GREENBELT, Md. — The next great space telescope spread its golden wings this month.
Like the petals of a 20-foot sunflower seeking the light, the 18 hexagonal mirrors that comprise the heart of NASA’s James Webb Space Telescope were faced toward a glassed-in balcony overlooking a cavernous clean room at theGoddard Space Flight Center here.
Inside the room, reporters and a gaggle of space agency officials, including the ebullient administrator Charles Bolden, were getting their pictures taken in front of the giant mirror.
Now, after 20 years with a budget of $8.7 billion, the Webb telescope is on track and on budget to be launched in October 2018 and sent a million miles from Earth, NASA says.
The telescope, named after NASA Administrator James Webb, who led the space agency in the 1960s, is the long-awaited successor of theHubble Space Telescope.
Seven times larger than the Hubble in light-gathering ability, the Webb was designed to see farther out in space and deeper into the past of the universe. It may solve mysteries about how and when the first stars and galaxies emerged some 13 billion years in the smoky aftermath of theBig Bang.
Equipped with the sort of infrared goggles that give troops and police officers night vision, the Webb would peer into the dust clouds and gas storms of the Milky Way in which stars and planets are presently being birthed. It would be able to study planets around other stars.
That has been NASA’s dream since 1996 when the idea for the telescope was conceived with a projected price tag then of $500 million But as recently as six years ago, the James Webb Space Telescope was, in the words of Nature magazine, “the telescope that ate astronomy,” mismanaged, over budget and behind schedule so that it had crushed everything else out of NASA’s science budget.
Unforgettable Hubble Space Telescope Photos
On the eve of the 25th anniversary of the launch of the Hubble Space Telescope, we asked astronomers and others involved in the telescope’s groundbreaking story to tell us about their favorite images.
A House subcommittee once voted to cancel it. Instead, the program was rebooted with a strict spending cap.
The scientific capabilities of the telescope emerged unscathed from that period, astronomers on the project say. The major change, said Jonathan P. Gardner, the deputy senior project scientist, was to simplify the testing of the telescope.
Most of the pain was dealt to other NASA projects like a proposedspace telescope to study dark energy, which the National Academy of Sciences had hoped to put on a fast track to be launched this decade. It’s now delayed until 2025 or so.
Typically for NASA, the Webb telescope was a technologically ambitious project, requiring 10 new technologies to make it work. Bill Ochs, a veteran Goddard engineer who became project manager in 2010 during what he calls the “replan,” said the key to its success so far, was having enough money in the budget to provide a cushion for nasty surprises.
The telescope smiling up at us like a giant Tiffany shaving mirror is 6.5 meters in diameter, or just over 21 feet, compared with 2.4 meters for the Hubble. The aim is to explore a realm of cosmic history about 150 million to one billion years after time began — known as thereionization epoch, when bright and violent new stars and the searing radiation from quasars were burning away a gloomy fog of hydrogen gas that prevailed at the end of the Big Bang.
In fact, astronomers don’t know how the spectacle that greets our eyes every night when the sun goes down or the lights go out wrenched itself into luminous existence. They theorize that an initial generation of stars made purely of hydrogen and helium — the elements created during the Big Bang — burned ferociously and exploded apocalyptically, jump-starting the seeding of the cosmos with progressively more diverse materials. But nobody has ever seen any so-called Population 3 stars, as those first stars are known. They don’t exist in the modern universe. Astronomers have to hunt them in the dim past.
That ambition requires the Webb to be tuned to a different kind of light than our eyes or the Hubble can see. Because the expansion of the cosmos is rushing those earliest stars and galaxies away from us so fast, their light is “red-shifted” to longer wavelengths the way the siren from an ambulance shifts to a lower register as it passes by.
So blue light from an infant galaxy bursting with bright spanking new stars way back then has been stretched to invisible infrared wavelengths, or heat radiation, by the time it reaches us 13 billion years later.
As a result, the Webb telescope will produce cosmic postcards in colors no eye has ever seen. It also turns out that infrared emanations are the best way to study exoplanets, the worlds beyond our own solar system that have been discovered in the thousands since the Webb telescope was first conceived.
In order to see those infrared colors, however, the telescope has to be very cold — less than 45 degrees Fahrenheit above absolute zero — so that its own heat does not swamp the heat from outer space. Once in space, the telescope will unfold a giant umbrella the size of a tennis court to keep the sun off it. The telescope, marooned in permanent shade a million miles beyond the moon, will experience an infinite cold soak.
The sunshield consists of five thin, kite-shaped layers of a material called Kapton. Way too big to fit into a rocket, the shield, as well as the telescope mirror, will have be launched folded up. It will then be unfolded in space in a series of some 180 maneuvers that look in computer animations like a cross between a parachute opening and a swimming pool cover going into place.
Or at least that is the $8 billion plan.
Engineers have done it on the ground, and it worked. The same people who refolded the shield after each test will fold it again, in a process Mr. Ochs compares to packing up your parachute before a jump. The test will come in space, where no one will be able to help if things go wrong.
That whole process will amount to what Mr. Ochs called “six months of high anxiety.”
“For the most part, it all has to work,” Mr. Ochs said.
The last time NASA did something this big astronomically, in 1990, things didn’t quite work. Once in orbit, the Hubble couldn’t be focused; it had a misshapen mirror that had never been properly tested. Astronauts eventually fitted it with corrective lenses, and it went on to become the crown jewel of astronomy.
Hubble Reflects the Cosmos
After 25 years, the Hubble Space Telescope is still surprising us. Hubble has been called the most important advance in astronomy since Galileo, and its greatest discoveries might still be ahead.
By Dennis Overbye, Jonathan Corum and Jason Drakeford on April 24, 2015. . Watch in Times Video »
Making sure that doesn’t happen this time is the agenda for the next two years. “Our telescope is finished,” Dr. John C. Mather, the senior project scientist, said. “Now we are about to prove it works.”
In the coming weeks, the mirror and the box of scientific instruments on its back will be put on a rig and shaken to simulate the vibrations of a launch, and then sealed in an acoustic chamber and bombarded with the noise of a launch.
If the parts survive unscathed, the telescope assembly will be shipped to a giant vacuum chamber at the Johnson Space Center in Houston. There it will be chilled to the deep-space temperatures at which it will have to work, and engineers will actually focus the telescope, twiddling the controls for seven actuators on each of the 18 mirror segments. No Hubble surprises here.
Then the telescope will go to Los Angeles to be mounted on its gigantic sunshield. That whole contraption, now too big for even the giant C-5Amilitary transport plane, will travel by ship through the Panama Canal to French Guiana.
It will be launched on an Ariane 5 rocket supplied by the European Space Agency as part of Europe’s contribution to the observatory, and go into orbit around the sun at a point called L2 about a million miles from Earth. Canada, NASA’s other partner, supplied some of the instruments.
Then come the six months of anxiety. Sometime in the spring of 2019, if all goes well, the telescope will record its first real image — of what, the assembled astronomers were not ready to guess. In a bonus undreamed of when the Webb telescope was first conceived, it looks as if the Hubble will still be going strong when the Webb is launched. They will share the sky and the potential for joint observing projects. A million miles apart, they can view objects in the solar system from different angles, providing a kind of stereoscopic perspective.
Besides the expected baby galaxies and the exoplanets, there are, as astronomers like to remind us, always new surprises (like colliding black holes when the LIGO observatory was turned on last year) when humanity devises a new way to look at the sky.
Asked what the telescope’s greatest discovery would be, Dr. Mather said, “If I knew, I would tell you.”
Nor would the project members talk about contingency plans to rescue the telescope if anything goes wrong a million miles from Earth. There are no plans to fix it or bring it back. They know how to attach a probe or robot to the telescope, Dr. Mather said, but “we are planning to not need it, thank you.”
Posts
No comments:
Post a Comment