Aerospace Assists NASA in Preparing the James Webb Space Telescope for Launch
By Richard Park
The James Webb Space Telescope (JWST) will serve as the successor to NASA’s Hubble space telescope, which has been orbiting Earth since 1990. Hubble is the world’s first space-based optical telescope and has been sending back never-before-seen images of the universe, helping scientists make discoveries about the formation and origins of the planets and stars. Hubble has outlived its 20-year life expectancy, and is slated to retire when the more advanced JWST takes its place in 2018.
The Webb telescope features longer wavelength coverage and improved sensitivity over Hubble. Webb will primarily look at the universe in infrared, while Hubble has mostly studied it in optical and ultraviolet wavelengths. JWST is destined to reach the second Lagrange (L2) point located a million miles from Earth. Unlike Hubble, which is in a very close orbit to Earth, the Webb telescope will instead sit at its destination. At L2, Webb’s solar shield will block light from the sun, moon, and Earth, helping the telescope to stay cool. The new telescope will search for the first galaxies thought to have formed after the big bang, and will assist scientists in determining how the galaxies have evolved. It will observe the formation of stars and planetary systems, measure their physical and chemical properties, and investigate the potential for life.
Chamber A with the door closed. The personnel to the right of the door indicate the chamber’s massive size. (Photo courtesy of NASA)
JWST must undergo rigorous environmental testing before it can be launched into space. This will occur in NASA’s Chamber A, located at the Johnson Space Center in Houston, Texas. Chamber A is the world’s only vacuum chamber that is large enough and cold enough to provide a near space-like thermal environment for testing JWST. The chamber was built in 1964 and has been in use since the Apollo program. It has been used to conduct environmental testing on numerous large spacecraft assemblies and the components for all the major space programs, and was designated a national historic landmark in 1985.
Members of The Aerospace Corporation are working with NASA to upgrade and modify Chamber A in preparation for JWST testing. A feasibility study was conducted in 2004, design work and planning in 2007 and 2008, and reconstruction of the chamber began in 2009. Because of the upgrades, the chamber has now been able to reach 11 kelvin (-440 degrees Fahrenheit) at a vacuum of 10-8 torr.
Aerospace has assisted NASA in efforts to achieve the stringent cleanliness requirements for Chamber A’s environment and has performed preliminary certification of its internal surfaces. As part of the upgrades, the airflow system was redesigned to reverse the flow of air from bottom up to top down. New filter systems were installed with high-efficiency air particulate and charcoal filters. Precision cleaning will occur once the remaining new systems are installed in the chamber.
Chamber A in its premodification configuration. (Photo courtesy of NASA)
Rajiv Kohli, senior project engineer, Johnson Space Center, is the lead engineer for contamination control for JWST activities and is responsible for maintaining the surface and air cleanliness of Chamber A. This work includes inspection, testing, and certification of the chamber. “Our work has resulted in no evidence of offgassing contaminants released during the preliminary bakeout, evacuation, and repressurization cycles of the functional tests,” said Kohli. “Surface analysis of samples by ion-trap gas chromatography and mass spectrometry did not indicate the presence of volatile contaminants. Strict controls on the cleanliness of materials, such as the shrouds and controls on personnel contamination, have been instrumental in maintaining the chamber’s cleanliness,” he said.
Aerospace has worked with NASA on other Chamber A enhancement efforts including developing methods and processes for contamination control; the selection and usage of materials in the chamber; specification, selection, and operation of monitoring instrumentation; personnel training; preparing corrective action plans and implementation; contamination protocol deviation requests; and the review and approval of subcontractor plans, procedures, and processes. A detailed plan addresses four key sources of contamination: environment, process, personnel, and materials, and has defined how each source should be controlled and mitigated.
Schematic layout of Chamber A for JWST testing. (Aerospace generated image)
Aerospace also has served as a consultant and as technical oversight to NASA for the design, fabrication, installation, and testing of the new cryogenic gaseous helium and liquid nitrogen delivery systems in Chamber A. To make it cold, clean, and vibration-free enough to test JWST, a number of physical and mechanical modifications had to be made to the vacuum chamber and the building where it is located. Gaseous helium and liquid nitrogen shrouds were installed along with their respective refrigeration and delivery systems. The vacuum system has been made oil-free, and the chamber’s data, power, control, and airflow systems have been upgraded. The entire system for supplying liquid nitrogen to the chamber interior was redesigned and replumbed. “This system has been converted from a powered, pump-fed system with more than one hundred valves (all potential reliability risks) to a passive, thermo-siphon system with less than two-dozen valves. It is now clean, economical, and reliable,” said Kohli.
With these physical and mechanical modifications complete, the next step is to add an ISO (International Standards Organization) Class 7 cleanroom to the front of the chamber. Aerospace will assist NASA with this effort. JWST hardware is scheduled to begin being tested in the chamber in 2014.