James Webb Space Telescope

A long-awaited launch

The James Webb Space Telescope launched in December 2021 aboard an Ariane 5 rocket, after decades of development. It is a partnership of NASA, the European Space Agency, and the Canadian Space Agency.

Reaching its station

Rather than orbiting Earth like Hubble, Webb travelled to a region near the Sun–Earth L2 point, roughly 1.5 million kilometres away, where the Sun, Earth and Moon all lie in the same direction — so a single sunshield blocks all three and the optics can cool passively to around 40 kelvin.

Thirty days of single-point failures

The most demanding part of the mission was not launch but deployment. Webb was too large to fly assembled: the sunshield and the primary mirror both had to be folded into the fairing and unfolded during the month-long cruise to L2, through a sequence of hundreds of individual mechanical steps.

Because the destination is far beyond any servicing capability, essentially all of that sequence had no backup — a jammed hinge or an unreleased pin could have ended the mission with the observatory intact but unusable. The deployment completed without a failure, which is why the operations phase is discussed as much as the science.

Commissioning, and what the launch bought

Ariane 5 delivered an unusually precise trajectory, so Webb spent far less propellant than budgeted on correction burns. That surplus is what allows a projected operational life well beyond the mission's original requirement, since propellant for station-keeping at L2 is the limiting consumable rather than any wearing component.

The first science images were released in July 2022 after several months of mirror alignment and instrument commissioning — eighteen mirror segments phased until they behave as one 6.5-metre optic.

Mission and instrument

This entry covers the mission — its launch and operations. For the observatory itself, including how it sees in infrared, see the James Webb entry under Space Telescopes.