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Credit: ROSAT

The German X-ray satellite ROSAT, which has been operating for more than four times longer than planned, may have to be abandoned after it was accidentally pointed towards the Sun.

The accident resulted in damage to one of its three main instruments, the high-resolution imager (HRI), developed at the Smithsonian Astronomical Observatory in Cambridge, Massachusetts. As a result, the latest call for research proposals, whose deadline was next month, has been put on ice as scientists attempt to determine the extent of the damage and assess whether a rescue is possible.

If not, the satellite's operation will not overlap with two new major X-ray astronomy missions, NASA's Advanced X-Ray Astrophysics Facility (AXAF) and the European Space Agency's XMM. An overlap would have kept new data flowing to the X-ray astronomy community without a break.

ROSAT was launched in summer 1990, with an intended lifespan of 20 months. One of its main goals was to carry out an all-sky survey of X-ray sources, and a catalogue of such sources was published by the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, in 1996.

As well as the HRI, ROSAT's other main instruments are a Position Sensitive Proportional Counter and a Wide Field Camera. After the satellite's positioning system failed last April, attempts were made to adapt the Wide Field Camera, developed at Britain's University of Leicester, to take over the control function. But a chain of events resulted in loss of positional control during a test at the end of September.

ROSAT scientists say there is little hope of reviving the HRI.

Funding for the satellite's operation has been guaranteed by the German ministry of research until the end of 1999, but none of ROSAT's instruments is likely to be usable for that long.

One consequence of the technical problems is that the life of the third main instrument, the Positional Sensitive Proportion Counter, has been reduced to a few days. This instrument measures both the position and energy of X-ray sources, and was developed at the Max Planck Institute for Extraterrestrial Physics.

The Wide Field Camera has already completed most of the viewing within its technical capability, says Martin Ward, director of the University of Leicester's X-Ray Astronomy Group.

But X-ray astronomers are facing additional disappointments. The launch of AXAF, originally planned for last August, was delayed until next January following technical problems, and last week a further delay of several months was announced. XMM has been delayed for six months, until February 2000 (see Nature 395, 732; 1998).

Ward says that, although the likely loss of ROSAT is unfortunate, there are still opportunities for X-ray astronomers to do new work, for example with the Italian mission SAX, launched in 1996.

Joachim Trümper, the director of the ROSAT project, is disappointed but pragmatic. “We expected two years,” he says, “so with a happy and fruitful life of eight years we can't complain. We knew it would have to end sometime.”