No. 64 - Fourth Passive Payload Checkout
The thermal characterisation was performed on the night between 31 August and 1 September to confirm that the spacecraft can remain indefinitely in an attitude corresponding to a solar aspect angle of 110 degrees at a Sun distance of 1 AU or more. The temperature of the bottom-mounted spacecraft units was closely monitored in near real-time. All units almost reached steady state well within their defined temperature limits.
The third passive payload checkout (PC2) was performed outside visibility in the period 25 - 29 August. In addition the RSI passive checkout, which requires ground contact, took place on 22 August over New Norcia. All instruments (except GIADA and ROSINA) were activated and checked out in sequence. The data generated during the checkout were dumped over the following two ground station passes and are under analysis by the instrument teams.
SREM was kept continuously active in the background for the entire reporting period.
A total of 4 New Norcia passes of 8.7 hours commanding in average were taken during the reporting period. TM/TC links with the OCC have been established for all NNO passes. In addition, two tracking passes of 4 hours have been taken with DSN.
|906||22.08.06||234||RSI Checkout - Uplink Passive Checkout Timeline|
|907||23.08.06||235||Monitor pass - WOL|
|914||30.08.06||242||Dump Passive Checkout Data - WOL|
|915||31.08.06||243||Dump Passive Checkout Date - Thermal|
Characterisation (SAA 110° at 1 AU)
At the end of the reporting period (DOY 244) Rosetta was at 288.0 million km from Earth (1.93 AU; one-way signal travel time was 15 minutes 26 seconds). The distance to the Sun was 156.3 million km (1.04 AU).
The thermal behaviour of the spacecraft is nominal and stable. It remains configured for Active Near Sun cruise (ACM1 since DOY 207/2006).
A thermal characterisation was performed on DOY243/244 to confirm that the spacecraft can sustain thermally an attitude corresponding to a solar aspect angle (angle between the +Z spacecraft axis and the Sun direction) of 110 degrees at Sun distances of 1 AU or more. Until now, the maximum solar aspect angle that had been characterised successfully for indefinite operations was 95°.
The spacecraft remained in the characterisation's attitude for 13 hours. Two emergency slews which had been loaded on the Mission Timeline in case some spacecraft temperatures would reach their upper limits during the test were deleted in real-time during the pass.
The monitored units included the front and bottom thrusters, the RCS lines and the NTO tank temperatures. All units showed a clear temperature increase, but remained within the defined limits and almost reached steady state during the test. The maximum temperature was reached by thrusters 4 and 5 (bottom front attitude thrusters), which reported 52.5 °C during the test. This is well within the hard limit of 60 °C defined for these thrusters. The temperature of bottom thrusters 10 and 11 reached about 45 °C, leading to an expected spurious triggering of the on-board Thermal Control Application Program. The diagram below illustrates the evolution of the temperature of thrusters 4, 5, 10 and 11 during the test.
The instruments temperatures as reported by the TRPs decreased during the test. The test attitude was such that the HGA shaded partially the +X face of the spacecraft (angle between the +X spacecraft axis and the Earth direction of -40 °C). As a result, the temperature of the two MGAs, as well as of thrusters 2 and 7 (upper front attitude thrusters) decreased significantly during the test.
SREM remains active in the background for radiation monitoring with accumulation parameters configured for active cruise.
On DOY 234, the passive checkout 3 for RSI was successfully executed over New Norcia, according to the defined timeline. All TTC subsystem and ground station operations were executed nominally.
The payload passive checkout was executed between DOY 237 and DOY 241. All instruments were activated individually in sequence via MTL commands, with the exception of ROSINA and GIADA. All activities took place as usual outside coverage. All commands were successfully executed and all data downlinked over the two New Norcia passes on DOY 234/235 and 235/236. Many out-of-limit alarms and anomaly events were generated by the instruments, most of which were expected or have already been declared as normal by the relevant instrument teams. The data analysis is on-going and a final report of the checkout activities will be produced separately.
A total of 4 New Norcia passes were taken over the reporting period. The station performed nominally during the reporting period. On DOY 236, the station support to Rosetta was shortened by 7.25 hours due to a safe mode support request by Mars Express.
The Mars Swingby Phase formally started on the 28 July 2006. The actual swingby will take place on the 25 February 2007 and will be followed by a Deep Space Manoeuvre in April 2007.
Upcoming short-term operations include another thermal characterisation and a Deep Space Manoeuvre in September and the first payload Active Checkout (PC4) in November/December.