No. 72 - First Payload Active Checkout Completed
03 January 2007 09:10Report for Period 15 December to 29 December 2006
The reporting period covers two weeks of active cruise for Rosetta, including the last Active Checkout week and a thermal characterisation. The first payload Active Checkout campaign, which started on 22 November, was completed on 22 December.
During the reporting period, the operated instruments included ALICE, OSIRIS, ROSINA, COSIMA, MIDAS, RPC and SREM. In particular, interactive checkout operations were performed with ROSINA, RPC, MIDAS, OSIRIS and COSIMA. RPC and SREM remain active in the background throughout the campaign. The other instruments are only activated for execution of their checkout sequences.
All checkout operations during the reporting period have executed smoothly, except for one non-interactive RPC Ion and Electron Sensor (IES) activity on 19 December. An interactive OSIRIS health check was performed over DSN on 20 and 21 December and confirmed that the instrument is fully operational.
On 27 December, a thermal characterisation was performed to confirm that the spacecraft can remain indefinitely in an attitude corresponding to a solar aspect angle (SAA) of 140° for Sun distances of 1.2 AU or above. The test was successful. Though the front thrusters showed a large temperature increase, reaching a maximum of 48.3 °C (thruster 11), all monitored thermistors reached steady state temperatures well within their defined limits.
A total of 6 New Norcia (NNO) passes of 12.25 hours commanding were taken during the reporting period. Five tracking passes of 4 hours and one delta-DOR measurement have been taken with DSN.
At the end of the reporting period (DOY 363) Rosetta was at 309.2 million km from Earth (2.07 AU; one-way signal travel time was 16 minutes 33 seconds). The distance to the Sun was 180.6 million km (1.21 AU).
The Platform Thermal Monitoring application program triggered twice on DOY 353 due to crossing of the low temperature threshold for the –X SAS (Sun Acquisition Sensor) and MGA-X (Medium Gain Antenna) as the attitude was changed to a solar aspect angle of more than 90°. These triggers serve as notifications and there is no need for the software to take action upon them. The 90° limit defined on-board, is well below the critical value defined in the Rosetta System Data Base (RSDB).
A thermal characterisation was performed on DOY 361/362 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 140° at Sun distances down to 1.2 AU. This attitude had already been characterised successfully in May 2005 (see also Status Report No. 42), but only for a duration of 12 hours, insufficient to observe the temperatures reaching steady state.
This time, the spacecraft remained in the characterisation's attitude for 24 hours. The monitored units included the front and bottom thrusters and the NTO tank temperatures. All units showed a clear temperature increase, but remained within the defined limits and reached steady state during the test. The maximum temperature was reached by thruster 11 (bottom thruster on +X side), which reported 48.3 °C during the test. This is within the soft limit of 55 °C defined for these thrusters.
The Platform Thermal Monitoring application program reported an out-of-limit on the –X SAS and the MGA-X temperature during the test. No action was taken by the on-board software, and the actual unit temperatures were well within their RSDB-defined limits.
The Payload Thermal Monitoring application program triggered twice on the same line during the test, because the RPC IES temperature went below -10 °C during the thermal characterisation. The on-board software switched ON the corresponding heater line on PL-LCL 40A, but the temperature kept dropping, stabilising around -14 °C. The lower soft limit defined for this parameter is -35 °C.
The fourth PC4 non-interactive block executed outside ground station coverage and involved ALICE, RPC and SREM. The data acquired during this block were retrieved on DOY 352 and completed as expected during the same pass. All operations were successful. RPC remained ON continuously until DOY 355, with the exception of occasional RPC switch-off when required by other instruments. SREM remains active continuously.
During the Mars swingby rehearsal, a few IES commands failed, mainly because the execution of one on-board control procedure (OBCP) command took longer than expected, thereby preventing further occurrences of the OBCP to execute. The timing issue is under investigation.
The instrument was switched off on DOY 355.
MIDAS was switched off on DOY 355.
The tests confirmed that the instrument is fully functional.
The Mars Swingby Phase formally started on 28 July 2006. The actual swingby will take place on 25 February 2007, followed by a Deep Space Manoeuvre in April 2007.
The next short-term activities include an observation of asteroid Lutetia by OSIRIS between 2 and 4 January, and a test of the pre-eclipse Mars observation attitude on 7 January.