JWST: Almost Ready for Launch

Well, kids, the James Webb Space Telescope (JWST, sometimes jokingly called the “Just Wait Space Telescope” due to the long time it has taken to get it to the launch pad) is finally atop its rocket and just about ready to go. The propulsion systems that will take it to its LaGrange orbit and keep it pointed correctly were all fueled a few days ago. Scientists are ready for it to go—heck, they’ve been ready for years. And, the technical crew is working round the clock on final arrangements for the launch, now scheduled for December 22nd. People around the world will be watching from their homes, classrooms, planetarium domes, and science centers. There’s a growing collective sense of anticipation and we all hope this long-awaited telescope will finally take flight and begin to deliver data.

Beauty, Complexity, and Danger

The James Webb Space Telescope is a complex and (to me, anyway) stunningly beautiful piece of space hardware. There are thousands of pieces and parts that make up its spacecraft bus, mirrors, instruments, and solar shade that all have to work perfectly once the observatory is released to head for its LaGrange point. The idea of the solar shields and mirrors unfolding gracefully is nerve-wracking when you stop to think about it. They all have to deploy in the correct sequence, without a hitch. If they do, everything’s great. If they don’t—well, it just doesn’t bear thinking about, but it would be a disaster. I’m sure the NASA folk have worked through the scenarios so that they have a Plan A, Plan B, Plan C, and so forth, to deal with any problems. Still, there are many complex steps that have to happen perfectly before JWST is ready for science.

JWST: Launch and Deployment Rundown

First is launch, aboard an Ariane 5 rocket. Then, after it gets safely to space, the spacecraft fairing is ejected and the spacecraft is released. Very shortly after that, the JWST solar panel, which supplies power, is deployed. The next step is a mid-course correction burn to get the scope on the right path to L2—shorthand for LaGrange 2, a point in Earth’s orbit that allows the spacecraft to “follow” Earth (and face its night side) at a distance of 1.5 million kilometers. There are actually three correction burns to fine-tune the trajectory to L2.

The next big (and breathtaking) step is the sun shield deployment. That’s the one action that I’ve wondered about ever since I saw a full-scale model of the JWST at a meeting in Seattle a few years ago. It’s a very delicate but necessary piece of the spacecraft that protects the instruments from sunlight. That’s needed because JWST is infrared-sensitive, and the instruments need to be as cold as possible to do their work.

JWST: Unfolding the Mirrors

Only after the sunshield assemblies are in place will the mirrors themselves unfold. JWST doesn’t just have one mirror, it has a segmented main mirror and a single secondary mirror. The main gathers all the light of interest to the instruments inside the spacecraft and directs it to the secondary, which directs it to the instrument bay behind the main mirror. After the secondary is in place, the segmented mirror unfolds itself. That’s the second process that fascinates me—and I sure hope it all goes well!

JWST: Getting Ready for Science

All this happens while the spacecraft is on its way to deployment at L2. That trip will take about a month. Once it gets to its final destination the telescope starts a cooling process that takes roughly five months. It will also fine tune-its instruments, do final mirror alignments, and in general, get ready to do the science astronomers have waited to conduct for more than a decade.

That’s a little look at the process of getting JWST to its “workplace in space.” I’ll focus on JWST’s proposed science program in my next article. For now, though, check out NASA’s well-illustrated pages about the telescope, including a guided tour of its launch, unfolding, and deployment. And, tune in for launch if you can!

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