Final Deep Freeze Thermal Vacuum Testing Wraps Up on James Webb Space Telescope

The vault-like, 40-foot diameter, 40-ton door of Chamber A at NASA’s Johnson Space Center in Houston was unsealed on November 18, signaling the end of cryogenic testing for NASA’s James Webb Space Telescope. Credit: NASA

Cryogenic thermal vacuum testing on NASA’s multi-billion dollar James Webb Space Telescope (JWST) has wrapped up at the agency’s Johnson Space Center (JSC) in Houston, TX, after undergoing 93 straight days of around-the-clock thermal vacuum testing in “Chamber A”, the largest high-vacuum, cryogenic-optical test chamber in the world, once used to test Apollo hardware and suited up astronauts.

“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 Center in Greenbelt, Maryland. “The completion of the test is one of the most significant steps in the march to launching Webb.”

In order to detect the infrared light from faint and very distant objects, JWST needs to operate in an environment of 40 Kelvin (or about -387 F, -233 C), so NASA had to test it under those conditions on the ground to verify and prove its sensitive optics and instruments will perform as planned in space; there’s nobody to call for a repair one million miles away.

The primary mirror of JWST. Photo Credit: NASA/Desiree Stover

From NASA, “Tests included an important alignment check of Webb’s 18 primary mirror segments, to make sure all of the gold-plated, hexagonal segments acted like a single, monolithic mirror. This was the first time the telescope’s optics and its instruments were tested together, though the instruments had previously undergone cryogenic testing in a smaller chamber at Goddard. Engineers from Harris Space and Intelligence Systems worked alongside NASA personnel for the test at Johnson.”

“The Harris team integrated Webb’s 18 mirror segments at Goddard and designed, built, and helped operate the advanced ground support and optical test equipment at Johnson,” said Rob Mitrevski, vice president and general manager of intelligence, surveillance, and reconnaissance at Harris. “They were a key, enabling part of the successful Webb telescope testing team.”

More from NASA:

“Before cooling the chamber, engineers removed the air from it, which took about a week. On July 20, 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 nitrogen and cold gaseous helium shrouds in Chamber A. Webb remained at “cryo-stable” temperatures for about another 30 days, and on Sept. 27, 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.”

NASA’s James Webb Space Telescope sits in front of the door to Chamber A, a giant thermal vacuum chamber located at NASA’s Johnson Space Center. The telescope will operate below an extremely cold 50 K (-223° C or -370° F) in space, so NASA simulated those conditions on the ground, ensuring the optics and instruments will perform perfectly after launch. Photo Credit: NASA / Chris Gunn

“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.”

“While Webb was inside the chamber, insulated from both outside visible and infrared light, engineers monitored it using thermal sensors and specialized camera systems. The thermal sensors kept tabs on the temperature of the telescope, while the camera systems tracked the physical position of Webb to see how its components very minutely moved during the cooldown process.”

“This test team spanned nearly every engineering discipline we have on Webb,” said Lee Feinberg, optical telescope element manager for the Webb telescope at Goddard. “In every area there was incredible attention to detail and great teamwork, to make sure we understand everything that happened during the test and to make sure we can confidently say Webb will work as planned in space.”

NASA’s upcoming James Webb Space Telescope will be positioned at the Earth-Sun L2 Lagrange point, 1.5 million km away from the low-Earth orbiting Hubble Space Telescope. Taking advantage of the telescopes’ relative distance, astronomers could image celestial objects in the Solar System with depth perception. Image Credit: NASA/STScI

Webb will now be removed from its test platform, rotated from vertical to horizontal, packed for shipment and carefully hoisted into a climate-controlled shipping container for transport to Northrop Grumman Aerospace in California in early 2019, where Webb’s combined science instruments and optics will be integrated with the spacecraft element, which is the combined sunshield and spacecraft bus.

The tennis-court sized sunshield is critical in preventing background heat from the Sun, Earth and Moon from interfering with the telescope’s sensitive infrared instruments; JWST simply cannot science without it. Five sunshield membrane layers, each as thin as a single human hair, will reduce the temperatures between the hot and cold sides of the JWST by an incredible 570 degrees Fahrenheit; equivalent to SPF 1 million sunblock.

“Imagine you are the telescope”, note the engineers standing where the telescope will within its protective 5-layer sunshield. Photo Credit: Northrop Grumman

Together, the pieces will form the complete James Webb Space Telescope observatory.

The fully assembled JWST will then undergo more tests during what is called “observatory-level testing”, followed by flight and deployment testing on the whole observatory before being packed and shipped to its launch site at the edge of the Amazon rainforest in French Guiana, South America, for flight atop a European Space Agency Ariane 5 rocket in Spring 2019.

The first targets for the powerful new observatory were recently chosen as well, including Jupiter, organic molecules in star-forming clouds and baby galaxies in the distant Universe; read about it HERE!


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