Artist's impression about the Kepler mission. Image credit: NASA.
During a regularly scheduled contact with the Kepler spacecraft on Dec. 13, 2010, the project team discovered Kepler had experienced an anomaly. Kepler was found in coarse point attitude, as opposed to finepoint. Coarse point means the Kepler is using its star trackers for pointing at the Kepler Field-of-View (FOV) instead of the fine guidance sensors that are hard-mounted to the Kepler focal plane array. To properly track Kepler’s target stars with fine accuracy, Kepler must be in finepoint attitude.
Project engineers began analysis of the situation to determine the cause of the anomaly. They determined that Kepler failed to transition properly from coarse point to finepoint attitude after a pre-planned momentum wheel de-saturation. Momentum wheel de-saturations occur on a regular basis for the spacecraft, approximately every three-and-one-half days. The de-saturation uses thrusters to dump momentum buildup on Kepler’s reaction wheels, which spin continuously to counter the solar wind, which pushes on the spacecraft body as Kepler points at its FOV.
The project team was able to recover the spacecraft to finepoint relatively quickly. Only 13 hours of science data collection were interrupted by this anomaly. The team will continue to evaluate telemetry from the event to confirm the root cause, and develop any further mitigations. The Kepler mission budgets for interruptions in the mission, including scheduled maintenance on the spacecraft and anomalies such as this. The mission remains well within the budget outages allowed.
Meanwhile, the project science team is preparing for Kepler-related sessions at the upcoming American Astronomical Society meeting in Seattle in early January. The Science Team also is preparing for the planned Feb. 1, 2011 release of Quarter 2 data and release of sequestered target data from Quarter 0 and Quarter 1.