Modeling Ice Detachment Events on Cryopumps During Space Propulsion Ground Testing

At DLR’s electric space propulsion vacuum test facility in Goettingen, spontaneous pressure rise events were observed, which led to interruptions of thruster testing. This study investigates the causes of four such events and presents a model that is able to simulate pressure rise events due to xenon ice sheet detachment from operating cryogenic pumps. The model results show good agreement with the observed pressure curves and can reproduce the pressure rise slope, event duration, down slope, and maximum pressure during these events. The masses of the detached xenon ice sheets are in the range from 2 g to 0.4 kg, which is reasonable with respect to the amount of ice on cryopump cold plates. This first modeling step is based on a phenomenological approach, but the good results show that it is worth expanding and refining the model, e.g., by introducing more ice shape options, adding ice bonding layer properties, and adding other gases and physical condensate properties.