Strategic Monitoring of Spacecraft Mechanical Parts Assemblies

Bearing failure in satellite applications is related to lubricant starvation rather than fatigue, and health monitoring systems for these applications must be able to observe subtle changes related to lubrication state. Phase I included an experimental study to identify candidate monitoring approaches, and the data collected confirmed that cage motion characteristics and instability are highly sensitive to lubrication state, as suggested by previous researchers. Furthermore, at least two sensors studied in Phase I produced good data on cage motion. With appropriate signal processing, both signatures were shown to change with lubrication state. Phase II will build upon this with a more extensive experimental effort, including long-term tests were the lubrication state is allowed to degrade naturally. Since cage motion is the most promising state indicator, ball-cage friction and cage lubricant absorption will also be studied in detail to gather ground truth data. This data will be used to refine a model of cage dynamics being developed at Purdue University, which will improve understanding of the relationship between lubrication and cage motion and allow the experimental results to be extrapolated to other conditions (e.g. microgravity) and other bearing designs. Based on analysis of the experimental data and model results, an operational prototype Spacecraft Bearing Health Monitoring (SBHM) system will be implemented on Sentient’s space environment test rig. The SBHM will include the sensors, signal processing algorithms, parameter fusion, and reasoning logic needed to convert raw data into actionable information that can be utilized by ground crews and/or on-board automated lubricant applicators. The SBHM system will be demonstrated at the end of Phase II by monitoring bearings operating under realistic conditions over several months. Lubricant will be administered manually when indicated by the SBHM system, and the bearings will be thoroughly inspected at the end of the test to validate the ability of the system to prevent wear.