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T. B. Ake, R. M. Boyer (JHU/CSC), B-G Andersson, W. P. Blair, W. V. Dixon, M. E. Kaiser, J. W. Kruk, H. W. Moos, D. J. Sahnow (JHU)
After the failure of the roll reaction wheel on the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite in December 2004, we have developed a new control system to point the spacecraft with three magnetic torquer bars (MTBs) and the remaining skew reaction wheel. Building on earlier two-wheel operations and gyroless development, we modified the attitude control system to use the MTBs to control two of the satellite axes. In this mode, our initial jitter performance has increased from 1 to about 2 arcseconds RMS, which is well within the 30x30 arcsec LWRS aperture and still smaller than the 4x20 arcsec MDRS aperture. Pointing excursions due to gravity gradient torques on the satellite are more numerous than when using the two-wheel mode. Improvements in the CALFUSE pipeline to correct photon positions for pointing offsets work well to maintain spectral resolution for long time-tagged observations, while short histogram exposures of bright targets are mostly unaffected. Further enhancements in pointing control are expected as we continue to gain experience with the new system. We will describe the new control scheme and provide an update of its performance.
This work is supported by NASA Contract NAS5-32985 to The Johns Hopkins University.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.