After several tense days of deploying and putting its various parts into place, the largest and most sophisticated space telescope ever launched is now complete.
On January 8, NASA’s James Webb Space Telescope slowly flipped the last 3 of its 18 hexagonal mirror segments into position, locking them together in a 6.5-meter-wide gold-covered cosmic eye. The move capped two weeks of essentially flawless engineering maneuvers – the most complex astronomical deployments ever attempted in space – since the telescope launched on Christmas Day.
“The Webb deployments have been perfect,” says Paul Hertz, director of NASA’s astrophysics division in Washington DC.
“I feel absolutely thrilled,” says Antonella Nota, European Space Agency project scientist for Webb. “We are all part of history now as we watch this magnificent machine prepare to explore the Universe.”
The $ 10 billion observatory still faces many important tasks, such as aligning its mirror segments and calibrating its 4 scientific instruments. But he completed the riskiest engineering operations, without which he would have been inoperative. These include deploying a tennis court-sized kite-shaped sunshade to shield the telescope from the heat of the sun and positioning its primary and secondary mirrors to capture light from the sun. stars, galaxies and other cosmic objects.
Photons now bounce between Webb’s mirrors, making it an operational observatory. “It’s amazing,” said Bill Ochs, NASA’s project manager for Webb, during a Jan. 5 webcast of the Space Telescope Science Institute‘s mission control in Baltimore, Maryland. “We actually have a telescope.”
Webb, which was launched from the European spaceport at Kourou in French Guiana, is now over a million kilometers from Earth. It is expected to reach its final destination, a gravitationally stable point in space known as L2, on January 23. From there, he will study astronomical phenomena such as the most distant galaxies in the Universe, emerging stars shrouded in dust, and the atmospheres of extrasolar planets.
Unlike its predecessor, the Hubble Space Telescope, Webb detects infrared wavelengths of light. This allows him to peer into previously unexplored areas, but also forces him to work in extremely cold temperatures, so that he can detect weak heat signals from the distant Universe. Webb’s sun visor is crucial in achieving this frigidity.
This is why many scientists were very nervous about opening it and stretching it into place. After launch, Webb had to unfold two rectangular pallets containing the sunshade, unroll its protective covers, pull it in the shape of a kite, and finally pull its five layers of sail so that it was taut. The process had been tested several times in a laboratory on Earth, but never in zero gravity in space, which could have introduced unexpected problems.
“I think I was just nervous about deploying something big and floppy,” Hertz says. No other space observatory has had such a shield, so it is “new and unknown,” he adds.
Any step could have failed dramatically, but none failed. Webb pulled the last of his sunshade coats in the correct tension on Jan.4. “There was a lot of joy – a lot of relief,” said Hillary Stock, an engineer at Northrop Grumman in Redondo Beach, Calif., Who designed and built the sunshade. After that, Hertz said, he was no longer nervous.
But other scientists were worried until the next day, when Webb deployed his secondary mirror. This process involved extending a giant articulated tripod in front of the telescope’s primary mirror to lock its 74-centimeter-wide secondary mirror in place. The light bounces off the primary concave mirror and hits the secondary convex mirror, which focuses the light and reflects it back through a small hole in the primary mirror and into the scientific instruments for analysis. Once the secondary mirror was deployed, Webb became an operational telescope by definition.
Cool it down now
The last major milestone was at 10:29 a.m. EST on January 8, when the last segment of the primary mirror fell into place. This mirror is so large that, like the sun visor, it had to be folded up for launch in order to fit the top of the Ariane 5 rocket that carried it into space.
Other successful deployments over the past two weeks include the tilting of a radiator that will remove excess heat from the telescope’s science instruments and throw it into space.
Next, Webb will start fine-tuning the positions of the 18 main mirror segments to align them to properly focus the light they collect. The telescope also continues to cool to its operating temperature of about 40 ° C above absolute zero, or -233 ° C. It is currently close to –200 ° C on its cold side, behind the sun visor.
After Webb hits L2 in about two weeks, he’ll have about five months of setup left before he can start returning scientific results. “I can’t wait to see the first data,” says Nota.
Webb took three decades to develop and has repeatedly eaten into NASA’s budget. European and Canadian space agencies are also project partners.