Ariane 5 launches JWST – Europe's venerable rocket's greatest achievement

(25 Dec 2021) Rocket: Ariane 5; Payload: James Webb Space Telescope (JWST); Date: 25 December 2021, 1220 UTC; Launch site: Kourou, French Guiana. The rocket, operated by Arianespace on behalf of the European Space Agency (ESA), successfully injected NASA's Webb telescope into its transfer orbit towards its final position at the second Lagrange point (L2).

The space telescope, the most ambitious one ever sent into space, has now embarked on a voyage lasting 29 days to reach its destination.

Approximately 30 minutes after launch, Webb unfolded its solar array, and mission managers confirmed that the solar array was providing power to the observatory.

On the third day, the heat shield will begin to deploy. On the eleventh day, the secondary mirror will begin positioning. Between the 13th and 14th day, the primary mirror, comprising 18 hexagonal segments and measuring 6.5 meters in diameter, will be assembled. The telescope is slated to arrive at its final destination, 1.5 million kilometers from Earth, approximately 29 days after launch.

At the end of its six-month commissioning phase, Webb will deliver its first images. The space telescope carries four state-of-the-art science instruments with highly sensitive infrared detectors of unprecedented resolution. It will study infrared light from celestial objects with much greater clarity than ever before.

The space agencies of the United States (NASA), Europe (ESA) and Canada (CSA) teamed up to develop this telescope. Europe played an important role in this mission, with ESA providing the launch onboard Ariane 5, as well as the NIRSpec spectrometer built by Airbus. The astrophysics department of the CEA (French Alternative Energies and Atomic Energy Commission) and the Paris Observatory designed the MIRI camera.

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"There are just five more Ariane 5 launches scheduled before this legendary launcher bows out," said André-Hubert Roussel, CEO of ArianeGroup. But this was by no means a standard launch. Despite approaching the end of its life cycle, it probably was the rocket's most important launch ever. [Okay, delete "probably". – Ed.]

Engineers from ArianeGroup, Arianespace and their European industrial partners developed specific solutions for this mission to ensure compatibility between Ariane 5 and its passenger.

A special adapter for the satellite was designed and built in compliance with the available space under the fairing: the telescope measures 10.5 meters high and nearly 4.5 meters wide under the fairing, versus 21 × 14 meters once deployed.

The fairing underwent a special cleaning to ensure that no dust could come in contact with the telescope and its essential mirrors.

Pistons were placed near the purge vents in the fairing to force their opening and reduce as much as possible any pressure differential between the inside of the fairing where the telescope is located and the vacuum of space;

To protect the telescope's fragile components from any undesirable thermal effects, the flight software has been set up so that Ariane 5 performed a specific roll manoeuvre to control its exposure to the Sun once the fairing was jettisoned.

Following the separation of the telescope from the upper stage of the launcher, in order to avoid any risk of possible collision between the two, a specific manoeuvre was carried out to move the stage away after the end of its propulsion phase using its propellants and residual gases.

Reference: Arianespace PR, NASA PR, ESA PR

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