sci21010 — Announcement

Webb Thanks Ariane

29 December 2021

-By Daniel de Chambure, Maurice Te Plate, Antonella Nota & Bethany Downer-

As watched from around the world with excitement, a very major milestone for this mission has just been successfully completed: Europe’s Ariane 5 delivered Webb into the first phase of its planned trajectory, with a launch mass of about 6200 kg, toward its final position orbiting the L2 Lagrange point, which will be reached in 4 weeks time.  

As we all held our collective breath, lift-off took place on December 25, 2021 at 13:20 CET from Europe’s Spaceport in Kourou, French Guiana, for a flight lasting about 27 minutes before spacecraft separation. About seven seconds after the ignition of the main-stage cryogenic engine, the two solid propellant boosters were ignited, enabling liftoff. The launcher first climbed vertically for about 13 seconds, and then rotated towards the east. The solid boosters were jettisoned 2 minutes and 14 seconds after liftoff. It was an impressive sight, and a remarkably smooth launch, as we have come to expect from the workhorse Ariane 5.

The fairing that was protecting Webb from acoustic, thermal and aerodynamic stresses during the ascent, was jettisoned 3 minutes and 19 seconds after liftoff. In order to protect Webb’s delicate thermal sunshield blankets, the fairing had been modified to minimise the shock of depressurisation at separation. Updated venting ports allowed the pressure inside the fairing to properly equalise prior to opening. As predicted, the recorded residual pressure was well below the requirement.

Once the atmospheric part of the flight was completed, Ariane’s onboard computers optimised the trajectory in real time, and brought the launcher to the intermediate orbit targeted at the end of the main stage propulsion phase, at 8 minutes and 35 seconds after launch. Ten seconds later, the HM7B engine of the cryogenic upper stage, with Webb still on top, was ignited and operated for 16 minutes. After engine shut-down, the upper stage underwent a number of positioning manoeuvres using its attitude control system, in order to separate JWST at the required attitude.

After separation, the upper stage underwent a delicate series of contamination and collision avoidance manoeuvres, making sure that its thruster plumes did not impinge on Webb and its precious optics.

Finally, an End-of-life Manoeuvre was performed to avoid potential long term collision risks with Webb.

As Webb starts its amazing journey to explore the Universe, the first step is now completed. Webb is on its way!

Please follow the new ESA/Hubble website for updates and new outreach products over the coming months!


Antonella Nota
ESA/HST & ESA/JWST Project Scientist
STScI Baltimore, USA

About the Announcement



Webb Liftoff on Ariane 5
Webb Liftoff on Ariane 5

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