The $10 billion James Webb Space Telescope has to unfold itself in space — a nail-biting maneuver NASA's never attempted
- NASA is launching its next major space observatory. The real nail-biter is the weeks after liftoff.
- The James Webb Space Telescope must unfold in space — a complex maneuver NASA has never attempted.
NASA has loaded its most valuable, delicate telescope onto a 15-story rocket in French Guiana. On Friday, the agency will fill the rocket with highly combustible liquid oxygen and hydrogen fuel, fire the engines, and watch it scream through the atmosphere with a $10 billion observatory in tow.
The James Webb Space Telescope — JWST, or simply "Webb," for short — is the largest and most powerful space observatory ever built. If all goes according to plan, it will revolutionize astronomy.
But first the telescope has to safely get into position. Launch, which is scheduled for December 24, is only half the battle.
Webb's main feature is a 21-foot-wide mirror made up of 18 gold-coated beryllium panels, which sits atop a diamond-shaped sunshield the size of a tennis court. Both were too big to fit in any existing rocket without folding up like a drop-leaf table. Instead, they'll have to unfold, or "deploy," in space.
Unfolding a telescope as large and complex as Webb is a risky maneuver and one that NASA has never tried before. If any of the deployment mechanisms snag or malfunction, NASA can't send an astronaut to the spacecraft to fix it or replace the broken part.
Failure could mean $10 billion wasted and the hopes of countless astronomers down the drain.
"When I started in this business about 40 years ago, I remember one of the first lessons I got taught was avoid deployments on orbit," Mike Menzel, NASA's lead mission systems engineer for Webb, said in a November press briefing. "James Webb cannot avoid the deployments. In fact, James Webb has to perform some of the most complex sequence of deployments ever attempted."
Webb must also align its mirrors, calibrate its instruments, and fall into an orbit trailing Earth around the sun from about 1 million miles away — four times the distance between the moon and Earth. The whole process is expected to take about six months.
"We've built it, we've aligned it, we've tested it, we've proved it worked. Now we're going to have to break it up, fold it up, and actually rebuild it on orbit," Menzel said, adding, "That's never been done before."
Webb is a decades-long project of NASA, the European Space Agency (ESA), and the Canadian Space Agency. Redesigns, technical errors, and extreme weather events repeatedly delayed launch and drove up its price tag from the original $500 million. Now it faces one last barrier to the new era of space astronomy.
"Unfolding Webb is hands down the most complicated spacecraft activity we've ever done," Menzel said in a NASA video.
Webb will spend its first 2 weeks in space unfolding itself
The deployments should happen within two weeks of launch. If anything goes wrong, NASA can't send humans or robots to fix it. Webb is on its own.
The sunshield will unfold first, since it's critical to Webb's functioning. Five layers of Kapton film have to block sunlight from hitting the rest of the telescope, allowing the mirrors and science instruments to cool to a frigid minus 380 degrees Fahrenheit — far colder than any place on Earth.
It will take Webb about two months to reach that temperature, which is how cold the observatory must be to detect faint heat of distant stars and planets in the form of infrared light. For its mid-infrared instrument, which needs to reach an even lower temperature of minus 447 degrees Fahrenheit, cooling will take about 100 days.
That can only happen if the sunshield unfolds properly. But its floppy material makes it deployment's biggest wild card.
"Take a string and put it on a tabletop and push on it, and see if you can predict the shape of that string. Chances are you will not be able to, and so it is with the membranes of the sunshield," Menzel said.
If that floppy material opens into the wrong shape, or snags on other parts of the observatory, it could be a disaster for Webb. So NASA and its contractor, Northrop Grumman, have built a complex unfolding system for the sunshield, employing 140 release mechanisms, 70 hinge assemblies, eight motors, 400 pulleys, and 1,312 feet of cable.
Webb has 344 opportunities for failure. Most are part of unfolding.
All of the sunshield's release mechanisms are what NASA calls "single-point failures." If they don't work, there is no backup for them. They either let the sunshield unfold or they don't. No sunshield could mean no functional telescope.
If a release mechanism fails, NASA has a few troubleshooting options: resend the command to release, spin the observatory or rock it back and forth to dislodge anything that's stuck, or turn the telescope toward the sun to heat up the troublesome mechanism. But it can't rely on backup hardware. Each mechanism must work in order to unfold the sunshield.
Overall, Webb has 344 single-point failure items. About 80% of those items are part of the deployment process, Menzel said. Many of them are necessary to prevent the sunshield from being dangerously floppy. But each single-point failure item adds its own risk to the deployment process.
To strike the right balance — controlling the sunshield without adding too many opportunities for failure — NASA conducted several studies and consulted independent review groups, according to Menzel.
"We've all agreed we found the sweet spot on this," he said.
NASA has also inspected and tested each single-point failure item to identify all the ways it could malfunction and reduce the likelihood of such a failure, he added.
Once the sunshield is open, Webb must unfold a tripod holding its secondary mirror, then open the two flaps of its main mirrors. If that's successful, it will still be five months before Webb can start conducting science. It needs three months to get its mirror into alignment and two to calibrate its science instruments.
Only then can Webb engineers in the US, Europe, and Canada breathe a sigh of relief.