NASA has completed a milestone test of the James Webb Space Telescope’s (JWST) sunshield, which will protect the flagship observatory from the Sun’s radiation as it unravels the secrets of the cosmos. The telescope has fallen foul of a series of delays and budget overruns, and is currently expected to launch no earlier than March 30, 2021.
The launch and subsequent deployment of the JWST is spectacularly complex. Even by the high standards of space exploration, it's a high-risk endeavor. In order to fit inside the fairing of its Ariane 5 launch vehicle, the massive structure will be folded like a piece of origami art. Upon reaching orbit, a tense period will follow as the telescope methodically unfurls.
This complex process will start as the JWST deploys the solar array, that will provide it with power over the course of the mission. Once out past the orbit of the Moon, Webb deploys its sunshield pallets, and extends the tower that separates the telescope structure from the protective element.
The sunshield membrane launch restraints are then released and pulled taught as the hexagonal structure gradually takes shape. Finally, the telescope’s magnificent golden mirrors slide into place.
If all goes to plan, the operational JWST will be positioned roughly a million miles away, at a fixed orbital point relative to the Sun and Earth known as the second Lagrange point. From this lofty perch, the next-generation observatory has the potential to make detailed observations that could profoundly alter our understanding of the cosmos. However, the success of the telescope depends entirely on the performance of its sunshield.
Fully deployed, the sunshield is roughly the length of a tennis court. The structure is made up of five distinct layers of a polymer known as Kapton. The outer layers of the shield have also been treated with vapor-deposited aluminum to help reflect heat away from the observatory.
After launch, the underside of the sunshield will be orientated to constantly face the Sun, bathing the telescope structure in perennial shadow, and in so doing granting the JWST the ideal conditions to gaze into the far reaches of the universe. The two sunshield layers closest to the Sun - which can reach a maximum temperature of 383 Kelvin (230 °F/110 ) - are coated in treated silicon, which deflects ultraviolet radiation that would otherwise interfere with observations.
If the sunshield does its job, the ‘night side’ of the telescope will experience temperatures of around 36 Kelvin (-394°F) – an excellent temperature at which to operate the telescope’s sensitive infrared instruments.
The recently-completed test represents an important milestone on the road to launch.
“This was the first time that the sunshield has been deployed and tensioned by the spacecraft electronics and with the telescope present above it,” said James Cooper, JWST Sunshield Manager at NASA’s Goddard Space Flight Center in Maryland. “The deployment is visually stunning as a result, and it was challenging to accomplish."
During an earlier test the sunshield had been damaged during deployment, suffering a number of tears that, along with other issues had delayed progress towards launch.
In the latest test deployment, engineers observed as the vast silver structure moved into place. A zero gravity environment was simulated during the event using pulleys and weights. The tension of each layer was carefully measured. Thankfully, the test went to plan, revealing that the shield had successfully weathered an earlier barrage of tests, and emerged fully functional on the other side.
The team are now busy repacking the sunshield before carrying out further electrical and mechanical testing. The JWST will then undergo one further simulated deployment prior to its much anticipated and desperately overdue launch.
Source: NASA