Derivation of the design loads for the instrument pointing system in the Shuttle environment

The design phase for the Instrument Pointing System (IPS) used for obtaining arcsecond accuracy for stellar observations with instruments on Spacelab pallets is reviewed. The IPS consists of a three axes gimbal system on a support structure fastened to a pallet, and must support loads ranging from 200-3000 kg. Pointing is performed by three orthogonal drive units on the bases of data from sun/star sensors, gyroscopes and accelerometers. Design loads for each mission phase were projected with transient response, coupled dynamic and modal analyses. The IPS is required to last 50 missions and to accept payloads with different distances from the floor to the pointing line of sight. Sufficient levels of uncertainty were included in the design so that the IPS passed static load, modal and acoustic noise flight readiness tests.