Last December 2nd marked the 10th anniversary of the launching of one of the most productive spacecraft ever built. The hard-working $1.2 billion Solar and Heliospheric Observatory(SOHO) satellite blasted into space in 1995 to a special vantage point around the Sun some 1.5 million kilometers from the sunward side of Earth.
A joint project of NASA and the European Space Agency, SOHO's primary mission is to study the Sun and continuously monitor its activity, as well as to alert Earth of impending geomagnetic storms. Despite being plagued by technical problems (a communications blackout and the failure of its last gyroscope in 1998 and a stuck main antenna in 2003), ground controllers have been able to keep the spacecraft alive. They developed new software to stabilize and control it without a gyroscope and are using its secondary antenna to keep the data flowing. In fact, SOHO's service is now being extended at least until 2007, a decade longer than originally planned, so it can cover a complete 11-year solar cycle.
SOHO has also gained the distinction of being the most prolific comet "discoverer" in history. A growing number of amateur astronomers worldwide regularly search for sungrazing comets captured on images taken mainly by the spacecraft's LASCO coronagraphs (see the cover story of the August 2005 Sky & Telescope). These images are posted in near-real time at the SOHO comet site. To date, SOHO has 1,062 comet discoveries to its credit.