Some 100 scientists and engineers gathered last week at the European Space
Technology Research Centre (ESTEC) in the Netherlands for the 36th Cluster
Science Working Team (SWT) meeting. They were greeted with the news that the
four Cluster spacecraft — Rumba, Salsa, Samba and Tango — are now dancing
in a new formation around the Earth.

At the start of the two-day gathering, Cluster deputy project manager Alberto
Gianolio told the SWT that the recent orbital manoeuvres had been extremely
successful. With the quartet now flying some 2000 km apart in a tetrahedron
formation, the spacecraft are ready to begin their first observations of the
Earth’s huge magnetic tail or magnetotail.

Further details were provided by Cluster spacecraft operations manager Sandro
Matussi, who explained that the complex sequence of engine firings had been
completed with great precision. The manoeuvres had been carried out so
meticulously that only two of the four spacecraft orbits had to be altered
on 3 June, the final day of the four-week phase to set up the new orbital

“Rumba and Salsa had been moved so precisely during previous manoeuvres that
there was no need to fire their thrusters,” said Matussi. “Even Samba and
Tango required only very small drift manoeuvres.”

“Our original plan was designed to cover possible errors in the manoeuvres,”
he explained. “However, the excellent performance of the spacecraft and the
very thorough mathematical calculations of our flight dynamics colleagues
at the European Space Operations Centre in Darmstadt, Germany, meant that
we only had to make 23 of the 28 scheduled engine firings.”

Even as the Cluster quartet were beginning their latest celestial dance, the
11 Cluster principal investigators met to discuss their preferences for the
next mission phase that will start in February 2002. They eventually agreed
to close the gap between each spacecraft to just 100 km — an intimacy
unrivalled by any flotilla of scientific spacecraft during more than four
decades of space exploration.

“By bringing the spacecraft so close together, we will be able to study
the key regions of the magnetic bubble that surrounds the Earth — the
magnetosphere — in unprecedented detail,” said Cluster project scientist
Philippe Escoubet. “This will probably be our only opportunity to obtain
small-scale, three-dimensional measurements of the polar cusps, the bow
shock and the magnetopause.”

“The observations will revolutionise our understanding of the physical
processes taking place where the electrically charged particles in the
supersonic solar wind collide with the Earth’s magnetic field,” he said.

Meanwhile, the global community of more than 200 Cluster scientists has
begun to analyse the avalanche of results from the first six months of
Cluster science operations. The SWT was given a foretaste of some of the
papers to be published later in the year in a special edition of the
journal Annales Geophysicae. They included remarkable new studies of radio
waves generated above the Earth, never-before-seen fluctuations in the
magnetic field, and particle motions in the inner magnetosphere.

“Since four identical spacecraft have never before examined near-Earth
space, the data from Cluster are continually breaking new ground,” said
Dr. Escoubet. “The analysis is very complex but also extremely exciting.”

“We have completed the first chapter of the Cluster adventure, but the rest
of the story promises to be even more compelling,” he added.

For more information please contact:

Dr. Philippe Escoubet, Cluster project scientist

Tel: +31 71 5653454



* Cluster home page

* Cluster quartet move in step


[Image 1:]
The Cluster quartet — Rumba, Salsa, Samba and Tango — recently completed
manoeuvres which mean that they are now flying some 2000 km apart in a
tetrahedron formation.

[Image 2:]
This schematic diagram illustrates Cluster’s orbit at the beginning of June
2001, after orbital manoeuvres. (The view is of the magnetosphere from above
the North pole.) The interspacecraft distance is about 2000 km and the
tetrahedron is located at apogee. The Cluster orbit is indicated in red.

[Image 3:]
In this schematic diagram the grey lines trace out the individual orbits which
each of the Cluster spacecraft follow.