Engineers working at NASA’s James Webb Space Telescope have successfully folded and packaged its parasol for its next million-mile (about 1.5 million kilometers) journey, which begins later this year. The parasol, a diamond-shaped five-layer structure the size of a tennis court, was specially designed to fold around both sides of the telescope and fit within the confines of its launch vehicle, the Ariane 5 rocket. Now After the folding was completed at Northrop Grumman in Redondo Beach, California, the parasol will remain in this compact form until launch and the first few days the observatory will spend in space.
Designed to protect the telescope’s optics from any heat source that could interfere with your view, the hood 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 background light and heat from the Sun, Earth, and Moon. Thermal models show that the maximum temperature of the outermost layer is 383 Kelvin, or about 230 degrees Fahrenheit. Meanwhile, the other side of the sunshade will always face deep space, with the coldest layer having a modeled minimum temperature of 36 Kelvin, or roughly minus 394 degrees Fahrenheit.
Fully deployed, the telescope’s hood measures nearly 70 feet by 47 feet (21 meters by 14 meters). When stored inside the rocket for launch, the folded hood will pack into a highly confined area between other observatory structures to accommodate the limited space within the 18-foot (5.4-meter) diameter rocket fairing.
“There is nothing really analogous to what we are trying to accomplish with folding a tennis court-sized parasol, but it is similar to packing a parachute,” said Jeff Cheezum, principal engineer for parasol design at Northrop Grumman. “Just as a skydiver needs his parachute packaged correctly to open perfectly and successfully return to Earth, Webb needs his parasol to be perfectly stowed to ensure that it also opens perfectly and holds its shape, in order to successfully hold the telescope at the required operating temperature. “
The month-long process of folding the parasol began by laying the five layers as flat as possible. In its unfolded state, the sunshade resembles a multi-layered silver ship, so its inherently curved surfaces added a degree of complexity to this step. Subsequently, the layers were lifted vertically and supported by special support equipment so that they could be properly fastened for folding. Then, a team of technicians carefully folded each layer in a zigzag pattern to create accordion-shaped stacks of membranes on either 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 finesse of folding such thin layers. The folding process also had to take into account components such as the sunshade’s 90 different tension cables, which need to be stored in a specific way to ensure the sunshade unfolds smoothly.
With the successful completion of the sunshade folding, the engineering team has prepared the sunshade for complex deployment in space. The parasol will unfold at the end of the telescope’s first week in space after launch, extending to its full size and then separating and tensioning each of its five layers. Testing for this deployment and tension procedure was last completed on Earth in December 2020.
“Think backwards; we want the unfolded sunshade to achieve a specific shape for us to get the performance we need. The entire folding process was designed with that in mind. We have to neatly and carefully fold the same way every time, to ensuring deployment happens exactly the way we want it to, “said James Cooper, senior sun visor engineer at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
For example, one of the most intricate aspects of the folding process was aligning the membrane stacks. Each of the hood’s layers has hundreds of intentional holes, which are deliberately arranged to prevent light and heat from passing to the telescope’s optics when the hood is fully deployed. These holes must be aligned during folding so that Webb technicians can insert “pins” through the holes in each stack of membranes. The 107 “pins,” or membrane release devices, will help contain the layers for launch, but will release to deploy the hood once the telescope is in space.
“It’s a very methodical process that we use to make sure everything is lined up correctly,” said Marc Roth, Northrop Grumman mechanical engineering leader. “Our team has gone through multiple training cycles and we have implemented many lessons learned from the previous times we did this process, all culminating in this final fold of the sunshade.”
Over the next three months, engineers and technicians will finish storing and securing the packed sunshade. This process will involve installing the membrane release devices, rigging and securing all the sunshade cables, and storing the covers for the sunshade membranes. It will also include storing the two “arms” of the shade – the mid-boom assemblies – that will extend the shade horizontally outward during deployment, as well as storing the two paddle frames that hold the shade in place.
The observatory will also undergo a final mirror deployment before being shipped to its launch site in French Guiana, South America.
Webb’s engineering team continues to follow personal safety procedures in accordance with current guidelines from the Centers for Disease Control and Prevention and the Occupational Safety and Health Administration related to COVID-19, including the use of masks and the social distancing.
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