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Friday, July 17, 1998 Published at 12:06 GMT 13:06 UK


Solar satellite lost because of mistakes

The suns turbulent surface

Scientists have conducted a post-mortem into the loss of the solar observatory satellite SOHO. They conclude that incompetence was to blame. Our science editor Dr David Whitehouse reports.

On June 25th ground controllers were putting the Solar and Heliospheric Observatory (SOHO) through routine tests when a safeguard program started unexpectedly. This was designed to help the spacecraft find the correct direction in space if it ever lost its orientation towards the Sun.

Just after the safeguard program started all contact with SOHO was lost. Since then, despite using the worlds largest radio-telescopes to look for it, no contact with SOHO has been obtained.

SOHO is a joint project of Nasa and Esa. It was launched in December 1995 and has been monitoring the Sun with 11 different instruments from a vantage point 1.5 million kilometres closer to the Sun than the Earth.

[ image: SOHO - now lost in space]
SOHO - now lost in space
Until June the mission has been a spectacular success, revealing new details of the motions of the Sun's surface and magnetic activity of its hot, thin atmosphere.

This success persuaded planners to extend its life - originally due to end last spring - until 2003. This would have allowed the spacecraft to observe the Sun as its 11-year cycle of activity peaks.

Scientists now believe that faulty computer programs were to blames for the loss of SOHO. This is what happened:

One of SOHO's gyroscopes started malfunctioning. The satellite's onboard computer should then have activated a backup gyroscope and with its help pointed the satellite back at the Sun.

Unfortunately the computer program lacked the crucial command to turn on the backup gyroscope.

The ground controllers stepped in but were not sure which of the two gyroscopes was not working. Unfortunately they issued a command to SOHO to turn off the working gyroscope.

Having to rely on a faulty gyroscope SOHO went into a spin. Its solar panels pointed away from the sun and it lost power.

Currently the spacecraft may be spinning out of control. Hopes are dim that SOHO can be rescued.

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