Shooting for the Stars With the Webb Telescope
Monday, February 5, 2007
Last week's news that the orbiting Hubble observatory's most productive and far-seeing camera may be irreparably damaged sent a chill through the world of astronomy. Even if astronauts return to the Hubble next year as planned to repair and replace several instruments, fixing the electrical malfunction in the Advanced Camera for Surveys is not expected to be on the schedule.
Though the renovated Hubble should still provide important information about distant galaxies for years to come, the loss of the deep-space camera inevitably has astronomers looking ahead to what NASA and other space agencies might have coming in the star-gazing future.
NASA has a small fleet of space-based observatories already in orbit or in the pipeline, but for many scientists, it is the James Webb Space Telescope -- the largest, most complex and potentially most groundbreaking space probe ever created -- that sets off the keenest anticipation.
If all goes according to plan, the Webb will be sent into solar orbit 1 million miles from Earth in 2013 and will do nothing less than peer out and back to the origins of the universe. Using a mirror many times as large and powerful as Hubble's, the telescope is designed to pierce the dusty clouds of the universe's instant past to the period approaching 13.7 billion years ago, when scientists calculate the big bang occurred. A primary goal will be to detect the formation of the first stars in the universe.
Webb will also have unparalleled capabilities to scan the outer reaches of the solar system to better understand how it came into being, and whether there are other large but undiscovered "loose" planets out there now.
Astronomers had hoped that the Webb telescope would be able to work in tandem with the deep-space camera on Hubble, but that instrument's demise does not change the essential mission of the Webb observatory.
"You could say that the Webb telescope will help us understand the most basic aspects of how we got here -- how the exploding stuff of the big bang expanded and cooled, how the first stars and galaxies were formed," said John C. Mather, NASA's senior project scientist on the Webb. Mather was last year's winner of the Nobel Prize for physics for work that essentially proved the big bang occurred, using data collected by instruments he developed for an earlier NASA satellite.
"We have a huge reservoir of untested theories of how it all played out, and Webb can tell us for the first time which ones might be correct," he said.
The Webb telescope has the potential to answer some of these questions because its mirror is not only six times as big and advanced as the one on Hubble, but also because it focuses most of its unprecedented power on light in the infrared portion of the spectrum. This is key because the expansion of the universe has stretched out the wavelengths of light emitted from the first stars, creating a situation where the most distant light reaches Earth only as infrared radiation -- its wavelength elongated out of the visible or ultraviolet range.
Other orbiting and land-based telescopes have observed infrared light from distant galaxies, but none had the capacity to pick up faint and distant stars that Webb will have.
Infrared light is best collected and studied in conditions that are very dark and very cold, and having a telescope on or near Earth limits astronomers' ability to work in that part of the spectrum. The Webb observatory will be 1 million miles away from Earth and that much farther from the sun, but even that was not considered sufficient. A unique light shield the size of a tennis court will be deployed after the telescope reaches its orbit, both to keep it in greater darkness and to allow temperatures to decline to minus 370 degrees Fahrenheit.
The observatory will circle the sun at what is called a Lagrange point -- named after an 18th-century French mathematician -- where the gravitational pull of the Earth and the sun is in balance, allowing the telescope to maintain a stable orbit largely without the need of onboard rockets to keep it steady.
If these conditions are met, Mather said, the telescope just might observe the formation of the earliest stars, which scientists believe burned for only a very short 3 million years before exploding. If Webb can reach back that far, he said, then it is likely to see a world of stars lighting up and popping off "like firecrackers."
But achieving this kind of unprecedented performance will be neither easy nor cheap. The Webb observatory is among the most expensive science projects ever undertaken by NASA -- the Government Accountability Office estimated last year that its design, assembly, launch and use will cost $4.6 billion, about $1 billion over its budget -- and it is already two years behind schedule.
What's more, because the Webb will be 1 million miles away, astronauts will not be able to repair it if -- as happened when Hubble was launched in 1990 -- something goes seriously wrong. The agency is looking at the possibility of adding equipment to the observatory that would allow astronauts flying in the next generation of American spaceships to dock with it, but that is still in the very early planning (or dreaming) stage.
Adding to the complexity of the mission, both the sun shield and the 20-foot diameter Webb mirror -- consisting of 18 hexagonal mirror segments made of the lightweight metallic element beryllium -- would be folded up inside the observatory until it reaches outer space. The telescope won't work if either does not deploy properly.
Mather acknowledged that the design of the mission, coupled with the inability to send up a repair crew, increases the pressure that the Webb team feels; other NASA officials call the whole endeavor "very scary." The Webb observatory, Mather said, will be tested and retested on Earth like no other payload before it.
Webb is now scheduled to launch, on an European Ariane 5 rocket, at a time when all of NASA's other orbiting telescopes may be gone or near the end of their projected life cycles.
"There may be a period of time when the only thing we have in space is Webb," Mather said. "So we just have to get it right."