First light ...

The evolution of infrared astronomy, from Spitzer to WISE to JWST. Image credit: Andras Gaspar.

It's just the beginning, in a good way, in terms of viewing the universe in a totally new way. :)

The astronomers and engineers actually seem astounded how good JWST’s resolution is turning out to be. You may find that surprising. I mean, don’t they do tests on the ground to know the capabilities of telescopes before they launch? Yes, but ground tests don’t always tell the whole story, as Marshall Perrin, deputy project scientist for Webb at the Space Telescope Science Institute explained on Twitter.

“Yes, we had tested the whole optical train in cryo in Houston – but that didn’t actually tell us the ultimate performance,” he wrote. “Not fully. In many ways, the ground test environment was challenging and different from space.”

Perrin explains how gravity plays a role, in that JWST’s mirrors are designed to have a certain shape in Zero-g, but in all ground tests they were inevitably deformed by gravity, requiring numerical models to compensate.

Then, there’s no way to test on the ground how the telescope might work in Zero-g, as far as stability or if there will be any vibrations from the spacecraft. And while the ground test at Johnson Space Center’s thermal vacuum chamber could match the temperatures JWST would experience in space, Perrin said certain effects in the test chamber induced optical instabilities.

“A performance prediction must be not just a handwave or a wish, it has to be based in quantitative numerical models and budgets including assessing risks and uncertainties,” he wrote.

First light ... beginning in July. :)

First light of WISPR on the Parker Solar Probe, September 2018