What the Webb Space Telescope Will Show Us Next | Space

When the Hubble Space Telescope launched, we soon learned its images were blurry. Engineers had to build the equivalent of eyeglasses for it. Were there any such problems with J.W.S.T. early on, given its very complicated deployment?

Because of the way it worked, when Hubble went up in space, the optics had to be perfect. For J.W.S.T., we launched mirrors that were able to fix themselves. There are eighteen primary mirror segments—those beautiful gold hexagons—and the idea is that you design them to be correctable in space. You just move them until they’re in the right places. When J.W.S.T. first deployed, through this long, iterative process of looking at bright stars, we got all of those mirrors to work together like a chorus—where, at the beginning, everybody’s in their own key, their own song, their own genre, doing their own thing. And, at the end, they’re coördinated, singing in a tight, multipart harmony.

The real problem with J.W.S.T. was that we needed a telescope bigger than rockets are. The rocket we launched on is a little more than five metres across. But just the telescope part of J.W.S.T. is 6.6 metres across (and then there’s this whole sunshield underneath it that’s the size of a tennis court). One way to overcome the size limit, which is a fundamental challenge for space telescopes, is to have them fold up. Six of the primary mirror segments were tucked back behind the rest of the mirrors for launch. Then they unfolded on hinges. So that led to a design where we didn’t need to align them perfectly on the ground.

If size is but one challenge for space telescopes, what you would say is the greatest one?

Oh, my gosh. I think, right now, the greatest challenge is just time. The telescope is about one hundred times more powerful than anything we’ve had before. In the same observing time, it can see things that are a hundred times fainter than we could see with Hubble or with the Spitzer Space Telescope. So it is this powerful beast,…

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