Kepler searches for planets by monitoring around 150,000 stars in the Cygnus and Lyra constellations for blips that could indicate the presence of planets transiting in front of the stars. A unique feature of the spacecraft is that it will stare at these same stars continuously for its 3-4 mission lifetime, enabling the possibility of detecting several transits by planets in year-long, Earth-like orbits. NASA says that during the scheduled contact, Kepler was found to be using the wrong system to keep focused on its chosen catalog; it was using star trackers, instead of fine guidance sensors needed to track the stars with sufficiently fine accuracy. The problem came about after a regular procedure to dump momentum that builds up as Kepler pushes against the solar wind.
Kepler's next data release is expected on February 1st, 2011.