The first days of the James Webb Telescope in space, a journey without false notes

Before it can study the first stars and galaxies or characterize nearby exoplanets, the James Webb Telescope will first have to survive its launch. There will follow a long sequence of deployment in deep space before joining its observation post: the Lagrange point L2.

A few weeks ago, the engineering teams closed the program of “long-term tests” at the Northrop Grumman facilities to ensure that the observatory can go through the launch phase without problems. The teams are now working hard to prepare for his trip to Guyana during which he will cross the Panama Canal. NASA recently announced that its launch is now scheduled for the December 18.

The JWT is arguably the most advanced space telescope ever designed and built. The infrared gaze of the spacecraft, just like that of Spitzer before him, will be powerful enough to pierce the densest cosmic dust clouds. Behind these veils of smoke, stellar nurseries and other embryonic protoplanets will be revealed before our eyes, to the delight of astrophysicists. This gaze will also be sensitive enough to capture the weakest photons emitted by the first stars and galaxies to form after the big bang.

In short, the James Webb Telescope has the power to rewrite our cosmic history. Obviously, this assumes that everything goes as planned.

A journey over 1.5 million kilometers from Earth

Assuming it takes off on the morning of December 18, firmly seated in the fairing of its Ariane 5 rocket, the James Webb Telescope will take an easterly course over the Atlantic Ocean. Once he has traveled approximately 10,400 kilometers, Webb will detach from the second stage of his launcher. From then on, the most trying part of his journey will only begin.

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Before starting its work, the observatory of 10 billion dollars will indeed have to position itself at the point of Lagrange 2, or L2, more than 1.5 million kilometers from Earth. The gravitational tugs of the Earth and the sun balance in it to create a perfect long-term parking space for this type of observatory.

In this image, engineers use dry ice to clean the telescope’s large mirrors without scratching them at NASA’s Goddard Space Flight Center in Greenbelt, Md. Credit: Chris Gunn / NASA

Just moments after separating from its rocket, the telescope’s solar power array will begin to deploy to provide it with electricity. Of course, the success of this operation will be essential. About twelve hours after launch, the spacecraft’s thrusters will then fire to correct its trajectory.

From the third day, the JWT will then begin to deploy its sun visor, one of the most essential pieces of the mission. Imagine a stack of five polyimide “sheets” the size of tennis courts. Its purpose will be to prevent sunlight from reaching the telescope’s infrared sensors. To probe the depths of the universe, the latter must indeed operate at extremely low temperatures. To open this lens hood, approximately 150 triggers will need to fire properly in three days. These operations will involve around 7,000 parts.

james webb telescope
In this photo, technicians carefully inspect the telescope’s sunshade before deployment tests begin. Credits: Credits: NASA / Chris Gunn

Music without false notes

After six days of flight, the telescope’s secondary mirror, placed at the end of three long arms, will then snap into place. The next day, place in the 6.5 m primary mirror, a collection of eighteen gold-plated hexagonal segments cut with beryllium. Tiny actuators will push or pull each of these segments to align them to the nearest micrometer. Again, everything will have to work properly at the risk of dropping the mission.

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Finally, a month after launch, the JWT should finally reach its Lagrange Point, concluding one of the most daring and risky space flights ever attempted for an observatory. “It’s like an orchestral concert involving hundreds of people all playing different instruments“, Underlines Heidi Hammel, vice-president of the Association of Universities for Research in Astronomy, to Scientific American. “All the instruments should be ready and everyone should have practiced their part. And then we play the music“.

And this music must not have any wrong notes.

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