No 23-98 - Paris, 26 June 1998

SOHO spacecraft observations interrupted

At 01:16 Paris time on 25 June 1998, during routine maintenance operations, ground controllers lost contact with the SOHO (Solar and Heliospheric Observatory) spacecraft and the satellite went into Emergency Sun Reacquisition (ESR) mode. The ESR mode is activated when an anomaly occurs and the spacecraft looses its orientation towards the Sun. When this happens, the spacecraft automatically tries to point itself towards the Sun again by firing its attitude control thrusters under the guidance of an on board Sun sensor.

Efforts to re-establish nominal operations did not succeed and telemetry was lost. Subsequent attempts using the full NASA Deep Space Network capabilities have so far not been successful.

ESA and NASA engineers are continuing with the task of re-establishing contact with the spacecraft.

The SOHO mission is a joint undertaking of ESA and NASA. The spacecraft was launched aboard an Atlas II rocket from Florida on 2 December 1995 from the Cape Canaveral Air Station. Mission operations are directed from the control center at NASA Goddard Space Flight Center in Maryland, USA.

In April 1998 SOHO successfully completed its nominal two-year mission to study the Sun's atmosphere, surface and interior. Major science highlights include the detection of rivers of plasma beneath the surface of the sun; the discovery of a magnetic "carpet" on the solar surface that seems to account for a substantial part of the energy that is needed to cause the very high temperatures of the corona, the Sun's outermost layer; the first detection of flare-induced solar quakes; the discovery of more than 50 sungrazing comets; the most detailed view to date of the solar atmosphere; and spectacular images and movies of Coronal Mass Ejections, which are being used to improve the ability to forecast space weather.

For further information:

Franco Bonacina, ESA, Paris (Phone: + 33 1 5369 7713) Don Savage, NASA Headquarters, Washington DC (Phone + 1 202 358 1727) Bill Steigerwald, Goddard Space Flight Center, Greenbelt, Md. (Phone + 1 301 286 5017)

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