The long-delayed Hubble Space Telescope is still months away from launch, but scientists gathered in Baltimore have already begun planning for a new space telescope so much bigger and better they say it might detect life on planets outside our solar system.
Nothing is final, but the consensus appeared to favor development of a telescope with a mirror 10 to 16 meters across--four to seven times the size of Hubble--for assembly at a permanent base on the moon by the year 2010.
About 120 scientists, engineers and astronomers gathered recently at the Space Telescope Science Institute at Johns Hopkins University for the first workshop on this next generation of space telescope.
Garth Illingworth, coordinator of the workshop and a former deputy director of the Space Telescope Science Institute, said planners hope to keep the telescope's cost under $5 billion, but that will not include the costs of developing the technology to get the telescope to the moon.
"Obviously, it's an expensive project," he said.
And a long one. The 20-year head start is not extravagant.
The first planning sessions for the 2.3-meter Hubble Space Telescope were held in 1962. It is scheduled for launch aboard the Shuttle Discovery on March 26, 1990. Its life expectancy in space is 15 years.
"Since the Hubble has a lifetime of 15 years, clearly we have to start (planning its successor) well before its launch," said Illingworth, an astronomer at the University of California's Lick Observatory.
Astronomers expect the Hubble Space Telescope, soaring far above most of the distorting effects of the Earth's atmosphere, to provide images of planets, stars, galaxies and the very edges of the universe with unprecedented clarity.
Its 2.3-meter mirror (about 7.4 feet across) will be the largest and finest ever placed in space and promises to expand the visible universe seven times beyond what can be seen from ground-based telescopes.
But even Hubble has its limitations, Illingworth said.
One, ironically, is its size.
Hubble's mirror will be the biggest in space, nearly six times the size of the mirror in the International Ultraviolet Explorer telescope operating in a high Earth orbit.
But astronomers on the ground have learned to build 10-meter mirrors--giants almost 33 feet across.
Impossibly heavy and costly to build using a single piece of glass, telescopes this large are being built by assembling a mosaic of smaller hexagonal mirrors. Each mirror segment is movable, and all are controlled by computer to perform like a single piece of glass.
A 10-meter segmented mirror will form the heart of the W. M. Keck Observatory being built in Hawaii. When completed, it will be the largest telescope in the world.
"But to really take advantage of these mirrors, we'd like to put it into space," Illingworth said.
That kind of light-gathering power elevated above the Earth's atmosphere, he said, would allow astronomers to see even more clearly "how galaxies formed and evolved, how stars formed, and what happens in the disc around stars where planets may be forming," all things only hinted at by ground telescopes.
But the scientists also want to get a telescope that big far beyond the 370-mile altitude where the Hubble Space Telescope will fly.
Swinging around the Earth once every 90 minutes, Hubble's views will be repeatedly interrupted by the bright light from the Earth, the moon and the sun. It will be in constant motion relative to ground controllers and the stars, and the heat from the Earth will sharply limit its ability to see in infrared wavelengths.
But a space telescope placed on the moon, Illingworth said, would be shielded from the sun for two uninterrupted weeks every month. And if it is placed on the side of the moon that always faces away from Earth, it would be permanently shielded from the Earth's reflected light.
A lunar observatory would be easier to build where there is gravity, and once built it would be more stable, Illingworth said.
Even a geosynchronous orbit 22,300 miles above the Earth--the scientists' second choice--would be an improvement over Hubble. Interruptions caused by light from the sun, moon and Earth would occur once a day rather than every 90 minutes.
But perhaps best of all, a space telescope on the moon or in high earth orbit would be free of the Earth's heat, enabling it to "see" in infrared wavelengths.
Although the Hubble Space Telescope may be able to find the first planets ever discovered outside our solar system, astronomers believe a 16-meter space telescope in the cold and dark of the moon could not only find them but study the infrared spectrum of light reflected from them.
"They hope to look for the molecules of life," said Ray Villard, a spokesman for the Space Telescope Science Institute. Oxygen, ozone, methane and other chemicals found in the right proportions would "scream of life."
But first the engineers have to build the new telescope. And it will not be easy.
"They will have to build it 10 times lighter than how we do it on Earth," Villard said. "And the quality (of the mirror) they want to be 10 times better than what's been done so far."
The new telescope can weigh no more than 20 tons if it is built for a high earth orbit and maybe 40 to 50 tons if it goes to the moon. "These are very tough goals," Illingworth said.
If the telescope is going into a high Earth orbit, "we'll have to take it up in chunks and have it assembled robotically," Illingworth said. The vehicles to get it to the high orbit and the robots to assemble it have not been invented yet.
The United States does not have the machinery to carry men and telescopes to the moon, either, but President Bush has committed the nation to establishing a permanent lunar outpost.
Although some scientists are questioning the value of such a manned presence on the moon, Villard said that if the United States is going to develop the capability to carry large cargoes and people to the moon, the astronomers "want to hitch a ride."