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On Fri, Jun 01, 2001 at 07:32:16PM -0000, Frederick M. Spinner wrote:
> LEILA seems to be a success as well.  RUDAK is well on its way to being a 
> success.  The power budgets seem very good on the bird. The propulsion was a 
> bust.  Stuff happens.  We do not have enough $$ to be fully risk adverse as 
> amateur satellite enthusiasts. Failures happen on commercial sats.  They 
> just usually have the $$ to send up replacements!  AO-40 wasn't a total 
> success, but its redundant systems mean that its a >50% success.  And it 
> was/is so diverse that half of all that went up there is still tremendous!

Liquid propulsion systems are inherently risky and complex. Solid rocket
motors are much more common within the industry I work in since failures are
unacceptable. Redundancy is key on any spacecraft. There have been a lot of
complete failures of micro/pico satellites over the past few years due to 
the lack of redundant systems. Even with redundant systems, it is important
that they not all be the same as witnessed be the failure of 3 identical 
computers on ISS a month or so ago.

> The only three things I'm a bit sad about is that the intended orbit would 
> have meant that to work apogee, two sets of small antennas and no rotors 
> would have been necessary.  But the sat moves so slowly at apogee anyway, 
> that manual pointing from the ground is feasible!
> A 45K apogee would have shown what a simple Mode-S station could do better-- 
> and thats why small dishes are now required instead of tiny helixes (at 
> 60K).  The thing I'm most sad about though is the decision to not three-axis 
> stabilize future sats.  I do, however, understand the extra complexity here 
> as well.  Maybe electronically steerable pattern antenna could be developed 
> as an alternate solution?!?

Steerable satellites/antennas are probably a necessity for the microwave
bands, but in the Ka band and up, an antenna on a gimbal behind a radome
might be good enough. Location of the antennas has seemed to become a 
valid concern on AO-40 where all the omnidirectional antennas *were* on 
one side. I certainly hope the momentum wheels still work...
one thought that came to mind though was if they would be tested in
some small way before the solar panels were released (irreversible).

> Actually to a techie like myself this makes the satellite more appealing to 
> me.  If it were really simple, it'd be boring.


Mike N4CNW

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