From: European Space Agency
Posted: Wednesday, February 4, 2004
We are just starting the fourth year of Cluster operations. The spacecraft are working nominally and the instruments are returning data as expected from the Master Science Plan. The data return was, on average, 99.6 % between September and December 2003. The VILSPA-1 and Maspalomas ground stations are operating nominally. The separation distance between the spacecraft is now 250 km to investigate the small structures and measure the electric current at the magnetopause and bow shock.
Attitude manoeuvres were performed at the beginning of January on all four spacecraft. The orbit is more stable than preliminary estimates and a combination of large constellation manoeuvres with a decrease of argument of perigee will allow all four spacecraft to stay in orbit until at least mid-2009.
Shock waves are very important to planetary and astrophysical objects since they accelerate particles to very high energy that can then be detected in-situ near the Earth or through X rays for distant objects. The terrestrial bow shock is one of the main objectives of the Cluster mission. Cluster is able to measure the speed of the shock using the four spacecraft and then derive its thickness. A recent study on 98 bow shock crossings has shown that the thickness of the shock front is best parametrized by the gyro-radius of a small population of solar wind ions trapped by, and gyrating around, the shock front itself. This is in contrast to earlier studies that suggested that the shock front was best characterized by a wave in a fluid.
Reconnection in the magnetotail is believed to occur around 40 Earth radii. One of the consequences of the reconnection process is the release of plasmoids and flux ropes, big magnetic bubbles, that propagate away from the reconnection point. Cluster is located at a maximum of 20 Earth radii and is therefore ideally located to study the flux ropes propagating toward Earth. A recent study identified such flux ropes and, using the four spacecraft, their speed and direction of propagation could be determined very accurately (mean speed about 413 kms-1). In addition the centre of the magnetotail, the plamasheet, became thicker by about 1 Earth radii (6400 km) as the flux rope was passing by.
Operations and Archiving
SOC is successfully co-ordinating the scientific operations including the US instrument with DSN. ESOC is successfully carrying out the spacecraft operations and is delivering the data to the Cluster community as expected. The Japanese spacecraft Servis 1, using the same transponder frequency as Cluster spacecraft 3, was successfully launched on 30 October 2003. The ESOC Flight Dynamic team routinely analyses the orbital parameters to find potential conflicts during ground stations passes of Cluster 3. Up to now no interference events were observed.
The nationally funded Cluster Science Data System (CSDS) is accessed continuously. The average download by individual users over the last three months was around 7 Gbytes/month.
The review of the Cluster Active Archive took place in November 2003. The outcome was positive and the Review Board made recommendations on the instruments. archiving plans and recommended to accelerate the process of building the archiving team. Negotiations are progressing well with the instrument agreements, 7 out of 10 almost ready to be kicked-off. The core archiving team has been interviewed and selected and should be in place in Spring 2004.
// end //