Engineers working on NASA̵
The sun visor – a five-layer, diamond-shaped structure the size of a tennis court – was specially designed to fold around the two sides of the telescope and fit within the frame of its launch vehicle, the Ariane 5 rocket. Now that the folding has been completed at Northrop Grumman in Redondo Beach, California, the sunshade will remain in this compact shape through launch, and the first few days the observatory will spend in space.
The sun visor is designed to protect the telescope’s optics from any heat source that may interfere with its vision, and is one of Webb’s most critical and complex components. Because Webb is an infrared telescope, mirrors and sensors must be kept at extremely cold temperatures to detect weak heat signals from distant objects in the universe.
In space, one side of the sunshade will always reflect light and background heat from the sun, earth and moon. Thermal models show that the maximum temperature in the outermost layer is 383 Kelvin, or about 230 degrees Fahrenheit. Meanwhile, the other side of the sunshade will always face deep space, where the coldest layer has a modeled minimum temperature of 36 Kelvin or approx. minus 394 degrees Fahrenheit.
Fully deployed, the telescope’s sun visor measures nearly 70 feet by 47 feet (21 feet by 14 feet). When stored inside the rocket for launch, the folded sun visor will be packed in a very limited area between other structures in the observatory to accommodate the limited space inside the 18-foot (5.4-meter) rocket cover.
“There’s nothing really analogous to what we’re trying to achieve by folding a parachute in the size of a tennis court, but it’s like packing a parachute,” said Jeff Cheezum, a senior sunshade design engineer at Northrop Grumman. Just as a skydiver needs their parachute properly packed to open perfectly and successfully return to Earth, Webb needs its sunshade to be perfectly stored to ensure that it also opens perfectly and maintains its in order to successfully maintain the telescope at the required operating temperature. “
The month-long process of folding the sunshade began by laying the five layers as flat as possible. In its widespread state, the sunshade resembles a multilayer silver ship, so its inherently curved surfaces added a degree of complexity to this step. Afterwards, the layers were lifted vertically and encountered special support equipment so that they could be held firmly for folding. A team of technicians then carefully folded each layer in a zigzag pattern to create accordion-like stacks of membranes on each side of the telescope.
The first layer of the sunshade 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 delicacy of folding such thin layers. The folding process should also take into account components such as the sun visor’s 90 different voltage cables, which must be stored in a certain way to ensure that the sun visor runs smoothly.
With the successful completion of sunshade folding, the engineering team has prepared the sunshade for its complex use in space. The sunshade unfolds at the end of the telescope’s first week in space after launch, extending to its full size and separating and then spanning each of its five layers. Testing of this unfolding and tension procedure was completed for the last time on Earth in December 2020.
“Think about it backwards; we want the inserted sunshade to achieve a certain shape so we get the performance we need. The whole folding process was designed with that in mind. We need to fold clean and carefully in the same way every time. to ensure unfolding happens exactly the way we want it to, ”said James Cooper, lead sunscreen technician at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
For example, one of the most complicated aspects of the folding process involved adjusting the membrane stacks. Each of the layers of the sun visor 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 sun visor is fully used. These holes must be set up during folding so that Web technicians can insert “pins” through the holes in each membrane stack. The 107 “pins” or diaphragm release devices help limit the layers for launch, but are released to unfold the sun visor when the telescope is in space.
“It’s a very methodical process that we use to make sure everything is adjusted correctly,” said Marc Roth, mechanical engineer at Northrop Grumman. “Our team has been through several training cycles, and we’ve implemented a lot of experience from the previous times we’ve performed this process, all culminating in this last sunshade fold.”
Over the next three months, engineers and technicians will complete the stowage and securing of the packed sunshade. This process will involve installing membrane release devices, rigging and securing all sunshade cables, and storing covers for the sunshade membranes. It will also include storage of the sunshade’s two “arms” – Mid-Boom Assemblies – which will horizontally stretch the sunshade outwards during roll-out, as well as storage of the two pallet structures that hold the sunshade in place.
The observatory will also undergo a final mirror installation before being sent to its launch site in French Guiana, South America.
Sunshield layer fully integrated on NASA’s James Webb Space Telescope
Provided by NASA’s Goddard Space Flight Center
Citation: NASA’s Web Telescope Packs Its Sunshade for a Million Mile Trip (2021, April 7) Retrieved April 7, 2021 from https://phys.org/news/2021-04-nasa-webb-telescope-sunshield-million. html
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