NASA’s most expensive telescope ever is in space at last. The $10 billion James Webb Space Telescope, an instrument expected to revolutionize astronomy by gathering light from the atmospheres of alien worlds and the universe’s first galaxies, launched at 7:20 a.m. Eastern Time on a sultry Christmas morning from Europe’s spaceport in French Guiana.
Some 30 minutes after launch, the telescope detached from the top of its Ariane 5 rocket and deployed its solar array, which is needed to charge its batteries and support communication with Earth. Webb is now en route to its observing station, a gravitational balance point known as L2 at 1.5 million kilometers from Earth. Before it gets there, mission controllers will have a tense month, as they unfurl parts of the telescope too large to fit inside the rocket fairing, including its tennis court–size sunshield and 6.5-meter wide mirror. Until those are successfully deployed and Webb’s four instruments are chilled and tested, astronomers will not rest easy.
As NASA’s first major space observatory in more than a decade and the successor to the Hubble Space Telescope, a lot is riding on Webb. The European Space Agency (ESA), a partner in the mission, and French rocket company Arianespace will be happy to have sent the craft on its way.
The final prelaunch days were not without incident. In mid-December, as Webb was lifted onto the payload adapter—its connection to the rocket—the sudden, unplanned release of a clamp caused a vibration throughout the observatory. And after Webb was lifted to the top of the rocket, engineers detected intermittent data loss in the communication cable connecting Webb to the launcher. Resolving these issues pushed the launch back to 24 December. Then unsettled weather intervened, delaying the launch one more day—and leaving Webb competing with Santa’s sleigh for airspace. “Nothing is routine with Webb,” NASA science chief Thomas Zurbuchen said at a briefing last week.
Webb’s ambitious science goals required numerous technological firsts in its design, such as a folding mirror made of 18 hexagonal gold-plated segments, and instruments chilled to just 7° above absolute zero (-266° C). That complexity led to schedule slips totaling 10 years and a cost that ballooned from $2 billion to about five times as much.
It also led to a telescope that, to a degree, must assemble itself in space—a process fraught with risks. Two hours after launch, a high-gain antenna is expected to sprout from the craft to speed communications; 12 hours in, Webb will make its first course correction burn, followed by another after 2.5 days.
So far, so simple. But on day 3, it is the turn of the sunshield. The parasol, currently folded up against the mirror, will drop down to form a platform below it. Two telescopic booms will stretch out and separate the sunshield’s five plastic layers, each no thicker than a human hair, creating a thermal barrier that keeps the shaded side at -234°C—cool enough to avoid interference with the infrared instruments. That cooling takes time, however: The telescope and instruments won’t reach their operating temperature until 3 weeks after arrival at L2. While that chill is enough for three of the sensors, the mid-infrared instrument must be actively cooled to 7° above absolute zero, which takes a further 6 weeks.
With the sunshield deployed, week two is when the telescope comes into play. First the tripod holding the secondary mirror in front of the main mirror unfolds, then the two wings of the main mirror, folded back for launch, swing into place. At a prelaunch briefing, ESA Director of Science Günther Hasinger said it was like “a pupating butterfly unfurling its golden wings.” Once at L2 and fully cooled, operators must make sure the 18 mirror segments form a single reflecting surface. Using the near-infrared camera as a sensor, they will measure any discrepancies. Tiny mechanical motors will adjust the segment positions and even their curvature until they are perfectly aligned and shaped to nanometer accuracy, a process that takes several months.
Finally, with the mirror ready, Webb will point at a selection of well-studied astronomical targets to test and calibrate the four instruments. Then, roughly 6 months after launch, the nearly 300 teams of astronomers who will use Webb in its first year will finally get to view the universe with space’s largest eye. As NASA Deputy Administrator Pam Melroy said at a briefing this week: “We’ve done everything we can to make Webb a success. Now we just have to make it happen.”
Source by www.science.org