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AO-27 schedule logic (Was Re: Chit-chat on AO-27 [Was: FN45 on AO-27] -Resposta)

On 2 Sep 1998, John Mock wrote:

> This is just speculation, but it may be that software limitations also
> preclude non-operation on the basis of longitude.  But that's probably
> just as well, for it doesn't discriminate other than on North vs. South.

The following are my personal recollections from when Eyesat-1/AO-27 was
launched and first operating.  They may not reflect current procedures or
guidelines.  Hopefully, this will clear up some of the questions about how
AO-27's operating schedule works.

The original need was for a simple way to control the satellite's
transmitters to stay within the available power budget while minimizing
the need to manually control the transmitters via ground command or
frequently update control data.

The software controlling AO-27's schedule uses eclipse entry and exit as
triggering events.  So adjusting for seasonal variations, the schedule is
based on latitude.  Maintaining a relatively correct schedule over the
course of a year requires infrequent adjustments to the on/off times
relative to eclipse exit. 

To control operation based on longitude, the satellite would have to know
where it is in its orbit AND where the orbit is relative to specific
meridians.  Offhand, I can think of a few ways to do this - ranging from
uploading reference data (the sub satellite point at eclipse exit at this
approximate time is on this meridian) to running tracking software on the
satellite and updating the keplerian elements as necessary.  These methods
are more complicated and require more care and feeding than a schedule
based solely on latitude. 

The latitude based system was probbaly "good enough" for what was needed

Current AO-27 status is provided by the AO-27 control station, N4USI, and
appears in each week's ANS Bulletins.

73, Steve KA1LM@amsat.org

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