1. Gamma Ray Observatory
Potential attitude control problems may force NASA to deorbit one of its largest orbiting observatories as early as March.
Launched in 1991 into 450 km orbit, which decayed to 340 km by 1993 and was reboosted to 450 km. In 1997 it was reboosted to 515 km.
9  21 m, 15.3 metric tons
1 of 3 gyros failed 12/9/99
Second gyro failure would lead to an eventual uncontrolled reentry
Sun sensors and magnetometers might be able to provide adequate info
C. Hall, Randolph 228