Chandra Aspect Operations

Guide Star Tracking Statistics

We have compiled statistics on guide star tracking success covering the period Jan-2001 through Dec-2005. This is an update to the 2003 report. In this study we quickly look at the tracking success as a function of magnitude and mission elapsed time (years).

The scatter plots below show the fraction of observation time during which each guide star was not tracking. Each point represents a unique star, where a random offset of +/- 1e-4 has been added for visual clarity in the low end. The upper panel for each year shows the raw fraction of time during an observation for which the camera reports not tracking (Image function != 1). The lower panel shows the fraction of time when the camera reports not tracking or when any of the image status bits are set, indicating a condition such as ionizing radiation or defective pixel. The lower panel corresponds to what the OBC uses on-board to accept a star for Kalman processing.

2001 2002

2003 2004

2005

Table of tracking results

The table below lists the fraction of stars (in percent) which were not tracking (or having bad status) at least 5 percent of the time. This is the treshold in the ground aspect pipeline above which a star is declared bad.

2001 2002 2003 2004 2005
Tracking 1.48 1.20 0.66 0.52 0.77
Tracking or Status 6.76 11.19 9.77 6.78 9.34

Interestingly, this indicator of tracking success improved between 2001 to 2003 and has been stable since then. This may be a consequence of improved star selection via the SAUSAGE tool.

Magnitude dependence

The plot below shows the magnitude dependence of tracking success.

Analysis

The analysis scripts and data are in /proj/sot/ska/analysis/guide_success


Last modified:02/03/06



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