For nearly 100 days at NASA’s Johnson Space Center in Houston, the telescope sat inside Chamber A—an airless, pitch-black, unimaginably cold compartment that simulates the lethal conditions of the cosmos.
Temperatures throughout the chamber, regulated by NASA engineers, can go as low as minus 440 degrees Fahrenheit.
Within those otherworldly surroundings, the telescope and its instruments were put through their paces.
Says Eric Smith, Webb’s program director: “An incredible number of components had to come together and work in cryogenic temperatures.”
And Webb worked.
“The performance beat expectations,” says NASA. Cryogenics testing is over.
Now, with a rescheduled launch date, the telescope is set for liftoff sometime between March and June of 2019.
But Smith, a NASA scientist for nearly thirty years, remembers when Webb was scarcely more than a sketch.
“We started in the spring of 1996,” he says. “We drew it on a whiteboard.”
More than twenty years later, those crude whiteboard renditions have morphed into the most sophisticated space telescope ever.
Webb’s primary mirror is enormous—21 feet across, divided into 18 sections, and capable of collecting more than six times the light of the Hubble Space Telescope, its predecessor. Unfolded, the mirror shapes as a hexagon, like the cell of a honeycomb.
Factor in the mirror’s size with NASA’s upgraded technology and a superior observational spot in space, and Webb’s capabilities far surpass Hubble’s.
“It’s 100 times more powerful than Hubble,” says Smith.
One critical component is the sunshield, a celestial parasol to shade the electronics from the Sun.
Five layers of plastic essentially provide the protection. Each membrane, astoundingly slight, is comparable to the thickness of a single human hair.
“Very thin plastic, but extremely tough,” says John Mather, Webb’s senior project scientist.
But unfurling the sunshield, the size of a tennis court when fully opened, could be tricky in space.
“You’ve got a good part of an acre of plastic film that’s got to do the right thing,” says Mather, a NASA astrophysicist since 1974 and a winner of the 2006 Nobel Prize in Physics. “So naturally, we are rehearsing that a lot.”
Along with rehearsal, there’s redundancy. The telescope is not serviceable in space. One million miles from Earth is too far for a house call. And a list of what could go wrong—such a list literally exists—is scarily long: “It has probably a thousand entries,” Mather says. “That’s why, where we can, we have two of everything.”
Webb, which sees in infrared, will observe the first stars and galaxies to light up after the Big Bang. “We’re looking back about 13.7 billion years,” says Mather.
The telescope will also search for signs of life on exoplanets—specifically, by examining the chemical composition of their atmospheres.
Already, NASA has targeted a few exoplanets for Webb’s evaluation, including TRAPPIST-1d, discovered earlier this year, one of seven Earth-sized worlds in the TRAPPIST-1 system.
To astronomers, finding a substantial quantity of oxygen in an alien atmosphere qualifies as a holy grail. Oxygen doesn’t prove life is present, certainly. “But it’s a hint the planet might be alive,” says Mather.
Big discoveries from Webb are surely ahead, says NASA. But what those might be, nobody knows. Almost always, the most stunning revelations of science are unexpected.
“Some of the most exciting things Hubble did, nobody foresaw,” says Smith. “I’m sure the same is going to be true for Webb.”
Agrees Mather: “Very few discoveries in astronomy were predicted. But I think we’ll have all new textbooks.” The galaxy’s most common element, it seems, is not hydrogen, but surprise.