NASA has been working on the James Webb Space Telescope (JWST) for the better part of two decades, and it’s almost ready for launch. When operating in space, the JWST will be the most powerful telescope ever built, but it’ll all be for naught if the giant segmented mirror cannot deploy correctly. NASA has just completed the final pre-launch test of the mirror. The next time it deploys, the JWST will be hanging in the inky blackness of space.
The Webb telescope is the long-awaited follow-up to the aging Hubble Space Telescope, which saw its final service mission in 2009 just before the end of the Shuttle program. Whereas Hubble relied on a single-piece reflector, the JWST will have a segmented Korsch-style mirror. The 18 hexagonal segments combine to form a 6.5-meter reflector, but the gold-coated beryllium panels cannot launch in their extended configuration because the Ariane 5 rocket that will hoist it into space is only 5.4 meters in diameter.
The array is broken up into three sections with the central column holding 12 segments, and the left and right foldable wings consisting of three each. The optical components are now fully assembled, so the JWST has thermal shielding around the segments that wasn’t attached in previous checks. To test the mirror, NASA hooked it up to special gravity offsetting rigs that simulate the environment in space.
With the mirror at the ready, the team sent commands from the control room at Northrop Grumman’s Redondo Beach, California facility. The commands relayed to the telescope were exactly the same as those it will receive while nestled in the Earth-Sun L2 Lagrange point. If the wings failed to extend properly under these conditions, that could lead to yet another delay in the already overdue project. Luckily, everything worked perfectly, marking the end of testing on the optics.
Following the test, NASA technicians locked the mirrors into their launch configuration, but this isn’t the end of the pre-launch checks. NASA still plans to look at the performance of two radiators that help keep the observatory cool and run the deployable tower through a full extension and restowing cycle. This component keeps the mirror separate from the comparatively warmer sun-facing side and spacecraft bus, which is essential for the infrared performance of the instruments.
Assuming all these final tests go as planned, the James Webb Space Telescope will finally head into space on October 31, 2021. To date, the project has cost more than $10 billion, but it could deliver an incredible return on that investment if it’s even half as successful as Hubble has been.
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