After years of frustration and hard work following the tragic loss of all four Cluster spacecraft in 1996, UK scientists are eagerly awaiting the launch of the first two Cluster II satellites from Baikonur Cosmodrome in Kazakhstan on 15 July.

The second pair are currently scheduled to follow on 9 August. Both launches will involve a Soyuz rocket with a newly developed Fregat upper stage.

Cluster II comprises four identical spacecraft that will fly in a close, tetrahedral (triangular pyramid) formation as they gather information about how the Sun interacts with near-Earth space.

Following highly elongated, polar orbits which take them between 19,000 and 119,000 km from the planet (almost one third of the way to the Moon) they will investigate most of the major boundaries and regions of interest within the Earth’s magnetic environment – the magnetosphere.

Sometimes, they will be inside this magnetic shield and sometimes they will be outside, fully exposed to the charged particles (mainly electrons and protons) of the solar wind.


Cluster II is part of an international collaboration to investigate the physical connection between the Sun and Earth.

Cluster’s role is to investigate the interaction between the solar wind – a continuous stream of plasma (electrified gas) that flows from the Sun – and the magnetosphere. It will also investigate what happens during more violent solar events. At such times, near-Earth space is struck by high energy particles from solar flares and plasma clouds that are blasted free during coronal mass ejections (CMEs).

These sudden eruptions are expected to become more numerous in the summer of 2000 – around the time of the dual Cluster launches – when the Sun will reach the peak in its 11 year cycle of activity.

Travelling at speeds of 400 km/s or more, CMEs can cross the 150 million km gulf between the Sun and Earth in 2 – 3 days. When they arrive in the Earth’s vicinity, the magnetic shield suffers a tremendous buffeting, often resulting in widespread aurorae (the northern and southern lights).

Particularly severe magnetic storms on the Sun can cause widespread power cuts, damage to TV broadcasting, weather and communication satellites, and disruption to radio communications.


The four Cluster spacecraft each carry eleven identical instruments to measure the complex interplay of charged particles and electromagnetic fields in near-Earth space.

As the spacecraft travel through different regions of the magnetosphere, they will provide scientists with their first simultaneous measurements of these phenomena from four nearby locations.

By comparing and analysing this data, scientists will be able to obtain the first detailed three-dimensional ‘map’ of near-Earth space and to understand better the physical processes taking place around our planet.

Early in the mission, the spacecraft will spend most of their time flying through the windsock-shaped magnetic tail, which extends many Moon distances into space on the side of the Earth that faces away from the Sun.

Six months later, they will investigate the polar cusps, weak points in Earth’s magnetic shield where charged particles penetrate the upper atmosphere and generate the aurorae.

Since plasma is the most common form of matter in the Universe, investigations such as these will be of value for plasma research in terrestrial laboratories. Cluster will also improve our understanding of how space weather results in power cuts, communication breakdowns and damage to satellites used for communication, navigation and weather forecasting.


U.K. scientists have played a leading role in the development of four out of the 11 science instruments on each Cluster satellite.

 FGM, the Fluxgate Magnetometer. (Principal Scientific Investigator: Professor AndrÈ Balogh from Imperial College, London.)
Uses two magnetometers to measure magnetic fields along the orbit. These sensors are located along a 5 metre long boom to minimise interference from the spacecraft. The University of Leicester is also involved in FGM.

 PEACE, the Plasma Electron and Current Experiment. (Principal Scientific Investigator: Dr. Andrew Fazakerley, of Mullard Space Science Laboratory in Surrey.)
This experiment captures low to medium energy electrons in the space plasma (electrified gas), counts them and measures their direction of travel, speed and temperature. It may also reveal electron beams and plasma waves. Queen Mary & Westfield College, London, and Rutherford Appleton Laboratory (RAL) are also involved in PEACE.

 DWP, the Digital Wave Processing experiment. (Principal Scientific Investigator: Dr. Hugo Alleyne of Sheffield University.)
DWP is the control and computing brain for the five instruments that study waves in the surrounding plasma. Its precise timing allows scientists to correlate the studies being made by all four spacecraft. It also has a particle correlator for comparing frequency variations in the electrons around the spacecraft (measured by PEACE) with the wave measurements. Professor Paul Gough of the University of Sussex is responsible for DWP’s particle correlator. Queen Mary & Westfield College, London is also involved in DWP.

 RAPID, the Research with Adaptive Particle Imaging Detectors experiment. (Co-Principal Scientific Investigator: Dr. Manuel Grande of RAL.)
Scientists at RAL are responsible for the Imaging Electron Spectrometer, one of two instruments on this German-led experiment. This UK contribution will measure electron energies and sort the resulting data.

Cluster’s space-based measurements will be combined with data from the
ground-based CUTLASS and EISCAT radars in the Arctic in order to learn more about the complex interactions in the upper atmosphere caused by the solar wind and solar storms. The UK plays a leading role in these ground stations.

U.K. scientists also run the Cluster Joint Science Operations Centre (JSOC) at RAL. Its main task is to co-ordinate the Cluster science operations, but it will also collect and process the data needed to plan these operations and will monitor the performance of the mission and individual instruments. Dr. Mike Hapgood at RAL is the Project Scientist for JSOC.

RAL is also home to one of eight Cluster National Data Centres established around the world. These have been set up to process the raw data from a specific set of instruments and then make the information available to the other data centres. Professor Steve Schwartz of Queen Mary & Westfield College, London, is the Project Scientist for the UK Cluster Data Handling Facility, while Dr. Chris Perry is the manager of the Cluster Data Centre at RAL.

UK industry has also played a leading role in Cluster. Astrium UK (formerly Matra-Marconi Space UK) has provided a number of major subsystems, including attitude and reaction control, and launch support. Logica has provided important software for mission planning and data distribution. Other UK companies have provided components for instruments and spacecraft systems.

Notes for Editors

Cluster II and the Solar and Heliospheric Observatory (SOHO) make up the first Cornerstone – the Solar-Terrestrial Science Programme – in the European Space Agency’s Horizons 2000 long term science plan.

Images and data from SOHO have revolutionised our understanding of the Sun since its launch in December 1995. The first Cluster quartet was destroyed in a launch failure during the maiden flight of the Ariane 5 rocket on 4 June 1996. However, its scientific programme was considered so important that the following year ESA and its member states (including the UK) agreed to rebuild the four satellites and their experiments.

UK funding for the Cluster II instruments has been provided by the Particle Physics and Astronomy Research Council (PPARC).


Professor Andre Balogh, Imperial College, London. Tel: +44 (0)207-594-7768

Dr. Andrew Fazakerley, Mullard Space Science Laboratory, Surrey. Tel: +44 (0)1483-204175. E-mail:

Dr. Hugo Alleyne, University of Sheffield. Tel: +44 (0)114-222-5630

Dr. Manuel Grande, Rutherford Appleton Laboratory, Oxon. Tel: +44 (0)1235- 446501. E-mail:

Dr. Mike Hapgood, Rutherford Appleton Laboratory, Oxon. Tel: +44 (0)1235-446520. E-mail:

Professor Steve Schwartz, Queen Mary & Westfield College, London. +44 (0)207-882-5449. E-mail:


ESA Cluster II site:

ESA Space Weather site:

NASA Space Weather site:

UK Web sites:
Imperial College, London (Fluxgate Magnetometer).

Mullard Space Science Laboratory (Plasma Electron and Current Experiment).

Rutherford Appleton Laboratory (Cluster Joint Science Operations Centre).

The launches will be broadcast live by ESA TV. Further details of the ESA broadcasts are available from: