No. 47 - Cruise Mode
26 Aug 2005 14:49
Report for Period 29 July to 20 August 2005
The reporting period was originally dedicated to spacecraft monitoring in Passive Cruise Mode. However, an unexpected fuel over-consumption of 20 grams and a delta-V of 2.5 mm per second were detected off-line on data acquired during DOY 216. On DOY 220, a short pass was taken on short-notice to confirm the delta-V.
Spacecraft telemetry indicated that the fuel consumption had gone back to normal, and that the acceleration had disappeared. Telemetry downlinked on DOY 223 finally showed anomalous spacecraft dynamics between DOY 213 and 216. Therefore, the decision was taken on DOY 224 to return the spacecraft to Active Cruise Mode as soon as possible.
The system transition to Active Cruise Mode took place successfully on DOY 230. The transition was completed on DOY 231, when the telecommunications were reconfigured to HGA-X and maximum TM/TC bit rates. All telemetry acquired during Passive Cruise Mode was successfully recovered on DOY 231.
Since DOY 216, no anomaly could be detected in the spacecraft dynamics and RCS behaviour. Since DOY 231, the spacecraft is being monitored on a weekly basis.
No payload operations were carried out in the reporting period. SREM was kept active in the background for the entire period, and configured for a lower data collection rate to cope with the reduced visibility periods and bitrates available during the passive cruise period.
A total of 8 New Norcia passes of a max duration of about 10 hours commanding were taken over the reporting period, 4 of which scheduled on short notice to support investigation of the spacecraft anomaly in Near Sun Hibernation Mode (NSHM) and anticipated transition to Active Cruise Mode.
At the end of the reporting period (DOY 238) Rosetta was at 152 million km from the Earth. The one-way signal travel time was 8 minutes 7 seconds.