By Irene Klotz
Cape Canaveral, Florida
The US space agency (Nasa) has reversed its decision to scrap the Dawn mission to two large asteroids.
Nasa reversed its decision after intense lobbying
The robotic probe had been cancelled, the agency said, because of technical problems and cost overruns.
But intense lobbying by scientists prompted Nasa management to reappraise the mission and then reinstate it.
Dawn, so named because it will study objects dating from the beginning of the Solar System, is expected to visit the giant space rocks Vesta and Ceres.
But on 2 March, the agency had decided otherwise and axed Dawn, despite having already spent about two-thirds of the $373m (£213m) earmarked for the mission. Contract termination fees would have added another $14m (£8m) to Nasa's bill.
The principal investigator Chris Russell, with the University of California at Berkeley, said he was told only that Nasa did not have the money for the programme.
But in a teleconference with reporters on Monday, top Nasa managers said funding for Dawn had been included in the agency's proposed budget for the year beginning 1 October, and that the decision to cancel the programme stemmed from "significant management and technical problems".
"We had a very gut-wrenching decision," said Colleen Hartman, Nasa's deputy associate administrator for science. "We thought at the time that there was too much risk to go forward."
"The decision didn't make any sense," said Mark Sykes, director of the Planetary Science Institute in Arizona and a member of the Dawn science team.
With backing from programme managers at Nasa's Jet Propulsion Laboratory in Pasadena, California, scientists appealed against the decision and asked Nasa to reinstate funds.
On Monday, they got their wish. The agency also increased Dawn's budget by an additional $70m (£40m) to cover the programme's initial $40m (£23m) cost overrun and another $30m (£17m) incurred as a result of the work suspensions.
"I'm glad that there were no fatal technical flaws, and that they were able to find the money after all," said Dr Sykes. "But this is not a good way to do business."
In cancelling Dawn, Nasa also ignored an international team of scientists and institutions that had contributed $40m (£23m) worth of instruments for the spacecraft.
These researchers are also part of the Dawn science team.
Hartman said the international partners had been notified and no doubt were pleased the asteroid mission was saved.
"This is a welcome development," added Bruce Betts, with the Planetary Society, a space advocacy organisation based in Pasadena, California.
"We're happy to be moving forward," added Dr Hartman.
Work suspensions pushed the launch from June this year to the summer of 2007, with the first asteroid encounter expected in 2011.
Dawn's two targets, Vesta and Ceres, are the largest known asteroids in the asteroid belt, which lies between the orbits of Mars and Jupiter.
Nearly as big as planets, the asteroids are believed to have been formed in different parts of the Solar System. They bear little resemblance to one another and are of keen interest to scientists seeking clues to the formation of the early Solar System.
Nasa said its technical concerns stemmed primarily from the probe's innovative ion engine.
Unlike traditional chemical-burning thrusters, Dawn's engine expels electrically charged particles, or ions, stripped from xenon gas. Nasa tested a similar technology on its Deep Space One probe.
It is a slow but efficient form of propulsion, and will allow the probe to do something that has never been done before: Dawn will be able to go into orbit around each asteroid for extended studies before moving on to its next target.