At intervals, and particularly when the spacecraft has its apogee over the South Atlantic, the memory of the BCS microprocessor can be corrupted by a Single Event Upset (SEU). Often this affects a part of the memory that does not disturb the running of the BCS, but whenever an SEU is detected (most are flagged as a result of a checksum calculation), the BCS microprocessor is rebooted. Occasionally, several hours, or days of data have been lost before this is done.