17.10 News Feat Telescopes Mx

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A million-mile service NASA

NASA wants many of its space telescopes to orbit far from Earth. So how will they be repaired if they go wrong? Tony Reichhardt investigates.

f you keep the Sun at your back and head Washington, likens it to a ridge trail in the one-and-a-half-million kilometres away mountains. Stay on the trail, and you’ll use Ifrom Earth, you’ll hit astronomy’s most far less energy than if you hike up and down. sought-after location. This unassuming The plan has yet to be fully evaluated, but spot, known as L2, is set to become home to it would require expensive new technologies, eight new space telescopes over the next 15 including vehicles to ferry astronauts to and years, and many more could follow. from the outpost, and a low-thrust propul- L2 has obvious attractions. It is a sion system to move the telescopes. The lagrangian (or libration) point, which means outpost would, however, have other uses. that objects stationed there are held in a fixed Astronauts could be dispatched to the Moon position relative to Earth, as a result of the from it, and it could also be a base from which combined gravitational pull of the Sun and to assemble and launch an expedition to Mars. Earth. Ground-based antennas are always But if telescope servicing is the main aim, in sight, and the detectors, some of which NASA could avoid building an outpost, says require cooling, can more easily be protected Robert Farquhar, a veteran space-mission from heat given off by Earth. designer at the Applied Physics Laboratory Placing telescopes at L2 could also boost in Laurel, Maryland. Farquhar, who also pre- Will astronauts be NASA’s plans for human space flights. Astro- sented his ideas in Houston, believes that the able to reach and nauts have repaired and upgraded the Hub- telescopes could be moved from L2 into a service equipment ble Space Telescope four times in the past very high Earth orbit and serviced there. farther away than the decade. If NASA decides that astronauts Hubble telescope? should service the L2 telescopes, it will have to Safety catch reinvent its human spaceflight programme, He and others say that direct missions to the which hasn’t ventured beyond Earth’s orbit L2 telescopes may also be possible. At dis- Hubble (see Nature 419, 235–236; 2002), it since the final Apollo lunar mission in 1972. tances greater than about 40,000 kilometres was not built to be serviced by astronauts. Some of the possibilities were discussed from Earth, the planet’s magnetic field no “There’s nothing better than an astronaut this week at the World Space Congress, held longer protects astronauts from the danger- in the loop,” says Charles Beichman of NASA’s in Houston, Texas. One suggestion, devel- ous charged particles emitted by the Sun and Jet Propulsion Laboratory (JPL) in Pasadena, oped over the past two years by a group of other sources. To play it safe, NASA would California, chief scientist for the Terrestrial about 100 NASA scientists and engineers keep long-distance human missions as short Planet Finder (TPF), an L2 telescope that known as the NASA Exploration Team as possible, although it has made radiation- should start hunting for Earth-size planets in (NEXT), is to build an intermittently occu- protection research a priority on the Inter- the middle of the next decade. “But it will be a pied astronaut outpost at a lagrangian point national Space Station. Round trips to L2, significant investment. We don’t want to stop in the Earth–Moon system. which would take at least a month, could be what we’re doing while waiting for them.” A station at this point, about three-quar- possible if the agency solves this problem. The situation may have changed, however, ters of the way to the Moon, would orbit So will any of the first generation of L2 by the time larger, more complex telescopes Earth in sync with the Moon (see diagram, telescopes require human involvement? One, are ready to follow the TPF. The NEXT team, below). More importantly, moving the tele- the Microwave Anisotropy Probe, designed for example, is honing its plans by assessing scopes from L2 to this point and back again to measure background levels of microwave the needs of the Dual Anamorphic Reflector would require relatively little energy. Gary radiation, is already in place. But like the oth- Telescope, currently under study at JPL. Martin, director of the Advanced Systems ers now on the drawing board, such as NASA’s This large but lightweight infrared tele- Office at NASA’s Office of Space Flight in James Webb Space Telescope, the successor to scope is unlikely to be launched within the next 15 years. But if NASA does decide to use astronauts to service such telescopes, it would present a historic opportunity to align the Moon agency’s science and human spaceflight pro- Astronaut Telescope grammes, says Wesley Huntress, NASA’s for- outpost at L2 mer associate administrator for space science who now directs the Carnegie Institution of To the Sun Earth Washington’s Geophysical Laboratory. From Apollo onwards, astronaut missions have On location: an outpost Moon’s been dictated by space engineering capabili- between Earth and the orbit ties and politics. If human telescope servicing Moon could offer easy is needed, says Huntress, scientists could find access to the L2 telescopes. themselves setting the agenda. I Tony Reichhardt writes for Nature from Washington.