Engineers working on NASA’s James Webb Space Telescope have successfully assembled and packed its umbrella for its upcoming million-mile journey (approximately 1.5 million kilometers), which begins later this year. The sun protection – a five-layer diamond-shaped structure the size of a tennis court – is specially made to fold around two sides of the telescope and fit into the frame of its Ariane 5 launch rocket. Now that the overlap is complete at Northrop Grumman in Redondo Beach, California , the umbrella will remain in this compact shape until launch and the first few days the observatory will spend in space.
Designed to protect the telescope’s optics from any heat sources that could interfere with its vision, the umbrella is one of Webb’s most critical and complex components. Because the Webb is an infrared telescope, its mirrors and sensors need to be kept at extremely cold temperatures to detect weak thermal signals from distant objects in space.
In space, one side of the sunshine will always reflect the light and background heat of the Sun, Earth, and Moon. Thermal models show that the maximum temperature of the farthest layer is 383 Kelvin or about 230 degrees Fahrenheit. Meanwhile, the other side of the solar shield will always be facing deep space, with the coldest layer having a modeled minimum temperature of 36 Kelvin, or about minus 394 degrees Fahrenheit.
Fully installed, the telescope’s umbrella measures almost 70 feet by 47 feet (21 meters by 14 meters). When placed in the launch rocket, the folded umbrella will be packed into a very cramped space between the other structures of the observatory to accommodate the limited space within the 18-foot (5.4-meter) diameter rocket shell.
“Nothing is really analogous to what we’re trying to achieve by folding umbrellas the size of a tennis court, but it’s similar to packing a parachute,” said Jeff Cheezum, a leading solar shield design engineer at Northrop Grumman. “Just as a parachutist needs their parachute properly packaged to open perfectly and return to Earth successfully, Webb needs his sunshade to be perfectly tidied to ensure that it too opens and maintains its shape perfectly, to successfully hold the telescope at the required operating temperature. “
The one-month process of folding the sunflower began by placing five layers as flat as possible. In its arranged state, the umbrella resembles a multi-layered silver boat, so its inherently curved surfaces added a certain degree of complexity to this step. After that, the layers are lifted vertically and leaned on special support equipment so that they can be properly tied to the fold. A team of technicians then carefully folded each layer into a zigzag pattern to create piles of harmonic-like membranes on either side of the telescope.
The first layer of the sun shield is two thousandths of an inch thick (0.005 centimeters), while the other four layers are only a thousandth of an inch thick. The built-in challenge for this was the delicacy of folding such thin layers. The folding process also had to take into account parts such as 90 different parasol tension cables, which must be laid in a specific way to ensure that the parasol is distributed smoothly.
With the successful completion of the solar shield overlap, the engineering team prepared the umbrella for its complex deployment in space. The parasol will open at the end of the first week of the telescope in space after launch, stretching in full size, and then separating and tightening each of its five layers. Testing of this unwinding and tightening procedure was last completed on Earth in December 2020.
“Think about it backwards; we want the set umbrella to take on a certain shape to get the performance we need. The whole folding process is designed with that in mind. We have to fold it cleanly and carefully every time in the same way to ensure the unfolding happens right the way we want it, ”said James Cooper, a senior sun protection engineer at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
For example, one of the most complex aspects of the folding process involved the alignment of membrane deposits. Each of the layers of the sun shield has hundreds of intentional holes, which are intentionally placed so as to avoid the passage of light and heat to the optical elements of the telescope when the sun is fully set. These holes must be arranged during folding so that Webb technicians can insert “needles” through the holes in each membrane stack. 107 “pins” or membrane release devices will help retain the launch layers, but release to open the sunshade when the telescope is in space.
“It’s a very methodical process that we use to make sure everything is properly aligned,” said Marc Roth, head of mechanical engineering at Northrop Grumman. “Our team has gone through several training cycles, and we have implemented many lessons learned from previous times when we did this process, and it all culminated in this last set of sun shield.”
Over the next three months, engineers and technicians will complete the storage and securing of the packed umbrella. This procedure will include installing a membrane release device, installing and securing all sun protection cables, and storing sun protection membrane covers. It will also involve disposing of two “arms” of the sun shield – Mid-Boom assemblies – that will horizontally extend the umbrella outward during installation, as well as disposing of the two pallet structures that hold the umbrella in place.
The observatory will additionally undergo a final mirror installation before being shipped to its launch site in French Guiana, South America.
The Webb engineering team continues to follow personal safety procedures in accordance with the applicable guidelines of the Centers for Disease Control and Prevention and the COVID-19 guidelines, including wearing masks and social distancing.
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