Since the current Cluster mission is a replacement for the original Cluster spacecraft, the science payloads remain the same as on the original spacecraft.
The four Cluster spacecraft carry identical sets of 11 scientific instruments. They are designed to study space weather inside and outside the region influenced by Earth's magnetic field - the magnetosphere. By using the same instruments on all four spacecraft, scientists will obtain the first detailed, three-dimensional picture of what happens within different regions of the Earth's magnetic shield.
Each instrument is built by a team under the leadership of a Principal Investigator (PI). Most of the PIs have worked on the same instrument for both missions.
The Cluster scientific community includes the ESA Project Scientist, Philippe Escoubet, 11 Principal Investigators and more than 200 Co-Investigators from ESA member states, the United States, Canada, China, the Czech Republic, Hungary, India, Israel, Japan and Russia.
Principal Investigator: Chris Carr, Space Physics and Atmospheric Group, Blackett Laboratory, Imperial College, London, United Kingdom
Located on a five metre long boom to avoid interference from the spacecraft, two magnetometers measure the magnetic fields along the orbit. FGM can take high resolution measurements with up to 67 samples per second. The instrument is highly fault-tolerant, with full redundancy of all its vital functions.
EDI: Electron Drift Instrument
Principal Investigator: Roy B. Torbert, Department of Physics, University of New Hampshire, USA
EDI fires two weak beams of electrons 10 km or more into the space around each spacecraft. When properly aimed, the electrons eventually return to receivers on the opposite side of the spacecraft. The returning beams are affected by the strength of the electric field in space and by the gradient in the ambient magnetic field. From beam firing directions and electron travel times, scientists can determine the strength of the electric field. As a by-product, the magnetic field strength is also measured.
ASPOC: Active Spacecraft Potential Control experiment
Principal Investigator: Klaus Torkar, Austria
Electrical charging of a Cluster spacecraft in orbit can have a severe impact on the performance of the scientific instruments. ASPOC is designed to 'earth' or neutralise the spacecraft by preventing a build up in positive electrical charge. It does this by emitting ions (charged particles) of the metal indium into space through a small needle. These ions cancel out the electrical charge that the satellite acquires. The ion current is adjusted by using measurements made by other onboard instruments, which record the spacecraft's electrical potential (EFW and PEACE)
STAFF: Spatio-Temporal Analysis of Field Fluctuation experiment
Principal Investigator: Patrick Canu, Laboratoire de Physique des Plasmas, CNRS/Ecole Polytechnique /UPMC, Plaiseau, France
A magnetometer on the end of a five metre long boom looks at waves (rapid variations in the magnetic fields), particularly in regions where the charged particles of the solar wind interact with the magnetosphere. Low frequency data are analysed on the ground, while the electric and magnetic components of the higher frequency waves are processed on board. One of the five complementary experiments which form the Wave Experiment Consortium.
EFW: Electric Field and Wave experiment
Principal Investigator: Mats André, Swedish Institute of Space Physics (Institutet för rymdfysik, IRF), Sweden
Uses sensors on four 50 m long wire booms to measure the electric field to study plasma convection and waves. Currents generated in each sensor reveal the density of nearby electrons. It can take up to 36 000 samples per second of the electric field and fluctuations in the plasma density. This allows it to measure the motion of plasma structures and wave fronts travelling at thousands of kilometres per second. One of the five complementary experiments which form the Wave Experiment Consortium
DWP: Digital Wave Processing experiment
Principal Investigator: Michael Balikhin, Space Systems Laboratory, Department of Automatic Control and Systems Engineering, University of Sheffield, United Kingdom
The control and computing brain for the wave experiments. DWP enables the Wave Experiment Consortium (WEC) instruments to make effective use of the limited spacecraft resources of power and telemetry-information. It provides precise timing that allows correlation studies between the four spacecraft. It also has a particle correlator that enables variations in the electron population around the spacecraft to be compared with the wave measurements. Plasma waves can last from a few milliseconds to many minutes and are caused by energy redistribution processes in the plasma.
WHISPER: Waves of High frequency and Sounder for Probing of Electron density by Relaxation experiment
Principal Investigator: Jean Louis Rauch, Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E) and Centre National de la Recherche Scientifique (CNRS), France
Near-Earth space is populated by charged particles whose density governs wave generation and energy transfers. To measure this fundamental quantity, WHISPER makes use of a resonance sounding (radar) technique. Brief radio pulses, sent out from two 50-metre-long wire antennas, trigger oscillations or 'echoes', which are detected after a short delay. Their frequencies reveal the particle concentration in the medium. In addition, WHISPER monitors natural wave activity in the frequency range (2 to 80 kHz) covered by the sounder. WHISPER is one of the five complementary experiments which form the Cluster Wave Experiment Consortium (WEC).
WBD: Wide Band Data instrument
Principal Investigator: Jolene Pickett, Department of Physics and Astronomy, University of Iowa, USA
Designed to provide high-resolution measurements of both electric and magnetic fields in selected frequency bands. WBD listens for radio whistles and hisses from particles that bounce around near the Earth's magnetic poles. Part of the Cluster Wave Experiment Consortium (WEC).
PEACE: Plasma Electron And Current Experiment
Principal Investigator: Andrew Fazakerley, Mullard Space Science Laboratory, University College, London, United Kingdom
Like CIS, this experiment also sifts incoming particles. PEACE looks at all electrons in the space plasma which have low to medium energies, counts them and measures their direction of travel and speed. One part measures faster electrons, while another part detects slower electrons.
CIS: Cluster Ion Spectrometry experiment
Principal Investigator: Iannis Dandouras, Institut de Recherche en Astrophysique et Planétologie (IRAP)
CNRS and Université Paul Sabatier, Toulouse, France
Analyses the composition, mass and distribution functions of ions in the nearby (magnetosphere) space plasma and in the solar wind during each four second spin of the spacecraft. (Space plasma is a gas composed of electrically charged particles, mainly electrons and protons plus some other ions.) It consists of two different instruments, a Hot Ion Analyser (HIA) and a time-of-flight ion Composition and Distribution Function analyser (CODIF), plus a sophisticated instrument control and data processing system, which permits extensive onboard data processing.
RAPID: Research with Adaptive Particle Imaging Detectors
Principal Investigator: Patrick Daly, Germany
An advanced particle detector which records the highest energy electrons and ions which enter it from space. The particles pass through pinholes to reach the electron detectors. This enables it to build up a picture of where both the electrons and ions come from. Identification of the ions is based on analysis of the particles' velocities and energy.
WECA combined effort - Wave Experiment Consortium (WEC)
Current Chairman: Per-Arne Lindqvist, Sweden
Five of the Cluster instruments (DWP, EFW, STAFF, WBD, and WHISPER), which are designed to measure electric and magnetic fields and waves, have been grouped together to form the Wave Experiment Consortium in order to maximise resources.