During a planned contact on March 14, the Kepler spacecraft experienced a safe mode event. A safe mode is a self-protective measure that the spacecraft takes when something unexpected occurs. During safe mode, the spacecraft points the solar panels directly at the sun and begins to slowly rotate along a sun-aligned axis. This safe mode orientation provides the vehicle with the maximum power and limits the buildup of momentum from solar wind. The spacecraft also swapped to its backup subsystem interface box (SIB), an electronics component that controls power distribution to all spacecraft subsystems, and powered off the photometer, the instrument used to measure light intensity to detect planets. This is a normal procedure when a safe mode is entered.
The anomaly occurred immediately after the network interface card (NIC) reset command was issued to implement a firmware update. The NIC is a key component of the SIB and supports the SIB's functions. The SIB performs power control and distribution, and thermal control; it interfaces to the attitude determination and control subsystem and to the reaction control subsystem. The update to the NIC firmware has been in development since January and is designed to mitigate the effects of the coarse sun sensor noise discovered late last year. Coarse sun sensors assist in providing spacecraft orientation.
Shortly after the safe mode entry, the team analyzed the spacecraft data and determined all subsystems remained healthy. During recovery actions, the Deep Space Network was used to downlink telemetry and began recovery of files to assist in the anomaly analysis. The team has since successfully reinitiated power to the primary SIB, confirmed its health and status, and also verified the new version of the NIC firmware had loaded correctly, and passed a health and safety check.
The star trackers have been powered on and the spacecraft has been commanded to standby orientation, with solar arrays aligned toward the sun and Kepler pointed to ecliptic north. Updates will be posted as the team makes progress in the recovery.