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Re: Who or what controls AO-16's RC PSK TX Out?



At 02:15 AM 8/26/99 -0400, Dquagliana@aol.com wrote:
>    In looking through some of the recent telemetry 
>from AO-16 I've noticed that the raised cosine PSK 
>transmitter output seems to vary between about 
>0.2 watts and about 0.6 watts.
>
>    Is the power output managed by ground control or
>is it under software control based on spacecraft
>health? (or both)?  How exactly does this work?

The spacecraft regulates its own transmit power as part of the
realtime battery management algorithm, using several tuning
parameters that have been set by the command stations.
AO-16 uses a load-based battery management strategy.
That is to say, the primary way it controls battery charging
is by varying the transmitter output power. If the batteries are
getting low, it reduces output power. If the batteries are getting
full, it increases output power to prevent overcharging. It's
actually more complex than that, of course, and there are
also some source-based components to the algorithm.

If you look in the telemetry (for instance the sample telemetry
published in the weekly satellite report in the ANS bulletin,
http://www.amsat.org/amsat/news/ans.html#ao-16), you'll see
a line like this:
TX:010B BCR:88 PWRC:59E BT: A WC:25 EDAC:4E
The three-character field tagged "PWRC" are the main tuning
parameters for power output. Each character is a hex digit
representing a power level. Roughly, they represent the
absolute minimum power, the bottom end of the normal range,
and the top end of the normal range, and power is expected to
settle near the middle of the normal range.

Command stations may change the PWRC values seasonally,
as the average sun angles on the solar panels vary. One of
AO-16's faces is only partially covered with solar panels, so
its power generation does vary with attitude. Solar panel
efficiency varies with temperature, so power generation is
also sensitive to the duration of eclipses (which occur on
every orbit). When these effects add up to a significant
change in average power generation, it's sometimes necessary
to adjust the power ranges used.

The power ranges would also be changed if the S-Band
transmitter were turned on, since it uses up a lot of battery
power. It hasn't been on lately, because it doesn't leave much
power for the 70cm downlink.

Other than those seasonal changes, AO-16 is on its own.
It requires very little help from command stations on the
ground.

73  -Paul
kb5mu@amsat.org


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