“Cool down” in space, NASA has deployed “shading” equipment for the Webb Telescope

On January 4th, the James Webb Space Telescope (JWST), the successor of the Hubble Telescope, completed a very important and complicated step in space-unfolding a huge sun visor. For NASA, this is an "incredible milestone."

Why is sun visor so important? Let's start with the mission of JWST.

After approximately 25 years of development, JWST was launched on December 25, 2021. Astronomers hope to use JWST to explore every stage of the history of the universe-from the interior of our solar system to the most distant observable galaxy in the early universe, and everything in between, to help humans understand the origin of the universe, the evolution of galaxies, and Our place in it.

▲ Fully unfolded JWST (art rendering). Picture from: NASA

In other words, we are expected to observe the early state of the visible universe today, and see the first galaxies formed only a few hundred million years after the Big Bang.

Observation in infrared spectroscopy is the key technology to achieve this goal, so JWST is equipped with high-sensitivity infrared electrical sensors, spectrometers, and so on. The temperature of the observation component must be kept below 40K (-233.15°C) in order to see the weak infrared light.

The sun visor plays a role in temperature control.

Otherwise, the signal of the observation target will be submerged in the infrared radiation from the telescope itself, the sun, the earth and the moon.

However, the telescope is too large to be launched directly into space in a complete form. It can only be deployed after launch, and the sun visor becomes part of the mission.

▲ The sun visor was tested on the ground before launch. Picture from: NASA

On December 28, three days after the launch, the JWST team began to deploy the sun visor remotely, and it was done at around 11:59 AM Eastern Standard Time on January 4th.

The sun visor consists of five layers of polyimide film coated with silicon and aluminum. Each layer is as thin as a hair. It protects the telescope from the light and heat of the sun, the earth and the moon, and cools it to the extremely low temperature required.

NASA pointed out that under the combined effect of the five layers of materials, the solar energy of more than 200 kilowatts can be reduced to a few tenths of a watt.

The complexity of unfolding the sun visor is embodied in that each joint must be executed perfectly before the sun visor can be opened. There are as many as 344 single points of failure in the entire JWST, and the sun visor contains a large part of them.

A single point of failure refers to a component in the system that will make the entire system inoperable once it fails. In other words, a single point of failure will cause an overall failure, which shows how tight the deployment of the sun visor is. The accidental tearing of the film during the 2018 test was also one of the factors that delayed the project.

▲ The sun visor was tested on the ground before launch. Picture from: NASA

The entire process involved 139 release mechanisms, 70 hinge assemblies, 8 deployment motors, approximately 400 pulleys, and 90 individual cables with a total length of approximately a quarter mile.

After unfolding, each layer of sun visors is 70 feet (approximately 21.34 meters) long and 47 feet (approximately 14.33 meters) wide, equivalent to the size of a tennis court. They are finally fully tensioned and fixed in place, similar to adjusting the sails.

The deployment of the sun visor took more than a week to complete, which was slightly longer than the original plan. During the period, there were minor problems with the solar array, sun visor motor and other equipment, but it finally succeeded. NASA stated that "some of the most exciting moments have passed, and 70% to 75% of single points of failure are officially completed."

After completing the sun visor, JWST still has a lot of work to do, including the deployment of the secondary and primary mirror wings, the alignment of the telescope optical system, and the calibration of scientific instruments. When everything is ready, JWST, which has spent a total of nearly tens of billions of dollars, will provide its first picture and begin to collect light from distant galaxies for humans.

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