Scientists lose contact with solar craft.

The past couple of weeks should have been an easy transition for solar astronomer Arthur I. Poland. Retiring from his administrative role with an orbiting solar observatory so that he could devote his full attention to data acquired by it, Poland had been looking forward to obtaining new information on the giant flames of gas that are high above the sun's surface.

Alas, the spacecraft that Poland had pinned his hopes on may no longer be able to make these or any other observations. On June 25, ground controllers lost contact with the Solar and Heliospheric Observatory (SOHO), and some fear the $1 billion spacecraft may remain silent.

Launched in December 1995, SOHO houses 12 instruments that probe the interior of the solar cauldron as well as its million-degree outer atmosphere. The observatory has already revealed new details of how gas and magnetic clouds shoot out from the sun, events that can trigger large-scale power outages on Earth (SN: 2/1/97, p. 68). It has also helped generate a three-dimensional view of the sun's interior and has provided spectacular images of sun-grazing comets and solar flares (SN: 5/30/98, p. 342). For most astronomers, however, SOHO's raison d'etre was to have come 2 to 3 years from now, when the sun is expected to reach the peak of its 11-year activity cycle.

Able to stare continuously at the sun from a vantage point 1.5 million kilometers from Earth, SOHO was central to the observations planned for the coming solar maximum. Without the craft, "we're going to be blind," says John W. Leibacher of the National Solar Observatory in Tucson. "It's as if you lived in Houston and you were in hurricane season and there were no weather satellites."

He emphasizes, however, that it's premature to mourn SOHO's passing. The craft is "missing in action, it's not known to be dead," he says.

Mission controllers at NASA's Goddard Space Flight Center in Greenbelt, Md., speculate that they lost contact with the craft because it tumbled out of control, leaving its power-producing solar panels pointing away from the sun. Recent calculations suggest that over the coming weeks, the craft's motion may allow an increasing amount of sunlight to strike the panels.

If this prediction holds true, the panels may eventually absorb enough sunlight to charge the craft's batteries and allow SOHO to resume operation. Ground controllers are already trying to locate the craft using radar. Although the tumbling may have damaged instruments on the observatory, the mission scientists are guardedly optimistic.

In the meantime, Poland, who is based at Goddard, is already devising a backup plan. Contacting their colleagues, he and other SOHO scientists have begun making an inventory of spare parts and duplicates of instruments aboard SOHO. From that list, they hope to put together a smaller, less costly satellite that might be launched just after the turn of the century, in time to record solar activity at its most turbulent.