No. 62 - Rosetta Enters Active Cruise Mode
On 26 July, the spacecraft was reconfigured to Active Cruise Mode. This system-level transition involved a reconfiguration of the AOCS subsystem to Normal Mode, a reconfiguration of the thermal subsystem hardware, and a reconfiguration of the telecommunications subsystem to High Gain Antenna and maximum bit rates. The mode performance is being closely monitored on a weekly basis using real-time housekeeping telemetry and radiometric data.
The Rosetta Plasma Consortium (RPC) was activated for five days on 4 July as the spacecraft crossed the tail of comet Honda. As this operation took place with the spacecraft in Near Sun Hibernation Mode, science and housekeeping telemetry were stored on-board and will be dumped at the next opportunity in August. In addition, SREM was kept active in the background for the entire period.
A total of 6 New Norcia passes of 8 hours commanding were taken during the reporting period. TM/TC links with the OCC have been established for all passes.
| NNO Pass |
Date | DOY |
Main Activity |
| 858 | 05.07.06 | 186 | NSHM monitor pass |
| 865 | 12.07.06 | 193 | NSHM monitor pass |
| 872 | 19.07.06 | 200 | NSHM monitor pass |
| 877 | 24.07.06 | 205 | NSHM Exit Preparation - Reaction Wheel check |
| 878 | 25.07.06 | 206 | NSHM Exit |
| 879 | 26.07.06 | 207 | Monitor pass - TTC to HGA / high bit rates |
At the end of the reporting period (DOY 209) Rosetta was at 307.8 million km from Earth (2.06 AU; one-way signal travel time was 16 minutes 29 seconds). The distance to the Sun was 174.8 million km (1.17 AU).
Spacecraft Status
Thermal
The thermal behaviour of the spacecraft is nominal and stable. Its configuration changed from NSHM1 to ACM1 on DOY 207.
The Antenna Pointing Mechanism Electronics (APME) Motor temperature remained under close monitoring until the APME Hot settings were applied on DOY 208. The APM heater switch was found open at AOS (acquisition of signal) on DOY 200, indicating that two out of three of the APME temperatures had reached 47 °C. Though direct monitoring of the temperature evolution with the heater active was not possible anymore, telemetry trending indicated that in case of a safe mode before the APME Hot settings would be applied, the temperature would have remained well within the soft limit of 60
The Reaction Wheels were also monitored in NSHM, to assess the need for heating prior to reactivation at NSHM exit. The wheels temperatures at NSHM Exit were between 12 and 15 °C, thus not requiring any warm-up prior to their reactivation on DOY 207.
On DOY 208, the TCT configuration table in RAM was updated to apply Close-To-Sun temperature limits for the APME and some thrusters.
Payload
The only instruments operated in the reporting period were RPC and SREM. RPC was activated between DOY 185 and 189 to take measurements as Rosetta crossed the tail of comet Honda. This is the first time an instrument performs scientific measurements with the spacecraft in Near Sun Hibernation Mode. Due to the limited access to the spacecraft in this mode, the instrument was operated fully off-line, and telemetry will be retrieved only several weeks after the end of the observation, with the spacecraft back in Normal Mode.
SREM remains active in the background for radiation monitoring. The accumulation parameters were updated for Active Cruise on DOY 207/208.
Future Milestones
The Mars Swingby Phase formally started on 28 July. The phase includes two deep space manoeuvres in September 2006 and April 2007, while the actual swingby will take place on 25 February 2007.
Upcoming short-term operations include a payload passive checkout (PC3) and two thermal characterisations in August/September and the first payload active checkout (PC4) in November/December.