Adrien GUIGNABERT, Comat
TBD TBD, Qualification challenges of an SADM using the slipring technology, Comat
The qualification sequence went through the typical path of mechanical and thermal vacuum environments followed by a lifetime operational test under high vacuum and thermal conditions. Functional tests were regularly performed in order to monitor the good health and the evolution of the main performances of the SADM throughout the qualification campaign. Other important tests like magnetic moment measurement and EMC verifications were also performed.
A previous magnetic moment measurement performed on the EM1 revealed a value exceeding the 20mAmĀ² target, caused by the use of slightly ferromagnetic 15-5PH steel. The design was updated for the final configuration mounted on the QM. The new measurement revealed a significant decrease in the magnetic moment value, from 60mA.mĀ² on the EM1 to less than 10mA.mĀ² on the QM, confirming the positive effect of the 15-5PH replacement .
The baseline mechanism does not include a position sensor for compactness reason, hence two reed switches top-turns are positioned 180Ā° apart in order to regularly be able to adjust the software position indication. The reed switches are magnetically activated, normally open devices. They close when the magnet mounted on the rotor passes nearby. Due to the compact size of the mechanism the reed switches are positioned close to the stepper motor, causing a series of abnormal reed triggers when the magnet is closing in. This issue was solved by implementing a dedicated software filter.
For the lifetime test, 100 000 full rotations were performed under vacuum, distributed at 3 thermal operational plateau of +50Ā°C, -20Ā°C and +20Ā°C. The QM performed well throughout the entire lifetime, but some issues were detected regarding the top-turns, with a noticeable number of false ānegativeā (reed bouncing near the end of the activation range, inducing an incorrect front edge). In order to avoid this kind of phenomenon and solve this issue, the software reed filter was reinforced with the addition of a falling edge filter and a stricter variation criteria .
The SADM was submitted to vibration tests, with 2 accelerometers monitoring stator and rotor (on solar array interface plane) accelerations. The SADM is mounted on its stator interface (link to satellite wall) and free on the rotor interface (no mass, no link to stator). The measured modal landscape revealed that the first structural mode (rotor swinging mode) is lower than expected from the design analysis. The investigation allowed to identify the deviation sources : added mass on the rotor, lower bearing stiffness and additional stiffness not taken into account in the model. The FEM was adjusted and refined accordingly to better fit the actual mechanism behavior.
The mechanical environment also revealed some frequency shifts above the ECSS limits, detected from the low level frequency search performed before and after each random vibration. This kind of modal evolution has already been detected and accepted in other mechanisms with flexible bearing preload (reaction wheels). No impact on performances were detected and the QM went through the qualification campaign without issues.
The paper will detail all these challenges and issues faced, along with some potential new findings once the qualification will be fully completed in early 2025 (EMC measurements and QM disassembly and final inspection).