A report describes a model that estimates the orientation of the backup reaction wheel using the reaction wheel spin rates telemetry from a spacecraft. Attitude control via the reaction wheel assembly (RWA) onboard a spacecraft uses three reaction wheels (one wheel per axis) and a backup to accommodate any wheel degradation throughout the course of the mission. The spacecraft dynamics prediction depends upon the correct knowledge of the reaction wheel orientations. Thus, it is vital to determine the actual orientation of the reaction wheels such that the correct spacecraft dynamics can be predicted.
The conservation of angular momentum is used to estimate the orientation of the backup reaction wheel from the prime and backup reaction wheel spin rates data. The method is applied in estimating the orientation of the backup wheel onboard the Cassini spacecraft. The flight telemetry from the March 2011 prime and backup RWA swap activity on Cassini is used to obtain the best estimate for the backup reaction wheel orientation.
This work was done by Farheen Rizvi of Caltech for NASA’s Jet Propulsion Laboratory. NPO-48350
This Brief includes a Technical Support Package (TSP).
Estimating the Backup Reaction Wheel Orientation Using Reaction Wheel Spin Rates Flight Telemetry from a Spacecraft
(reference NPO-48350) is currently available for download from the TSP library.
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Overview
The document titled "Estimating the Backup Reaction Wheel Orientation Using Reaction Wheel Spin Rates Flight Telemetry from a Spacecraft" is a technical support package developed by NASA's Jet Propulsion Laboratory (JPL). It focuses on the methodology for estimating the orientation of backup reaction wheels (RWAs) on spacecraft, specifically using telemetry data from the Cassini spacecraft.
Reaction wheels are critical components in spacecraft attitude control, allowing for precise adjustments in orientation without the need for thrusters. The document outlines the angular momentum conservation principles that govern the behavior of the entire system, including the spacecraft and its reaction wheels. It emphasizes that during operations, particularly during wheel swaps, the total angular momentum of the system should remain constant, assuming no external torques are applied.
The document presents equations that describe the angular momentum contributions from each of the four reaction wheels, detailing how these contributions can be calculated and analyzed. It highlights the importance of telemetry data, which includes spin rates and corresponding spacecraft event times, to derive the orientation of the backup reaction wheel (RWA 4) in relation to the other wheels.
A significant part of the analysis involves calculating the orientation of RWA 4 in the B-frame (a specific frame of reference) and determining the angular difference between RWA 3 and RWA 4. The results indicate that the orientation of RWA 4 is primarily aligned with RWA 3 but also has components along the RWA 1 and RWA 2 axes. The document provides specific numerical results for the orientation and the angular difference, including mean values and standard deviations derived from telemetry data collected before and after a wheel swap.
Overall, the document serves as a comprehensive guide for understanding the dynamics of reaction wheel systems in spacecraft, particularly in the context of estimating backup wheel orientations. It underscores the significance of accurate telemetry data and mathematical modeling in ensuring the effective operation of spacecraft attitude control systems. The research was conducted under NASA's sponsorship, and the findings are intended to have broader applications in aerospace technology and engineering. For further inquiries, the document provides contact information for JPL's Innovative Technology Assets Management.
