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Drift of the Actual Pointing from Commanded Values

Image name: att_cmd_pointing_drift.png (click image to enlarge)
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Date submitted: 05-May-1995

These plots show the variation in actual pointing versus commanded
pointing over the duration of the mission.  There is a seasonal
component which causes both an E/W and N/S offset and a long term
pointing drift in the N/S direction.  The pointing discrepancy is
seen in the SXT data and in the HXT/HXA data (they both agree with
some other smaller correction).  This may imply that the flexure is
on the front panel of the spacecraft.

"Actual pointing" is from the ATT database which is derived from the
HXA and IRU with some seasonal correction applied to match the data
seen in SXT images.  The "Commanded Pointing" is the pointing from
a given command (translated into SXT pixels using a single "tie point").

The routine SXT_CMD_PNT takes applies this correction to the commanded
value whenever the /CMD option is used (in routines like GT_CENTER, ...)

The plots can be made using the routine PLOT_ATT_CMD and either use
a saved file, or to regenerate the data (bring it up to date) which
takes about 45 minutes.  The routine has found a single image per day
to create the plot.

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