Qualification of motors for deep space under extreme thermal environments to be encountered during the Mars Science Laboratory (MSL) mission is required to verify the reliability and validate mission assurance requirements. The motor assembly must survive all ground operations, plus the nominal 670 Martian-day (or sol) mission that includes summer and winter seasons of the Mars environment. The motor assembly was tested and characterized under extreme temperature conditions with reference to hardware requirements. The motor assembly has been proved to be remarkably robust and displayed no sign of degradation due to the 3× (three times per JPL design principles) thermal environmental exposure to the punishing Mars surface operations cycles. The motor characteristics obtained before, during, and post-test comparisons for the surface operations cycles are within measurement error of one another.
The motors withstood/survived 2,010 extreme temperature cycles with a ΔT of 190 °C deep temperature cycles, representing three times the expected thermal cycling exposure during the MSL surface operations. The qualification test hardware elements (A200 motor assembly, encoders, and resolver) have not shown any signs of degradation due to the PQV (Package Qualification and Verification) testing. The test hardware has demonstrated sufficient life to survive the deep thermal cycles associated with MSL mission surface operations for three lives.
This work was done by Rajeshuni Ramesham, Michael R. Johnson, Darren T. Cooper, Warren S. Lau, Kobie T. Boykins, Jonathan D. Perret, and Richard A. Rainen of Caltech; and Andrea Greb of Orbital for NASA’s Jet Propulsion Laboratory. NPO-48760
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Motor Qualification for Long-Duration Mars Missions
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Overview
The document titled "Motor Qualification for Long-Duration Mars Missions" outlines the rigorous testing and validation processes undertaken by NASA's Jet Propulsion Laboratory (JPL) to ensure the reliability of motor assemblies used in the Mars Science Laboratory (MSL) mission. The primary objective is to confirm that these motors can endure the extreme thermal environments encountered on Mars, particularly during the mission's nominal 670 Martian days, which include both summer and winter seasons.
To achieve this, a qualification test was developed for the A200 motor assembly, which includes an integrated encoder assembly and four standalone cold encoders, as well as a representative resolver stator. The testing involved subjecting these components to a total of 2010 thermal cycles, significantly exceeding the expected in-flight exposure. This included 600 cycles from -130°C to +60°C to simulate winter conditions and 1470 cycles from -105°C to +85°C for summer conditions, thereby ensuring a 3x design margin.
Throughout the testing process, intermittent functional tests and continuous monitoring of the hardware were conducted. The results demonstrated that the motor assembly exhibited remarkable robustness, showing no signs of degradation after exposure to the extreme thermal cycles. Pre-test and post-test comparisons of motor characteristics indicated that the health of the motors remained unchanged, confirming their capability to perform reliably during the MSL mission.
The document also details the configuration of the test setup, which included health monitoring systems for the motor and encoder assemblies. While the standalone encoders were not actively monitored during the thermal cycling, health checks were performed using a POGO-pin test fixture during periodic breaks in the testing. Visual inspections and functional tests were conducted to establish baseline performance prior to the thermal cycling.
Overall, the findings validate the survivability of the motor assemblies, brakes, resolvers, and encoders in the harsh Martian environment. The successful qualification of these components supports the JPL design principles and MSL requirements, ensuring that the flight motors will function without incident during the mission. This comprehensive testing approach underscores the commitment to developing reliable technologies for future space exploration.
