FM6: 16 July 2000, 12:39 UTC (2000-07-16UTC12:39Z) FM7: 16 July 2000, 12:39 UTC (2000-07-16UTC12:39Z) FM5: 09 August 2000, 11:13 UTC (2000-08-09UTC11:13Z) FM8: 09 August 2000, 11:13 UTC (2000-08-09UTC11:13Z)
Cluster II[2] was a space mission of theEuropean Space Agency, withNASA participation, to study theEarth'smagnetosphere over the course of nearly twosolar cycles. The mission was composed of four identical spacecraft flying in atetrahedral formation. As a replacement for the originalCluster spacecraft which were lost in a launch failure in 1996, the four Cluster II spacecraft were successfully launched in pairs in July and August 2000 onboard twoSoyuz-Fregatrockets fromBaikonur,Kazakhstan. In February 2011, Cluster II celebrated 10 years of successful scientific operations in space. In February 2021, Cluster II celebrated 20 years of successful scientific operations in space. As of March 2023[update], its mission was extended until September 2024.[3] TheChina National Space Administration/ESADouble Star mission operated alongside Cluster II from 2004 to 2007.
The first of the satellites of Cluster II to re-enter the atmosphere did so on 8 September 2024. The remaining three are expected to follow in 2025 and 2026.[4] The scientific payload operations of all satellites ended as the first satellite re-entered the atmosphere (other flight operations are still being performed with the remaining flying satellites until the satellites have all re-entered).[5]
The four identical Cluster II satellites studied the impact of the Sun's activity on the Earth's space environment by flying in formation around Earth. For the first time in space history, this mission was able to collect three-dimensional information on how thesolar wind interacts with themagnetosphere and affects near-Earth space and itsatmosphere, includingaurorae.
The spacecraft were cylindrical (2.9 x 1.3 m, seeonline 3D model) and were spinning at 15 rotations perminute. After launch, theirsolar cells provided 224watts power for instruments and communications. Solar array power gradually declined as the mission progressed, due to damage by energetic charged particles, but this was planned for and the power level remains sufficient for science operations. The four spacecraft maneuvered into various tetrahedral formations to study the magnetospheric structure and boundaries. The inter-spacecraft distances could be altered and varied from around 4 to 10,000 km. Thepropellant for the transfer to the operational orbit, and the maneuvers to vary inter-spacecraft separation distances made up approximately half of the spacecraft's launch weight.
The highlyellipticalorbits of the spacecraft initially reached aperigee of around 4 RE (Earth radii, where 1 RE = 6371 km) and anapogee of 19.6 RE. Each orbit took approximately 57hours to complete. The orbit evolved over time; the line of apsides rotated southwards so that the distance at which the orbit crossed the magnetotail current sheet progressively reduced, and a wide range of dayside magnetopause crossing latitudes were sampled. Gravitational effects imposed a long term cycle of change in the perigee (and apogee) distance, which saw the perigees reduce to a few 100 km in 2011 before beginning to rise again. The orbit plane rotated away from 90 degrees inclination. Orbit modifications by ESOC altered the orbital period to 54 hours. All these changes allowed Cluster to visit a much wider set of important magnetospheric regions than was possible for the initial 2-year mission, improving the scientific breadth of the mission.
TheEuropean Space Operations Centre (ESOC) acquiredtelemetry and distributed to the online data centers the science data from the spacecraft. The Joint Science Operations Centre (JSOC) atRutherford Appleton Laboratory in the UK coordinated scientific planning and in collaboration with the instrument teams provided merged instrument commanding requests to ESOC.
TheCluster Science Archive is theESA long term archive of the Cluster and Double Star science missions. Since 1 November 2014, it is the sole public access point to the Cluster mission scientific data and supporting datasets. The Double Star data are publicly available via this archive. The Cluster Science Archive is located alongside all the otherESA science archives at theEuropean Space Astronomy Center, located near Madrid, Spain. From February 2006 to October 2014, the Cluster data could be accessed via theCluster Active Archive.
TheCluster mission was proposed to ESA in 1982 and approved in 1986, along with theSolar and Heliospheric Observatory (SOHO), and together these two missions constituted the Solar Terrestrial Physics "cornerstone" of ESA's Horizon 2000 missions programme. Though the original Cluster spacecraft were completed in 1995, the explosion of theAriane 5 rocket carrying the satellites in 1996 delayed the mission by four years while new instruments and spacecraft were built.
On July 16, 2000, a Soyuz-Fregat rocket from theBaikonur Cosmodrome launched two of the replacement Cluster II spacecraft, (Salsa and Samba) into a parking orbit from where they maneuvered under their own power into a 19,000 by 119,000 kilometreorbit with a period of 57 hours. Three weeks later on August 9, 2000, another Soyuz-Fregat rocket lifted the remaining two spacecraft (Rumba and Tango) into similar orbits. Spacecraft 1, Rumba, was also known as thePhoenix spacecraft, since it is largely built from spare parts left over after the failure of the original mission. After commissioning of the payload, the first scientific measurements were made on February 1, 2001.
TheEuropean Space Agency ran a competition to name the satellites across all of theESA member states.[6] Ray Cotton, from theUnited Kingdom, won the competition with the namesRumba,Tango,Salsa andSamba.[7] Ray's town of residence,Bristol, was awarded with scale models of the satellites in recognition of the winning entry,[8][9] as well as the city's connection with the satellites. However, after many years of being stored away, they were finally given a home at theRutherford Appleton Laboratory.
Originally planned to last until the end of 2003, the mission was extended several times. The first extension took the mission from 2004 until 2005, and the second from 2005 to June 2009. The mission was ultimately extended until September 2024, when the scientific payload operations on the satellites ended.[3] The ultimate end of the Cluster project (especially the Cluster II satellites) will happen in 2026 as the last satellite enters the atmosphere and is destroyed.[5]
Previous single and two-spacecraft missions were not capable of providing the data required to accurately study the boundaries of the magnetosphere. Because theplasma comprising the magnetosphere cannot be viewed using remote sensing techniques, satellites must be used to measure it in-situ. Four spacecraft allowed scientists make the 3D, time-resolved measurements needed to create a realistic picture of the complex plasma interactions occurring between regions of the magnetosphere and between the magnetosphere and the solar wind.
Each satellite carried a scientific payload of 11 instruments designed to study the small-scale plasma structures in space and time in the key plasma regions: solar wind,bow shock,magnetopause, polar cusps,magnetotail,plasmapause boundary layer and over the polar caps and the auroral zones.
Thebow shock is the region in space between the Earth and theSun where the solar wind decelerates from super- to sub-sonic before being deflected around the Earth. In traversing this region, the spacecraft made measurements which helped characterize processes occurring at the bow shock, such as the origin of hot flow anomalies and the transmission ofelectromagnetic waves through the bow shock and themagnetosheath from the solar wind.
Behind the bow shock is the thin plasma layer separating the Earth and solar wind magnetic fields known as themagnetopause. This boundary moves continuously due to the constant variation in solar wind pressure. Since the plasma and magnetic pressures within the solar wind and the magnetosphere, respectively, should be in equilibrium, the magnetosphere should be an impenetrable boundary. However, plasma has been observed crossing the magnetopause into the magnetosphere from the solar wind. Cluster's four-point measurements made it possible to track the motion of the magnetopause as well as elucidate the mechanism for plasma penetration from the solar wind.
In two regions, one in the northern hemisphere and the other in the southern, the magnetic field of the Earth is perpendicular rather than tangential to the magnetopause. Thesepolar cusps allow solar wind particles, consisting of ions and electrons, to flow into the magnetosphere. Cluster recorded the particle distributions, which allowed the turbulent regions at the exterior cusps to be characterized.
The regions of the Earth's magnetic field that are stretched by the solar wind away from the Sun are known collectively as themagnetotail. Two lobes that reach past the Moon in length form the outer magnetotail while the centralplasma sheet forms the inner magnetotail, which is highly active. Cluster monitored particles from theionosphere and the solar wind as they passed through the magnetotail lobes. In the central plasma sheet, Cluster determined the origins of ion beams and disruptions to the magnetic field-aligned currents caused bysubstorms.
The precipitation of charged particles in the atmosphere creates a ring of light emission around the magnetic pole known as theauroral zone. Cluster measured the time variations of transient particle flows and electric and magnetic fields in the region.
Regulation of spacecraft's electrostatic potential
Enabled the measurement by PEACE of cold electrons (a few eV temperature), otherwise hidden by spacecraft photoelectrons
2
CIS
Cluster Ion Spectroscopy experiment
Ion times-of-flight (TOFs) and energies from 0 to 40 keV
Composition and 3D distribution of ions in plasma
3
DWP
Digital Wave Processing instrument
Coordinates the operations of the EFW, STAFF, WBD and WHISPER instruments
At the lowest level, DWP provided electrical signals to synchronise instrument sampling. At the highest level, DWP enabled more complex operational modes by means of macros
4
EDI
Electron Drift Instrument
Electric fieldE magnitude and direction
E vector, gradients in local magnetic fieldB
5
EFW
Electric Field and Wave experiment
Electric fieldE magnitude and direction
E vector, spacecraft potential, electron density and temperature
6
FGM
Fluxgate Magnetometer
Magnetic fieldB magnitude and direction
B vector and event trigger to all instruments except ASPOC
7
PEACE
Plasma Electron and Current Experiment
Electron energies from 0.0007 to 30 keV
3D distribution of electrons in plasma
8
RAPID
Research with Adaptive Particle Imaging Detectors
Electron energies from 39 to 406 keV, ion energies from 20 to 450 keV
3D distributions of high-energy electrons and ions in plasma
9
STAFF
Spatio-Temporal Analysis of Field Fluctuation experiment
Magnetic fieldB magnitude and direction of EM fluctuations, cross-correlation ofE andB
Properties of small-scale current structures, source of plasma waves and turbulence
10
WBD
Wide Band Data receiver
High time resolution measurements of both electric and magnetic fields in selected frequency bands from 25 Hz to 577 kHz. It provided a unique new capability to performVery-long-baseline interferometry (VLBI) measurements
Properties of natural plasma waves (e.g.auroral kilometric radiation) in the Earth magnetosphere and its vicinity including: source location and size and propagation
11
WHISPER
Waves of High Frequency and Sounder for Probing of Density by Relaxation
Electric fieldE spectrograms of terrestrial plasma waves and radio emissions in the 2–80 kHz range; triggering of plasma resonances by an active sounder
Source location of waves by triangulation; electron density within the range 0.2–80 cm−3
In 2003 and 2004, theChina National Space Administration launched theDouble Star satellites, TC-1 and TC-2, that worked together with Cluster to make coordinated measurements mostly within themagnetosphere. TC-1 stopped operating on 14 October 2007. The last data from TC-2 was received in 2008. TC-2 made a contribution to magnetar science[10][11] as well as to magnetospheric physics. The TC-1 examined density holes near the Earth'sbow shock that can play a role in bow shock formation[12][13] and looked at neutral sheet oscillations.[14]
2018 Hermann Opgenoorth (Univ. of Umea, Sweden), former Cluster Ground Based Working Group lead, was awarded the 2018 Baron Marcel Nicolet Space Weather and Space Climate medal[20]
2016Stephen Fuselier (SWRI, USA), Cluster CIS CoI, received EGU Hannes Alfvén Meda[21]
2016 Mike Hapgood, Cluster mission scientific operations expert was awarded the Baron Marcel Nicolet Medal for Space Weather and Space Climate[22]
2014Rumi Nakamura (IWF, Austria), Cluster CIS/EDI/FGM CoI, received EGU Julius Bartels Medal[23]
2013Mike Hapgood (RAL, UK), Cluster JSOC project scientist received RAS service award[24]
2013Göran Marklund, EFW Co-I, received the EGU Hannes Alfvén Medal 2013.[25]
2013Steve Milan, Cluster Ground based representative of the Cluster mission received UK Royal Astronomical Society (RAS) Chapman medal[26]
2012Andrew Fazakerley, Cluster and Double Star PI (PEACE), received the Royal Astronomical Society Chapman Medal[27]
2012Zuyin Pu (Pekin U., China), RAPID/CIS/FGM CoI, received AGU International Award[28]
2012Jolene Pickett (Iowa U., USA), a Cluster WBD PI, received the State of Iowa Board of Regents Staff Excellence[29]
2012Jonathan Eastwood (Imperial College, UK), FGM Co-I, received COSPAR Yakov B. Zeldovich medal[30]
December 1 - Cluster, Helios and Ulysses reveal characteristics of solar wind supra thermal halo electrons[60]
November 1 - Cluster, Swam and CHAMP join forces to explain hemispheric asymmetries in the Earth magnetotail[61]
October 21 - Space plasma regimes classified with Cluster data[62]
October 1 - Effects of Solar Activity on Taylor Scale and Correlation Scale in Solar Wind Magnetic Fluctuations[63]
September 1 - Van Allen Probes and Cluster join forces to study Outer Radiation Belt Electrons[64]
August 9 - Cluster's 20 years of studying Earth's magnetosphere], celebrating 20 years after the launch of the second pair of Cluster spacecraft[65]
July 31 - ESA science highlight: Auroral substorms triggered by short circuiting of plasma flows[66][67]
July 16 - BBC skyatnight podcast with Dr. Mike Hapgood on 20 years of ESA's Cluster mission,[68] celebrating 20 years after the launch of the first pair of Cluster satellites
April 20 - What drives some of the largest and most dynamic auroral forms?[69]
March 19 - ESA science highlight: Iron is everywhere in Earth's vicinity, suggest two decades of Cluster data[70][71]
February 27 - What makes Kelvin Helmholtz vortices grow at the Earth's magnetopause?[72]
Taylor, M.; C.P. Escoubet; H. Laakso; A. Masson; M. Goldstein (2010). "The Cluster Mission: Space Plasma in Three Dimensions". In H. Laakso; et al. (eds.).The Cluster Active Archive. Astrophysics and Space Science Proceedings. pp. 309–330.doi:10.1007/978-90-481-3499-1_21.ISBN978-90-481-3498-4.
All 3806 publications related to the Cluster and the Double Star missions (count as of 30 June 2025) can be found on thepublication section of the ESA Cluster mission website. Among these publications, 3309 are refereed publications, 342 proceedings, 124 PhDs and 31 other types of theses.
^Qiu, H.; Han, D.-S.; et al. (2022). "In situ observation of a magnetopause indentation that is correspondent to throat aurora and is caused by magnetopause reconnection".Geophys. Res. Lett.49 (15).Bibcode:2022GeoRL..4999408Q.doi:10.1029/2022GL099408.S2CID250718001.
^Huang, S.Y.; et al. (2021). "Multi-spacecraft measurement of anisotropic spatial correlation functions at kinetic range in the magnetosheath turbulence".Journal of Geophysical Research: Space Physics.126 (5).Bibcode:2021JGRA..12628780H.doi:10.1029/2020JA028780.S2CID235556211.
^Lai, H.R.; Russell, C.T.; Jia, Y.D.; Connors, M. (2019). "First observations of the disruption of the Earth's foreshock wave field during magnetic clouds".Geophysical Research Letters.46 (24):14282–14289.doi:10.1029/2019GL085818.S2CID213497617.
^Yushkov, E.; A. Petrukovich; A. Artemyev; R. Nakamura (2017). "Relationship between electron field-aligned anisotropy and dawn-dusk magnetic field: nine years of Cluster observations in the Earth magnetotail".Journal of Geophysical Research: Space Physics.122 (9):9294–9305.Bibcode:2017JGRA..122.9294Y.doi:10.1002/2016JA023739.S2CID134267682.
^Darrouzet, F.; et al. (2013). "Links between the plasmapause and the radiation belt boundaries as observed by the instruments CIS, RAPID, and WHISPER onboard Cluster".Journal of Geophysical Research: Space Physics.118 (7):4176–4188.Bibcode:2013JGRA..118.4176D.doi:10.1002/jgra.50239.hdl:2027.42/99669.S2CID55200569.
^Hwang, K.-J.; et al. (2012). "The first in situ observation of Kelvin-Helmholtz waves at high-latitude magnetopause during strongly dawnward interplanetary magnetic field conditions".Journal of Geophysical Research: Space Physics.117 (A8): A08233.Bibcode:2012JGRA..117.8233H.doi:10.1029/2011JA017256.hdl:2060/20140009615.
^Nykyri, K.; et al. (2012). "On the origin of high-energy particles in the cusp diamagnetic cavity".Journal of Atmospheric and Solar-Terrestrial Physics.87–88 (Special Issue on Physical Process in the Cusp: Plasma Transport and Energization):70–81.Bibcode:2012JASTP..87...70N.doi:10.1016/j.jastp.2011.08.012.
^Echim, M.; et al. (2011). "Comparative investigation of the terrestrial and Venusian magnetopause: Kinetic modeling and experimental observations by Cluster and Venus Express".Planetary and Space Science.59 (10):1028–1038.Bibcode:2011P&SS...59.1028E.doi:10.1016/j.pss.2010.04.019.
^Masson, A.; et al. (2011), "A decade revealing the Sun-Earth connection in three dimensions",Eos, Transactions American Geophysical Union,92 (1): 4,Bibcode:2011EOSTr..92Q...4M,doi:10.1029/2011EO010007
^Engwall, E.; et al. (2009). "Magnetosheath plasma turbulence and its spatiotemporal evolution as observed by the Cluster spacecraft".Nature Geoscience.2 (1):24–27.Bibcode:2009NatGe...2...24E.doi:10.1038/ngeo387.
