What Has the James Webb Space Telescope Been Up To?

PVL MSc student Madeline Walters has been following the launch and deployment of the James Webb Space Telescope with bated breath. This observatory will be a boon not only to the astronomical community, but also to the planetary science community. Above: the telescope's alignment evaluation image catches not only the target star, but myriad faint galaxies in the background.

by Madeline Walters

Since my last post about the James Webb Space Telescope (JWST), the telescope has reached its observing point and made some initial observations. The Webb is currently in orbit around L2, the second sun-Earth Lagrange point which is a gravitationally stable point about 1.5 million kilometers away from us. Since its launch, the spacecraft has gone through a few metamorphoses in preparation for its eventual observations. From testing a key antenna, to deploying its sunshield, each movement and maneuver has been integral to the telescope’s success. After successfully deploying the structure that binds the Webb’s two halves together, there was enough room to begin unfurling the massive sunshield that protects the telescope from harsh radiation. 

Soon after the sunshield was fully unfolded, the Webb deployed its two sunshield mid-booms, which stretched the sunshield out to its full length. This process requires the membranes to stretch to their proper tension, taking up to two days to tighten the sunshield. "As photons of sunlight hit the large sunshield surface, they will exert pressure on the sunshield, and if not properly balanced, this solar pressure would cause rotations of the observatory that must be accommodated by its reaction wheels," writes NASA public affairs specialist Alise Fisher in a blog post on December 30 after the launch. "The aft momentum flap will sail on the pressure of these photons, balancing the sunshield and keeping the observatory steady." It is a lot of very intricate and detailed steps that are necessary for every step of the operation-and for good reason. Every part of the unfolding must work in order to get the Webb to start observing. 

The next crucial part of the mission was the mirrors. On January 5, the telescope deployed its secondary mirror, unfolding a series of booms that hold the mirror out in front of the main mirror. This secondary mirror allows light to be collected and focused into a beam, which is then pushed down through the center of the telescope to a third mirror and other smaller ‘fine-steering’ mirrors which allow light to be properly allocated into the scientific instruments. 

Several days after the secondary mirror was deployed, the main mirror’s side panels were deployed, gearing up for the alignment of all 18 individual mirrors that make up the entire main mirror. And if you don’t think the word ‘mirror’ has been said enough so far - the observatory team spent about ten days working to move each mirror segment out of their preliminary launch alignments, and a lot longer for more precise alignment after that. However, for an instrument that will bring us observations for perhaps up to 20 years, a few months of alignment is worth it. 

Now at its destination for its science mission, the Webb has woken up, turned its instruments on, and has looked out into space to provide us with its first images. Its first telescope alignment evaluation image, made to only focus on the bright star in the center for alignment evaluation, shows background stars and galaxies due to the telescope’s optical sensitivity. Although there are still many months left before the JWST delivers its first full view of the cosmos, the telescope has already gone through an incredible journey made possible by an incredibly patient group of engineers and scientists.