Cluster Status Report – February 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.

Science highlights

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.