It's been a long journey for NASA's James Webb Space Telescope (JWST), and it hasn't even begun its million-mile trip into the Sun's orbit yet. Almost two decades in the making, the world's largest space telescope to be has edged closer to the launchpad, passing a series of cryogenic tests designed to simulate the harsh space environment.

The JWST's science instrument module and optical element had been sealed away inside a chamber at NASA's Johnson Space Center in Houston for a period of 100 days, before scientists opened up the 40-ton door late last month. Inside this cryogenic, vacuum-sealed chamber, these key components of the multi-billion-dollar space instrument were put through a series of tests to make sure they function as planned in the cold, airless environment of space.

This included an alignment check of the Webb's 18 primary mirror segments to make sure they act as a single, giant mirror, and also the first tests of the telescope's optics and instruments together. Preparing the chamber for the tests involved spending an entire week removing the air and then 30 days bringing it down to cryogenic temperatures. The telescope spent 30 days at "cryo-stable" temperatures, before engineers starting warming the chamber up, pumping air back in and unsealing the door on December 1.

Keeping the telescope cool in space is integral to the mission's success and its ability to detect infrared light from faint and distant objects. Its instruments are shielded from the Sun and other heat sources like the Moon and Earth by a tennis-court-sized parasol. This allows most of those instruments to maintain an operating temperature of 40 Kelvin (-387° Fahrenheit, -233° C), except for the mid-infrared instrument (MIRI), which uses a cryocooler to work at less than 7 Kelvin (-447° Fahrenheit, -266° Celsius).

"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. "The completion of the test is one of the most significant steps in the march to launching Webb."

From the Johnson Space Center, JWST will travel to Northrop Grumman Aerospace Systems in Redondo Beach, California to be integrated with the spacecraft element, which consists of the sunshield and spacecraft bus. It is expected to launch from Kourou, French Guiana, in the spring (Northern Hemisphere) of 2019.

Source: NASA 1, 2

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