SPACE: How we sharpened the James Webb telescope’s vision from a million kilometres away.

Hubble started its life seeing out of focus – its mirror had been ground precisely, but incorrectly. By looking at known stars and comparing the ideal and measured images (exactly like what optometrists do), it was possible to figure out a “prescription” for this optical error and design a lens to compensate.

The correction required seven astronauts to fly up on the Space Shuttle Endeavour in 1993 to install the new optics. Hubble orbits Earth just a few hundred kilometres above the surface, and can be reached by astronauts.

By contrast, Webb is roughly 1.5 million kilometres away – we can’t visit and service it, and need to be able to fix issues without changing any hardware.

This is where AMI comes in. This is the only Australian hardware on board, designed by astronomer Peter Tuthill.

It was put on Webb to diagnose and measure any blur in its images. Even nanometres of distortion in Webb’s 18 hexagonal primary mirrors and many internal surfaces will blur the images enough to hinder the study of planets or black holes, where sensitivity and resolution are key.

AMI filters the light with a carefully structured pattern of holes in a simple metal plate, to make it much easier to tell if there are any optical misalignments.

We wanted to use this mode to observe the birth places of planets, as well as material being sucked into black holes. But before any of this, AMI showed Webb wasn’t working entirely as hoped.

If you’re at all interested in the technical details behind the fix, there are tons of them at the link.