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Solar power: a false-colour image from TRACE, which may take on some of SOHO's tasks. Credit: ALAN TITLE/ STANFORD LOCKEED INST. SPACE RES./NASA

Ground controllers lost contact last week with the $1 billion Solar and Heliospheric Observatory (SOHO), the centrepiece of an international programme to study the Sun and its interaction with Earth. Scientists involved in the US-European project were pessimistic at the beginning of this week about its chances of being recovered.

Engineers at the US space agency NASA's Goddard Space Flight Center were performing routine maintenance on 24 June of SOHO's position-keeping ability when the spacecraft lost its orientation to the Sun.

Although it went into an automatic routine designed to reorient itself to the Sun, the spacecraft lost radio contact with the Earth. Attempts to regain contact were unsuccessful, even using the large dish antennas of the Deep Space Network. If its solar arrays were pointing in the wrong direction at the time, its on-board batteries would have drained quickly, leaving it without power.

Launched in December 1995, SOHO had completed its nominal two-year mission, but the European Space Agency (ESA) and NASA, who shared the development costs, had extended its operations to 2003.

The decision had strong backing from the scientific community. A report from the National Research Council urged NASA to continue operating SOHO and the other satellites of the International Solar Terrestrial Program (ISTP), including WIND and POLAR, through the “solar maximum”, the peak in the 11-year cycle of solar activity expected between 1999 and 2002.

SOHO has returned important results ranging from the detection of solar quakes caused by flares to a detailed study of coronal mass ejections. Parked in a stable orbit between the Sun and Earth, it monitors the Sun's surface and extended atmosphere.

Failure to recover the observatory would be a “tremendous loss” to the solar-maximum observing campaign, says project scientist Art Poland. No other satellite has spectrometers and coronagraphs trained on the Sun, or can return data on solar seismology and magnetic fields.

NASA's recently launched Transition Region and Coronal Explorer (TRACE) spacecraft could offset the loss using its ultraviolet telescope, according to Alan Title of the Stanford Lockheed Institute for Space Research in Palo Alto, California, a principal investigator for TRACE and member of the SOHO team. But it would have to record data more frequently, he says, because it has a narrower field of view than SOHO.

Plans would probably involve placing duplicate instruments on a variety of different spacecraft, rather than relying on another single observatory such as SOHO.

One investigator thinks the capability of the mission could be duplicated for 20-30 per cent of the cost of SOHO. But NASA and ESA would have to act quickly, and funding would have to be approved.