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CONTACT: David F. Salisbury, News Service (650) 725-1944

Solar physics spacecraft in serious trouble

The billion-dollar SOHO spacecraft that has been producing a steady stream of spectacular images and important new information about the Sun for more than two years is in serious jeopardy. On June 24, SOHO controllers lost contact with the spacecraft during maintenance operations. Efforts to re-establish contact have not been successful.

The news has been a serious blow to the 27 Stanford researchers who have been operating one of the key instruments on the spacecraft, whose official name is the Solar and Heliospheric Observatory. The group, called the Solar Oscillations Investigation team, has been operating an instrument called a Michelson Doppler imager that reads ripples on the Sun's surface that provide information about the conditions in its deep interior.

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"It looks quite bad," says Phil Scherrer, professor of physics and principal investigator of the Stanford team. Apparently the spacecraft has assumed an orientation that keeps its solar panels from receiving much sunlight so they are not producing the vital power that the spacecraft needs to operate.

"The only remaining hope is that in a week or so the spacecraft will have moved into a position where the solar panels are receiving enough sunlight to repower the spacecraft," Scherrer says. Then, if SOHO's instruments and radios have not been too damaged by the heat build-up that is expected, it might be possible to regain control.

SOHO, which was launched in 1995, already has fulfilled its original mission. An extended mission would allow it to operate for a full six years so that it could document the changes that take place in the sun through a full solar cycle.

The solar physicists are consoling themselves with the fact that they already have collected a tremendous amount of data: more than 30 terabytes, or 1.1 million minutes of solar observation time. This data will take years to analyze fully. Scherrer says that they can count on at least 1.5 years of NASA support for this purpose.

In addition, the group is working hard on a proposal for the follow-up to SOHO. This consists of a Doppler imager placed on a satellite in geosynchronous orbit above Earth that would be controlled from Stanford. The proposal is due in August.

"Now we are going to have to take this proposal even more seriously than we did before," Scherrer says.


By David F. Salisbury

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