Webb and Ariane 5: a tailor-made launch

The European launch vehicle will carry the new space telescope to its final destination. Tailor-made adaptations had to be made so that Ariane 5 could accommodate this unique passenger.

• The thrust: Ariane 5 must first enable the telescope to reach its orbit at the L2 Lagrangian point, 1.5 million kilometres from Earth. To do this, the upper stage will provide greater acceleration, to give sufficient impetus to reach the target orbit.

• The trajectory: some of the JWST’s equipment is sensitive to luminosity and to temperature variations. As a result, the launcher trajectory was adjusted to maintain the satellite’s constant orientation with respect to the Sun after separation of the fairing, thereby avoiding overheating.

• The fairing: JWST requires a much lower pressure level than on a conventional mission for its heat shield to withstand the shock of depressurisation during separation.  To address this issue, the solution adopted was to seal the edges of the sandwich panels that make up the fairing and modify the 28 vents located around the fairing. These will remain open throughout the flight thanks to a mechanical locking system and will continue to expel air.

• The launch time: the launch has been scheduled for around midday, with the sunlight falling on the launcher nose, so that when the telescope separates, the Sun is behind the launch vehicle.

• The size of the telescope: In its folded position, Webb stands at 10.66 meters tall and 4.5 meters wide, taking up 95% of the cap's total volume. Consequently, integrating the telescope with the launcher requires a delicate operation that involves a specific process and additional checks throughout the journey. 

The adjustments made enabled Ariane 5 to validate its qualification for this unique flight.

Before being deployed at Europe’s spaceport, the Webb telescope must meet stringent cleanliness standards, especially for its mirrors and the observatory’s instruments. Consequently, during the filling process, fuel technicians were also subjected to particle detection using UV light. See images below: