The spacecraft attitude control system contains attitude error sensors such as gyroscopes and actuators such as momentum wheels and reaction wheels. The control moment gyros (CMG), in which the momentum wheels are mounted in gimbals, are also used in attitude control of spacecrafts. All these systems are designed to operate continuously till the end of the mission at varying speeds of several thousand rpm. The on-orbit performance of spacecrafts depends largely on the performance of the momentum/reaction wheels which in turn depends on the bearings used and its lubrication, since the only component which undergoes wear in these systems are the ball bearings. Currently, the life cycle of spacecrafts are aimed to be around 20–30 years. However, the increases in size, complexity and life expectancy of spacecrafts demand advanced technologies especially in tribology and in turn the development of more innovative lubrication systems for long-term operation. Space tribology is a subset of the lubrication field dealing with the reliable performance of satellites and spacecraft including the space station. Lubrication of space system is still a challenging task confronting the tribologists due to the unique factors encountered in space such as near zero gravity, hard vacuum, weight restriction and unattended operation. Since the beginning of space exploration, a number of mission failures have been reported due to bearing system malfunction (Robertson & Stoneking 2003; Kingsbury, et.al., 1999; Bedingfield, et. al., 1996) and the most recent is the bearing failure in the control moment gyro (CMG) of the international space station on July 2002 (Burt and Loffi, 2003).