Life after Hubble<< page 1: Hubble alternatives A more cost-effective solutionThese and other alternatives (including some off-the-wall suggestions, such as having a manned Soyuz mission service the telescope) are all predicated on the belief that Hubble is worth saving. That is, it’s worth the considerable cost—perhaps $500 million for a shuttle mission, and possibly similar amounts for some alternatives—not to mention the risk to astronauts’ lives for manned missions, to extend the life of Hubble for several years. This is a broadly accepted opinion among astronomers, the general public, and even politicians, all of whom have been lobbying against the decision. Yet, in recent years the advantages Hubble had over its terrestrial counterparts has been eroding.
The key advantage that an orbiting telescope has over a groundbased one is that it is above the atmosphere. The atmosphere is a nuisance to astronomers: it blocks some wavelengths of light, particularly in the ultraviolet and infrared; it distorts images; it scatters sunlight during the day, preventing optical observations; and it supports the formation of clouds (usually when you’re most in need of telescope time, any observational astronomer will tell you.) Above the atmosphere, Hubble is freed from those constraints, and can operate virtually 24/7, providing sharp images at wavelengths not visible from the ground. Groundbased telescopes, though, have found their own solutions to some of these problems. Their key advantage is size: while the Hubble’s 2.4-meter mirror was moderately large by terrestrial standards when it was built, new advances in telescope technology now regularly permit far larger mirrors. Besides the Keck Observatory, with its twin 10-meter telescopes, observatories with telescopes six and eight meters in diameter are increasingly common. Moreover, adaptive optics systems—which rapidly reshape mirrors to cancel out the blurring effects of atmospheric turbulence—allow these telescopes to look at fainter objects and take images of a quality similar to Hubble. Astronomers are even considering larger ground-based telescopes, such as the aptly-named Overwhelmingly Large (OWL) telescope, with a mirror 100 meters across. Terrestrial telescopes have another advantage over space telescopes: cost. Even the largest groundbased telescopes cost a fraction of Hubble, which cost roughly $1.5 billion. The twin Keck telescopes cost about $140 million to build. The Gemini Observatory, a pair of eight-meter telescopes located in Hawaii and Chile, cost under $200 million. Even the OWL project has an estimated budget on the order of $1 billion. In addition to the lower construction costs, the operational and maintenance costs are lower: if a part breaks on a groundbased telescope, one doesn’t need to pay for a shuttle mission to fix it! These large new telescopes can’t do everything Hubble can: they’re still blind to some wavelengths of light, and their operations are modulated by diurnal, meteorological, and lunar cycles (groundbased telescopes often reserve the time around full moons for engineering work or observations of bright objects not drowned out by the glare of the Moon.) Still, there may be a low-cost solution here. The cancellation of the SM4 mission means that two instruments already built for Hubble—the Cosmic Origins Spectrograph and Wide Field Camera 3—won’t be installed on the telescope. There has been some discussion, however, about flying one of both of these instruments separately on dedicated low-cost Explorer-class missions. It’s not clear such a strategy would work—the instruments are designed to work with Hubble, and it may be difficult or cost-prohibitive to adapt them to a new mission—but it could keep the instruments from being consigned to permanent storage on Earth.
Here, then, is the question that NASA and the astronomical community must answer: is it worth the cost and the risk to service Hubble again, extending its life for perhaps three to five years, or are there better ways to spend the money and get good science in return? For the cost of a shuttle servicing mission—say, $500 million—one could get two Medium-class Explorer (MIDEX) missions, currently capped at $170 million each. There would still be enough money left over for NASA to build a world-class groundbased observatory (or two) that, unlike Hubble or the Explorer spacecraft, could last for decades. NASA could also “buy in” to existing telescopes, paying for instruments and/or operating costs in exchange for a share of telescope time, which the agency could then make available to astronomers. These alternatives could, combined, do much of what Hubble could do, and provide the public with all the pretty pictures it could want. There’s certainly a compelling case to be made for a Hubble servicing mission: if successful, the science returned over the next several years would be excellent, and despite the risks there is probably no shortage of volunteers in the astronaut corps to participate in such a flight. However, the realpolitik of the day suggests that it’s unlikely that Congress can force NASA to fly a mission that the agency thinks, for whatever reason, is not prudent to fly. Instead, NASA and Congress may seek out some kind of compromise to fund alternative astronomy missions to Hubble to help fill the gap between when it shuts down—which could still be several years from now—and the launch of the James Webb Space Telescope in 2011. As noted above, compelling alternatives exist that would cost no more, and perhaps significantly less, than a shuttle servicing mission. The lesson everyone—astronomers, politicians, the general public, and NASA itself—has to keep in mind is that Hubble is not the only means by which to do good astronomy. There is indeed life after Hubble. Home |
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