Completion of the JWST Spacecraft/Sunshield and Telescope/Instrument Elements Randy A. Kimble1, Charles W. Bowers1, Michael W. McElwain1, Malcolm B. Niedner1, Erin C. Smith1, and the JWST Project Team 1NASA Goddard Space Flight Center

The other deployable features of the Spacecraft The final environmental test for the Spacecraft Introduction OTIS Activities Element were also tested thoroughly in Element was a ~40-day thermal-vacuum test. In appropriate configurations. this test, the sunshield was in its stowed (launch) Several years ago, the integration of the James at Northrop Grumman configuration, but the Spacecraft Bus (with all of its Webb Space Telescope converged to two major Solar Array Release avionics) was exposed to the relevant temperature components: 1) the combination of the telescope The OTIS was delivered to Northrop Grumman’s Redondo Beach facility in early 2018. Key (tested on the ranges expected in flight operations, plus margin. and instruments (with their support structure and Spacecraft Bus) activities since then have included cleaning the electronics), known as the OTIS (a name derived Thermal Vacuum from the OTE = Optical Telescope Element plus ISIM primary mirror and completing the final OTIS- element post-environmental deployment tests. Spacecraft Bus Test Chamber = Integrated Science Instrument Module), and 2) the (bottom-loading) Spacecraft Element, which is the combination of the Five-panel Solar Array warm spacecraft bus (with all of the usual systems (Bottom) End Cap for power, attitude control, communications, of Chamber propulsion, command & data handling, etc) and (to which payload JWST’s critical, deployable, five-layer sunshield. mounts) In 2019, the integration and test programs for Configuring the both of these elements were completed. We payload for testing, in present here some of the highlights along the way the pit by the chamber toward those milestones. The two components have since joined to form the full-up JWST Spacecraft/Sunshield Observatory, whose integration and test program is OTIS Simulator Brush cleaning of the JWST primary mirror described in the companion poster (372.09) by Solar Array Deployment Testing – Panel Unfolding McElwain et al. In April 2019, the primary mirror segments were Thermal Control Panels (test equipment) carefully cleaned with a light-contact brush technique. The solar array, for example, was tested for release This cleaning was very effective and essentially reset of the launch restraint devices while mounted to the OTIS Cryo-Vacuum Testing spacecraft; however, for proper unfolding of the five the clock with respect to particulate accumulation. Maneuvering the The secondary mirror, which remains accessible late panels, a specialized gantry system was used to payload beneath the provide gravitational offloading. chamber in preparation in the flow, will be cleaned shortly before shipment to for loading the launch site. Current projections indicate that the payload will comfortably meet its contamination requirements at the time of shipping. Thermal Control Panels

Sunshield Pallets (stowed)

Mounted to the chamber end cap, about OTIS Simulator to be raised for final Secondary Mirror Stowed electrical and thermal hookups for thermal- Deployed vacuum testing Spacecraft Bus Deployment testing of the Secondary Mirror Support JWST OTIS, configured for cryo-vacuum testing Structure During the Spacecraft Element thermal-vacuum test, The culmination of the environmental test The final post-environmental deployment test for the the Spacecraft Bus was taken through four thermal program for the OTIS was a remarkable hundred- OTIS was the gravity-offloaded deployment of the After complete deployment and functional testing cycles between hot and cold proto-flight temperatures day cryo-vacuum test of the payload conducted at Secondary Mirror Support Structure. This tripod of the Spacecraft Element, it was configured for (flight expectations plus margin), while the Sunshield the Johnson Space Center in July-October 2017. features two rigid struts and one hinged strut with the environmental testing: acoustics, vibration, and was taken through two cycles. Comprehensive The test functionally exercised the telescope plus drive and latching mechanisms. Final deployment thermal-vacuum. For that test program, the functional tests (for primary and redundant systems) instrument suite at their cryogenic operating testing of the Aft Deployable ISIM Radiator was also Spacecraft was configured with an OTIS simulator, were executed at both the hot and cold temperature temperatures, with interferometric testing of the full accomplished after delivery to Northrop Grumman. which emulated the mass, center-of-gravity, and plateaus. In addition, there were soaks at cold primary mirror, end-to-end sub-aperture optical stiffness of the real OTIS. survival temperatures and cold turn-ons. Primary and testing to the instrument focal planes, thermal While waiting for the Spacecraft Element to redundant heaters were tested. Thermal balance balance measurements for model validation, along complete its integration and test program, the Spacecraft Element measurements were taken at hot and cold for thermal with numerous operational tests and demonstrations. OTIS team also accomplished significant risk- model correlation. Finally, 23 of the Sunshield’s An overview of this highly-successful campaign is reduction testing, validating software updates on the Environmental Testing Membrane Release Devices were released at given by Kimble et al. Proc. SPIE 10698 (2018). flight hardware, and previewing electrical test temperature; the rest were released later at ambient. activities that will be carried out with the Spacecraft. Thermal blankets in regions that interface with the Spacecraft were installed. The Two Final Pieces of JWST Came Together in August 2019 Spacecraft-Level Deployments

Frill

Closeouts

In the Acoustic Test Chamber On the Vibration Table Frill/closeout repair at Northrop Grumman After careful transporting of the payload to the environmental test facilities on Northrop One of the few technical issues identified in the OTIS Deployed, tensioned sunshield Grumman’s campus, the Spacecraft Element cryo-vacuum test was that the frill/closeout assembly underwent successful acoustic and vibration surrounding the primary mirror (pictured above) had Prior to the Spacecraft Element environmental testing (sine sweep, in all three axes). Testing was insufficient slack and exerted unwanted forces on the test program, deployment testing of the five-layer at so-called “Proto-flight Levels”, meaning that the After the successful completion of the Spacecraft mirror backplane at operating temperature. This sunshield was accomplished. Enhancements to goal of the tests was to expose the payload to +3dB Element functional and environmental test introduced the potential for wavefront instability with the Membrane Tensioning System to improve its above expected flight loads. program, the two final pieces of the Observatory temperature variations in flight. One of the key reliability were identified, which have since been were ready for mating, which was initiated in activities after delivery of OTIS to Northrop Grumman implemented successfully. August 2019. See poster 372.09 (McElwain et al.) was to carefully rework this assembly to restore the for a report on the Observatory-level integration intended slack, mitigating the concern for flight. and test program, which is now well underway.