Investigation and Mitigation of Hydraulic Noise in the Orion Service Module ATCS Fluid Control Assembly

The Orion Multi-Purpose Crew Vehicle (MPCV) Active Thermal Control System (ATCS) acquires, transports, and rejects waste heat generated in the crew cabin, batteries, and vehicle electronics. Heat is acquired and transported by a pair of redundant “internal” coolant loops, transferred through an Interface Heat Exchanger (IFHX) to a pair of “external” coolant loops, then transported by the external loops to thermal radiators and rejected to space. The Fluid Control Assemblies (FCAs), located in the European Service Module (ESM), are responsible for controlling the flow rate through the external loops and for controlling the temperature of the HFE7200 coolant that is delivered to the IFHX. When the FCA operates in mass flow rate control mode, its electronic control unit measures the fluid temperature and pressure drop across a venturi nozzle, calculates the coolant mass flow rate, and adjusts the pump speed accordingly to maintain the flow set point. During Acceptance Testing of the first shipset of FCAs, the signal from the venturi ∆P sensors was extremely noisy, which precluded the FCA from operating in mass flow rate control mode. The subsequent investigation determined that the venturi ∆P sensor was sensitive enough to detect the hydraulic pressure ripple emanating from the fluid pumps directly upstream, resulting in a noisy signal. When the same unit was subjected to a random vibration test, a similar instability occurred.
This paper describes the development test campaign that was conducted to characterize the noise and the subsequent design changes that were implemented to mitigate the pump and vibration induced hydraulic noise.