AAS 207th Meeting, 8-12 January 2006
Session 175 Recent Discoveries in the Far UV
Poster, Thursday, 9:20am-4:00pm, January 12, 2006, Exhibit Hall

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[175.16] FUSE Science Planning Under One-Wheel Attitude Control

H. M. Calvani (The Johns Hopkins University), M. Kochte (The Johns Hopkins University/Computer Sciences Corporation), A. F. Berman (The Johns Hopkins University), J. R. Caplinger (The Johns Hopkins University/Computer Sciences Corporation), T. Civeit (The Johns Hopkins University/CNES), M. N. England (The Johns Hopkins University/Computer Sciences Corporation)

The Far Ultraviolet Spectroscopic Explorer (FUSE) is a low-Earth orbit NASA astronomy satellite requiring 3-axis stabilized pointing control to perform high resolution spectroscopy in the far ultraviolet regime. In December 2004, one of two remaining reaction wheels failed, temporarily suspending science operations.

An intensive research and development effort in 2005 has allowed us to successfully revise the flight software to control the satellite in all three axes using a hybrid control system consisting of the remaining reaction wheel and the on-board magnetic torquer bars. Operations with this new control system is more restricted than was the case with two reaction wheels, significantly complicating the task of generating science observing timelines. The primary constraint is the difficulty in simultaneously achieving pointing control and managing momentum on the remaining wheel when observing a target. Since secular momentum build up is a function of target direction with respect to gravity gradient disturbance, we have found that proper target sequencing can perform most of the momentum unloading for the satellite, allowing better pointing control when scheduling an observation.

We discuss modifications made to the science planning tools and procedures to accommodate the revised operations constraints on the satellite.

This work is supported by NASA Contract NAS5-32985 to The Johns Hopkins University.

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