Washington

Petal power: an artist's impression of the new telescope, whose mirror will open like a flower. Credit: TRW SPACE & ELECTRONICS

It has a basic design, a team of scientists to oversee it and a new name. Now one of astronomy's most challenging projects is poised to begin development.

NASA announced last week that the Next Generation Space Telescope will be named after James Webb, the administrator who led the agency during its glory days of the 1960s, which culminated in the Moon landing of July 1969. The James Webb Space Telescope, which is designed to continue operating for at least five years after its launch in 2010, is expected to cost $2.8 billion.

The telescope, which will have a diameter of 6 metres and be optimized to view infrared light, topped the US astronomy community's ten-year wish-list of projects released in 2000 (see Nature 405, 381; 200010.1038/35013206). A large light-collecting area and sensitive detectors will enable it to see galaxies that are fainter, older and farther away than any seen by the Hubble Space Telescope. Astronomers are hoping they will be able to learn how large structures formed in the early Universe, and to observe the birth of stars and planets with unprecedented clarity.

This won't be easy. The design incorporates several untested ideas, including the first placement of a large observatory at the L2 point, 1.5 million kilometres away from Earth in the opposite direction to the Sun. As a result of the combined influence of the gravitational attraction of the Sun and Earth, objects stationed at L2 orbit the Sun once a year and remain in roughly the same position relative to Earth.

L2 is colder than Hubble's orbit around Earth, so the Webb can cool itself using a sunshield instead of bulky and expensive mechanical systems. Stationing the telescope at L2 also makes it easier to target than Hubble, which has to avoid pointing at the Earth or Moon. This should bring the operating costs of the new telescope down to around a quarter of those required for Hubble, says project manager Bernard Seery of NASA's Goddard Space Flight Center.

L2 does have one main disadvantage: a telescope stationed there cannot be repaired or upgraded by astronauts, as Hubble can. If a crucial onboard system fails and cannot be fixed by radio command, the mission is likely to end.

The winning design for the telescope — which was put forward by an industrial consortium led by TRW Space and Electronics of Redondo Beach, California and Ball Aerospace of Boulder, Colorado — borrows from research on large space mirrors developed for military satellites. The segmented primary mirror divides into three panels, which, once in space, will unfold like flower petals. The technical difficulty of testing this system is the main reason for a slip in the launch date from 2008 to 2010.

Once in space, the mirror, which will be made of glass or beryllium, will be tested and adjusted every few weeks to compensate for any changes in shape caused, for example, by heating.

These and other new technologies have pushed up costs, however. Last year, astronomers reluctantly agreed to NASA's proposal to decrease the size of the mirror from 8 to 6 metres, reducing the telescope's resolving power by 25% and its light-collecting ability by 44%. An orbital test of a scaled-down mirror was also scrapped.

Some outside observers worry that the current budget is still too small, but Seery says his team is far more savvy about the technological challenges and true costs than it was.

Others say that it is right to push the state of the art forward with the planned new telescope.

“These kinds of telescopes only come along once every decade or so,” says Jonathan Lunine, a planetary scientist at the University of Arizona in Tucson and a member of the Webb's recently appointed Science Working Group, which will meet for the first time next week. “Because of the size and the scope of this mission, the opportunity to do new technology is really there.”

→ http://ngst.gsfc.nasa.gov