JWST head reveals why the advanced telescope’s sunshield was surprisingly challenging

In the ongoing interactions with Interesting Engineering (IE), Dr. Massimo Stiavelli, project lead at JWST talks about the successes and failures of preparing the largest telescope in the world for deployment.

He also talks about the challenges of testing on the backdrop was like, and the unique cameras used to take images of distant galaxies and celestial bodies.

What the older stars tell us

In an in-depth look into what the older stars which are visible to the JWST, tell us about the universe and how it began, Dr. Stiavelli had a notion that we had yet to be really challenged by what the JWST was recording.

"JWST is an infrared telescope, so it can look at more distant galaxies that are redshifted more into the infrared. Such objects would not be visible, or if visible, would not be easy to characterize by HST. I don't think our understanding is really challenged yet," said Dr. Stiavelli.

"Some of the results that are reported will need to be verified. It is good that we [can now] see a number of galaxies at redshift — greater than 10 galaxies [which are less than 500 million years old] because it guarantees a lot of future-interesting science for JWST."

The Chandra data

Recently, astronomical data has been combined across observatories, especially the Chandra observatory and JWST, producing exciting results about celestial bodies.

The combination of data sparked interest in perhaps conducting other exciting telescope combinations that could work together. Dr. Stiavelli was extremely encouraged about combining data from other telescope pairings on this eventuality.

"Multi-messenger astronomy is becoming a new powerful tool. A lot of projects are combining Hubble and JWST. The combination of the ALMA ground-based telescope with JWST is also powerful. I am sure we will see all possible combinations, depending on the scientific results," he said.

"I could easily imagine JWST becoming involved with following up a gravitational wave detection, for instance, if one such event appears particularly interesting."

The sunshield

One of the difficulties encountered during the JWST's construction was the sunshield, which is a massive triangular that resembles a giant slice of pie. Dr. Stiavelli noted that there were some concerns regarding unfolding the heavy material's layers.

The sunshield is made up of ultra-thin layers, 0.002 inches for the top shield, and 0.001 inches for the other 4. This caused some worry during deployment, as they could tear and leave the telescope unprotected in place from the direct light of the sun. It was impossible to test how the deployment would go in space, and in zero gravity.

One of the other considerations with the sunshield was the drastic shifts in temperatures it would face, from frigid to blasting hot.

Dr. Stiavelli pointed out that the module and mirrors were exposed to temperatures as low as 40K (kelvin, an astronomy unit of measurement), which equates to -388F or -233C, while the hot side is only a few feet away from the cold side and experiences temperatures as high as 230F. (110C). This calls for the sunshield to be capable of handling extreme temperature variations.

Everyone was worried about the sunshield deployment sequence because there was little they could do if it didn't go smoothly or if tears emerged in the cloth. Dr. Stiavelli indicated on this topic that the deployment was intended to be as simple as possible.

To deploy the sunshield, the JWST team simply removed the protective covers, unlocked the layers from the mechanisms that held them in place, and extended the two side arms. Following that, tension was applied.

The team's challenges concerning the sunshield were resolved through testing and retesting before launch, along with many computer simulations.

During the actual deployment, there was similar analysis and computer modeling to make certain the mechanisms that needed to be released in space, had actually been released.

Dr. Stiavelli said, "if we could imagine 5 tennis court-sized layers of aluminum foil, like that used for wrapping food in the kitchen, unfolding in space without tearing and getting entangled." That's the level of complexity.

Importance of Wide Field Camera 3

The Wide Field Camera 3, is the Hubble Space Telescope's primary camera. It was created by a group of scientists that utilized a variety of design ideas originally offered by Dr. Stiavelli for a camera that was never picked for the Hubble Space Telescope.

However, the designs demonstrate the extent to which the "box" concept worked on both the Hubble and James Webb Space Telescopes and significantly impacted the NiCam (Near-infrared Camera) used on the James Webb Telescope.

These instruments are camera's in the sense they capture images, but they are able to do this at great distances — hundreds of millions of light years into space.

Dr. Stiavelli was the deputy of a team that designed an earlier instrument for HST that was not selected.

A lot of the ideas for the Wide Field Camera 3 (WFC3) were derived from that concept. From the beginning, the primary proposer of that instrument (Dr. John Mackenty) and Dr. Stiavelli were involved in WFC3.

It is sometimes assumed that a single person was responsible for designing a certain telescope component, such as the camera on a space telescope.

However, HST's crucial component was designed by a large team working on various projects. These plans eventually led to the creation of the JWST's near-infrared cameras.

Neither HST nor JWST instruments use AI or IoT to decode images.

The lens on the WFC3 has two channels. The UV channel is fully reflective (so it uses mirrors). The IR channel has one element that is refractive (i.e., a lens) to correct for a Hubble spherical aberration.

One of the unique aspects of the space equipment is that it is the first telescope with a primary mirror that is deployed and adjusted in orbit.

JWST has generated a lot of curiosity, and IE anticipates continuing the discussions that will further educate us about this very distinctive piece of space technology in the future.