Cluster II (spacecraft)


Cluster II was a space mission of the European Space Agency, with NASA participation, to study the Earth's magnetosphere over the course of nearly two solar cycles. The mission was composed of four identical spacecraft flying in a tetrahedral formation. As a replacement for the original Cluster 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 two Soyuz-Fregat rockets from Baikonur, 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., its mission was extended until September 2024. The China National Space Administration/ESA Double Star mission operated alongside Cluster II from 2004 to 2007.
The first of the four Cluster II satellites to re-enter the atmosphere did so on 8 September 2024 and the second one on 22 October 2025. The remaining two are expected to follow in summer 2026. The scientific payload operations of all satellites ended as the first satellite re-entered the atmosphere.

Mission overview

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 the solar wind interacts with the magnetosphere and affects near-Earth space and its atmosphere, including aurorae.
The spacecraft were cylindrical and were spinning at 15 rotations per minute. After launch, their solar cells provided 224 watts 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. The propellant 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 highly elliptical orbits of the spacecraft initially reached a perigee of around 4 RE and an apogee of 19.6 RE. Each orbit took approximately 57 hours 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 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.
The European Space Operations Centre acquired telemetry and distributed to the online data centers the science data from the spacecraft. The Joint Science Operations Centre at Rutherford Appleton Laboratory in the UK coordinated scientific planning and in collaboration with the instrument teams provided merged instrument commanding requests to ESOC.
The is the ESA 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 other ESA science archives at the European Space Astronomy Center, located near Madrid, Spain.

History

The Cluster mission was proposed to ESA in 1982 and approved in 1986, along with the Solar and Heliospheric Observatory, 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 the Ariane 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 the Baikonur Cosmodrome launched two of the replacement Cluster II spacecraft, into a parking orbit from where they maneuvered under their own power into a 19,000 by 119,000 kilometre orbit with a period of 57 hours. Three weeks later on August 9, 2000, another Soyuz-Fregat rocket lifted the remaining two spacecraft into similar orbits. Spacecraft 1, Rumba, was also known as the Phoenix 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.
The European Space Agency ran a competition to name the satellites across all of the ESA member states. Ray Cotton, from the United Kingdom, won the competition with the names Rumba, Tango, Salsa and Samba. Ray's town of residence, Bristol, was awarded with scale models of the satellites in recognition of the winning entry, 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 the Rutherford 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. The ultimate end of the Cluster project will happen in 2026 as the last satellite enters the atmosphere and is destroyed.

Scientific objectives

Previous single and two-spacecraft missions were not capable of providing the data required to accurately study the boundaries of the magnetosphere. Because the plasma 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.
  • The bow shock is the region in space between the Earth and the Sun 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 of electromagnetic waves through the bow shock and the magnetosheath from the solar wind.
  • Behind the bow shock is the thin plasma layer separating the Earth and solar wind magnetic fields known as the magnetopause. 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. These polar 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 the magnetotail. Two lobes that reach past the Moon in length form the outer magnetotail while the central plasma sheet forms the inner magnetotail, which is highly active. Cluster monitored particles from the ionosphere 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 by substorms.
  • The precipitation of charged particles in the atmosphere creates a ring of light emission around the magnetic pole known as the auroral zone. Cluster measured the time variations of transient particle flows and electric and magnetic fields in the region.

Double Star mission with China

In 2003 and 2004, the China National Space Administration launched the Double Star satellites, TC-1 and TC-2, that worked together with Cluster to make coordinated measurements mostly within the magnetosphere. 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 as well as to magnetospheric physics. The TC-1 examined density holes near the Earth's bow shock that can play a role in bow shock formation and looked at neutral sheet oscillations.

Awards

Cluster team awards:
Individual awards:
  • 2023 Hermann Opgenoorth, former Cluster Ground Based Working Group lead, was awarded the 2023 EGU Julius Bartels Medal
  • 2020 Daniel Graham was awarded the COSPAR Zeldovich medal
  • 2019 Margaret Kivelson, Cluster FGM CoI, received RAS gold medal
  • 2018 Hermann Opgenoorth, former Cluster Ground Based Working Group lead, was awarded the 2018 Baron Marcel Nicolet Space Weather and Space Climate medal
  • 2016 Stephen Fuselier, Cluster CIS CoI, received EGU Hannes Alfvén Meda
  • 2016 Mike Hapgood, Cluster mission scientific operations expert was awarded the Baron Marcel Nicolet Medal for Space Weather and Space Climate
  • 2014 Rumi Nakamura, Cluster CIS/EDI/FGM CoI, received EGU Julius Bartels Medal
  • 2013 Mike Hapgood, Cluster JSOC project scientist received RAS service award
  • 2013 Göran Marklund, EFW Co-I, received the EGU Hannes Alfvén Medal 2013.
  • 2013 Steve Milan, Cluster Ground based representative of the Cluster mission received UK Royal Astronomical Society Chapman medal
  • 2012 Andrew Fazakerley, Cluster and Double Star PI, received the Royal Astronomical Society Chapman Medal
  • 2012 Zuyin Pu, RAPID/CIS/FGM CoI, received AGU International Award
  • 2012 Jolene Pickett, a Cluster WBD PI, received the State of Iowa Board of Regents Staff Excellence
  • 2012 Jonathan Eastwood, FGM Co-I, received COSPAR Yakov B. Zeldovich medal
  • 2008 Andre Balogh, Cluster FGM PI, received RAS Chapman medal
  • 2006 Steve Schwartz, Cluster UK data system scientist and PEACE co-I, received RAS Chapman medal

Discoveries and mission milestones

2026

2025

  • November 1 – Cluster and THEMIS observe simultaneously Kelvin–Helmholtz instability on both flanks of the magnetopause
  • October 30 – Online release of the
  • October 22 – Re-entry of RUMBA over the Pacific Ocean at 20:59 CEST
  • April 3 – Cluster observes plasma in the high-latitude magnetotail associated With cusp-aligned arcs
  • March 19 – Earth ring current observed in-situ by Cluster, THEMIS and MMS compared
  • February 22 – A new dataset to localize the Cluster satellites in the geospace environment
  • January 21 – Ion flow vortex may serve as novel electron accelerator in space

2024

  • December 1 – 14 years of Cluster data to predict proton intensities around Earth
  • November 13 – Polar cap auroral arcs linked to lobe reconnection
  • September 8 – Re-entry of SALSA satellite, the first of the Cluster II satellites to re-enter the atmosphere
  • September 4 – Strong effects of chorus waves on radiation belts expected for future magnetic superstorms
  • August 30 – The pioneer Cluster mission: preparation of its legacy phase near re-entry
  • July 6 – Cluster data contributes to collisionless shocks database acquired at Earth, Venus and Mars
  • May 24 – Cluster releases list of plasma jets found in the magnetosheath
  • April 5 – Unveiling the journey of a highly inclined CME
  • January 20 – Global-scale magnetosphere convection driven by dayside magnetic reconnection

2023

  • April 28 – Magnetic reconnection at high and low latitudes during the passage of an ICME
  • March 24 – Properties of the Martian Magnetotail compared Cluster data in the Earth magnetotail
  • March 23 – Scaling laws for the energy transfer in space plasma turbulence
  • March 1 – Turbulent MHD cascade in the Jovian magnetosheath compared to Cluster measurements
  • January 26 – Evidence for lunar tide effects in Earth's plasmasphere
  • January 20 – Ion Outflow in Middle Altitude LLBL/Cusp from Different Origins

2022

  • December 5 - Magnetosphere distortions during the "satellite killer" storm of February 3–4, 2022
  • October 14 - New insights on the formation of transpolar auroral arc
  • September 20 - A highway for atmospheric ion escape from Earth during the impact of an interplanetary coronal mass ejection
  • August 3 - Joint Cluster/ground-based studies in the first 20 years of the Cluster mission
  • July 18 – In situ observation of a magnetopause indentation that is correspondent to throat aurora and is caused by magnetopause reconnection
  • June 16 - Kelvin-Helmholtz vortices as an interplay of Magnetosphere-Ionosphere coupling
  • June 2 - ESA highlight: Magnetic vortices explain mysterious auroral beads
  • May 16 - The influence of localized dynamics on dusk-dawn convection in the Earth's magnetotail
  • April 1 - Dawn-dusk ion flow asymmetry in the plasma sheet
  • February 1 - South Pole Station ground-based and Cluster satellite measurements of leaked and escaping Auroral Kilometric Radiation
  • January 1 - Massive multi-mission statistical study and analytical modeling of the Earth's magnetopause

2021

  • December 15 - ESA highlight: Swarm and Cluster get to the bottom of geomagnetic storms
  • November 7 - Unique MMS and Cluster observations about magnetic reconnection extent at the magnetopause
  • November 2 - Spatial distribution of energetic protons in the magnetosphere based on 17 years of data
  • October 11 - Unique MMS and Cluster observation of disturbances in the near-Earth magnetotail before a magnetic substorm
  • September 7 - AGU EOS spotlight: Understanding Aurora Formation with ESA's Cluster Mission
  • May 2 - Cluster and MMS uncover anisotropic spatial correlation functions at kinetic range in the magnetosheath turbulence
  • April 9 - The Solar-cycle Variations of the Anisotropy of Taylor Scale and Correlation Scale in the Solar Wind Turbulence
  • February 18 - Heavy Metal and Rock in Space: Cluster RAPID Observations of Fe and Si

2020

  • December 1 - Cluster, Helios and Ulysses reveal characteristics of solar wind supra thermal halo electrons
  • November 1 - Cluster, Swam and CHAMP join forces to explain hemispheric asymmetries in the Earth magnetotail
  • October 21 - Space plasma regimes classified with Cluster data
  • October 1 - Effects of Solar Activity on Taylor Scale and Correlation Scale in Solar Wind Magnetic Fluctuations
  • September 1 - Van Allen Probes and Cluster join forces to study Outer Radiation Belt Electrons
  • August 9 - Cluster's 20 years of studying Earth's magnetosphere], celebrating 20 years after the launch of the second pair of Cluster spacecraft
  • July 31 - ESA science highlight: Auroral substorms triggered by short circuiting of plasma flows
  • July 16 - BBC skyatnight podcast with Dr. Mike Hapgood on 20 years of ESA's Cluster mission, 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?
  • March 19 - ESA science highlight: Iron is everywhere in Earth's vicinity, suggest two decades of Cluster data
  • February 27 - What makes Kelvin Helmholtz vortices grow at the Earth's magnetopause?

2019

  • December 23 - Magnetized dust clouds penetrate the terrestrial bow shock
  • November 18 - Earth's magnetic song recorded for the first time during a solar storm
  • October 10 - What is the source of the energetic oxygen ions found in the high-altitude cusp region?
  • August 27 - Cluster and XMM pave the way for SMILE
  • August 20 - Asymmetric transport of the Earth's polar outflows by the interplanetary magnetic field
  • August 5 - Energetic electron acceleration found by Cluster in unconfined reconnection jets for the first time
  • May 1 - Kelvin‐Helmholtz waves magnetic curvature and vorticity: Four‐spacecraft Cluster observations
  • March 4 -
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2018

  • November 28 –
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2017

  • December 11, 2017 –
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  • August 28, 2017 –
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2016

  • October 3, 2016 –
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2015

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2014

  • December 18 –
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  • August 28 –
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2013

  • November 26 -
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  • April 15 -
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2012

  • December 18 –
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2011

  • November 16 –
  • September 6 –
  • August 31 -
  • July 5–10 -
  • July 4 –
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  • February 5 –
  • January 7 -

2010

  • November 22 -
  • October 4 –
  • September 1 -
  • July 26 -
  • July 16 -
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2009

  • October 7 -
  • July 16 –
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  • April 29 -
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  • February 9 -
  • January 14 –

2008

  • December 15 -
  • December 5 -
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2007

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2006

  • December 29 -
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  • March 30 -
  • February 24 -
  • February 1 -
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2005

  • December 22 -
  • September 21 -
  • August 10 -
  • July 28 -
  • July 14 -
  • April 28 -
  • February 18 -
  • February 4 -

2004

  • December 12 -
  • November 24
  • September 17 -
  • August 12 -
  • June 23 -
  • May 13 -
  • May 11 -
  • April 5 -

2001–2003

  • 3 December 2003 -
  • 29 June 2003 -
  • 20 May 2003 -
  • 29 January 2003 -
  • 28 January 2003 -
  • 29 December 2002 -
  • 1 October 2002 -
  • 11 December 2001 -
  • 31 October 2001 -
  • 9 October 2001 -
  • 1 February 2001 –

Selected publications

All 3836 publications related to the Cluster and the Double Star missions can be found on the . Among these publications, 3339 are refereed publications, 342 proceedings, 124 PhDs and 31 other types of theses.