Chandra Aspect Operations

FSS Performance Trending (LEGACY - frozen April 26, 2023)

Summary

The 2012:150 entry to Safe Mode was caused by the FSS persistently reporting an incorrect value (~32 degrees vs. expected value of 0 degrees) for the Alpha angle (AOALPANG) while also reporting the Sun Presence flags (AOALPSUN and AOBETSUN) as SUN (indicating sun is present and data values are valid). This occurred in NPM while the Sun Position Monitor (SPM) was active at a sun pitch slightly above 139 degrees. The incorrect Alpha sun angle values caused two checks in the SPM to fail.

Swap from FSS-A to FSS-B on 2013:130

Pitch Angles for Bad Data (Primary updated 04/25/23, Secondary updated 08/27/13)

(For the last year)

The plots below show the sun pitch angle for data points where the FSS alpha angle (corresponding roughly to off-nominal roll) is different from the true off-nominal roll by more than 8.0 degrees. In other words, points when the FSS is reporting erroneous values. This is an expected situation outside of the nominal FSS FOV and when the FSS Sun Presence flag is False, but is anomalous for times when FSS Sun Presence is True (which means the OBC is allowed to use the data in active safing monitors).

In the first row of plots the red dots correspond to anomalous points where the alpha value is bad and Sun Presence is True.

The second row of plots shows that nearly all of the cases with bad alpha and Sun Presence True occur while maneuvering (big blue dots). The first red X corresponds to the 2012:150 Safe Mode. The second red X could have caused another Safe Mode if the FSS FOV extent had not been reduced.

FSS-Primary (1 year)	FSS-Primary (90 days)

FSS FOV (Primary updated 04/25/23, Secondary updated 08/27/13)

(For the last year)

The plots below show the sun pitch angle for data points when the FSS reports no sun presence in Alpha (AOAPLSUN = "NSUN") or Beta (AOBETSUN = "NSUN"). This illustrates the effective FSS field of view outside of which the data are marked invalid. The red points correspond to Kalman mode (AOACASEQ = "KALM" and AOPCADMD = "NPNT"). The cyan points are those when NOT in Kalman (corresponding mostly to maneuvers).

FSS-Primary	FSS-Secondary

FSS-Primary Historical Data (Updated 08/27/13)

(Since 2010:001 to illustrate long term trend circa Aug-2013)

The plots below are identical to the four plots above for FSS-Primary but with a different timescale in order to illustrate the current trend in FSS-Primary.

Analysis data

Last modified:04/26/23

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