Building Sequence Database Files for the Hopkins Ultraviolet Telescope

To acquire a star, the HUT DEP searches a 1\(fm region centered at the expected guide star position. This yields an effective field of 8\(fm 20" by 11\(fm 40" centered on the object position. Two circles representing these extremes are produced on the field plots mentioned above.

Hint: Choosing guide stars inside the smaller circle means that they will be available at any roll angle, while guide stars in the annulus between the two circles may or may not be available, depending on the IPS roll angle (and hence, the orientation of the TV on the sky). When the final roll angle is selected by MSFC, a value will be entered in the SDF entry called "PI_roll_angle." This angle is the astronomical position angle (degrees eastward from north=0 &de; ) of the long axis of the HUT TV field. (This is also the long dimension of the rectangular HUT apertures. For choosing guide stars, it is not necessary to break the 180 $/degree$; ambiguity. However, for completeness, the PA refers to the "-Y" end of the HUT slit.) Hence, once the PI_roll_angle is known, one can make a final guide star selection.