NASA’s Web Telescope packs its sunscreen for a million-mile journey

Engineers working on NASA’s James Webb Space Telescope have successfully folded and packed its sunshade for its upcoming 1.5 million-kilometer journey, which begins later this year.

The sunshade – a five-layer, diamond-shaped structure as large as a tennis court – is specially designed to fold around the two sides of the telescope and fit within the limit of its launch vehicle, the Ariane 5 rocket. After the fold is completed at Northrop Grumman in Redondo Beach, California, the sunshade will remain in this compact form through launch and the first few days the astronaut will spend in space.

The awning is designed to protect the optics of the telescope from any heat sources that may obstruct the view, and is one of Webb’s most critical and complex components. Because Webb is an infrared telescope, its mirrors and sensors must be kept at extremely cold temperatures to detect faint heat signals from distant objects in the universe.

In space, one side of the sunshade will always reflect the light and heat of the sun, the earth and the moon. Thermal models show that the maximum temperature of the outer layer is 383 Kelvin, or about 230 degrees Fahrenheit. Meanwhile, the other side of the sunshade will always face the deep space, with the coldest layer a modeled minimum temperature of 36 Kelvin, or about minus 394 degrees Fahrenheit.

The sunshade of the telescope is fully deployed and measures nearly 70 feet by 47 feet (21 feet by 14 feet). When stored in the rocket for launch, the folded awning will be packed in a very limited area between other structures of the observatory to accommodate the limited space in the 18-foot (5.4-meter) missile cover.

“There’s nothing analogous to what we’re trying to achieve by folding a sunshade-sized sunshade, but it’s similar to packing a parachute,” said Jeff Cheezum, chief engineer for sunshade design at Northrop Grumman. , said. ‘Just as a parachutist must pack their parachute properly to open perfectly and to return to Earth successfully, Webb must have stored his parachute perfectly to ensure that it also opens perfectly and retains its shape around the telescope on the required operating temperature. “

The month-long process of folding the sunscreen began with laying the five layers as flat as possible. In its deployed state, the sunshade looks like a silver ship with more layers, so the curved surfaces added some complexity to this step. Thereafter, the layers were lifted vertically and rested on special support equipment so that it could be properly held for folding. A team of technicians then carefully fold each layer into a zigzag pattern to create accordion-like stacks of membranes on either side of the telescope.

The first layer of the sunscreen is two thousandths of an inch (0.005 centimeters) thick, while the other four layers are only one thousandth of an inch thick. For the team, a built-in challenge was the fun of folding such thin layers. The folding process also had to take into account components such as the sunshade’s 90 different voltage cables, which must be stored in a specific way to ensure that the sunshade functions smoothly.

With the successful completion of the folding of the awning, the engineering team prepared the awning for its intricate deployment in space. The sunshade unfolds at the end of the first week of the telescope in space after launch, extending to its full size and separating and spanning each of its five layers. The testing for this unfolding and teaming procedure was completed for the last time on earth in December 2020.

“Think back to that; we want the deployed sunscreen to take on a specific shape so that we get the performance we need. The whole folding process is designed with that in mind. We have to fold clean and careful every time to ensure the unfolding is happening exactly the way we want it, ”said James Cooper, chief sunscreen engineer at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

One of the most complicated aspects of the folding process, for example, was the setting up of the membrane stacks. Each layer of the sunshade has hundreds of intentional holes that are deliberately arranged to prevent light and heat from passing to the optical elements of the telescope when the sunshade is fully in use. These holes must be set up during folding so that Webb technicians can place ‘pins’ through the holes in each membrane stack. The 107 “pins”, or diaphragm release devices, will help limit the layers for launch, but leave it to fold open the sunshade once the telescope is in space.

“It’s a very methodical process that we use to make sure everything’s right,” said Marc Roth, head of mechanical engineering at Northrop Grumman. “Our team has gone through several training cycles and we have implemented many lessons from the previous times we did this process, all of which culminated in this last sunscreen fold.”

Over the next three months, engineers and technicians will store and secure the packed sunscreen. This process involves installing the membrane release devices, erecting and securing all the sunshade cables and storing covers for the sunshade membranes. This will also include storing the two “arms” of the sunshade – the Mid-Boom Assemblies – which will extend the sunshade horizontally during deployment, as well as storing the two pallet structures that hold the sunshade in place.

The observatory will also undergo a final mirror deployment before being sent to the launch site in French Guiana, South America.

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