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Mission Operations

The tilt of Cluster 3 (45° with respect to Cluster 4) has been successfully performed in May 2008. This allowed the 3D electric field to be measured for the first time by combining both spacecraft measurements. Preliminary results show the successful measurement of parallel electric fields in the auroral zone. The tilt also improved significantly the localization of the sources of radio waves in the magnetosphere.

The recent long eclipse season - the most critical period of the Cluster mission since the launch in 2000 - has been passed successfully.

Constellation manoeuvres were finished on 4 July. C3 and C4 were put at 17 km from each other, their closest separation distance in the Cluster lifetime. This constellation will allow investigating very small plasma structures in the tail of the magnetosphere.

The four spacecraft and instruments are operating nominally. The short eclipse season has been passed successively. This year the eclipse period was 1.5 month long with a total of 50 eclipses. A cycling of batteries was introduced by ESOC to give a rest to some batteries in the middle of eclipse season.

All four spacecraft successfully went through the long eclipse season which has just finished. A new mode of operation called "decoder only", where the on-board computer and all other sub-systems are switched off, was defined on spacecraft 1 since the batteries are now very weak. This spacecraft came out successfully of the eclipse and was re-configured by the ESOC flight control team.

The four spacecraft and instruments are operating nominally. The short eclipse season has just finished and a few anomalies have been observed due to the aging of the batteries. These have proven, however, that the spacecraft can survive a short eclipse with minimum power in the batteries and it will give some experience for the next long eclipses in September 2006.

The four spacecraft and instruments are operating nominally. The phasing manoeuvres were executed in November 2005. The spacecraft multi-scale configuration (C1, C2 and C3 spacecraft separated by 10 000 km and C3 and C4 separated by 1000 km) was changed to a perfect tetrahedron of 10 000 km to observe the polar cusp in February/March 2006. The solid state recorder capacity was increased from 5 to 7.5 Gbit by switching on the 3rd memory module. This will allow more flexibility in the data.

The four spacecraft and instruments are operating nominally. The largest constellation manoeuvres ever performed with Cluster were successfully executed in June-July 2005. The spacecraft reached the largest separation distance of 10 000 km through a series of the most complex manoeuvres ever done with 49 individual manoeuvres executed over a total of 21 hours of thrusters firing. The spacecraft are now in a multi-scale configuration with 3 spacecraft (C1, C2, C3) at 10 000 km and 2 spacecraft (C3, C4) at 1000 km.

The four spacecraft and instruments are operating nominally. The short eclipse (less than 1 hour) season has been passed successfully. On spacecraft 1, one of the two batteries had a voltage drop about 3 minutes before the end of the eclipse and the second battery was not powerful enough to keep the spacecraft and instruments working. A switch over from the main on-board computer to the redundant one triggered and all instruments were switched off. After re-configuring the spacecraft, the instruments were successfully switched back on. To prevent this problem from happening again, a third battery was brought on line on each of the four spacecraft.

The spacecraft and instruments are operating nominally. An anomaly on one of the CIS (ion) detectors has been observed on spacecraft-2. The problem seems to be on the MCP high voltage. Further investigation is on-going. Ion measurements are being performed on this spacecraft by the second CIS detector. An on-board computer switch-over from main to redundant occurred on 18 October on spacecraft-4 and on 31 October on spacecraft-3. This was due to an error in the computer memory most likely due to energetic particles. The spacecraft and payload were reconfigured with success a few days later.

The spacecraft and instruments are operating nominally. In connection with the Perseid meteor shower in August 2004, the electron instrument PEACE on C3 detected anomalously high counts and one of the sensors (HEEA) was automatically switched off. It was later switched back on and is presently working nominally.

Cluster is now in its 4th year of operations and the four spacecraft and instruments are working nominally. The data return was, on average, 99.7 % in March 2004 and April 2004. The VILSPA-1 and Maspalomas ground stations are operating nominally. The spacecraft will be moved away from each other from a starting distance of 250 km to a final one of 1000 km. At the same time, the argument of perigee will be brought down to compensate the natural drift. This means that four long manoeuvres, around 1 hour and 20 minutes, and 11 small ones (less than 5 minutes) will be executed on each spacecraft.