Hubble Space Telescope huggers are celebrating the iconic observatory's 20th birthday, even as scientists anticipate the next generation of bigger and more powerful successors to the famed orbital instrument.
The Hubble Space Telescope launched on April 24, 1990 with a flawed mirror, but survived for two decades due in large part to five repair missions by space shuttle astronauts. Its cosmic gaze has led to breakthrough discoveries about the universe and embedded stunning views of the cosmos in the hearts and minds of the public.
"Hubble has done all those things and become an icon of science because it can produce glorious images," said Rick Fienberg, an astronomer and press officer of the American Astronomical Society.
But there's bigger and better science yet to come.
NASA's James Webb Space Telescope is scheduled to go online in a few years. And a slew of new space observatories are also being considered, even if none have received the official go-ahead yet.
Together, the collective vision of such giant space telescopes would span a spectrum ranging from infrared to X-rays, and could allow scientists to peer even further back in time to the beginning of the universe.
"Each generation of telescopes you're launching into space is vastly more capable than the ones before, partly because of larger apertures but also because of better detectors," Fienberg told SPACE.com. "You're getting a double whammy."
The Hubble Successor
NASA's hotly-anticipated James Webb Space Telescope (JWST) represents the next big successor for the aging Hubble with its scheduled launch in 2014.
A 21-foot primary mirror gives JWST nearly seven times the light-collecting power of Hubble's almost 8-foot main mirror. JWST also beats its predecessor with a 72-foot length just shy of a tennis court, compared to the school bus-sized Hubble, which is about 44 feet long.
Hubble looks at the universe primarily in the visible light and ultraviolet wavelengths, with a little infrared vision on the side. But JWST will focus its observations on the longer infrared wavelengths. That means JWST can see the very first galaxies that have moved farther away due to the universe's expansion, because the light emitted by baby galaxies has shifted toward the longer red end of the spectrum.
There's an even bigger Hubble and JWST successor on the drawing board. The Advanced Technology Large Aperture Space Telescope (ATLAST) would have a main mirror at least 26 feet wide, but possibly as large as 52 feet. This NASA concept telescope could represent a flagship mission for sometime between 2025 and 2035.
The Farther Ends of the Spectrum
Other space telescopes would complement the direct Hubble successors and help replace existing space observatories such as the Chandra X-ray Observatory, Spitzer Space Telescope and Herschel Space Observatory. Such instruments cover the more extreme ends of the light spectrum that rarely make it through the Earth's atmosphere to ground-based telescopes.
A more powerful successor for Spitzer and Herschel might launch as soon as 2015. The Single Aperture Far-InfraRed observatory (SAFIR) would use a single primary mirror about 16 to 33 feet wide, compared to Spitzer's main mirror at less than 3 feet in diameter.
That gives SAFIR more than 1,000 times the sensitivity than Spitzer and Hershel for detecting far-infrared and microwave signals.
Another project, the International X-ray Observatory (IXO), represents a joint effort between NASA, the European Space Agency and the Japan Aerospace Exploration Agency. It would deploy a multi-part X-ray mirror with about 20 times more collecting area than any existing X-ray observatory, based on a tentative launch around 2021.
But unlike the telescopes peering at the infrared or ultraviolet universe, IXO would use primary and secondary mirrors placed almost edge-on toward incoming X-rays so that the X-rays bounce off both at a shallow angle. That prevents the X-rays from simply being absorbed by the mirrors.
Onward and Upward
Another project calls for an X-ray telescope on a scale beyond even that of the IXO. The Generation-X Mission would have 500 times the collecting area of the Chandra X-ray Observatory, so that it could examine the birth and evolution of the first stars, galaxies and black holes.
More telescope projects, like NASA's proposed Terrestrial Planet Finder (TPF), would link together an array of two or more space telescopes. Such instruments could imitate the angular resolution of much bigger telescope lenses, or have complementary observatories looking at different phenomena in TPF's case.
Astronomers naturally look to the next generation of bigger and better space telescopes, because each of the giant flagship missions costing $1 billion or more could take 10 or 20 years to develop. Servicing missions have helped the venerable Hubble exceed its life expectancy, but most instruments might only last 5 to 10 years.
"Even when you build one today and launch one tomorrow, you're already thinking about the one that will come next and laying the groundwork," Fienberg explained. "Otherwise you'll end up with a decade-long gap between missions."
JWST alone will cost NASA and its European and Canadian partners about $5 billion for the instrument's entire life cycle. Such huge costs mean that the fate of many telescope concepts will depend upon what the National Research Council says in its Astro2010 Decadal Survey later this year.
"Right now all of these projects except James Webb are pie-in-the-sky," Fienberg said. "[JWST] will be the largest astronomical telescope in orbit for a good long while."
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