No abstract

Bearing retainer instability is one of the major causes of failure in the ball bearings used in spacecraft systems. These bearing failures lead to mission failure or performance degradation of the spacecraft. The instability is characterized by intermittent torque fluctuations and severe audible noise in both low-and high-speed bearings. It also generates severe transient forces that result in high cage wear or fracture. A series of retainer designs was made and the possibility of instability under various operating conditions of a momentum/reaction wheel used in a spacecraft was studied. Various tests such as run-in test, temperature test, and overlubrication test were conducted to study the instability and select a design that is stable under all operating conditions. The study results showed that square pocket retainers are more stable compared to circular pocket retainers.

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The success of any satellite mission largely depends upon the performance of the attitude control systems such as gyroscopes and momentum/reaction wheels. The required life and performance quality of these rotating mechanisms are ensured by the selection of bearings and its lubrication. The design and development of lubrication system to meet the long-term uninterrupted performance is a challenging task before the tribologists. This article describes the developmental study of a lubrication system for long-term requirements of momentum/reaction wheels. The developed system is compact and can be placed inside the bearing unit assembly. It works on centrifugal force and able to supply lubricant continuously at a very low rate of few micrograms per hour for many years. Further, the system can be tuned for any flow rate depending on the requirement.