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Re: A Question About InstantTrack and AO-40



At 10:37 PM 5/6/2002 -0500, Joel Black wrote:
>    "...Note that this type of attitude calculation will only work as long
>as AO-40 is in spin mode. After the orbital maneuvers are completed, AO-
>40 is supposed to go into a 3-axis stabilized mode. InstantTrack 1.50 can't
>handle that type of attitude mode. Perhaps there will be a
>new version that can, someday."
>
>My question is in regards to the next to last statement.  Is this still a
>problem with InstantTrack?

Yes it is, and as far as I know this is also a limitation of EVERY other 
satellite tracking program in the world. The problem is that nobody knows 
how the command team will manage AO-40's attitude.

One possibility (at certain times of year) is that they will keep the 
antennas exactly nadir-pointing at all times. InstantTrack can handle that, 
since it is the same attitude as a gravity-gradient stabilized spacecraft 
(ideally). For this case, enter "L" for "Local Vertical" in InstantTrack's 
attitude coordinates field.

However, they won't be able to keep it that way all the time. Other times, 
perhaps they will have it fixed nadir-pointing during certain MA periods 
near apogee and pointing somewhere else at other times. A practically 
infinite number of other combinations are possible. Until the whole range 
of possibilities is known, software authors will be at a loss to implement 
a suitable attitude prediction mechanism for AO-40.

I imagine that even the command team doesn't know yet. They probably have 
an idea of what they would like to do, but until they have characterized 
the capabilities of the 3-axis stabilization system and gained some 
experience operating it, they won't be able to predict with any certainty 
what the attitude management scheme will look like.

I hope the command team will let us know what they're planning to try, 
somewhat in advance. If they announce the scheme they are writing up for 
the IHU, then software authors have a chance of getting the corresponding 
scheme into tracking programs. I hope and believe that I'll be able to 
update InstantTrack in a timely way to keep up with AO-40.

73  -Paul
kb5mu@amsat.org

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