Inside a very big and very clean room at NASA’s Goddard Space Flight Center in Greenbelt, Md., nearly 30 workers dressed in white protective suits, goggles and blue booties cluster around the parts of a time machine.
These parts — gold-covered mirrors, tennis-court-size sun shields, delicate infrared cameras — are slowly being put together to become the James Webb Space Telescope.
Astronomers are hoping that the Webb will be able to collect light that is very far away from us and is moving still farther away. The universe has been expanding ever since the big bang got it started, but scientists reckon that if the telescope is powerful enough, they just might be able to see the birth of the first galaxies, some 13.5 billion years ago.
“This is similar to archaeology,” says Harvard astrophysicist Avi Loeb, who helped plan Webb’s science mission. “We are digging deep into the universe. But as the sources of light become fainter and farther away, you need a big telescope like the James Webb.”
Named for a former NASA director, the 21-foot-diameter Webb telescope will be 100 times as powerful as the Hubble Space Telescope, which was launched in 1990. Although Hubble wasn’t the first space telescope, its images of far-off objects have dazzled the public and led to breakthroughs in astrophysics, such as determining how fast the universe is expanding.
The Webb will be both bigger and located in a darker part of space than Hubble, enabling it to capture images from the faintest galaxies. Four infrared cameras will capture light that is moving away from us very quickly and that has shifted from the visible to the infrared spectrum, described as red-shifted. The advantage of using infrared light is that it is not blocked by clouds of gas and dust that may lie between the telescope and the light. Webb’s mirrors are covered in a thin layer of gold that absorbs blue light but reflects yellow and red visible light, and its cameras will detect infrared light and a small part of the visible spectrum. As objects move away from us, the wavelength of their light shifts from visible light to infrared light. That’s why the Webb’s infrared cameras will be able to see things that are both far away and moving away from us.
The cameras will also probe the atmospheres of planets that revolve around nearby stars, known as exoplanets, for the chemical signatures of life: water, oxygen and maybe even pollution from alien civilizations.
But before any of that dazzling science happens, there’s a lot of testing to do at Goddard, in the clean room and a nearby “cryo-chamber.”
Various tests will squeeze, shake, freeze and twist thousands of individual parts in an effort to make sure the spacecraft will survive blastoff from a spaceport in French Guyana and the cold environment of its orbiting position almost a million miles from Earth. By comparison, Hubble circles just 375 miles above our planet, depending on its orbit.
The project, which began in 2004, peaks in October 2018 when the telescope is launched on an Ariane 5 rocket from the European Space Agency. From now on, NASA engineers will find the pace picking up and deadlines getting even tighter.
As a young engineer in the early 1990s, Paul Geithner helped fix tiny bumps on Hubble’s glass mirror, a flaw discovered after the telescope was in space. Today, at 52, Geithner is making sure everything stays on track on the Webb assembly line at Goddard. He says testing of individual parts, including each of the 18 hexagonal mirrors, the backplane (which NASA describes as the spine holding the mirrors) and all the scientific instruments will be done by the end of this year. Beginning in early 2015, portions of the telescope and its spacecraft will be joined together with special glue and bolts.
“It’s not feasible to test it as a complete system,” said Geithner, NASA’s deputy project manager for technical issues. “So what that means is we have to test different pieces of it and convince ourselves through testing and analysis that when it’s put together, it will work.”
Back in the 1990s, NASA sent shuttle astronauts to repair Hubble’s mirror during a dangerous operation that required five days of spacewalks. But that’s not an option for the Webb: It will be parked too far away.
Geithner said everybody learned lessons from the Hubble mistake, which NASA blamed on a contractor. Now, the need for independent testing of the optical surfaces is clear. “You don’t use the same tools that you use to make the optics to tell you it is okay,” he said.
This year concluded several “cryo-tests” (testing reactions at extremely low temperatures), in which the boxlike structure containing the infrared cameras — called the Integrated Science Instrument Module, or ISIM — was lowered into a 60-foot-tall vacuum chamber at Goddard. The air was pumped out to simulate conditions in space, liquid nitrogen flooded an inner chamber and super-cooled helium was pumped into a smaller interior chamber. The four-camera package faced temperatures of 11 degrees Kelvin, which is minus-440 degrees Fahrenheit.
“The biggest stress is not the shaking from the [spacecraft] launch,” Geithner explained. “But the whole thing shrinks when it cools down, so there’s a lot of stress on the joints and it tries to tear itself apart.”
ISIM survived the cryo-test in July, was warmed up to room temperature and then removed from the cryo-chamber in October. It needs to be pulled apart, then put back together for final tests next year.
Measuring everything twice means the Webb telescope will function as it is supposed to, according to Geithner. But the extra testing is expensive.
Cost overruns and early delays nearly killed the project in 2011. Webb’s price tag soared from initial estimates of $1 billion in the late 1990s to the current figure of $8.8 billion. But Congress gave NASA a second chance, and the agency revised its construction budget to keep it within limits. Still, the Webb is NASA’s most expensive science mission. Some critics say it has sucked money away from other worthy projects, such as other missions around the solar system or monitoring environmental changes on Earth.
NASA chief Charles Bolden told Goddard workers in February that the project is on budget and on schedule, as long as Congress keeps the money flowing.
In the meantime, scientists such as Sara Seager of MIT, who studies exoplanets that revolve around distant stars, are imagining the discoveries that will occur once Webb directs its mirrors toward deep space. As a planet moves in front of a star, researchers hope to see the fingerprints of its atmosphere, which absorbs starlight. By analyzing the chemical spectrum of the light, they may be able to determine the atmosphere’s composition. Oxygen has a spectral fingerprint, as does methane, carbon dioxide and other gases found in atmospheres.
Seager and other scientists can point the Hubble at exoplanets, but they don’t get much time to use it because the entire telescope heats up and cools down as it passes from day to night.
Exoplanet hunters need to point the telescope for a long time at one place. The Webb telescope represents a big step forward, according to Seager, because it won’t be bothered by light or radiation from the sun and the Earth and therefore will be able to see more-distant objects. (A five-layer sun shield and distance from the Earth will protect the telescope.)
“Anytime you put something new in space, the astronomy world changes dramatically,” Seager said.
When NASA began planning the Webb telescope, exoplanets were just being discovered. The early ones were huge, Jupiter-size bodies that were too cold or too poisonous to harbor the conditions needed for life. Now, scientists have found more than 5,000 exoplanets, from big gas giants to smaller rocky worlds that lie within what’s called the “Goldilocks zone” — neither too close nor too far away from their star, meaning conditions are neither too hot nor too cold.
“These [space telescopes] take so long to build,” Seager said. “Originally we didn’t know about the richness of exoplanets, and we didn’t know they were so diverse. I see the James Webb as the tool for the second generation of exoplanet studies.”
As they wait for the Webb’s launch in four years, Seager and other planetary scientists are drawing up a list of star systems that could be candidates for the first studies.
Seager says she likes to remind people about the value of big, complex scientific projects, even if they cost a lot of money, take a long time to build and don’t have a concrete scientific payoff.
“As a nation, should we be building complicated things and pushing the limit of progress in technology? It’s a question I like to pose to people,” she said. “Should we just get by, or is it critical for our future to invest in complicated technologies? That usually makes them think for a while.”
Niiler is a freelance writer.
A tale of two telescopes
|Weight||24,500 pounds||14,300 pounds|
|Mirror diameter||8 feet||21 feet|
|Distance from Earth||375 miles||930,000 miles|
|Launch date||April 1990||October 2018|