Washington

Over the Moon: some say the Sun–Earth libration point L2 is a good target for human missions. Credit: IAA

Think more broadly and don't forget international cooperation: that is the message from a veteran group of space scientists and engineers. Together they presented an alternative to NASA's vision for human space exploration at a Paris press conference on 19 July.

Their report, called The Next Steps in Exploring Deep Space, caps a three-year, informal study sponsored by the International Academy of Astronautics. Although it was a volunteer effort with no official government backing, the study reflects the judgement of more than 100 space professionals. These include former NASA space-science chief Wesley Huntress and Bernard Foing, project scientist for SMART-1, Europe's first lunar mission, which was launched last year.

NASA is making plans for a return to the Moon by 2020, to act as a stepping stone to Mars. But the academy suggests two other short-term destinations for astronauts: a Sun–Earth libration point (L2), where future astronomical telescopes will be stationed (see Nature 419, 666; 2002), and near-Earth asteroids. The group recommends that the decision about which goal to tackle first should be based on scientific objectives, and that each successive step should require only one major technology to be developed, partly to lower costs.

The authors call their study “an example of what could be done, not a prescription of what will be done”. Yet they clearly intend to broaden the ‘where next?’ debate beyond what some feel is too narrow a focus on the Moon.

The construction and maintenance of astronomical facilities at L2 (see above, not to scale) may provide a good rationale for a programme of human exploration beyond low-Earth orbit, the study's authors write. Astronauts could also be sent to explore asteroids — collecting data to aid in protecting the Earth from possible future collisions.

Huntress, now director of the Carnegie Institution of Washington's Geophysical Laboratory and the study's leader, says its recommendations are in line with President George W. Bush's directive to send humans beyond Earth orbit. But the committee adds that its alternative priorities for space exploration make more economic sense. Making L2 — a point in space four times farther away than the Moon — an early goal for astronauts would defer the cost of a lunar lander and base until after a deep-space vehicle is proven, for example.

The academy places stronger emphasis on the possibility of international cooperation than did a recent US presidential commission. So far, international discussion of Bush's Moon–Mars programme has produced only polite interest. The European Space Agency is conducting its own study of possibilities for human space exploration, but this is not expected to be finalized until next year.