- 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.
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- 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.
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- 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.
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- 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.
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- 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.
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- 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.
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- Scientists now believe that faulty computer
programs were to blames for the loss of SOHO. This is what happened:
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- 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.
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- Unfortunately the computer program lacked
the crucial command to turn on the backup gyroscope.
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- 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.
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- Having to rely on a faulty gyroscope
SOHO went into a spin. Its solar panels pointed away from the sun and it
lost power.
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- Currently the spacecraft may be spinning
out of control. Hopes are dim that SOHO can be rescued.
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