Managing TVAC Vibration for Optical Testing of the Roman Space Telescope

Final optical testing of the Roman Space Telescope payload will take place at NASA Goddard Space Flight Center (GSFC), in the Space Environment Simulator (SES) Thermal Vacuum (TVAC) chamber. The SES chamber was originally designed for thermal balance and survivability testing, not optical verification. As such, the chamber is subject to significant vibration disturbances that will manifest as optical jitter. This jitter must be accurately predicted and maintained below optical test error allocations. After introducing the test configuration and general jitter analysis assumptions, this paper will highlight lessons learned from two test campaigns aimed to reduce uncertainty in TV AC jitter predictions: The first campaign presented is a series of chamber disturbance characterizations. Accelerometer data was collected at chamber interface points while chamber pumps and coolant flow were sequentially turned on. The primary objective of this testing was to derive seismic disturbance signatures for input to jitter models, however, the data also revealed disturbance load paths and structural dynamics within the chamber. Lessons learned prompted design modifications to the chamber internal structure and revision of the jitter analysis model to include this structure. The second campaign presented is the optical verification of the “Stimulus Of Ray Cones” (SORC) projector system performed inside the SES TV AC chamber. The SORC testing acted as an unofficial pathfinder, as it used a vibration isolation system similar to the systems to be used for the full-up RST telescope. Attempts to verify the SORC isolation system performance showed the test bed was highly sensitive to ambient air flow, changing expectations/plans for future isolation system functionality check-outs. Furthermore, SORC optical jitter was measured at TV AC and cross-checked against predictions. These cross-checks verified the method used to account for analysis uncertainties. This paper will conclude with discussion of ongoing efforts to reduce jitter uncertainty prior to final TV AC testing, currently scheduled for summer 2025.