The SOHO saga has taken a turn for the worse. Just months after miraculously rescuing the Solar and Heliospheric Observatory (SOHO) from a near-fatal accident, NASA researchers today said the satellite's last stabilizing gyroscope has failed. The breakdown is expected to deny scientists' use of the sun-spotting satellite for at least a month, and it could doom the $1-billion craft if engineers can't figure out a quick fix.
Since its 1995 launch, SOHO's adventures have delighted and dismayed researchers. The joint U.S.-European craft has produced stunning images of the solar furnace and revelations about its inner workings. But last June, SOHO spun out of control during a routine maneuver, and it took frenzied ground controllers 5 months to recapture it (ScienceNOW, 16 September 1998). While the craft's dozen instruments survived the mishap, SOHO endured temperature swings that broke fine wires leading to two of its three gyroscopes. These spinning navigational aids periodically provide information that keeps the craft in its proper orbit and pointed at the sun. The remaining gyro apparently failed on 21 December, sending SOHO into a self-protective sleep and forcing it to burn precious fuel to remain stable.
Engineers expected the failure but weren't sure when it would occur. Now they are scrambling to write software that will allow SOHO to limp along without the gyro. But they are racing the clock: the craft will burn up decades worth of fuel in about 6 months if no solution is found. And even the best solution will probably rob SOHO of some mobility and limit the use of several instruments.
SOHO's setback is "no fun, especially after all that's been done to save it," says Joe Gurman, a SOHO scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "The hope is to develop an interim solution in the next couple of weeks."