By: Ángela Posada-Swafford – Science Writer
Photos: NASA, Northrop Grumman
Standing in front of the James Webb Space Telescope (JWST) in the visitor center of NASA’s Goddard Space Flight Center was an unforgettable experience. On that occasion, some five years before the telescope’s wondrous launch on December 25, 2021, the device was being assembled on its giant frame and the last of the 18 hexagonal segments in its primary mirror was being positioned.
I remember witnessing this remarkable scene in silence. The cavernous, sterile hangar struck me as an altar to advanced science, where dozens of technicians, wrapped head to toe in white slick overalls meant to repel dust, bustled about like priests tending to a machine.
In the middle of it all, the enormous golden eye gazed arrogantly down from atop its pedestal. It was as if its pupil (21 feet 4 inches wide) knew it had to gather not just particles of star light, but the dreams and work of a generation of astronomers whose indefatigable efforts began with an idea in 1996 and culminated 26 years later in the successful launch from French Guiana.
Cocooned inside its protective capsule for one month after launch, the JWST journeyed nearly 1 million miles. On January 24, 2022, it arrived somewhere that is, in a way, nowhere: a point in space known as Lagrange Point 2 (L2), where the gravitational forces of the sun and the Earth are roughly equal, allowing a spacecraft to circle L2 as if it were orbiting a planet.
As described in NASA news releases, entering the L2 orbit was a delicate exercise. The spacecraft had to fire its main engine for 297 seconds, altering its speed by 3.6 mph. The JWST will need to periodically fire its thrusters to make minor course corrections to remain in its assigned orbit. Since the telescope has a full tank of fuel for maneuvering, it is estimated that it can operate for at least 10 years. In contrast, the Hubble, which does not need fuel since it stays in Earth’s orbit, has been operating for the past 32 years.
The JWST —named for the man who led NASA during the first years of the Apollo program— is the largest, most expensive, most complex, and most extraordinary telescope ever built: the primary mirror is nearly three times the diameter of the mirror on its venerable predecessor, the Hubble, and it is seven times more sensitive. And it is foldable! The three “panels” of the primary mirror must fold to fit inside the launch shroud of the rocket. Once in space, the mirror can return to its original configuration. This concept was really quite a bold suggestion to put to the engineers.
Now that the huge mirror (with a light-collection area of some 270 square feet) is deployed in space, each one of its segments will have to be controlled individually and with nanometric precision to make them function like a single, monolithic, perfectly-focused mirror. To achieve this, each hexagon is mounted on six actuators that control its orientation; one more in the center adjusts the curvature with a precision of 1/10,000 of the width of a hair.
Astronomers have high hopes of being able to cast their gaze farther afield, looking into the past for clues to the fundamental questions of how the universe works. With its ultra-sensitive cameras and spectrographs, the JWST is designed to seek out the earliest and most distant stars and galaxies, which appeared 13.7 billion years ago out of the smoke left by the big bang, which occurred some 13.8 billion years ago. In other words, the goal is for scientists to catch a glimpse of the infancy of the universe as we know it, to watch it crawl and take its first steps, as it were.
Astronomers note that studying the heat of these young stars and galaxies could also provide important clues about the formation of the super massive black holes that squat at the centers of galaxies. Further, the new instruments will make it possible to analyze the chemical signals in the atmospheres of distant planets in other solar systems and —who knows?— perhaps even detect signs of life.
The JWST is optimized for infrared wavelengths because visible light from the most distant objects stretches so much —owing to the expansion of the universe— that it has become part of that portion of the electromagnetic spectrum by the time it reaches us. Many chemical signals in exoplanetary atmospheres are also revealed in the longitude of infrared waves, which are blocked by Earth’s atmosphere. The new telescope’s mirrors are coated with an extremely thin film of gold to improve the reflection of infrared light.
The JWST is expected to be an incredible boon to the global scientific community. When NASA selected Northrop Grumman as the prime contractor in 2002, mission directors estimated that the telescope would cost between 1 billion and 3.5 billion dollars and would launch in 2010. Overly-optimistic timeline projections, occasional development accidents, and haphazard cost reporting dragged the timeline out to 2021, and inflated the cost to 10 billion dollars. Keeping the project alive meant killing off other NASA science projects, but it had to be done.
The challenges have been daunting, sometimes bordering on the absurd. The first challenge was heat: to prevent the infrared glow produced by the telescope itself from overwhelming faint astronomic signals, the telescope needs to operate at minus 370 °F, which required completely new materials and designs.
The sunshield, for example, consists of five layers, each of a unique composite material of a specific size and thickness, with special seams and reinforcements to limit meteorite damage.
The backplane support frame is a technological marvel. It had to be absolutely rigid, but light enough to keep the weight of the entire space observatory under 6 tons, which is light in comparison with mammoth terrestrial telescopes. Beryllium, a strong, yet cotton-weight metal that behaves predictably in both extreme heat and cold, was used to keep the weight of the mirrors down.
The components of the telescope were subjected to a series of byzantine punishments and tortures that included being put in what looks like a giant pressure cooker.
They then spent days at -418 °F, were bathed in infrared light, shaken vigorously, and bombarded with vibrations of 150 decibels emitted by monstrous loudspeakers; this final test is fittingly named the Severe Sound Test.
The tests paid off, since they permitted the observatory to withstand the rigors of the launch with the resilience of an Olympic athlete. Now that the telescope is in position, there is still a long way to go before we begin to receive the dazzling images of the cosmos that scientists are awaiting with bated breath. Over the next four months, mission engineers will meticulously adjust and test the telescope to prepare the spacecraft for its mission of observing the universe for the course of its useful life.
Now we wait.