The James Webb Space Telescope (JWST) program was supported by a unique team of Contamination Control Technicians (CCTs) who received Webb specific training from Webb Contamination Control Engineers (CCEs) and Lead CCTs. Webb’s design featured exposed optics and thermal control surfaces. These remained susceptible to damage or degraded performance from particulate and molecular contamination if a systematic approach to controlling contamination generating processes was not strictly enforced. Cleanroom maintenance is typically performed by janitorial services throughout the industry. However, Webb’s requirements necessitated a team who safely and effectively performed various tasks including daily facility cleaning to flight hardware handling. The CCT team performed daily cleanings of the processing facilities and effortlessly switched to inspecting and cleaning flight hardware, assisting CCEs with inspections, lab work, and performing on-demand cleaning of all items entering the cleanroom facilities. The versatility of the CCT team was on display as each CCT took on additional responsibilities and maintained ownership of subtasks such as Image Analysis and Ellipsometry, transportation, Self-Contained Atmospheric Protection Ensemble (SCAPE) suit support, inventory, and cleanroom garment laundering, while supporting the demanding launch campaign. The CCTs maintained a constant presence on the integration floor, allowing for quick resolution to CC issues and elevation of more serious problems that required further guidance. These dedicated CCTs broke new ground in efficient collaborative work with the integration and testing team while cultivating positive attitudes towards contamination control.
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.
KEYWORDS: James Webb Space Telescope, Contamination, Picture Archiving and Communication System, Rockets, Mirrors, Inspection, Telescopes, Optical fibers, Observatories, Contamination control
Over the life of the James Webb Space Telescope (JWST), Integration & Test (I&T) has taken place in areas that needed considerable work to make the facility itself and/or the protocols used while working in the rooms suitable to meet JWST percent area coverage (PAC) and molecular accumulation requirements. In addition to normal particulate matter, JWST had a uniquely significant challenge: fibers! Fibers not only cause much higher PAC levels, but they also risk damaging the angstrom sized Near Infrared Spectrometer (NIRSpec) microshutter array (MSA), which is critical to NIRSpec instrument performance. The primary emphasis of this paper is to address particulate and fiber contamination. The success of the JWST mission required effective cleanrooms, protocols, and mitigations in non-cleanroom areas that were pressed into service to house contamination-sensitive optics and scientific instruments. Some presented profound challenges. These included: NASA’s 60-year-old Johnson Space Center (JSC) Chamber A, which had never been used for anything contamination-sensitive, and the European tropical launch facilities, which were designed to meet International Standard Organization (ISO) Class 8 processing for communication satellites. The final challenge for JWST, as if to stare us in the face and say, “I dare you to try and make me clean enough,” was preparing the 4 areas in the Centre Spatial Guyanais (CSG) Final Assembly Building (BAF) located in French Guiana, a building in which one entire side opens for Ariane 5 rocket ingress and egress. This paper will describe our initial evaluation processes and the actual work undertaken to transform even the most challenging areas into first class cleanrooms that met JWST particulate and fiber requirements.
Maintaining molecular cleanliness during the JWST’s Optical Telescope/Instrument Module (OTIS) Cryogenic Thermal Vacuum (TV) test campaign was critical to the success of its optical mission on orbit. In the thermal vacuum tests leading up to the final cryogenic test to validate the OTIS flight hardware, NASA Johnson Space Center’s (JSC’s) TV Chamber A was fully characterized for molecular contamination. It was found to contain common volatile condensable materials (VCM), including hydrocarbons, plasticizers, and silicones, all of which absorb in JWST’s infrared wavelength region. Due to the risks involved, cleaning molecular contamination from the OTIS mirrors was not an option and heating the Primary Mirror (PM) segments would have also been a risky and expensive endeavor. As a result, a monitoring process was developed and implemented during four different Pathfinder or risk reduction tests that were scheduled to occur prior to the flight hardware test. The goal was to quantify and assess the risk of molecular contamination depositing on the PM resulting from relatively warm chamber shrouds “leading” colder PM mirrors during warmup, by a margin of 10-50 Kelvin (K). This was accomplished using Cryogenic Quartz Crystal Microbalances (CQCMs), held at temperatures slightly cooler than the segments to signal the onset of contamination events. Per the JWST Contamination Control Plan (CCP), the total Primary Mirror molecular allocation requirement was 50 angstroms. In all tests, the results showed an average accumulated molecular contamination of <10 angstroms.
This paper summarizes a recent numerical analysis of water vapor and volatile condensible material deposition on the James Webb Space Telescope from the initial orbit insertion up to 180 days post launch. The analysis utilized 17 distinct geometry files capturing observatory configuration changes during the deployment. Surface temperature was set from a time-dependent thermal analysis solution. A vapor pressure model was used to calculate the net water ice adsorption. Molecular contamination included a contribution from UV photopolymerization. The analysis predicted levels of ice and molecular accumulation were found to be within the allowable limits specified by the observatory contamination control plan.
The James Webb Space Telescope (JWST) has a primary mirror, made of 18 segments, and a secondary mirror (SM) that are used to direct the light of desired targets. After launch, the secondary mirror assembly (SMA) is stowed for approximately 10 days and is subject to molecular contamination outgassing from the cavity of the secondary mirror support structure (SMSS) in-board hinge (IBH) which contains cables, motors, resolvers, and coatings. The main concern during this period before SMA deployment is the accumulation of ice due to the lack of a heater on the SMA. The temperature differentials between the IBH surfaces and SMA could cause redistribution of water vapor contamination. To address this concern, single layer insulation (SLI) was reconfigured to direct the vent path of IBH outgassing sources away from the SM. Two separate thermal vacuum (TVAC) tests were performed to quantify this contamination: a Z307 ASTM E 1559 materials test of the radiator paint used on the motor of the IBH and a separate test on the hinge motor from the primary mirror backplane assembly (PMBA) qualification engineering test unit (ETU). The PMBA ETU hinge was similar in design to the IBH. These tests approximately followed the predicted SMA predeployment thermal environment. To quantify source rates in case of a leak in the new SLI enclosure or baffle, the motor and resolver sides were separated, and quartz crystal microbalances (QCM) were used to measure the deposition of water. The SLI redesign and implementation and outgassing measurements to understand leak effects from the IBH were essential to mitigate the deposition of contamination on the SMA.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.