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Operating and Maintaining the JWST Cleanroom attached to JSC's Chamber A during preparations for the OTIS Cryogenic Thermal Vacuum Test

In order to maintain cleanliness during preparations for JWST’s OTIS (Optical Telescope Element-Integrated Science Instrument Module) Cryogenic Thermal Vacuum Test, a cleanroom was built that attached directly to the 60-year-old Chamber A. The cleanroom and chamber were outfitted with independent environmental control systems each providing ISO Class 71 air cleanliness. To maintain balanced, positive pressure in both the cleanroom and chamber volumes, a special control protocol was developed and successfully implemented. Dual back-up environmental control units (one each for the chamber and cleanroom) were installed just outside the building to provide environmental control redundancy due to a single source chilled water supply and weather threats. In addition, lack of a dedicated cleanroom airlock facilitating clean ingress and egress made it necessary to perform additional cleaning and packaging, as well as augment the uncontrolled truck lock space with small clean tents for pre-cleaning. Special procedures were developed to allow ingress of extra-large support equipment required for load testing of the cleanroom crane, installation of optical equipment in Chamber A and accommodation of the OTIS shipping container. A thorough bake-out and cleaning of Chamber A was also necessary to reduce volatiles from the shroud’s black thermal paint and to reduce particle fallout. Acrylic adhesive fracture discovered during early cryo-testing represented a significant challenge that was successfully mitigated prior to OTIS testing. A dedicated team of Contamination Control (CC) Technicians was specifically trained to clean support equipment and screen materials entering the cleanroom and chamber to ensure cleanliness and vacuum compatibility.

Optics↗

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Predicting contamination accumulation in facilities with limited data

In preparation for the James Webb Space Telescope (JWST) launch at Centre Spatial Guyanias (CSG) in French Guiana, particulate contamination accumulation predictions were necessary for each facility in which the hardware would be exposed because the Telescope would be uncovered in each of the facilities and had strict particulate requirements. These included facilities for final integration and testing, fueling, transportation and encapsulation. Minimal heritage data existed from CSG and previous launch campaigns to use as a basis for contamination predictions. Data from the Automatic Transfer Vehicle and Herschel & Planck launch campaigns were used in conjunction with facility monitoring data provided by ESA and data collected during JWST working group visits to CSG. These campaigns were conducted at varying cleanliness levels that were typically less stringent than JWST requirements. Each facility was evaluated using the data provided and likely performance improvement with the addition of High Efficiency Particulate Air filter (HEPA) banks operating when possible. Once the launch campaign was completed, the predicted fallout was compared with actual data collected throughout the campaign. Based on the actual measurements, JWST’s primary and secondary mirrors turned out to be much cleaner than what was predicted.

James Webb Space Telescope, contamination, cleanro↗