Thermal Model Performance for the James Webb Space Telescope OTIS Cryo-Vacuum Test



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48th International Conference on Environmental Systems


The James Webb Space Telescope (JWST), set to launch in early 2019, is currently undergoing a series of system-level environmental tests to verify its workmanship and end-to-end functionality. As part of this series, the Optical Telescope Element and Integrated Science Instrument Module (OTIS) Cryo-Vacuum (CV) test, the most complex cryogenic test executed to date by NASA, has recently been completed at the Johnson Space Center’s Chamber A facility. The OTIS CV test was intended as a comprehensive test of the integrated instrument and telescope systems to fully understand its optical, structural, and thermal performance within its intended flight environment. Due to its complexity, extensive pre-test planning was required to ensure payload safety and compliance with all limits and constraints. A system-level pre-test thermal model was constructed which fully captured the behavior of the payload, ground support equipment, and surrounding test chamber. This thermal model simulated both the transient cooldown to and warmup from a 20K flight-like environment, as well as predicted the payload performance at cryo-stable conditions. The current work is a preliminary assessment of thermal model performance against actual payload response during the OTIS CV test. Overall, the thermal model performed exceedingly well at predicting schedule and payload response. Looking in depth, this work examines both the benefits and shortcomings of assumptions made pre-test to simplify model execution when compared against test data. It explores in detail the role of temperature-dependent emissivities during transition to cryogenic temperatures, as well as the impact that model geometry simplifications have on tracking of critical hardware limits and constraints. This work concludes with a list of recommendations to improve the accuracy of thermal modeling for future large cryogenic tests. It is hoped that the insight gained from the OTIS CV test thermal modeling will benefit planning and execution for upcoming cryogenic missions.


Kan Yang, NASA
Stuart Glazer, NASA
Shaun Thomson, NASA
Lee Feinberg, NASA
William Burt, Genesis Engineering Solutions Inc.
Brian Comber, Genesis Engineering Solutions Inc.
Wes Ousley, Genesis Engineering Solutions Inc.
Randy Franck, Ball Aerospace
ICES108: Thermal Control of Cryogenic Instruments and Optical Systems
The 48th International Conference on Environmental Systems was held in Albuquerque, New Mexico, USA on 08 July 2018 through 12 July 2018.


James Webb, Space Telescope, JWST, OTIS, Optical Telescope Element, OTE, ISIM, Integrated Science Instrument Module, Cryogenic, Vacuum, Testing, Thermal