As the Hubble Space Telescope begins its second and final decade in orbit, NASA already is making plans for a successor observatory that could extend our vision of the universe back to nearly the beginning of time.
Scheduled for launch as soon as 2007, the Next Generation Space Telescope is still on the drawing board. Three concepts under consideration share some design features, including an operating orbit far from Earth and thin, fast-steering, adjustable mirrors at least twice the size of those on Hubble -- NASA's visible and infrared observatory currently circling the planet.
"Were working very hard on all technologies that have to go to NGST," said David Leckrone, a manager with NASAs Goddard Space Flight Center.
Scientists hope the new observatory will help answer questions about how the universe looked shortly after its creation.
NASA's Cosmic Background Explorer (COBE) spacecraft already has detected radiation left over from the birth of the universe and Hubble can explore the universe back to when it was about 1 billion years old. But what happened between about 300,000 years after the universe's formation and the time it was about 1 billion years old is largely a mystery.
"COBE has seen before the first of the galaxies and Hubble has seen what would be about the five- or six-year-old in a human lifetime. We're trying to see the youngsters. A lot happens in the first few years after birth," said NASA space science chief Ed Weiler.
Telescope to study first stars
The Next Generation Space Telescope will use imagers and spectrographs to study to study the first stars and galaxies that were created after the universe cooled enough for distinct structures to form. The observatory would be sensitive enough to detect the likely presence of planetary systems around nearby stars from their infrared radiation.
Telescope designs by Lockheed Martin, TRW and NASAs Goddard Space Flight Center propose different types of materials for the primary mirror, which will be between four and eight meters in diameter. The mirrors design and construction is expected to be the most difficult part of the mission. The proposals make use of spy satellite technology in which the mirror would unfold like an umbrella in orbit.
"There's all kinds of technology available now that wasn't available before because of the Cold War," said Weiler.
NASA wants to keep the cost of the observatory to about $500 million (in 1996 dollars) and launch the spacecraft folded up atop an expendable rocket. Unlike Hubble, the Next Generation Space Telescope will not be placed in low-Earth orbit. For that reason, it could not be serviced by space shuttle crews, like Hubble can.
Rather than long-life, NASA is opting for lower cost and better thermal conditions by planning to place the telescope in an orbit farther away from Earth than the moon. That location and low temperature would make the observatory thousands of times more sensitive than Earth-based telescopes and able to resolve the red-shifted light of distant galaxies formed soon after the Big Bang.
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