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Webb telescope next generation of stargazer

The Baltimore Sun

Imagine a window with 62,000 shutters - each the width of a human hair.

That's what scientists at NASA's Goddard Space Flight Center are building to capture light from the most distant stars ever seen - in the most complex stargazer they have ever constructed.

They say their contribution to the $4.5 billion James Webb Space Telescope will help answer lingering questions about the dawn of the universe, the fate of the earliest stars and the formation of the planets.

"Nothing like this has ever been put in space before," said Murzy Jhabvala, chief engineer of Goddard's Instrument Technology Center in Greenbelt.

The Webb telescope - slated for launch in 2013 - is regarded as the successor to the widely acclaimed Hubble Space Telescope and a logical next step in probing the origins of the universe.

As with Hubble, there is a strong Maryland connection. The instrument's management and operations will employ up to 200 people at the Space Telescope Institute in Baltimore and about 385 at Goddard, officials say.

"It's designed to address two fundamentals that drive astronomy: How did we get here, and are we alone?" Alan Dressler, an astronomer with the Carnegie Observatories, said of the telescope that he and colleagues first conceived of in the 1990s.

While Hubble is capturing mostly visible light from some of the more distant corners of the universe, the Webb will peer even farther, from an orbit almost a million miles out, using infrared light detectors to help scientists create a scenario for the earliest days of the universe.

"We think the first stars were just forming when the universe was a few hundred million years old, and we hope to use Webb to see that far back," said John Mather, Webb's project scientist and co-winner of the 2006 Nobel Prize in physics for his work on the big bang theory.

Unwanted light

Opened by magnets and controlled by computers, the microshutter system that Goddard is building will block out unwanted light in the distant sky so the telescope can focus on fainter and more distant objects. The principle is the same as using your hand to block out the sun to see in the distance.

Other telescopes have been able to block out large portions of unwanted light. But the microshutter system, designed specifically for Webb, will be the first to block out such tiny portions.

Engineers are assembling the device on sterile wafers in a "clean room" similar to facilities that the computer industry uses to make integrated circuits. Scientists verified the underlying technology in a series of tests last month that proved the shutters will work in space. The team has nine months to build four flight-worthy shutter systems for further testing, Jhabvala said.

Each shutter has a magnetic coating. As a magnet passes over the shutters, they open like tiny trap doors to let light through. A computer, controlled by scientists on Earth, will determine which microshutters close and which remain open.

The tiny silicon shutters are extremely fragile. "This is something that's so delicate, you blow on it and it'll shatter," Jhabvala said. "And yet it's got to survive this rocket from hell, a blast with amazing G-force."

To help the telescope survive the launch, engineers plan to mount the four microshutters on plates that will be attached to flexures - platforms mounted on springs that allow for limited movement to minimize the force at liftoff.

Overall design

Work began six years ago when NASA officials gave final approval to an overall microshutter design.

Once completed, the system will be part of Webb's Near Infrared Spectrograph, an instrument designed and being built by the European Space Agency. With the spectrograph, astronomers will be able to observe hundreds of objects at a time and read signals hidden in infrared light from the most distant stars.

Webb's other instruments will include a near-infrared camera, a mid-infrared instrument and a tunable filter imager, which NASA says it hopes will take the same kind of breathtaking images that Hubble has become known for. "We certainly designed it with that intent, to capture some of the beauty of the universe," Mather said.

In addition to $1 billion already spent on planning and design, NASA will spend $2.6 billion from now until the 2013 launch. Besides that, the agency has budgeted $900 million for operations and salaries of the scientists who will use Webb for studies, according to agency spokeswoman Pam Sullivan. Hubble has cost $7.5 billion, Sullivan said.

NASA has managed to avoid potential cost overruns that could delay the 2013 launch and were forecast in a July audit. An independent panel of experts also concluded last month that the Webb project is on schedule.

"NASA has put the Webb back on track," said Mattias Mountain, director of the Space Telescope Science Institute in Baltimore, which is advising the program.

Hubble is expected to return valuable scientific data for several years, with a space shuttle mission planned for 2008 to repair and replace several Hubble instruments.

Scientists conceived Webb as Hubble's successor, and Mather knows Hubble will be a tough act to follow. Launched 17 years ago, Hubble produced astonishing images of the Eagle Nebula, the Sombrero Galaxy and other distant interstellar objects.

With Webb, named for James E. Webb, NASA's second administrator, NASA says it's not trying to duplicate or top Hubble but build on its historic achievements. "You can't do a better job than Hubble has done," Mather said.

But even with a servicing mission planned for next year, Hubble's days are numbered. NASA reported last month that an electrical malfunction has crippled one of Hubble's most productive instruments, the Advanced Camera for Surveys.

The Webb telescope's 21-foot primary mirror is seven times larger than Hubble's, so that it can gather more light and peer deeper into space. Its detectors will also be able to read infrared light at wavelengths of up to 29 microns, a range that surpasses Hubble's 2.5-micron capacity.

Infrared readings

Webb's infrared capabilities are critical, astronomers say. Light is a form of energy that exists in a wide range of wavelengths, and human eyes can see only a small part of it.

As light travels through space at 186,000 miles per second, its wavelengths shift from the blue and visible portions of the spectrum to the infrared. This means that light generated by the most distant stars from Earth - those formed further back in time - display a greater shift toward the infrared.

While Hubble has some ability to see in the infrared, scientists have discovered that many of the most distant stars could be seen better with instruments that could probe deeper in that end of the spectrum. "If you want to go into areas where you're seeing the most distant stars, it's in the infrared," Mather said.

Webb will also be equipped with a sun shield the size of a tennis court to keep it at a chilly minus-370 degrees Fahrenheit. Such chilly temperatures will prevent Webb's heat from throwing off infrared readings, which is a problem when Hubble and other telescopes detect infrared light.

The telescope will orbit 940,000 miles from Earth after a three-month journey that places it too far away for the kind of space shuttle service missions that have served Hubble.

Webb's distant location will subject it to equal forces of gravity from the sun and Earth so that it will require less fuel than if it were closer to home.

One concern is Webb's sheer size and the number of moving parts, according to Carnegie's Dressler. When fully deployed, Webb will be two stories high, larger than the European Ariane rocket that will launch it. The sun shield and mirrors are so large that they will be folded up like origami during launch and released only after the telescope has traveled for three months.

But to see that far into space, you need a big telescope, scientists say.

"We can be concerned about that, but it's not like there were a lot of alternatives," Dressler said.


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