logo for Geotail project

Welcome to Geotail

The GEOTAIL mission is a collaborative project undertaken by the Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA), and the National Aeronautics and Space Administration (NASA). The Geotail spacecraft was designed and built by ISAS and was launched on July 24, 1992. After fulfilling Its original objective of studying the dynamics of the Earth's magnetotail over a wide range of distance, extending from the near-Earth region (8 Earth radii (Re) from the Earth) to the distant tail (about 200 Re) its orbit was changed. Since February 1995 Geotail has been in an elliptical 9 by 30 Re orbit where it has provided data on most aspects of the solar wind interaction with the magnetosphere.


Japan Geotail Project Manager:

Iku Shinohara

Institute of Space and Astronautical Science

Japan Aerospace Exploration Agency

e-mail: iku@stp.isas.jaxa.jp

tel. JP+50-3362-3279 fax JP+81-42-759-8405


Original Japan Project Manager:

Toshifumi Mukai


Japan Geotail Project Scientist:

Masaki Fujimoto

Institute of Space and Astronautical Science

Japan Aerospace Exploration Agency

e-mail: fujimoto@stp.isas.jaxa.jp

tel. JP+50-3362-7858 fax JP+81-42-759-8456


Original Japan Project Scientist:

Atsuhiro Nishida


US Geotail Project Scientist:

Guan Le

NASA Goddard Space Flight Center Code 674

Greenbelt, MD 20771

Email: guan.le-1@nasa.gov

Phone +1 301-286-1087

Fax: +1 301-286-1648


Original US Project Scientist:

Donald H. Fairfield


Spacecraft Diagram


CDAWeb data

Orbits plots

Orbit data and plots



The Comprehensive Plasma Instrumentation for the Geotail mission observes the three-dimensional velocity distributions of electrons and positive ions. The measurements are used to investigate physical processes in the terrestrial magnetosphere and the interplanetary medium (solar wind). Processed data are provided for use by the scientific community through NASA's CDAWeb, and through the University of Iowa (http://www-pi.physics.uiowa.edu/cpi/). Three sets of analyzers are employed to provide resolution of particle energies, directions, and Mass/Charge composition. The Solar Wind analyzer (CPI- SW) measures ions with energies/charge 150 V to 7 kV with high resolution of directions to characterize the plasmas of the solar wind. The Hot Plasma analyzer (CPI-HP) provides 3D coverage of electrons and positive ions with energies/charge 1 V - 50 kV to cover distributions typical of the magnetosphere. The Ion Composition analyzer (CPI-IC) includes five miniature imaging mass spectrometers at the exit aperture of the analyzer for discrimination of ion Mass/Charge. Sequencing of the energy analyzers and mass spectrometers, and other control functions, are provided by two microprocessors.


Related Links:

CPI Homepage: http://www-pi.physics.uiowa.edu/www/cpi/


Principal Investigator:

Dr. William R. Paterson

Department of Atmospheric and Planetary Sciences

Hampton University

Hampton VA 23692

Phone: 757 728-6401

Fax: 757 637-2515

E-mail: Bill.Paterson@Hamptonu.edu


Original Principal Investigator

Dr. L. A. Frank



The principal objective of the EPIC (Energetic Particles and Ion Composition) investigation is to explore the outer magnetosphere and the distant magnetotail region and obtain information on the origin, transport, storage, acceleration and dynamics of suprathermal and non-thermal particle populations. The instrument contains two main sensor heads. The STICS assembly (Supra-Thermal Ion Composition Spectrometer) uses a quadrispherical electrostatic analyzer followed by a foil/solid state detector time-of-flight (TOF) telescope to measure charge state, mass and energy of ions with energies of 10 - 230 keV/charge. The ICS assembly (Ion Composition Subsystem) measures the mass and energy of energetic ions with energies of less than 50 keV to 3 MeV. It uses a pair of collimators with sweeping magnets to reject electrons, followed by TOF and energy analysis. A thin foil/solid state detector electron telescope measures electrons higher than 30 keV. Directional measurements with a time resolution <3 s for all species are possible. A detailed instrument description, and a complete set of EPIC summary plots from launch to the present, plus on-line access to the digital data set, is available at the EPIC link below.


Related Links:

Geotail/EPIC SDC: http://sd-www.jhuapl.edu/Geotail/


Principle Investigator:

Dr. A. T. Y. Lui

Applied Physics Lab, Johns Hopkins University

John Hopkins Road

Laurel, MD 20723-6099

Phone: 240-228-5598

E-mail: Tony.Lui@jhuapl.edu


Original Principle Investigator :

Dr. D. J. Williams


2nd Principle Investigator

Dr. Richard McEntire



The objective of this experiment is to measure the geospace magnetic field and its variations in the frequency range below 50 Hz. The MGF experiment consists of dual three-axis fluxgate magnetometers and a three-axis search coil magnetometer. Triad fluxgate sensors, which utilize a ring core geometry, are installed at the end and middle of a 6 m deployable mast. Since December 27th 2006, fluxgate data has been obtained only from the inboard magnetometer. Three search coils are mounted approximately one-half of the way out on another 6 m boom together with search coils for the VLF wave in the PWI system.


The fluxgate magnetometers are of standard design and consist of an amplifier, filter, phase sensitive detector, integrator, and a voltage-current convertor. Until September 15, 1999 the fluxgate magnetometers operated in seven dynamic ranges to cover various regions of the Earth's magnetosphere and the solar wind: +/-16 nT, +/-64 nT, +/-256 nT, +/-1024 nT, +/-4096 nT, +/-16384 nT, and +/-65536 nT. Since September 15, 1999 the dynamic range of the fluxgate magnetometer has been fixed in the +/-256 nT range. Fluxgate vector data are supplied at a rate of 16 vectors/sec.


The search coil magnetometer system consists of three sensors, preamplifier, amplifier, filter, multiplexer, and an A/D converter. The search coil magnetometers operate in a frequency range of 0.5 kHz to 1 kHz, and supply 128 vectors/sec.


The fluxgate magnetometer operates in both real time and record modes, while the search coil data are used only in real time mode


Related Links:

DARTS (MGF and LEP, EFD high time resolution) http://darts.isas.jaxa.jp/stp/geotail/

Principle Investigator:

Dr. Tsugunobu Nagai

Tokyo Institute of Technology

Earth and Planetary Sciences, I2-5

2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551, Japan

Phone: +81-3-5734-2621

Fax: +81-3-5734-3537

E-mail: nagai@geo.titech.ac.jp


Original Principle Investigator:

Dr. Susumu Kokubun



The objective of this investigation is to determine the dynamic behavior of the plasma waves generated by wave-particle interactions in the earth's magnetosphere as well as in the magnetosheath and solar wind regions. Plasma waves reflect energy/momentum transport processes in collisionless space plasmas. They provide important clues in understanding the microscopic phenomena taking place in space.


The instrument measures electric fields over the range 5.6 Hz to 800kHz, and magnetic fields over the range 5.6 Hz to 12.5 kHz. Triaxial magnetic search coils are utilized in addition to two sets of electric dipole antennas. The instrument contains the sweep-frequency analyzer(SFA) (24 Hz to 800 kHz for the electric field and 24 Hz to 12.5 kHz for the magnetic field), a multichannel analyzer(MCA) (5.6 Hz to 311 kHz for the electric field and 5.6 Hz to 10 kHz for the magnetic field), and a wideband waveform capture receiver (WFC)(10 Hz to 4 kHz).


Related Links:

PWI Homepage http:// www.kurasc.kyoto-u.ac.jp/gtlpwi/

Multi-Channel Analyzer



(Frequency-time spectrograms(SFA/MCA) in periods of 2hours (with full time resolutions), and 24hours are opened to be accessed in public.)


Principle Investigator:

Dr. Hirotsugu Kojima

Research Institute for Sustainable Humanosphere, Kyoto University

Phone/Fax: +81-774-38-3816

E-mail: kojima@rish.kyoto-u.ac.jp


Original PI:

Prof. Hiroshi Matsumoto

Kyoto University

Yoshida-honmachi, Sakyo, Kyoto 606-8501, Japan

Phone: +81-75-753-2217

Fax: +81-75-753-2091




The objective of this experiment is to observe plasmas and energetic electrons and ions in the terrestrial magnetosphere and in the interplanetary medium with the Energy Analyzer for electrons (EA-e), the Energy Analyzer for ions (EA-i), and the Solar Wind analyzer (SW).


LEP-EA measures three-dimensional velocity distributions of hot plasmas in the magnetosphere. EA consists of two nested sets of quadrispherical electrostatic analyzers. The inner analyzer (EA-e) measures electrons in the energy range from 60 eV to 38 keV (or, 8 eV to 8 keV in the other mode), and the outer one (EA-i) measures positive ions from 32 eV/Q to 39 keV/Q (or, 5 keV/Q to 43 keV/Q in the solar wind region). The field of view for each quadrispherical analyzer covers 10 degrees by 145 degrees, where the longer dimension is parallel to the satellite spin axis. LEP-SW measures three-dimensional velocity distributions of solar wind ions in the energy range from 0.3 keV/Q to 8 keV/Q with a 270-degree spherical electrostatic analyzer with a field of view of 5 degrees by 60 degrees. Although it ceased operation shortly after launch, this experiment resumed operation in September 1993 and has worked well ever since.


Related Links:

DARTS (MGF, LEP, and EFD; high time resolution)http://darts.isas.jaxa.jp/stp/geotail/

LEP spectrograms http://www.stp.isas.jaxa.jp/geotail/QL/


Principle Investigator:

Dr. Yoshifumi Saito

Institute of Space and Astronautical Science

3-1-1 Yoshinodai, Sagamihara, Kanagawa 229-8510, Japan

Phone: +81-42-759-8171

E-mail: saito@stp.isas.jaxa.jp


Original PI:

Dr. Toshifumi Mukai

Japan Aerospace Exploration Aency

Marunouchi Kitaguchi Building

1-6-5 Marunouchi, Chiyoda-ku, Tokyo 100-8260, Japan

Phone: +81-3-6266-6607

Fax: +81-3-6266-6926




The objectives of this investigation are studies of (1) the large scale configuration of the electric field in the magnetotail, (2) tail electric field variations during substorms, (3) the electric field in the plasma sheet, (4) the electric field near the magnetopause and in the plasma mantle at locations tailward of those covered by similar measurements on ISEE 1, (5) micropulsation and low frequency wave measurements at frequencies covering the local gyrofrequency (<1Hz) and lower hybrid frequency (<10Hz) in the tail, (6) plasma density as deduced from measurement of the floating potential of the spacecraft, and (7) electric field comparisons (with the aid of the other spacecraft in the ISTP program) at different points along the same magnetic field line, at different points along a common boundary, or in different regions of the magnetosphere.


The antenna part consists of two orthogonal double probes. One of the pairs (PANT) has spherical probes at the tips of the antennas for the constant photoelectron emission. The other (WANT) has smaller masses at the tips. The separation distances between the pair of sensors are 100 m tip-to-tip. Electric field is measured in the spin plane which is nearly parallel to the ecliptic plane. In the DARTS data base the data from PANT is available.


Related Links:

DARTS (ASCII listing and plot of spin-period resolution data) http://darts.isas.jaxa.jp/stp/geotail/

Principle Investigator:

Dr. Hajime Hayakawa

Institute of Space and Astronautical Science

3-1-1 Yoshinodai, Sagamihara, Kanagawa 229-8510, Japan

Phone: +81-42-759-8165

Fax: +81-42-759-8456

E-Mail: hayakawa@isas.jaxa.jp


Original Principle Investigator:

Dr. Koichiro Tsuruda




There are three scientific objectives to be studied by this investigation: (1) plasma dynamics in the geomagnetic tail, (2) solar flare particle acceleration and propagation, and (3) the origin, lifetime and propagation of cosmic ray particles. There are five instruments that make up this investigation: Low-energy particle Detector (LD), Burst Detector (BD), Medium-energy Isotope detectors (MI-1 and MI-2), and High energy Isotope detector (HI).


LD and BD are mainly dedicated to magnetospheric studies.

MI and HI concentrate on solar flare and cosmic ray studies.


The LD sensor system consists of three identical Imaging Ion Mass spectrometers which use time-of-flight/energy measurement, and covers 180 degrees in polar angle over the energy range 20--300 keV for electrons, 2 keV--1.5 MeV for protons, and 2 keV--1.5 MeV per charge for ions. LD provides distribution of electrons and ions with complete coverage of the unit sphere in phase space, and electron and proton flux in 4 azimuth sectors, helium and oxygen flux at an azimuth of 0 degrees.


The BD sensor consists of three delta-E x E telescopes which identify particles by their energy loss and residual energy over the energy range 0.12--2.5 MeV for electrons, 0.7--35 MeV for protons, and 0.7--140 MeV for helium. The three telescopes each have an opening angle of 30 degrees by 45 degrees with look directions of 30, 90, and 150 degrees to the spin axis. BD provides count rates for high energy electrons, protons and helium, as well as electron and proton fluxes in four 90 degree azimuth bins.


The MI and HI instruments are all silicon semiconductor detector telescopes utilizing the well-known dE/dx x E algorithm for isotope identification: mass and nuclear charge. The MI instrument measures elemental and isotopic compositions of solar energetic particles and energetic particles in the heliosphere with 2&ltZ&lt28 in the 2.4--80 MeV/nucleon energy range , and measures the elemental composition of solar energetic particles heavier than iron. The HI instrument also measures elemental and isotopic compositions of solar energetic particles and galactic cosmic rays with 2&ltZ&lt28 in the 10-210 MeV/nucleon energy range.


HEP operates continuously with no change in allocated bit rate. LD has two operational modes: normal and burst. Burst mode is an internal high speed mode which does not change the data output.


BD has four operational modes for calculating energy spectra for electrons, protons, and helium: 16 sectors in 1 spin (time high resolution mode), 8 sectors in 32 spins (energy high resolution mode), 8 sectors in 2 spins, and 16 sectors in 4 spins. MI and HI have only one operational mode.


Principle Investigator:


Prof. Tadayoshi Doke

Waseda University

e-mail: jkikuchi@cfi.waseda.ac.jp



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