NASA Successfully Deployed the Sunshield on the James Webb Space Telescope

The process took eight days to complete.
Ameya Paleja
The JWST with its sun shield deployed.NASA

Five thin-as-human-hair plastic sheets coated with reflective material that will protect the James Webb Space Telescope (JWST) have now been successfully deployed, the National Aeronautics and Space Agency (NASA) said in its press release

Ever since its launch on Christmas Day, space enthusiasts were eager to know if the sunshield on the JWST that is designed to protect the sensitive instruments on board would be deployed to perfection. To rightfully take the place of the mighty Hubble, the JWST has to overcome its 344 potential points of failure, and deploying the sunshield is a major achievement. 

As NASA detailed in its press release, together, the five thin plastic sheets will provide a Sun Protection Factor (SPF) of the order of 1 million. In energy terms, it will reduce 200 kilowatts of solar energy received by the telescope to just a fraction of a watt and help in keeping the temperature of the onboard instruments at 40 Kelvin or  380°F below zero (233°C below zero) so that they pick the faint infrared light from far beyond. 

As with all things with the JWST, the sunshield deployment was not an easy task. To begin with, at 70 feet (21.3 m), the shield is about the size of a full-sized tennis court and needed to be neatly folded and packed to fit inside the Ariane 5 rocket that launched the telescope into space. The deployment began three days after the launch and continued over a period of eight days. 

The sunscreen had to be first unfolded and then pulled taut. During this time, 139 of the 178 release mechanisms on the telescope were involved along with 70 hinge assemblies, eight deployment motors, about 400 pulleys, and 90 cables that were about a quarter of a mile (400 m) long, the press release said. 

The deployment was originally scheduled to take place over six days but NASA staff took a break on New Year weekend while some continued to make adjustments based on the data received from the spacecraft, The Verge reported.

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The solar arrays on the telescope were generating limited power but a rebalancing of the arrays seems to have fixed the issue. The motors being used to pull the shield taut were also running at higher temperatures than anticipated, so NASA engineers reoriented the spacecraft just enough to stop sunlight from hitting them, following which the motors pulled the sun shield into its position, The Verge said in its report. 

The deployment of the shield that will protect the spacecraft not only from the sun but also light and heat from the Earth and its moon marks the completion of up to 75 percent of the single point failures in the mission, The Verge reported. The deployment phase still has about five and half months to go, with the primary and secondary mirrors, alignment of the telescope's optics, and calibration of the instruments to be completed before the first image can be received. 

In the meantime the only solace is that the telescope was launched to perfection by the Ariane 5 rocket and its onboard fuel is sufficient to keep it going for ten years and more. 

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