The $10bn James Webb Space Telescope (JWST), the most powerful space observatory ever built, and launched on December 25 after decades of waiting, is an engineering marvel which will help answer fundamental questions about the Universe, peering back in time 13 billion years. The liftoff marked only the beginning of the riskiest part of the mission. Months of work lie ahead after deployments to align the telescope mirrors and commission the instruments as they cool to their operating temperatures, a process that will take six months from launch.
JWST is currently cruising to its deep-space destination, a gravitationally stable spot 1.5mn km from our planet called the Sun-Earth Lagrange Point 2 (L2). The observatory will get there about 29 days after launch, slipping into orbit around L2 with a precise engine burn. While the sunshield and telescope deployments are among the riskiest phases of flight, Bill Ochs, JWST project manager at Nasa Goddard Space Flight Center, said he won’t relax after they’re done. “I won’t breathe a sigh of relief until we declare we’re operational 180 days after launch.” Procedures are ready for any number of potential issues during deployment, as he pointed out.
Most people are familiar with the Hubble, launched into orbit in 1990. This telescope has not only provided incredible insight to astronomers about the beginnings of our universe, but has also given us jaw-dropping images of planets, galaxies, nebulas and spectacular clusters of stars. JWST is bigger than Hubble, with new capabilities. For comparison, if Hubble is about the size of a school bus, JWST is about the size of a tennis court. Hubble’s mirror, which collects light from distant objects, is 2.4m in diameter. But JWST’s light-collecting ability is far superior, comprising 18 separate mirrors that will unfold once in orbit, for a total diameter of 6.5m.
There’s also a difference in the way in which both telescopes look at the universe. Hubble mainly sees the universe in visible or optical light, detectable by the human eye, though it can also operate in ultraviolet and near-infrared wavelengths. JWST, though, is optimised to see in the longer wavelengths of infrared, giving it much greater clarity and sensitivity and allowing to peer through dust clouds that might otherwise block the light from distant objects.
One of the most anticipated aspects of JWST is its ability to look at exoplanets. To date, approximately 4,800 exoplanets have been detected around stars, but we still don’t know a lot about them. JWST will completely open a new chapter on exoplanet atmospheres. In order to seek out the faint, heat signals from the early universe, JWST’s optics and instruments must be kept extremely cold, and that’s where the sunshield comes in. The five-layer structure will reflect sunlight and radiate heat extremely efficiently, allowing Webb to maintain its “cold side” at minus 223C, if all goes according to plan. The observatory’s sun-facing “hot side,” by contrast, will be around 110C.
The kite-shaped sunshield measures 69.5ft long by 46.5ft wide and hence the structure lifted off in a highly compact configuration and must now unfurl in space, in an incredibly complex process, involving many different delicate, time-consuming steps. To get an idea, JWST’s sunshield assembly includes 140 release mechanisms, approximately 70 hinge assemblies, eight deployment motors, bearings, springs, gears, about 400 pulleys and 90 cables totalling 1,312ft. All this just to keep the sunshield under control as it unfolds. Later, JWST’s primary and secondary mirrors are scheduled to be completely deployed by January 7 or so. Nasa officials and Webb team members have stressed, however, that these timelines are flexible. If everything goes well, regular science operations by JWST are expected to begin in late June or early July 2022.
