“Extraterrestrial Engineering!” –NASA Completes Tests of JWST to Ensure Functioning in Deep Space

 

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"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 the James Webb Space Telescope'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."


The vault-like, 40-foot diameter, 40-ton door of Chamber A  (below) 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. 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.

 

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The cryogenic vacuum test began when the chamber was sealed shut on July 10, 2017. 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.

These 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.

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.

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. Monitoring the telescope throughout the testing required the coordinated effort of every Webb team member at Johnson.."

In space, the telescope must be kept extremely cold, in order to be able to detect the infrared light from very faint, distant objects. Webb and its instruments have an operating temperature of about 40 Kelvin (or about minus 387 Fahrenheit / minus 233 Celsius). Because the Webb telescope's mid-infrared instrument (MIRI) must be kept colder than the other research instruments, it relies on a cryocooler to lower its temperature to less than 7 Kelvin (minus 447 degrees Fahrenheit / minus 266 degrees Celsius).

To protect the telescope from external sources of light and heat (like the Sun, Earth and Moon), as well as from heat emitted by the observatory, a five-layer, tennis court-sized sunshield acts like a parasol that provides shade. The sunshield separates the observatory into a warm, sun-facing side (reaching temperatures close to 185 degrees Fahrenheit / 85 degrees Celsius) and a cold side (minus 400 degrees Fahrenheit / minus 240 degrees Celsius). The sunshield blocks sunlight from interfering with the sensitive telescope instruments.

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.

The Daily Galaxy via NASA's Goddard Space Flight Center

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