The Evolution of the FUSE Mission Planning System and Operations

Abstract

The Far Ultraviolet Spectroscopic Explorer ( FUSE ) is a low-Earth orbit NASA astrophysics satellite requiring 3-axis stabilized pointing control to perform high resolution spectroscopy in the far ultraviolet regime (905-1187 A). FUSE was launched in 1999 and designed for a three year prime mission with the goal of operating for five years. During its eight years of operations (1999-2007), the FUSE mission encountered numerous unforeseen operational challenges; in particular, the successive failures of the four reaction wheels and four of the six gyroscopes required multiple innovative solutions to restore spacecraft control and meet mission requirements. As each new operations constraint was encountered, the FUSE Project successfully adapted to the new operations environment after modifying the ground system planning models and software, and the spacecraft on-board attitude control system software, albeit in some cases with changes in sky coverage, pointing performance and science scheduling efficiency. In this paper, we describe the evolution of the FUSE Mission Planning system and operations scheme, given the pre-launch mission assumptions, on-orbit realities, and the operational challenges due to attitude control system problems. We discuss the workarounds adopted in order to satisfy the unexpected operational constraints and share the lessons-learned from the FUSE experience, drawing conclusions pertinent to future missions in the areas of mission planning and operations design.