[amsat-bb] Re: Path to HEO

Burns Fisher burns at fisher.cc
Mon Apr 29 13:05:20 PDT 2013

One thing that would seem to be a concern to me is how to keep the attitude
steady while the ion engine is firing.  Yes, not much thrust, but to make
the most of it, you want it pointing in as close to the ideal direction as
possible.  I don't know how the various probes like Hayabusa and Dawn do
it..  Cold gas?  Gyro?  I would not think a bar magnet would be good enough
(certainly not for deep space probes, but even for earth orbit).  Starting
to get more complicated.

Another thought about the really cool energy analysis done by KK6MC:
 Besides the duty cycle imposed by wanting to be out of eclipse, there is
another duty cycle imposed by the starting orbit and the desired
eccentricity.  For example if you were starting from a highly elliptical
GTO and you want to get to high circular, you need to thrust mainly at the
apogee in order to raise the perigee.   If you are circular and you want to
be elliptical with perigee equal to the starting height, you thrust at what
will be the perigee to raise the apogee.  (Of course you probably want to
raise both ends some, and you may want to change the plane too but that's
the general idea.)

Thanks for bringing this up...great thought experiments, and that's how
real projects begin!

Burns, W2BFJ

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