After opening its solar panels, the James Webb Space Telescope has just passed the Moon

UPDATE. The James Webb's golden, honeycombed mirror began rolling out on January 7, 2022. It's the largest ever opened in space.

Since its launch by the Ariane 5 rocket on Christmas Day, the James Webb Space Telescope has continued its flawless trajectory. On the night of December 27 or 28, 2021, it crossed the orbit of the Moon and is now nearly 500,000 km from Earth. As it progresses, the instrument unfolds and refines its trajectory, in as many decisive stages.

A mixture of hydrazine and nitrogen peroxide

The first, 33 minutes after its separation from the launcher, consisted in opening the 6 m long solar panels, for a power of 2000W. As soon as the deployment was completed, the operators on the ground noticed that the telescope's battery was filling up, proof that it is now equipped with an autonomous energy source.

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12:30 after launch, the telescope carried out a first trajectory correction, essential to avoid missing its positioning at the Lagrange point despite the remarkable boost given by the Ariane 5 rocket. The telescope could not turn around in order to brake, the launcher did not quite communicate to him the speed necessary to reach his destination. The JWST therefore started up its own reactor, the SCAT (Secondary Combustion Augmented Thrusters) operating with a mixture of hydrazine and nitrogen peroxide, in order to increase its speed and slightly correct its heading. This sequence lasted 65 minutes and went perfectly.

24 hours after launch, he deployed the 60 cm diameter high-gain antenna. It will be used to transmit 28.6 Gbytes (28 Gigabytes) of scientific data to Earth, twice a day. Here again everything went well and the operators were able to verify that the antenna was working correctly.

60 hours after the launch - that is to say on the night of Monday 27 to Tuesday 28 December -, a second trajectory correction took place. This time the ignition of the reactor lasted only 9 minutes and 27 seconds. The next step, which should take place in the next few hours, will be to start deploying the sun visor. This operation will itself take place in several sequences, as this 150 m² infrastructure is imposing and crucial for the telescope.

"Blanket"

"The sun visor is made up of 5 layers of metallic polymers which will reflect external radiation. They will be separated by a vacuum that conducts very little heat, explains Pierre Olivier Lagage, astrophysicist at the CEA in Orsay on the occasion of our file published in issue 898 of Sciences et Avenir. They will behave a bit like survival blankets that will keep the machine in the dark and cold of space." This is indeed an essential condition for infrared observation instruments to work. The "telescope of the century" still has a lot of suspense in store for us...