The Small Radioisotope Power System (SRPS) utilizes a single Advanced Stirling Convertor (ASC) with passive balancer as shown in Figure 1. A single ASC produces approximately 80 We making this system advantageous for small distributed lunar science stations. The SRPS consists of an integrated product team of Sunpower, Inc., to provide the single ASC with a passive balancer, The Johns Hopkins University Applied Physics Laboratory (JHU/APL) to design an engineering model Single Convertor Controller (SCC) for an ASC with a passive balancer, and NASA GRC to provide technical support to these tasks and to develop a simulated lunar lander test stand. A balancer is necessary for single ASC operation to balance the dynamic forces produced by the ASC. The SCC, as shown in Figure 2, maintains stable operation of the ASC. It regulates the alternating current produced by the linear alternator of the convertor, provides a specified output voltage, and maintains operation at a steady piston amplitude and hot-end temperature.
The lunar lander test stand, as shown in Figure 3, was designed to characterize the effect of ASC vibration on a lunar lander and planetary surface. The single ASC with a passive balancer, simulated lunar lander test stand, and SCC were delivered to GRC and were tested as a system. The testing sequence at GRC includes SCC fault tolerance, integration, electromagnetic interference (EMI), vibration, and extended operation testing. The SCC fault tolerance test characterized the SCC’s ability to handle various fault conditions, including high or low bus power consumption, total open load or short circuit, and replacing a failed SCC card while the backup maintains control of the ASC.
The integrated test will characterize the behavior of the system across a range of operating conditions, including variations in cold-end temperature and piston amplitude, including the emitted vibration to both the sensors on the lunar lander and the lunar surface. The EMI test will characterize the AC and DC magnetic and electric fields emitted by the SCC and single ASC. The vibration test will confirm the SCC’s ability to control the single ASC during launch. The extended operation test allows data to be collected over a period of thousands of hours to obtain long term performance data of the ASC with a passive balancer and the SCC.