Tracing the Big Ideas that Led to Webb

At the end of large engineering projects, the design team is typically asked to develop a document, in some cases called a Theory of Operations. This document is meant to describe the design decisions, why they were made, and how they were implemented. The document intends to inform future engineers about why a system operates the way it does so they can assess if any modifications or improvements can be made. It also allows the design engineers to reflect on their work as a whole, sometimes in a new light. Recently, some original members of the design team of the James Webb Space Telescope decided to take their shot at a brief version of such a document, releasing a paper that describes the design history of what is now considered to be one of the crowning jewels of humanity’s space telescope fleet.

Pierre Bely, the (now retired) Chief Engineer for the Space Telescope and Science Institute (STScI), led the paper’s writing. He originally started conceptualizing the idea of a Hubble success back in the 1980s. He was prompted to do so by Riccardo Giacconi, the then-head of the STScI, who, given his experience on other satellites like Chandra and Einstein, knew how long it would take to develop a successor to Hubble. 

Hubble itself, the doyenne of Space Telescopes that served as the workhorse of astronomers for decades, wasn’t eventually launched when Bely was tasked with coming up with plans for a successor. It had taken almost 30 years of lobbying, building, and testing to launch Hubble in 1990, with an additional three years of extensive rework to repair it once it was in orbit. Hubble itself only had a 14-year mission lifetime, so even if its successor had started work before Hubble launched, it wouldn’t be ready to launch before its original mission ended.

Budget constraints at STScI proved an initial challenge. The Institute had the staff to operate Hubble but not to design a completely new instrument from scratch. But, Bely did find some time in his role as Chief Engineer to develop some concepts. Preliminary design requirements were hazy, but the consensus between the originators of the idea that became JWST was that it should be able to see into the infrared, which was beyond Hubble’s capabilities. It was also planned with a 10-m mirror, which was intended to match several ground-based telescopes in the design phase.

Fortunately, NASA’s Advanced Concepts Office had already done preliminary work on several designs for a next-generation space telescope. The Very Large Space Telescope (VLST) kept the traditional name of NASA’s telescopes but was designed to be assembled in space by astronauts using the space shuttle. It was essentially just a version of Hubble with a bigger mirror.

The Golay-9 concept was a bit more out-of-the-box. It consisted of nine 1.7m telescopes that would work in concert with one another. However, it was again designed to be assembled by astronauts and placed in LEO.

Another concept was the Large Deployable Reflector, which was 20m in diameter with segmented mirrors. It would need a significant amount of cryogenics to stay cool as it orbited in LEO close to the space station – mainly ease assembly by astronauts and resupply of cryogenics.

Bely and Francois Roddier, an optics specialist, considered those ideas when designing an original 10m Hubble successor that looks almost nothing like the final form of the satellite. Initially proposed in 1986, it had an all-encompassing shield that was supposed to protect it from the light and heat of the nearby Earth while still being able to fit in the fairing of a modified Energia rocket designed by the then-Soviet Union.

During this time, the project took on a new name—the Next Generation Space Telescope, which it would be known by until it was renamed JWST in 2002. But before that, it had several more preliminary design iterations, including a “Detour via the Moon.” 

A space telescope doesn’t necessarily have to be free-floating in space – it can also be located on another heavenly body. That was the basis for an idea initially to coincide with President George H. W. Bush’s Space Exploration Initiative to return to the Moon in the 1990s. To match this design, a version of the NGST that housed a 16m mirror on the surface of the Moon that looked more like a traditional Earth-bound telescope than a free-floating space one. However, that idea died with the SEI as it became clear a few years into Bush’s tenure that NASA would not return to the Moon anytime soon – and still hasn’t.

During the late 1980s and early 1990s, many workshops were held to discuss different trade-offs in the design of the NGST. These changed to a more formal structure in 1995, almost 5 years after Hubble had launched, at a workshop to define the design goals of the new Hubble successor that was called by Edward Weiler, NASA’s Chief Scientist for Hubble. That workshop kicked off two years of a study designed to result in a fully formed idea for a space telescope – and is what the modern version of JWST is based on today.

At the end of the study, the general outline of the space telescope was clear, with a sun shield facing the Sun and allowing radiative cooling on the other side while keeping a reasonable temperature for some operational electronics. It would also be located at the Earth-Sun L2 Lagrange point rather than on the Moon or in orbit around Earth. This had the advantage of being far enough away from Earth and the Moon that it no longer had to be completely enclosed as earlier concepts had been, giving it a much wider field of view.

This version of JWST, known as the “Yardstick,” focused heavily on the design of the optical system, with an 8 m mirror originally proposed. It utilized beryllium due to its advantages for cryogenics on space telescopes, including its high thermal conductivity. It was designed to fit in an Atlast II fairing and be fully expanded after launch.

Even at this early stage in the project, cost was already a consideration, and JWST ran notoriously over budget during its development and testing cycle. However, at the time, the expected budget seemed in line with comparable missions like Hubble. NASA designed to move forward with a concept phase study and asked three aerospace companies to present their NGST ideas at an STScI meeting. That meeting resulted in a report in the summer of 1997 that specified three very different ideas from TRW, Ball Aerospace, and Lockheed Martin.

NASA decided to move forward with the TRW and Ball concepts, though Lockheed continued developing its own project in an effort to win back the business. After a while, TRW and Ball decided to combine their forces into a single mission study. Eventually, in 2001, Northrup Grumman bought TRW, and the division that managed the NGST project changed its name to Northrup Grumman Space Technology (NGST). NASA granted them the right to take the lead contractor role on the JWST.

Budget constraints further limited the scope of the mirror down to 6 meters from the planned 8, but at this point, the overall design seemed pretty much in line with what is currently floating in space today. Twenty years later, after much design refinement, manufacturing, and testing, it was successfully launched, and despite being blasted by micrometeorites (which admittedly was always part of the planned design), it has been providing us with fascinating pictures from every corner of space. With this paper, some of the original team members can reflect on their contributions to this marvel of space technology and be proud. In the end, all their efforts seem to have been worth it.

Learn More:
Bely et al – Genesis of the James Webb Space Telescope architecture: The designers’ story
UT – How Webb Stays in Focus
UT – Hubble and Webb are the Dream Team. Don’t Break Them Up
UT – The JWST is Re-Writing Astronomy Textbooks

Lead Image:
Artist’s view of a 16-meter telescope on the Moon, proposed by Bely. Telescope pointing made use of a hexapod with linear actuators. During the lunar day, a shield was to be rolled over the telescope to protect it from heat coming from the Sun
Credit – P. Y. Bely / D. Berry / STSCI

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