NASA Facts Cluster II Spacecraft to Explore Earth's Turbulent Magnetic Environs

8/7/2019 NASA Facts Cluster II Spacecraft to Explore Earth's Turbulent Magnetic Environs

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NASA FactsNational Aeronautics andSpace AdministrationGoddard Space Flight CenterGreenbelt, Maryland 20771AC 301 286-8955

Cluster II Spacecraft to Explore Earth's TurbulentMagnetic Environs

Earth's Magnetic Field Stands Off TheSolar Wind

An unseen struggle rages in spacenear the Earth. The million miles per hoursolar wind, a gas comprised primarily ofelectrons and protons, relentlesslystreams toward our planet. It is held atbay by the Earth’s vast magnetic field,which deforms under the onslaught of thissolar gale, like a jellyfish buffeted by watercurrents, or a large tent flapping in a wind

storm.

The solar wind compresses theEarth’s magnetic field to about 40,000miles (64,374 kilometers) from Earth onEarth’s dayside and stretches it to about800,000 miles (1,287,000 kilometers) onthe night side. This volume of space con-taining the Earth’s magnetic field is knownas the magnetosphere. Once solar wind

particles have penetrated the magneto-sphere, they are guided by Earth’s mag-netic field.

The electrically charged particles ofthe solar wind infiltrate Earth’s magneticrealm with an intensity and impact thatdepends on solar conditions and direction

Artist concept of Cluster II spacecraft on orbit formation.

of the magnetic field carried by the solarwind. Electrons and protons spiral down afunnel-like region of the magnetic fieldabove Earth’s day-side polar regions (astructure called the polar cusp) and hit theupper atmosphere, eventually creating thehaunting glow that are the northern and



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southern lights. At the same time, theseparticles generate electrical currents thatdistort Earth’s magnetic field, especially athigh northern and southern latitudes. Themost severe disruptions of the magneticfield are known as geomagnetic storms,and these electric currents and energeticparticles occasionally disable satellites,radio communications, and power sys-tems.

This interaction is very complex andresearchers do not understand all theeffects of the solar wind on the Earth. Themagnetosphere’s enormous size andcomplexity have made it impossible tounderstand with isolated spacecraft. Clus-ter II, a fleet of four identical spacecraft,will explore portions of this turbulent re-gion beginning in the summer of 2000.

Surveying The Magnetosphere

Each Cluster II spacecraft will bepositioned so that each is located at one

of the four points of a pyramid. This ar-rangement will allow three-dimensionalstructures to be described, for the firsttime, in both the magnetosphere and solarwind. Instruments aboard Cluster II willobserve the response of Earth’s magneto-sphere to the ebb and flow of the solarwind in ways never before possible.

Distances between the Clusterspacecraft will be adjusted throughout themission in order to study different regionsand plasma structures. Comparison ofsimultaneous measurements from thedifferent spacecraft will be combined toproduce a three-dimensional picture ofplasma structures.

Because the separation of the fourspacecraft will vary from about 400hundred miles to more than 10,000 miles(643 to 16,093 kilometers), scientists willbe able to study several of the structureswhich characterize the Earth’s magneto-sphere. These include the bow shockwave that stands in front of the magneto-

Line Drawing showing the Cluster II formation



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sphere as the solar wind is deflected, polarcusp regions of the magnetic field andtemporal and spatial structure of the denseplasma in the center of the tail of the mag-netosphere on Earth’s night side called theplasma sheet.

The Cluster II fleet will be launchedin pairs into a polar orbit from the RussianAviation and Space Agency Cosmodrome,Baikonur, Kazakhstan, aboard two Soyuz-Fregat rockets. The launches, whichfeature a four-minute window, are sched-uled for July and August 2000. The space-crafts' intended apogee (farthest pointfrom the Earth) will be about 74,000 miles(119,091 kilometers) and its perigee(closest point) will be about 12,000 miles(19,312 kilometers).

Each Cluster II spacecraft is cylindri-cally-shaped, measuring 9.5 feet (2.9meters) in diameter and 4.3 feet(1.3 meters) high, and weighs about 1,213pounds (550 kilograms). An additional1,430 pounds (649 kilograms) of fuel isincluded for orbital maneuvering. To main-tain a stable orientation in space, eachspacecraft will spin like a slow gyroscope,making one complete revolution every fourseconds.

Cluster II Science Instruments

During its initial two-year mission,the Cluster II spacecraft will conduct scien-tific investigations using a complement of11 instruments and support provided by aninternational team of investigators.

Instruments onboard the Cluster IIspacecraft include:

Active Spacecraft Potential Control(ASPOC) – reduces the electric charge onthe spacecraft, so very low-speed elec-trons can be measured.

Cluster Ion Spectrometry (CIS) – measures the relative abundance of pro-tons and helium nuclei and determinestheir three-dimensional distribution in thesolar wind and magnetosphere.

Digital Wave Processor (DWP) –provides data processing for the plasmawave instruments.

Electron Drift Instrument (EDI) – determines the strength and direction ofthe ambient electric field.

Electric Fields and Waves (EFW) – measures fluctuating electric fields in theplasma surrounding the spacecraft.

Fluxgate Magnetometer (FGM) – measures static and fluctuating magneticfields at the spacecraft.

Plasma Electron and Current Experi-ment (PEACE) – provides three-dimen-sional measurements of electrondistributions in the solar wind and mag-netosphere.

Research with Adaptive Particle Imag-ing Detectors (RAPID) – measures ener-

getic ions and electrons.

Spatio-Temporal Analysis of Field Fluc-tuations (STAFF) – measureshigh-frequency waves in the local plasma.

Wideband (WBD) Plasma WaveInvestigation – detects very high fre-quency plasma waves at very high time



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resolution.

Waves of High Frequency and Sounderfor Probing of Density by Relaxation(WHISPER) – uses high-frequencyplasma waves to probe surroundingplasma, determining the local density ofcharged particles.

Program and Mission Management

Cluster II will join the Solar andHeliospheric Observatory (SOHO), whichlaunched December 2, 1995, as the sec-ond cooperative solar-terrestrial projectbetween the European Space Agency(ESA) and NASA. SOHO and Clusterconstitute the ESA Solar TerrestrialScience Programme, the first cornerstonemission of ESA’s long-term initiative calledSpace Science Horizon 2000 .

Each spacecraft will operate inconcert with Geotail, a joint Japanese/

NASA satellite, and NASA’s Wind andPolar missions, to provide coordinatedmeasurements throughout the geospaceenvironment.

The Wind and Polar missions, alongwith NASA’s contributions to SOHO, Clus-ter and Geotail, constitute the InternationalSolar-Terrestrial Physics (ISTP) scienceinitiative, whose purpose it is to under-

stand how the Earth’s geospace environ-ment responds to changes in the solarwind.

The Cluster II mission involves aninternational team of investigators from sixcountries. NASA has agreements with theUnited Kingdom for the FGM investigation,Sweden for the EFW experiment, France

for the WBD investigation and the CISexperiment, and Germany for EDI andRAPID.

NASA will provide Deep SpaceNetwork support for the acquisition of datafrom the WBD instrument, and for com-manding the Cluster II spacecraft andacquiring data.

The Cluster II management teamconsists of the following agencies andindividuals:

Dino Machi , NASA Program Manager,Goddard Space Flight Center;

John L. Christensen , NASA ProjectManager, Goddard Space Flight Center;

Dr. Melvyn Goldstein , NASA ProjectScientist, Goddard Space Flight Center;

Alberto Gianolio , Deputy ProjectManager, ESA; and

Dr. Philippe Escoubet , Project Scientist,ESA;

ESA will manage the spacecraft andscience operations, while several NASAcenters provide support to the missionthrough collection and dissemination ofscientific data.

For more detailed information aboutthe Cluster II spacecraft and its sciencemission, visit these websites:

http://international.gsfc.nasa.gov/http://sci.esa.int/cluster/

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NASA Facts Cluster II Spacecraft to Explore Earth's Turbulent Magnetic Environs