Astronomers eye life after Hubble Science: Researchers hope the space telescope of the future will shed light on the origins of the universe.

Sun Journal

September 08, 1996|By Frank D. Roylance | Frank D. Roylance,SUN STAFF

GREENBELT -- After a blurry start, the refocused Hubble Space Telescope has been, by almost any accounting, a fabulous success.

From its orbital perch beyond most of the Earth's shimmering atmosphere, the bus-sized observatory has sent back proof of the existence of black holes, stunning photographs of vast star nurseries in the Eagle nebula, and of the first planets ever seen circling a star other than the sun. There's hardly an astronomy meeting anywhere in the world whose scientific agenda is not peppered with reports of discoveries made with Hubble in the 2 1/2 years since shuttle astronauts equipped it with corrective optics.

But the space telescope's technological clock is ticking.

Two more upgrades are planned -- the next one this winter -- but the observatory has just nine years left in its engineered lifetime. Scientists at NASA, university labs and in industry have been given until next summer to propose a radically different design for its successor.

Despite its success, Hubble is a relic of 1970s technology and budgeting. It depends on the biggest, heaviest glass mirror that American rocketry could lift into orbit, and cost $6 billion to build and operate. NASA astronomers know they will never get that kind of money from Congress again.

The "Next Generation Space Telescope," or NGST, would be bigger, but lighter and far cheaper than Hubble, they say. It would fly at least a million miles from Earth, and could be launched by 2010.

If Congress provides the money, and the instrument works, the NGST could extend man's vision -- to the period when galaxies were forming. Researchers hope to find answers to ancient questions about the origins of the stars and galaxies that gave birth to life on Earth.

The new telescope will "rewrite textbooks in physics, chemistry, biology and quite possibly history," said NASA Administrator Daniel S. Goldin. "The results could literally change the way humans think about the universe and their place it it."

Goldin has set a cost target for NGST of less than $500 million, with another $500 million to run it for 10 years.

High on the planners' wish list is a bigger mirror. Hubble's 2.4-meter (about 7.8 feet wide) glass primary mirror is the biggest that could be lifted into space, and it has given astronomers glimpses of galaxies as they evolved early in the history of the universe.

"We can see how they have changed as they grew up," said Dr. John C. Mather, an astrophysicist and NGST planner at the Goddard Space Flight Center in Greenbelt. "But we haven't seen them being born yet."

To push their view back closer to the birth of the universe in the Big Bang, perhaps 12 billion to 14 billion years ago, astronomers must be able to resolve objects even farther out in space. That's because light travels at a fixed speed, and light from the farthest objects began its journey the longest time ago.

To see farther, astronomers need two things from the engineers: a big mirror and a telescope highly sensitive to infrared light.

Infrared sensitivity is crucial because light that has traveled so far, for so long, has changed since it began its journey: As the universe has expanded since the Big Bang, everything in it has expanded, too. Like the design on an inflating balloon, the wavelengths of the starlight traveling from those early galaxies has been stretched, lengthening from the visible light spectrum into the longer-wavelength infrared.

This stretching, called "redshift," means that only telescopes sensitive to the near- and mid-range of the infrared band can see the most-distant objects. It is an unexplored frontier, accessible only with bigger telescopes.

Ground-based telescopes have big enough mirrors, but the Earth's atmosphere is opaque to that portion of the infrared spectrum where the earliest galaxies would be visible. The air also warms ground telescopes to a point where they emit their own infrared radiation, obscuring the signals from space.

Orbiting observatories such as Hubble avoid most of those atmospheric problems, but their mirrors are too small to resolve the dim smudges of infrared light from the ends of the universe.

"Hubble knows there is interesting stuff out there, but Hubble isn't quite big enough," Mather said.

NGST planners hope for a mirror at least 4 meters (13 feet) across, and perhaps as large as 8 meters.

"If you had asked me a year ago if it were possible, I would have said, 'Of course not,' " Mather said. "That was before we established a team that has to do it."

"Forget glass," Goldin has said. It would cost billions of dollars to build and launch a glass mirror that big, even if there were a rocket big enough to do the job, which there isn't.

Under one design proposal, the NGST would carry an 8-meter mirror that would unfold in orbit like a flower. Its eight "petals" would be made of thin metal films and lightweight composites developed for the laser-based "star wars" anti-missile program.

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