Cluster II (spacecraft)

Cluster II

Artist's impression of the Cluster constellation.
Mission type	Magnetospheric research
Operator	ESA with NASA collaboration
COSPAR ID	FM6 (SALSA): 2000-041A FM7 (SAMBA): 2000-041B FM5 (RUMBA): 2000-045A FM8 (TANGO): 2000-045B
SATCAT №	FM6 (SALSA): 26410 FM7 (SAMBA): 26411 FM5 (RUMBA): 26463 FM8 (TANGO): 26464
Website	http://sci.esa.int/cluster
Mission duration	planned: 5 years elapsed:
Spacecraft properties
Manufacturer	Astrium
Launch mass	1,200 kg (2,600 lb)
Dry mass	550 kg (1,210 lb)
Payload mass	71 kg (157 lb)
Dimensions	2.9 m × 1.3 m (9.5 ft × 4.3 ft)
Power	224 watts
Start of mission
Launch date	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)
Rocket	Soyuz-U/Fregat
Launch site	Baikonur 31/6
Contractor	Starsem
Orbital parameters
Reference system	Geocentric
Regime	Elliptical Orbit
Perigee	FM6: 16,118 km (10,015 mi) FM7: 16,157 km (10,039 mi) FM5: 16,022 km (9,956 mi) FM8: 12,902 km (8,017 mi)
Apogee	FM6: 116,740 km (72,540 mi) FM7: 116,654 km (72,485 mi) FM5: 116,786 km (72,567 mi) FM8: 119,952 km (74,535 mi)
Inclination	FM6: 135 degrees FM7: 135 degrees FM5: 138 degrees FM8: 134 degrees
Period	FM6: 3259 minutes FM7: 3257 minutes FM5: 3257 minutes FM8: 3258 minutes
Epoch	13 March 2014, 11:15:07 UTC

Cluster II is a space mission of the European Space Agency, with NASA participation, to study the Earth's magnetosphere over the course of an entire solar cycle. The mission is composed of four identical spacecraft flying in a tetrahedral formation. 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. The mission has been extended until December 2016. China National Space Administration/ESA Double Star mission operated alongside Cluster II from 2004 to 2007.

Mission overview

The four identical Cluster II satellites study 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 is 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 are cylindrical (2.9 x 1.3 m, see online 3D model) and are spinning at 15 rotations per minute. After launch, their solar cells provided 224 watts power for instruments and communications. Solar array power has 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 maneuver into various tetrahedral formations to study the magnetospheric structure and boundaries. The inter-spacecraft distances can be altered and has 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 R_E (Earth radii, where 1 R_E = 6371 km) and an apogee of 19.6 R_E. Each orbit took approximately 57 hours to complete. The orbit has evolved over time; the line of apsides has 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 impose 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 has rotated away from 90 degrees inclination. Orbit modifications by ESOC have altered the orbital period to 54 hours. All these changes have 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 (ESOC) acquires telemetry and distributes to the online data centers the science data from the spacecraft. The Joint Science Operations Centre JSOC at Rutherford Appleton Laboratory in the UK coordinates scientific planning and in collaboration with the instrument teams provides merged instrument commanding requests to ESOC.

The Cluster Science Archive 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. From February 2006 to October 2014, the Cluster data could be accessed via the Cluster Active Archive.

History

The Cluster mission was proposed to ESA in 1982 and approved in 1986, along with the Solar 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 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, (Salsa and Samba) into a parking orbit from where they maneuvered under their own power into a 19,000 by 119,000 kilometer orbit 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, is 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 has been extended several times. The first extension took the mission from 2004 until 2005, and the second from 2005 to June 2009. The mission has now been extended until the end of 2016 and possibly 2018, subject to review in late 2016.

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 presently be accessed using remote sensing techniques, satellites must be used to measure it in-situ. Four spacecraft allow 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 carries 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 make measurements which help 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 make 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 south, 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 records the particle distributions, which allow 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 monitors particles from the ionosphere and the solar wind as they pass through the magnetotail lobes. In the central plasma sheet, Cluster determines 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 measures the time variations of transient particle flows in the region.

Instrumentation on each Cluster satellite

Number	Acronym	Instrument	Measurement	Purpose
1	ASPOC	Active Spacecraft Potential Control experiment	Regulation of spacecraft's electrostatic potential	Enables the measure 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 provides electrical signals to synchronise instrument sampling. At the highest level, DWP enables more complex operational modes by means of macros.
4	EDI	Electron Drift Instrument	Electric field E magnitude and direction	E vector, gradients in local magnetic field B
5	EFW	Electric Field and Wave experiment	Electric field E magnitude and direction	E vector, spacecraft potential, electron density and temperature
6	FGM	Fluxgate Magnetometer	Magnetic field B 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 field B magnitude and direction of EM fluctuations, cross-correlation of E and B	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 provides a unique new capability to perform Very-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 field E 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

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.

Here are three scientific highlights where TC-1 played a crucial role

1. Space is Fizzy

Ion density holes were discovered near the Earth's bow shock that can play a role in bow shock formation. The bow shock is a critical region of space where the constant stream of solar material, the solar wind, is decelerated from supersonic speed to subsonic speed due to the internal magnetic field of the Earth. Full story: http://sci.esa.int/jump.cfm?oid=39559 Echo of this story on CNN: http://www.cnn.com/2006/TECH/space/06/20/space.bubbles/index.html

2. Inner magnetosphere and energetic particles

Chorus Emissions Found Further Away From Earth During High Geomagnetic Activity. Chorus are waves naturally generated in space close to the magnetic equator, within the Earth's magnetic bubble called magnetosphere. These waves play an important role in the creation of relativistic electrons and their precipitation from the Earth's radiation belts. These so-called killer electrons can damage solar panels and electronic equipment of satellites and represent a hazard to astronauts. Therefore, information on their location with respect to the geomagnetic activity is of crucial importance to be able to forecast their impact. Chorus sound file: http://sci.esa.int/science-e/www/object/doc.cfm?fobjectid=38339

3. Magnetotail dynamics

Cluster and Double Star Reveal the Extent of Neutral Sheet Oscillations. For the first time, neutral sheet oscillations observed simultaneously at a distance of tens of thousands of kilometres are reported, thanks to observations by 5 satellites of the Cluster and the Double Star Program missions. This observational first provides further constraint to model this large-scale phenomenon in the magnetotail. Full story: http://sci.esa.int/jump.cfm?oid=38999

"The TC-1 satellite has demonstrated the mutual benefit of, and has fostered, scientific cooperation in space research between China and Europe. We expect even more results when the final archive of high resolution data will be made available to the worldwide scientific community", underlines Philippe Escoubet, Double Star and Cluster mission manager of the European Space Agency.

Discoveries and mission milestones

2015

• December 7 - Coalescence of magnetic flux ropes in the ion diffusion region of magnetic reconnection
• July 14 - Cluster solves the mystery of equatorial noise
• July 01 - Seven ESA satellites team up to explore the Earth's magnetic field
• April 09 - Heart of the black auroras revealed by Cluster
• March 25 - Cluster satellite catches up
• January 16 - Rejigging the Cluster quartet at the bow shock and in the solar wind

2014

• December 18 - Origin of high-latitude auroras revealed
• November 20 - The Cluster mission is extended by ESA up to 2018, subject to review in late 2016
• August 28 - A mixed-up magnetic storm
• June 15 - Solar wind breaks through the Earth's magnetic field
• May 7 - Cluster helps to model Earth's mysterious magnetosphere

2013

• November 26 - Cluster takes a tilt at radio wave sources
• September 20 - ESA's Cluster satellites in closest-ever 'dance in space'
• September 10 - Cluster shows plasmasphere interacting with Van Allen belts
• July 18 - Wobbly magnetic reconnection speeds up electrons
• July 2 - Cluster discovers steady leak in the Earth's plasmasphere
• May 2 - Cluster hears the heartbeat of magnetic reconnection
• April 15 - From solar activity to stunning aurora (ESA Space Science's image of the week)
• April 10 - Cluster finds source of aurora energy boost
• January 11 - 2013 UK Royal Astronomical Society (RAS) Chapman medal awarded to the Ground-Based Principal Investigator of the Cluster mission
• January 11 - 2013 RAS service award received by the Cluster Joint Science Operations Centre project scientist

2012

• December 18 - The solar wind is swirly
• October 24 - Cluster observes a 'porous' magnetopause
• October 10 - 2012 University of Iowa award for excellence received by the NASA funded PI of the WideBand instrument on the Cluster mission
• August 1 - Cluster looks into waves in the magnetosphere's thin boundaries
• July 2 - Hidden Portals in Earth's Magnetic Field (NASA science cast video)
• June 6 - Origin of particle acceleration in cusps of Earth's magnetosphere uncovered
• March 7 - Earth’s magnetic field provides vital protection
• February 27 - Northern lights mystery may be solved (Space.com)
• February 23 - Surprise Ions (Science News for kids)
• January 26 - Giant veil of cold plasma discovered high above Earth (National Geographic)
• January 24 - Elusive matter found to be abundant far above Earth (AGU press release)
• January 18 - 2012 Royal Astronomical Society Chapman medal awarded to the Principal Investigator of the Cluster PEACE experiment

2011

• September 6 - Ultra fast substorm auroras explained
• August 31 - 40 year old Mariner 5 solar wind problem finds answer
• July 5–10 - Aurora explorer: the Cluster mission exhibit at the Royal Society summer science exhibition 2011
• July 4 - Cluster observes jet braking and plasma heating
• June 30 - 'Dirty hack' restores Cluster mission from near loss
• March 21 - How vital is a planet's magnetic field? New debate rises
• February 5 - Cluster encounters a natural particle accelerator
• January 7 - ESA spacecraft model magnetic boundaries

2010

• November 22 - ESA extends the Cluster mission until December 2014
• October 4 - Cluster helps disentangle turbulence in the solar wind
• September 1 - 10 years of success for Cluster quartet
• July 26 - Cluster makes crucial step in understanding space weather
• July 16 - Cluster's decade of discovery
• July 8 - Announcement of opportunity for Cluster guest investigators
• June 3 - The Cluster archive: more than 1000 users
• April 24 - High-speed plasma jets: origin uncovered
• March 11 - Shocking recipe for 'killer electrons'
• January 20 - Multiple rifts in Earth's magnetic shield

2009

• October 7 - ESA extends the Cluster mission until December 2012
• July 16 - Cluster shows how solar wind is heated at electron scales
• June 18 - Cluster and Double Star: 1000 publications
• April 29 - Monitoring the impact of extreme solar events
• March 25 - Cluster's insight into space turbulence
• February 9 - ESA extends the Cluster mission until the end of 2009
• January 14 - Cluster detects invisible escaping ions

2008

• December 15 - The science of space weather
• December 5 - Looking at Jupiter to understand Earth
• October 17 - Highlights from Cluster-THEMIS workshop
• August 27 - Cluster examines Earth-escaping ions
• August 11 - Electron trapping within reconnection
• June 27 - Beamed radio emission from Earth
• June 9 - Reconnection - Triggered by Whistlers?
• March 7 - Solitons found in the magnetopause
• January 23 - Cluster result impacts future space missions

2007

• December 6 - Cluster explains nightside ion beams
• November 21 - Cluster captures the impact of a Coronal Mass Ejection
• November 9 - Cluster probes generalized Ohm's law in space
• October 22 - Cluster monitors convection cells over the polar caps
• September 11 - Cluster and Double Star pinpoint the source of bright aurorae
• July 26 - Cluster helps reveal how the Sun shakes the Earth's magnetic field
• June 29 - Cluster unveils a new 3D vision of magnetic reconnection
• June 21 - Formation flying at closest-ever separation
• May 11 - Cluster reveals the reformation of the Earth's bow shock
• April 12 - Cluster finds new clues on what triggers space tsunamis
• March 26 - First direct evidence in space of magnetic reconnection in turbulent plasma
• March 12 - A leap forward in probing magnetic reconnection in space
• February 9 - New insights in the auroral electrical circuit revealed by Cluster

2006

• December 29 - 1000th Orbit for the Cluster Mission
• December 6 - Cluster finds magnetic reconnection within giant swirls of plasma
• November 13 - Cluster takes a new look at the plasmasphere
• October 5 - Double Star and Cluster witness pulsated reconnection for several hours
• August 24 - Cluster links magnetic substorms and Earthward directed high-speed flows
• July 18 - Magnetic heart of a 3D reconnection event revealed by Cluster
• June 20 - Space is fizzy
• May 19 - New Microscopic Properties of Magnetic Reconnection Derived by Cluster
• March 30 - Cluster and Double Star reveal the extent of neutral sheet oscillations
• February 24 - Cluster reveals fundamental 3-D properties of magnetic turbulence
• February 1 - The Cluster Active Archive goes live
• January 11 - Cover of Nature Magazine: Feel the Force

2005

• December 22 - Cluster helps to protect astronauts and satellites against killer electrons
• September 21 - Double Star and Cluster observe first evidence of crustal cracking
• August 10 - From ‘macro’ to ‘micro’ – turbulence seen by Cluster
• July 28 - First direct measurements of the ring current
• July 14 - Five years of formation flying with Cluster
• April 28 - Calming effect of a solar storm
• February 18 - Cluster will become the first multi-scale mission
• February 4 - Direct observation of 3D magnetic reconnection

2004

• December 12 - Cluster determines the spatial scale of high speed flows in the magnetotail
• November 24 Four-point observations of solar wind discontinuities
• September 17 - Cluster locates the source of non-thermal terrestrial continuum radiation by triangulation
• August 12 - Cluster finds giant gas vortices at the edge of Earth's magnetic bubble
• June 23 - Cluster discovers internal origin of the plasma sheet oscillations
• May 13 - Cluster captures a triple cusp
• April 5 - First attempt to estimate Earth's bow shock thickness

2003-2001

• 2003.12.03 - Cracks in Earth's magnetic shield (NASA website)
• 2003.06.29 - Multi-point observations of magnetic reconnection
• 2003.05.20 - ESA's Cluster solves auroral puzzle
• 2003.01.29 - Bifurcation of the tail current
• 2003.01.28 - Electric current measured in space for the first time
• 2002.12.29 - Thickness of the tail current sheet estimated in space for the first time
• 2002.10.01 - Telescopic/Microscopic view of a substorm
• 2001.12.11 - Cluster quartet probes the secrets of the black aurora
• 2001.10.31 - First measurements of density gradients in space
• 2001.10.09 - Double cusp observed by Cluster
• 2001.02.01 - Official start of scientific operations

Selected publications

All 2735 publications related to the Cluster and the Double Star missions (count as of 30 November 2015) can be found on the publication section of the ESA Cluster mission website. Among these publications, 2278 are refereed publications, 335 proceedings, 101 PhDs and 21 other type of theses.

External links

• ESA Cluster mission website
• More on spacecraft operations
• NASA Cluster mission profile
• The Cluster Science Archive, the long term archive of the Cluster and Double Star missions
• Imperial College London role in the Cluster mission
• University College London's Mullard Space Science Laboratory's role in the Cluster mission
• Cluster: aurora explorer, an exhibit at the Royal Society Summer Exhibition 2011
• The Cluster Active Archive (closed for new users)