N° 05-99 - Paris, 3 February 1999


For the second time in six months, engineers have revitalised ESA's orbiting solar observatory SOHO, and have also set a space record.

The spacecraft went into a self-protection mode (called Emergency Sun Reacquisition - or ESR) on 21 December, when the last of its three gyroscopes failed. Having lost a fundamental orientation system, SOHO continually fired onboard jets to keep its sensors pointed toward the sun.

To stop the rapid depletion of hydrazine fuel, over the last month, engineers at ESA and Matra Marconi Space have designed a software program to enable the spacecraft to resume science operations without gyroscopes as from 2 February. The satellite is now reprogrammed to ignore faulty information from the gyroscopes and to use new software sent up by ground controllers. This is the first time that a spacecraft equipped with gyroscopes has carried on working without them.

"It's like instructing an airplane pilot from the ground to execute very complex manoeuvres and helping him make a successful landing" said ESA's Michel Verdant, SOHO's programme manager.

"SOHO is back at work and we are absolutely thrilled. Thanks to the outstanding efforts of so many highly competent people, SOHO has a new life ahead of it and many discoveries to come," said Roger Bonnet, Director of ESA's science programme.

Last summer engineers had already regained control of the observatory after it lost orientation and vanished in space.

SOHO was launched in December 1995. After three years of operations, ESA and NASA are now expecting the mission to continue until 2003. The extension will allow SOHO to observe intense solar activity when the number of sunspots reaches a maximum around mid-2000.

SOHO remains the flagship of a multinational fleet of solar observatories, including the on-going ESA/NASA Ulysses mission and ESA's forthcoming Cluster II spacecraft.

The first picture of the Sun taken by SOHO after the new recovery is available on the Internat at :http://sci.esa.int/soho

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