Ready to test: Segments of the James Webb Space Telescope's mirror are mounted for testing in an ultracold chamber
Image: Justin Fantl; Courtesy of NASA/MSFC/Emmett Givens
In Brief
- When the Hubble Space Telescope retires in a few years, a NASA-led collaboration plans to replace it with a telescope of an entirely new generation.
- The James Webb Space Telescope’s ultralight, shape-adjusting mirrors will have six times the light-collecting power of those of the Hubble, and its instruments will be sensitive in parts of the spectrum where most telescopes have been lacking.
- Infrared radiation will open new vistas on the earliest ages of the universe, when the first stars and galaxies formed, and also on planets orbiting other stars in our galaxy.
- The most delicate part of the mission will be when the telescope and its giant heat shields unfurl out of the rocket that will carry them into orbit. Even a small technical glitch could render the $5-billion observatory inoperable.
The mirror, a perfect hexagon of gunmetal gray, stands vertically on a low platform. It is about two inches thick and more than four feet wide, a precisely carved slab of beryllium that gleams in the low light of this optics laboratory near San Francisco Bay. My guide, chief engineer Jay Daniel, watches my footing as I step gingerly in front of the mirror to see my reflection. “It’s like your bathroom mirror,” Daniel says, chuckling.
The other side of this looking glass, though, is nothing like a household vanity. The slab of metal is mostly hollow, drilled out by machinists to leave an intricate triangular scaffold of narrow ribs. It is beautiful in its geometric precision, and I resist the urge to touch one of the knifelike edges. The polished front layer that remains, Daniel says, is a mere 2.5 millimeters thick. From its starting weight of 250 kilograms, the entire mirror now weighs just 21 kilos. That is light enough for a rocket to hoist 18 of them deep into space, where the curved mirrors will join as one to form the heart of the most audacious space observatory ever launched.
This article was originally published with the title Origami Observatory.
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5 Comments
Add CommentI have a question for anyone. How will they protect this mirror from micro meteor impacts?
Reply | Report Abuse | Link to thisWhen the Webb telescope reaches the end of its fuel for steering in about 10 years, what is the constraint that prohibits sending up an auxiliary spacecraft with the capability to steer the telescope and with its own fuel that could grab the telescope, using some type of ROV method, to extend its life?
Reply | Report Abuse | Link to thisIt would be a shame to lose such an exquisite (and expensive) instrument after only 10 years.
Richard K.
Salinas, CA
#SCA0008796385/9# DEC10
Hi ed842: There's no such protection for the mirror segments. Micrometeors will degrade the reflective surfaces over time -- but slowly enough that it shouldn't affect the telescope's image quality during its 10-year planned operation. Beyond that, they'll get gradualyl more pocked and worn by both micrometeors and the space radiation environment, as the end of the story alludes to. The chances of a larger impact ruining one of the segments (or the overall telescope body) are vanishingly small. Thanks for your question! --Robert Irion, author
Reply | Report Abuse | Link to thisHi Richard: The option you suggest is intriguing but would be incredibly expensive to implement. It's hard enough to design a remotely-operated vehicle that could grapple something in low-earth orbit, not to mention 1.5 million km away. Unlike Hubble, the telescope's body hasn't been designed to allow for anything to grab hold of it. It definitely was a sacrifice to send the Webb to such a distant perch, but the ultracold location and its size will make it sensitive to things other telescopes simply cannot see. The team definitely intends to make the absolute most out of those ten years! --Robert Irion
Reply | Report Abuse | Link to thisRobert: Thank you very much for your reply.
Reply | Report Abuse | Link to this"...would be incredibly expensive to implement."
More expensive than the original telescope or a replacement? On further thought, perhaps the idea was that in 10 years, plus the time to design & build a new one, the technology would have advanced to where they'd want it replaced anyway.
My thinking was that the other vehicle would be no more than a glorified fuel tank and not that expensive. If some hard points and pingers had been designed into it, then I wouldn't think distance would be too much of an obstacle. Don't the service vehicles dock autonomously to the Space Station? There could be some docking procedure holds programed in at shorter and shorter distances to allow time for pictures to be sent back to make sure everything was going according to plan or to send up fine tuning commands. The rovers on Mars seem capable of some pretty fine movements via commands from earth.
Just a thought.