Spacecraft offpointing for VIRGO and MDI

MEMO Concerning De-Pointing Tests for VIRGO and MDI

A de-pointing exercice will be performed for testing the off- pointing sensitivity of the VIRGO-SPM, and for getting information about flat-fielding and stray of the VIRG)-LOI and SOI/MDI. As MDI needs high telemetry rate this test can only be performed during a long contact period.

The MATRA procedure for off-pointing has the following capabilities: step-up n steps, stay there for thold (i1 steps), step back n steps, stay at zero for tzero (i2 steps), step down n steps, stay there for thold (i1 steps), step back to zero, stay there for tzero (i2 steps). The step length has to be >400 sec and the angular step <30 arcsec. Preliminiary information from MATRA indicates that about 300 sec are needed until the pointing is settled. As VIRGO needs 3 minutes of integration at each step the step length is 480 sec for the de-pointing test.

The parameters for the de-pointing tests are as follows:

This should run once for the N/S and once for E/W direction; for each direction it will take 10h40. Before and after the test VIRGO and MDI needs 5 minutes each for TSTOL procedure and NRCs respectively. Moreover, one should make sure that the guiding star is close to the center of the field of view (that the +/- 10 arcmin does not drive it out of its range). A contact time of at least 12h is required; during the test its self no commanding is needed from the FOT as the procedure runs automatically. The time of the execution should be after the commissioning of VIRGO has been completed (2 days after MCC2). MDI needs some time to set up the system and they propose to do the first test at the 5th day after completion of MCC2. With the present planning this means that the tests could be performed on 11 and 12 January 1996. They may be postponed if sheduling necessitates it, but not more than about 5 days. The preference is to run the test durig two consequtive days, but this is not mandatory.

Claus Fröhlich, December 14, 1995