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: http://xmm.vilspa.esa.es/sas/6.5.0/doc/newsiam/node3.html
Дата изменения: Tue Aug 16 05:51:18 2005 Дата индексирования: Sat Dec 22 08:38:57 2007 Кодировка: Поисковые слова: star formation |
The SIAM is used to point the satellite such that a nominal on-axis source position is imaged onto a specific point on the detectors. Due to the development of bad pixels in the imaging instruments, it will likely be necessary in future to slightly modify this prime pointing. The purpose of this task is to calculate new SIAM elements from existing SIAM and requested angular rotations about the space-craft axis.
New angles for the SIAM are calculated from shifts of the pointing of the instrument given in parameter Instrument relative to the pointing obtained by using the SIAM that is specified by parameter siamset.
The star-tracker attitude is calculated for a given bore-sight of the chosen instrument of Ra=0, Dec=0, APos=0 (similar to strbs/ccftools). Using this, the positions of 5 test sources in the FOV of the instrument are calculated. The test sources have celestial positions of
| Source Number | Ra (arcmin) | Dec (arcmin) |
| 1 | 0 | 0 |
| 2 | 15 | 0 |
| 3 |  |
0 |
| 4 | 0 | 15 |
| 5 | 0 | |
This establishes the position of a set of sources in the FOV of the instrument (similar to srcinfov/ccftools). The FOV angles for these test sources are shifted by the intended offsets (parameters ry and rz). These values are used as further reference.
The angles of the SIAM are iteratively modified and the calculations of strbs and srcinfov are repeated, until the spatial distances of these newly calculated FOV angles to those of the reference FOV angles is minimal.
Test sources close to the limit of the FOV are necessary to also constrain the rotation of the third angle of the SIAM (rotation around X). Obviously some redundant is included at marginal extra cost on computing time.
The output can directly pasted into the SIAM.