The vault-like, 40ft diameter, 40 tonne door of Chamber A at NASA’s Johnson Space Center in Houston was unsealed on 18th November, signaling the end of cryogenic testing for NASA’s James Webb Space Telescope.
The Webb telescope will be the premier space observatory of the next decade, and will study galaxy, star and planet formation in the universe. The historic chamber’s massive door opening brings to a close about 100 days of testing for Webb, a significant milestone in the telescope’s journey to the launch pad.
The cryogenic vacuum test began when the chamber was sealed shut on 10th July. Inside the chamber, the telescope was cooled with liquid nitrogen (N2) and cold gaseous helium (He). Scientists and engineers at Johnson put Webb’s optical telescope and integrated science instrument module (OTIS) through a series of tests designed to ensure the telescope functioned as expected in an extremely cold, airless environment akin to that of space.
The Webb telescope team persisted with the testing even when Hurricane Harvey slammed into the coast of Texas on 25th August as a category four hurricane before stalling over eastern Texas and weakening to a tropical storm.
“After 15 years of planning, chamber refurbishment, hundreds of hours of risk-reduction testing, the dedication of more than 100 individuals through more than 90 days of testing, and surviving Hurricane Harvey, the OTIS cryogenic test has been an outstanding success,” said Bill Ochs, Project Manager for the James Webb Space Telescope at NASA’s Goddard Space Flight Centre in Greenbelt, Maryland. “The completion of the test is one of the most significant steps in the march to launching Webb.”
Before cooling the chamber, engineers removed the air from it, which took about a week. On 20th July, engineers began to bring the chamber, the telescope, and the telescope’s science instruments down to cryogenic temperatures — a process that took about 30 days. During cool down, Webb and its instruments transferred their heat to surrounding liquid N2 and cold gaseous He shrouds in Chamber A. Webb remained at “cryo-stable” temperatures for about another 30 days, and on 27th September, the engineers began to warm the chamber back to ambient conditions (near room temperature), before pumping the air back into it and unsealing the door.
“With an integrated team from all corners of the country, we were able to create deep space in our chamber and confirm that Webb can perform flawlessly as it observes the coldest corners of the universe,” said Jonathan Homan, project manager for Webb’s cryogenic testing at Johnson. “I expect [Webb] to be successful, as it journeys to Lagrange point 2 [after launch] and explores the origins of solar systems, galaxies, and has the chance to change our understanding of our universe.”
Webb’s combined science instruments and optics next journey to Northrop Grumman Aerospace Systems in Redondo Beach, California, where they will be integrated with the spacecraft element, which is the combined sunshield and spacecraft bus. Together, the pieces form the complete James Webb Space Telescope observatory. Once fully integrated, the entire observatory will undergo more tests during what is called “observatory-level testing.” This testing is the last exposure to a simulated launch environment before flight and deployment testing on the whole observatory.
Webb is expected to launch from Kourou, French Guiana, in the spring of 2019.