Cluster - Investigating the physical connection between the Sun and Earth

Investigating the physical connection between the Sun and Earth

• In operation
• Launched in two parts on 16 July 2000 and 9 August 2000
• Due to end late 2009

Cluster quartet entering eclipse
Credit: ESA

Four Cluster satellites are orbiting the Earth in formation tens to thousands of kilometres apart. The spacecraft are examining the interaction between the solar wind - the stream of charged particles from the Sun - and the magnetosphere, the magnetic 'bubble' surrounding the Earth. Cluster is operated by the European Space Agency (ESA) and has been working in conjunction with China's Double Star mission.

The Cluster spacecraft have now completed more than one thousand orbits of the Earth. Each satellite carries 11 identical instruments, three of which were developed by UK scientists. By using four identical spacecraft flying in formation, Cluster can investigate the Earth's magnetic field in three dimensions.

The Cluster mission has proved so successful that it has been extended twice. After more than seven years in space, the instruments continue to function well.

For more information, visit the ESA Cluster home page.

Mission facts

• Every second a million tonnes of hot plasma and charged particles (electrons and ions) escape the Sun's gravity. Although the Earth's magnetosphere acts like a giant shield, high energy particles from the Sun can cause electrical storms - damaging satellites or even causing power cuts on the ground. The effect all these millions of charged particles are having on the Earth is known as space weather. By studying the processes taking place in the magnetosphere, scientists will be able to make improved predictions for the space weather 'forecast'.
  
  
• The results from Cluster enable us to better understand processes in the more distant Universe. UK scientists have used Cluster to study the so-called 'bow shock' - the region where the solar wind is decelerated from supersonic to subsonic speed before being deflected around the Earth. The lessons learned from Cluster can be applied to shocks observed in distant nebulae and other astronomical objects.
  
  
• This is the second Cluster mission. The first mission was designed around a single spacecraft with four satellites and was launched in June 1996 on the first flight of the Ariane 5 rocket. However, after leaving the ground, a computer malfunction caused the spacecraft to veer off course. Safety procedures led to the rocket being destroyed and the mission was lost.

Technology

Each of the spacecraft has exactly the same 11 instruments on board. These measure the weather in space, both inside and outside the areas affected by our planet's magnetic field.

UK involvement

The UK heads up three of the 11 major investigations being carried out by Cluster:

• Imperial College London leads investigations based on the measurements of our magnetic field.
  
  
• University College London's Mullard Space Science Laboratory (MSSL) heads up the investigations based on measurements of electrons.
  
  
• The University of Sheffield leads the team measuring electric and magnetic waves.
  
  
• STFC Rutherford Appleton Laboratory provides the Joint Science Operations Centre and works with teams at ESA in Germany to operate the instruments used aboard the four craft.