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Grounded: Champollion was to have drilled under the surface of Comet Tempel 1 to collect material. Credit: NASA

Faced with cost overruns and expensive delays to other, higher-priority science projects, the US space agency NASA has cancelled a $240 million comet landing mission that had been proposed for early in the next decade.

The Champollion spacecraft was to have been launched in 2003 as part of NASA's ‘New Millennium’ programme to demonstrate advanced spacecraft technologies.

It would have met up with Comet Tempel 1, anchored itself to the comet's nucleus and drilled for material below the surface to validate devices for use on future missions.

But Champollion was not primarily a science project and was still early in the planning stages — less than $10 million has been spent on preliminary studies — so it became vulnerable when NASA's science office ran into financial difficulties.

Normally, the agency's $2.1 billion science programme would be flexible enough to absorb tens of millions of dollars in unexpected costs in any given year, says Edward Weiler, head of NASA's space science office. But delays to the $1.5 billion Chandra X-ray observatory, resulting partly from problems with the upper-stage rocket, will add $100 million over the next few years.

Splitting a repair of the Hubble Space Telescope into two shuttle missions, partly because of earlier slips in the schedule, added $26 million. The $500 million Gravity Probe-B satellite, which was scheduled to reach orbit next year, is $20 million over budget, and NASA's Mars exploration programme was becoming low on reserves. Taken together, says Weiler, these were “not the usual year's money problems”.

Champollion design work conducted at the Jet Propulsion Laboratory in California can still be applied to other missions, including an expedition to Jupiter's moon Europa. “I'm sure NASA will get around to doing a major comet mission sometime in the future,” says Weiler.

For now, though, Europe's Rosetta mission, planned for launch in 2003, has that territory to itself. Champollion began life as the US contribution to Rosetta, but NASA backed out as a major partner three years ago to pursue its own comet lander as a low-cost New Millennium spacecraft (see Nature 383, 469; 1996).

US scientists will still be joint investigators on Rosetta, which will land a probe on the surface of Comet Wirtanen in 2012. Weiler says the existence of the international mission was another factor against keeping Champollion alive.

The Planetary Society, a California-based space advocacy group, was not happy with NASA's decision, and called on the US House of Representatives Science Committee to help restore money for Champollion.

In a statement, the society's director Louis Friedman said that penalizing a successful science and technology mission to pay for other programmes that are experiencing cost overruns “sets a disturbing precedent”.

But NASA could not count on a Congressional rescue in a year when law-makers are warning of a difficult appropriations battle to meet spending caps. Weiler says that cancelling Champollion “goes a long way” towards solving his impending budget problem, if Chandra launches on 20 July as planned.

The demise of the comet lander is a lesson in the difficulties of managing many “better, cheaper, faster” space missions at once. As one congressional staffer says: “There isn't the play in the NASA budget that there had been in the past.”