**5.3 Second extended mission experience (solstice mission)**

*Safe mode activation #6:* On November 2, 2010, during the S64 background sequence, a file was uplinked to reset the backup AFC computer during normal operations. The command was hit by a cosmic ray and corrupted (bit flip), causing the prime CDS computer to reset from receipt of this erroneous command (caused by a failure of the uplinked command to process properly). As a result, Safe Mode was called.

*Fix:* The chances of a cosmic ray hit on an uplinked command are so unlikely (millions to one), that no fix was implemented.

*CAPS instrument failure:* In April 2011, Cassini's power bus suffered unexpected swings. The imbalance remained in place until June of that year, when another shift occurred. Engineers suspected the high-rail short to be within the CAPS instrument and 3 days later the instrument was turned off. The bus returned to near preanomaly values, and the CAPS instrument was left off while an investigation was conducted into the cause of the short condition, and whether CAPS could be turned back on. The conclusion was that it was safe to turn the CAPS instrument back on. Two days later the short condition reappeared, causing the bus voltage to shift again. The CAPS instrument was left on and the shifted values remained until June 2012, until a series of voltage swings occurred over a 24-h period. The condition culminated until CAPS was autonomously shut off by the SSPS switch, by an overcurrent draw from the instrument. A second investigation was undertaken after this CAPS anomaly, leading to a decision to leave the CAPS instrument off for the remainder of the mission.

*Loss of the USO:* At the beginning of the DSN track on December 23, 2011, no downlink signal was received from Cassini. The suspected cause was bad predicts used at the DSN station. New predicts were built and two different DSN antennas were used to acquire the spacecraft's signal to no avail, ruling out the bad predicts as the cause of the anomaly. Attention then turned to the USO as the source of the problem. Cassini's signal was acquired after RTLT (when the USO is no longer used by the spacecraft, but switches over to the DST's VCO).

*Fix:* A test was devised to determine if the DST's downlink path or the USO was the cause of the loss-of-signal problem. It was determined that the USO had failed. The Auxiliary Oscillator was used for the remainder of the mission, which yielded a "rattier" signal. Spacecraft operations were not affected by the loss of the USO; however, the quality of radio science observations was reduced.
