Summary
This document describes the process for generating a comprehensive set of attitudes which are suitable for ACA dark current calibration. A link is provided to the actual list of attitudes.This document also describes the format of the dark_attitudes.dat file and provides information on how this file (and/or its accompanying rdb file) might be used.
Creation Details
The analysis files to determine the set of acceptable attitudes are located in the directory /proj/sot/ska/analysis/dark_attitudes. The file NOTES describes the actual steps.The basic concept to determine dark current attitudes is to search for areas on the sky with relatively few stars. This is done as follows:
- The IDL code find_attitudes.pro performs a raster scan of the entire sky in 0.5 degree increments and outputs the number of stars brighter than 8, 8.5, 9, 10.3, and 11.5 mags in a 2x2 degree box. (In practice only the latter three values were used.)
- All fields with fewer than 10 stars brighter than 10.3 mags are removed in order to assure reasonable guide stars.
- All fields with any stars brighter than 8.5 mag were removed.
- The remaining fields are sorted first by the number stars brighter than 9th mag (to prefer those fields without any very bright stars) and then by the number of stars brighter than 11.5 mag (to prefer fields with fewer stars likely to affect the dark calibration)
- Finally the code find_unique.pl goes through the list and removes any attitudes within 5 degrees of a "better" attitude. A better attitude is simply one that has a higher priority based on the above sorting rules.
File Description
The files created by the above process, dark_attitudes.dat and dark_attitudes.rdb,contain a sorted list of attitudes with the most preferred or "darkest" at the beginning of the file. The coordinates of each of the attitudes are presented in equatorial, galactic, and ecliptic.
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Last modified:12/27/13