SPACE	INSTRUMENT SCIENCE REPORT
	TELLESCOPE	CAL/FOS-017
	SCIENGE
LNSflTUTE
TrrLE:	IMPROVEMENTS IN FILTER/GRATING WHEEL REPEATABILITY
	AUIHOR:	Georye Hartig	DATE:  22 April 1985
	ABS11~AC~







The filter grating wheel repeatability can be sigriificantly irnproved
by applying an additional motor step after the initial, standard
positioning of the wheel. Because of uncertainties in the deqree to
which this remedy will operate in actual fliqht conditionS, especially
for the camera inirror, and the expected thermal drifts of the
entrance aperture irnaqes, previously sugqested ~odifications to the
FOS to permit direct location of the iinaqes remain hiqhly desireable.