Cassini Experiences Communications Problems

NASA Cassini Significant Events 12/21/11 – 1/3/12
“Friday, Dec. 23 (DOY 357) – No signal was detected from the spacecraft today at the beginning of track at Deep Space Station (DSS) DSS-43, the Canberra 70 meter station. Additional tracking was obtained at Canberra’s DSS-45 and Goldstone’s DSS-14 to no avail. The 2-way coherent signal was acquired at the one round trip light-time point into the track as usual, indicating it was a spacecraft problem and not a ground system error. Incident Surprise Anomaly (ISA) #50901 and Discrepancy Report (DR) C108400 were submitted to document this spacecraft anomaly. Commands were sent on Dec. 25 to inhibit the ultra-stable oscillator (USO) and use the auxiliary oscillator as the frequency source for the downlink signal. The spacecraft has operated in this mode for every pass starting on Dec. 27, and telemetry is being received for entire passes again. Data loss was limited to two round-trip light time periods. Analysis of the problem has been delayed because of the holidays with many of the key engineers being unavailable, but it is now well underway.”