The five layers of the sunshield are incredibly delicate. Each plastic-like sheet has the same thickness as a human hair and had to be stretched across a tennis-court-sized area. All of this had to be done in microgravity, an environment that could not be simulated in ground tests.

"It was the first time we deployed this system in zero-g, and we nailed it," said Alphonso Stewart, Webb deployment systems lead. "It's a really good testament to the work done by the teams."

So much could have gone wrong. During tests as recently as 2018, the sunshield layers were snagging during ground-based tests. It's not difficult to understand why. According to NASA, the unfolding and tensioning of the sunshield involved 139 of the telescope's 178 release mechanisms, 70 hinge assemblies, eight deployment motors, some 400 pulleys, and 90 individual cables totaling more than 400 meters in length.

By getting through the sunshield deployment process, therefore, NASA has surmounted the most complex aspect of unpacking the telescope in space and setting it up for operations.

"The sunshield deployment certainly was the most complex in terms of moving parts having to all work in harmony, and systems that were interrelated with one another," said James Cooper, the Webb telescope's sunshield manager. "The stuff that’s left from a deployment point of view is more conventional, such as hinges and motors."