Cluster II (spacecraft)

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Cluster II
The Cluster II constellation.
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: 19 years, 7 months and 13 days
Spacecraft properties
Manufacturer Astrium[1]
Launch mass 1,200 kg (2,600 lb)[1]
Dry mass 550 kg (1,210 lb)[1]
Payload mass 71 kg (157 lb)[1]
Dimensions 2.9 m × 1.3 m (9.5 ft × 4.3 ft)[1]
Power 224 watts[1]
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[2] 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 RE (Earth radii, where 1 RE = 6371 km) and an apogee of 19.6 RE. 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.[3] Ray Cotton, from the United Kingdom, won the competition with the names Rumba, Tango, Salsa and Samba.[4] Ray's town of residence, Bristol, was awarded with scale models of the satellites in recognition of the winning entry,[5][6] 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.[7]

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[8] 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

2014

2013

2012

2011

2010

2009

2008

2007

2006

2005

2004

2003-2001

References

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  • Taylor, M., C.P. Escoubet, H. Laakso, A. Masson, M. Goldstein (2010). H. Laakso (eds.); et al., eds. The Cluster Mission: Space Plasma in Three Dimensions. Astrophys. & Space Sci. Proc., Springer. pp. 309–330. <templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
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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.

  1. 1.0 1.1 1.2 1.3 1.4 1.5 "Cluster (Four Spacecraft Constellation in Concert with SOHO)". ESA. Retrieved 2014-03-13.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  2. "Cluster II operations". European Space Agency. Retrieved 29 November 2011.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  3. "European Space Agency Announces Contest to Name the Cluster Quartet" (PDF). European Space Agency.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  4. "Bristol and Cluster - the link". European Space Agency. Retrieved 2 September 2013.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  5. "Cluster II - Scientific Update and Presentation of Model to the City of Bristol". SpaceRef Interactive Inc.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  6. "Cluster - Presentation of model to the city of Bristol and science results overview". European Space Agency.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  7. "Working Life Extensions for ESA's Science Missions."ESA Science and Technology. Retrieved: 7 March 2015.
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  104. Paschmann, G., S.J. Schwartz, C.P. Escoubet, S. Haaland, ed. (2005). Outer Magnetospheric Boundaries: Cluster Results. reprinted from Space Sci. Rev., 118, 1-4, Springer, Berlin. pp. 1–434. <templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>

External links

de:Cluster (Satellit) es:Misión Cluster eu:Cluster misioa fr:Mission Cluster it:Missione Cluster hu:Cluster-program nl:Cluster-satellieten pl:Cluster pt:Missão Cluster fi:Cluster (avaruuslento) sv:Cluster (satelliter)