The Cassini Reaction Wheels: Drag and Spin-Rate Trends from an Aging Interplanetary Spacecraft at Saturn

Abstract

The purpose of this paper is to provide a summary of the long-term trends of the estimated drag torque and spin-rates of the Cassini reaction wheel assemblies during 11 years of intensive science operations at Saturn. Reaction wheel failure is a common fault for long-lived spacecraft, and in some cases can result in the loss of a mission. For this reason, it is important for spacecraft operators to closely monitor the health and behavior of operational reaction wheels to potentially identify trends or signatures in the reaction wheel telemetry that could portend forthcoming issues. This paper will present the historical trends in the estimated reaction wheel drag torque at various spin-rates over the course of the mission. The objective of this paper is to provide the aerospace community with examples of the types of aging trends that have been observed on Cassini’s reaction wheels as an in-flight example of real-world hardware performance. The Cassini reaction wheels usage and drag torque trends are of interest to the larger aerospace community because Cassini’s wheels have been operated continuously for over 11 years of science operations, and the Cassini RWA’s are frequently run through their full range of possible spin-rates, which gives the Cassini operations team a rich data set to use for health monitoring and trending of real-world reaction wheels.