Washington

A NASA mission that was to have measured the positions of stars with unprecedented accuracy has been cancelled because of cost overruns and problems with its detectors.

The Full-sky Astrometric Mapping Explorer (FAME), which was selected in 1999 as one of the agency's medium-sized Explorer missions, was due to launch in 2004. It would have mapped the positions of 40 million stars with 20 times the accuracy of Europe's Hipparcos mission, the best existing astrometric survey undertaken from space.

NASA wrote to FAME's principal investigator Kenneth Johnston, of the US Naval Observatory in Washington DC, on 4 January, saying that it was withdrawing its support because of growth in the project's estimated total budget from $180 million to $220 million. The agency also cited difficulties in obtaining charge-coupled device (CCD) detectors for the mission. The manufacturer, Scientific Imaging Technologies of Tigard, Oregon, has had trouble producing CCDs to the required specifications, Johnston says.

Project managers had already scaled back the mission, and Johnston offered to try to obtain further funds from the Navy to ease the cost overrun, but NASA saw too much risk in continuing with the mission. “There's a real problem at NASA headquarters with budgets,” Johnston says. “They have to do something. We just happened to be in the wrong place at the wrong time.”

FAME's cancellation leaves a gap in astrometry missions. NASA's more sensitive Space Interferometry Mission will not be launched until 2009, and Europe's proposed GAIA mission is itself in jeopardy and in any case is not scheduled to begin until 2011 at the earliest (see Nature 414, 383; 2001). Robert Reasenberg of the Harvard-Smithsonian Center for Astrophysics, a former project scientist for FAME, laments the loss of the science, but agrees that NASA has to take action to rein in projects that are running over budget. “If I were starting a programme now, this decision would loom pretty large,” he says.

Johnston confirms that the mission had problems procuring the CCDs. “CCDs sound like they're off the shelf,” he says, “but it's not a guaranteed process.”

Johnston still hopes eventually to secure funding from NASA or the Navy, although he admits that it's a “big mountain to climb”.