Fiducial light drift

This page shows the drift of fiducial light positions over the course of the mission. This apparent drift in position can be due to a combination of any of the following factors:

Shifting ACA alignment
Physical shift of the SIM relative to the OBA
Bending of the OBA
Alignment drift in the FTS

The first three factors are nearly degenerate. Only the last factor (FTS alignment drift) produces a change in the boresight calibration (i.e. celestial location offset).

Fid light drifts (Updated 04/22/25)

The data for these plots were generated by extracting Aspect L1 centroid data and fid properties data for all archived observations. The last 4 ksec of data are used, to minimize scatter due to thermal transients. Then a median centroid position is calculated for each fid light. Finally, for each science instrument and fid light, the "drift" is calculated by removing both the median centroid offset for that fid light (over observations from 2010 to 2020) and the SIM-Z offset (for that observation). In the plots below, different colors and symbols represent the different fid lights for each SI.

Fid light commanded search position versus telemetry (Updated 04/22/25)

The data for this plot represents the difference in Y and Z between the commanded search position for fids and the actual observed location at the beginning of each observation. The red dashed line represents the fid light search box half-width, at which point the likelihood of a failed fid acquisition is high. Within the green dashed region (35 arcsec half-width) the likelihood of failure is low.

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Last modified:04/22/25