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Re: Longevity-sat proposal



The way they built satelites back in the 70's has a lot to recommend it in 
terms of survivability, the batteries as you say were always the weak link.

Another important factor to consider is height of the orbit. Very low orbits 
such as the 800km one most sats go into these days would decay too quickly. 
For longevity an orbit around 1450 km (Oscar 6/7 type) would be required. 
This would have also have the advantage of longer access times and greater 
DX potential.

As to were to put long lifetime satellites? Well we still seem to have 
plenty of empty satellite bandwidth, 29.3-29.5 is empty as is most of  the 3 
MHz at 435. Only the 145.8-146 segment has a high level of use.

Trevor M5AKA
Chelmsford Amateur Radio Society
http://www.g0mwt.org.uk/

At 02:08 PM 10/28/2003 -0800, Cathryn Mataga wrote:
    The no-battery thing is just part of the concept.  And that
means when it's dark, it just goes off.


Does the satellite come up out of eclipse in the "transponder on" condition? 
  If so what happens if you have to command it off (like for a national 
security situation,)  You would have to have some persistent states.  If it 
comes out of eclipse in the off state, how does it get turned on?  PL Tone?

    As far as 'critical
systems' just don't have any.  And with a little planning,
it'd be possible to make it go down a little more gracefully
than AO7 does that starts to wig out.  As far as how the system
behaves with high power signals, seems to me easiest just to make
an AGC that can handle it.  I don't see why this requires a battery.


Possibly but you would still need a regulator of some sort to prevent over 
voltage and under voltage.

    Those are interesting numbers.  Both the battery and computer are the 
cause
of quite a few failures, looks like.


My guess is that the numbers would be consistent with military and 
commercial satellites as well.



            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.


Though my thought was that with the bigger gates, transistor or otherwise,
it'd be trickier to build and use more power, so to compensate for that
just limit control to the ultra-bare minimum.  Only a single on/off
switch and make that extra redundant.


I still think telemetry would be a good thing to add if only to collect data 
to prove your concept.

    Do you get spin for free as part of the launch?


No - but maybe you can use a passive system.  OSCAR 5 and others had 
permanent magnet attitude stabilization.

    I'm just thinking long
term here.  And if the goal is a satellite design life of 30 years,
[...]


AO-7 is one of the very few to last that long.  So while it's possible it's 
a long shot.  I didn't take numbers (probably should have) but very few last 
10 years without a failure of one subsystem or another.  FO-20 was one that 
seems to have made that without failure.  So perhaps a less lofty goal of 15 
years would be a quantum leap.  UO-14 also did, and I think it had a very 
good lesson - build a satellite in such a way that it can be reconfigured 
and repurposed.  I would propose a better way would be to start with a 
satellite that had batteries, was smart, and did many things, but the 
eventual failure mode is to whittle down failed subsystems to eventually run 
off panels with your one switch.

But I think a satellites will get more reliable and here are some reasons 
why I think this will be the case:

Radiation - We learn more about it all the time, and know now to combat it 
better and better.
Batteries - The quality and lifespan improves all the time.  They get 
smaller, cooler, can be recharged deeper and last longer.
CPUs - They get smaller, require less power, run cooler and can be 
self-healing.
Memory - Cheaper, faster, bigger and less power hungry
Solar Cells - Cheaper, more efficient, lighter.


    Simply, can we make a satellite that our grandchildren could use?


Depends on how old you are ;-)

    It seems
to me, if we planned for a super-mega-long lifetime of these things.
And, say we launched 1 every 3 years or so, then in 21 years, there'd be 
like
7 of them up there.   AO7 has proven the concept, by accident.  There'd
be some huge compromises, I guess I'm trying to figure out if there's
an intersection between the compromises and something actually useful.
and fun.


I'm not sure that would be a good idea unless you are proposing using 
frequencies we currently don't have. I don't know exactly how much bandwidth 
we have remaining, but I believe we will have to be careful about how we 
conserve it, especially in the lower frequency bands.

73.
Emily

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