Earth to SOHO, Come in Please

Ground controllers have lost contact with SOHO, the premier sun-watching satellite. Controllers were putting SOHO--the Solar and Heliospheric Observatory--through routine maneuvers on Wednesday when a safeguard program kicked in unexpectedly. The program is meant to help the spacecraft find its bearings when it has lost its orientation toward the sun. "We are sending commands and streams of data, but so far the baby does not talk back to us," says Franco Bonacina, a spokesman for the European Space Agency (ESA) in Paris.

A joint project of NASA and ESA, SOHO was launched in December 1995 and has been monitoring the sun with 11 different instruments from a vantage point 1,500,000 kilometers sunwards from Earth. It has gathered data on everything from the sun's internal structure (Science, 26 June, p. 2047) to the outbursts of gas from the sun's atmosphere, called coronal mass ejections. The success of the craft persuaded planners to extend its operations--originally meant to end last spring--through 2003, to allow the spacecraft to observe the sun as its 11-year cycle of activity peaks.

"It potentially is a tremendous loss," says Cambridge University's Douglas Gough, co-investigator on three experiments studying solar oscillations, which hold clues to the sun's structure and motions. "Next we wanted to find out how the structure was going to change through the solar cycle," he says.

Such plans could fade quickly. One dire possibility is that the spacecraft is tumbling, which would cause the batteries to discharge since the solar panels no longer point toward the sun. That would dim hopes for reestablishing contact with SOHO, and without supervision, the satellite could slowly drift out of its stable orbit, says Bernhard Flick, ESA deputy project scientist for SOHO at the Goddard Space Flight Center in Greenbelt, Maryland. But Flick and others point out that contact with other wayward satellites has been reestablished before. "We haven't lost [SOHO] yet," says Gough. "I'm still optimistic."