 
certainly higher efficiency solar cells and un/under-stressed batteries 
would contribute to longevity.

>2.  No microprocessor.  Do all the logic with chips with great big
>fat gates that can survive a long time.  Or maybe use transistors.

Discrete transistors alone would not guarantee immunity to radiation damage 
and would probably cause the weight and power budget to balloon.  For that 
matter eliminating the microprocessor doesn't really improve survivability 
though having a backup would.  However it's true that the more simple the 
design the more survivable it will be.  By eliminating complexity you 
improve your chances of survivability.

 From what I can gather out of AMSAT records, the reasons satellites go SK 
are varied but batteries lead the way.
  8 De-Orbits
14 Battery failures
  7 Computer failures
  5 Transponder or receiver failure
  1 Temperature failure
  1 Radiation related failure
  8 For unknown reasons
  3 Other reasons

>3.  Only provide the simplest control.  Transponder On and OFF. That's it.

That's pretty simple.  However once you provide controls for one action, 
adding additional controls is relatively easy.

>4.  Linear transponder with analog receiver and transmitter.
>Would need to be carefully designed so that the frequency was stable as
>the voltage went up and down.

See my comments in #1

>5.  Omni antennas.  Assume tumbling and prepare for that in
>advance.  Design it so if it tumbles it's still okay.

Good idea but this would mean more tx power.  If the satellite is tumbling 
it might run into a situation where the antenna gets partially or 
completely shadowed by the satellite body.  Spin stabilization would be 
much better.

>6.  Elliptical orbit.  The idea being without the CPU maybe it
>could take a decent amount of radiation without melting down.
>Simple stations could work it while low, and the big guns could
>work it while high.

Probably depends on how high you are talking about.  With low gain omni 
antennas it probably can't get very high.  What kind of inclination would 
you propose?

>7.  Solar panels on all the sides.  So, that there's power to the
>satellite most of the time.

I think all LEOs have panels on all sides (and I think presently so does 
AO-40).

>I was just thinking of AO7 and how it works with no cpu
>and no batteries, and well, why not make something that's
>designed to work like this from the start?  The idea being that
>if we accept limitations, maybe it could last a really long time.
>
>Has this ever been considered?  I'm not a satellite guru at all --
>so maybe I'm not aware of the 'horrible flaw' with this idea.

No flaws, just challenges :-)

- Emily

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