GEOTAIL is a collaborative mission of Japan and the USA, of the agencies JAXA/ISAS (Institute of Space and Astronautical Science), and NASA (National Aeronautics and Space Administration), respectively, within the program ISTP (International Solar-Terrestrial Physics). The spacecraft was built and integrated by ISAS, the launch was provided by NASA/GSFC. Responsibilities are shared in science instruments, telemetry data acquisition, and data processing and archiving. GEOTAIL inaugurates the Collaborative Solar-Terrestrial Research Program (COSTR). COSTR defines the NASA contributions to the GEOTAIL, SOHO, and Cluster missions.
Note: ISAS (Institute of Space and Astronautical Science) became part of JAXA (Japan Aerospace Exploration Agency) in October 2003.
Figure 1: Artist's view of the GEOTAIL spacecraft in orbit (image credit: JAXA)
• Determine the overall plasma, electric and magnetic field characteristics of the distant and geomagnetic tail.
• Determine the role of the distant and near-Earth tail in substorm phenomena and in the overall magnetospheric energy balance and relate these phenomena to external triggering mechanisms.
• Study the processes that initiate magnetic field reconnection in the near-Earth tail and observe the microscopic nature of the energy conversion mechanism in the reconnection region.
• Study plasma entry, energization, and transport processes in interaction regions such as the inner edge of the plasma sheet, the magnetopause and the bow shock, and investigate associated boundary layer regions.
GEOTAIL measures the flow of energy and its transformation in the magnetotail created by the interaction between the solar wind and the Earth. GEOTAIL also determines, in detail, the overall plasma characteristics of the distant geomagnetic tail - a comet-like tail of plasma millions of km long created by the solar wind.
The spacecraft was designed and built at JAXA/ISAS (formerly ISAS). The spacecraft structure has the shape of a drum and is spin-stabilized (cylinder of 2.2 m×diameter and 1.6 m in height) utilizing mechanically despun antennas. The spin axis is oriented nearly perpendicular to the ecliptic plane (85-89º), and the nominal spin rate is 20 rpm.
Figure 2: The GEOTAIL spacecraft (image credit: ISAS/JAXA)
Spacecraft mass of 1009 kg (330 kg propellant, 105 kg science payload). The dual-spinning satellite, equipped with two pairs of wire antennas of 50 m in length (100 m tip-to-tip) and two 6 m long masts, will contribute to deeper understanding of fundamental magnetospheric processes. Power is provided by surface-mounted solar cells, nominal power of 275 W. The design life of GEOTAIL is 4 years. The satellite employs Indium-Ion emitters (a multi-emitter module containing four individual ion emitters of the liquid metal indium field emission type) for S/C charge compensation. 7) 8)
RF communications: The communication system, built under prime contract to NEC, comprises S and X-band systems for command, telemetry, and ranging (mechanically despun antennas are utilized). Spacecraft communication is compatible with both the UDSC (Usuda Deep Space Center) and NASA's Deep Space Network (DSN). There are two on-board recorders at 450 Mbit each which allow daily 24 hour data coverage. Real-time/playback transmission rates at 16.384 kbit/s, 65.536 kbit/s, or at 131.072 kbit/s. Ground data reception at Usuda and Kagoshima stations (Japan) and at the NASA's DSN (playback only). ISAS is responsible for spacecraft operations.
Launch: A GEOTAIL launch took place on July 24, 1992 from Cape Canaveral with a Delta 2 vehicle. GEOTAIL is the first spacecraft launched within ISTP (the others are: WIND, POLAR, Cluster, SOHO, Equator-S, Interball).
Orbit: GEOTAIL objectives require spacecraft measurement in two orbits: a nightside double lunar swingby GeoTail orbit to distances from 80 to 220 RE, and a low inclination orbit (29º) at geocentric distances of about 8 to 30 RE. GEOTAIL uses the gravity of the moon to assist its orbit on the night side of the Earth, where the magnetotail is stretched out as a result of the impact of the solar wind encountering the Earth. In this phase, GEOTAIL's orbit extends from 220 RE (1,401,620 km) at its farthest point to 8 RE (50,960 km) at its nearest point.
In the first two years of the mission, the apogee was kept on the night-side of the Earth by means of the lunar double swing-by maneuvers, ranging from 80 to 220 Re in order to explore the distant tail.
• Distant tail orbit: 1.75 years in distant tail configuration (double lunar swingby to an 8 x 220 RE orbit). This orbit also allows the study the boundary region of the magnetosphere as it skims the magnetopause at perigees. In the first two years the double lunar swing-by technique was used to keep apogees in the distant magnetotail.
• Near tail orbit: 1.45 years in near tail configuration (reduced to an 8 x 30 RE orbit, 7.5º inclination).
The apogee was lowered down to 50 RE in mid November 1994 and then to 30 RE in February 1995 in order to study substorm processes in the near-Earth tail region. In June 1997, the perigee was slightly lowered to 9-9.5 RE in order to increase the probability that the spacecraft is just inside the dayside magnetopause. The near-tail orbit of 9 RE x 30 RE (with an inclination of -7º to the ecliptic plane) has allowed extensive study of the magnetosheath, the bow shock and the upstream region as well..
Figure 3: The GEOTAIL spacecraft with booms, antennas and instruments (image credit: NASA, JAXA)
Science background: The solar wind, emanating from the sun, injects plasma into the magnetosphere and transfers energy to it. Several times a day the magnetosphere undergoes a disturbance called a substorm. As the substorm grows, most of the solar energy is dissipated within the magnetosphere, ionosphere and upper atmosphere. This disturbance ultimately causes auroral displays, the acceleration of charged particles to high energies, the emission of intense plasma waves, and the generation of strong ionospheric currents that produce significant changes in the upper atmosphere. These waves and currents often result in severe problems on Earth with regard to communications, power supplies, and spacecraft electronics.
GEOTAIL is the first mission making extensive observations in the distant geotail beyond the lunar orbit and in the neutral sheet of the near-Earth tail region.
• In 2013, the GEOTAIL spacecraft and its payload continue to operate.
• The GEOTAIL spacecraft and its payload are operating nominally in 2012. On July 24, 2012, the spacecraft was 20 years on orbit.Geotail's instruments continue to function, sending back crucial information about how aurora form, how energy from the sun funnels through near-Earth space, and the ways in which magnetic field lines move and rebound creating explosive bursts that rearrange the very shape of our magnetic environment. 9)
• The GEOTAIL spacecraft and its payload are operating nominally in 2011. GEOTAIL has made substantial contributions to humanity's understanding of space, with exciting prospects for the extended mission, in at least the following areas:
1) The structure and variability of Earth's magnetosphere. GEOTAIL has been studying the process of magnetic reconnection process (important throughout modern space physics, astrophysics, and plasma physics and the spatial distribution of the plasma density, temperature, and magnetic field in Earth's magnetotail, as well as their variability as a function of solar activity and space weather events.
2) The microphysics of wave-particle interactions and very localized "packets" of plasma waves. This physics is quite fundamental, with applications throughout plasma physics, space physics and astrophysics.
• GEOTAIL is operational in 2010, in its 18th year on orbit. The project is expecting some more years of operations. 10)
• In early 2008, a mission extension was granted by JAXA. At JAXA/ISAS, GEOTAIL will be operated at least until 2012. GEOTAIL will remain to be a member of the alliance of the spacecraft that enable to perform multi-spacecraft data analysis of the magnetospheric dynamics for the next at least several years. 11)
Legend to Figure 4: It was reported that the gamma-ray intensity just after the flare appeared is bigger than that of a solar flare.
- The upper part of the image shows the electrons count by the LEP (Low Energy Particles experiment) instrument
- The lower part of the image shows the ion count by the LEP instrument
A vertical stripe appears at the time indicated by an arrow in Figure 4. This indicates the signal of gamma rays from SGR1806-20.
• During its mission, the GEOTAIL satellite has identified numerous new phenomena in the magnetosphere. It has collected important data in particular on the issue of magnetic reconnection, taking advantage of in situ observations. In space plasma physics, GEOTAIL is providing data on the generation of non-thermal particles by shock waves and the process of energy reduction by wave-particle interaction.
• During January and February 1997, a number of conjunctions between the FAST (Fast Auroral Snapshot Explorer) and GEOTAIL satellites occurred when FAST was at apogee above the nightside auroral zone in the northern hemisphere and Geotail was close to midnight near the equatorial plane. These events provided an opportunity to examine physical processes connecting the magnetotail at 20 to 40 RE to the auroral zone during substorms and quiet times.
• In the first two years the apogee was kept on the night-side of the Earth by means of the lunar double swing-by maneuvers, ranging from 80 to 220 RE in order to explore the distant tail. Later from November 1994, the apogee was lowered first to 50 RE and then to 30 RE in order to study substorm processes in the near-Earth tail region. -In February 1995, phase two was commenced as the apogee was reduced to 30 RE to study the near-Earth magneto-tail processes.
Sensor complement: (EFD, MGF, HEP, LEP, PWI, EPIC, CPI)
EFD (Electric Field Detector):
PI: K. Tsuruda, ISAS. Objectives: study of the coupling of the E-Field in the near-Earth magnetosphere and in the ionosphere (in particular during substorms). EFD uses electric-field antenna sampling at 64 samples/s, and an electron beam technique at 2 samples per spin. 17) 18)
The instrument consists of two orthogonal double probes, each of which is a pair of separated spheres on wire booms that are located in the satellite spin plane and whose difference of potential is measured. The separation distances between the pair of sensors are variable and as great as 160 m tip-to-tip. One operating mode involves length ratios of the two antennas of about 2:1 in order to verify instrument operation through showing that the electric field signature is proportional to the boom length. A second reason for two pairs of wire booms in the satellite spin plane is the requirement for measurements having a time resolution far better than the satellite spin period.
MGF (Magnetic Field Measurement):
PI: S. Kokubun, U. of Tokyo, R. Lepping, GSFC, instrument sponsored by ISAS. Objectives: study of the transport dynamics of mass, momentum, and energy between the magnetospheric and ionospheric plasma (frequency range < 50 Hz). Study of merging in the magnetotail. Instrument: MGF uses fluxgate and search coil magnetometers for DC and AC measurements, respectively. Two sets of the fluxgate magnetometers were deployed at distances of 4 and 6 m along the 6 m mast.
MGF also contains the GEOTAIL Inboard Magnetometer provided by the US. The fluxgate magnetometers operate 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, and supply 16 vectors/s. 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 0.5-1 kHz, and supply 128 vectors/s. 19)
Figure 5: Functional block diagram of the MGF instrument (image credit: JAXA/ISAS)
HEP (High Energy Particles Experiment):
T. Doke, Waseda University, Tokyo, instrument sponsored by ISAS. Objectives: measurement of high energy particles up to 25 MeV for electrons, 35 MeV for protons, and 210 MeV/charge for ions. Measurements may indicate the plasma boundary surfaces and reflect whether magnetic field lines are open or closed.
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. 20) 21)
• The HEP-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 0º. 22)
• The HEP-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 30º x 45º with look directions of 30, 90, and 150º to the spin axis. BD provides count rates for high energy electrons, protons and helium, as well as electron and proton fluxes in four 90º azimuth bins.
• The HEP-MI and HEP-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 < Z< 28 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 < Z < 28 in the 10-210 MeV/nucleon energy range.
LEP (Low Energy Particles Experiment):
PI: T. Mukai, ISAS. Objectives: study of the dynamics of the magnetotail plasmas, plasma circulation and its variability in response to fluctuations in the solar wind and in the interplanetary magnetic field. Measurement of electrons from 6 eV to 36 keV, and ions from 7 eV to 42 keV/ charge. The LEP consists of three sensors: LEP-EA, LEP-SW, and LEP-MS, with common electronics (LEP-E). 23)
• LEP-EA measures the 3-D velocity distributions of hot plasma in the magnetosphere. EA consists of two nested sets of quadrispherical electrostatic analyzers. The inner analyzer measures electrons in the energy range from 6-36 eV, and the outer one measures positive ions from 7 eV/Q to 42 keV/Q. The field of view for each quadrispherical analyzer covers 10º x 145º, where the longer dimension is parallel to the satellite spin axis.
• LEP-SW measures the 3-D velocity distributions of solar wind ions in the energy range from 0.1-8 keV/Q with a 270º spherical electrostatic analyzer with a field of view of 5º x 60º.
• LEP-MS is an energetic ion mass spectrometer, which provides the 3-D determinations of the ion composition in 32 steps over the energy range of 0-25 keV/Q. All sensors operate continuously as long as the spacecraft power budget can allow, except for the orbit/attitude maneuvering operation.
When spacecraft power budget is not sufficient to fully operate the instruments, priority is given to LEP-EA and LEP-E.
Figure 6: Schematic view of the three LEP sensor units (image credit: JAXA/ISAS)
PWI (Plasma Waves Investigation):
PI: H. Matsumoto, Kyoto University, instrument sponsored by ISAS. Objectives: study of the wave phenomena related to plasma dynamics in the different regions on various scales (phenomena include magnetic-field-line merging, moving plasmoids, and particle acceleration). Measurement of plasma waves in the frequency range of 5 Hz - 800 kHz. PWI contains also the Multi-Channel Analyzer provided by the US. The instrument measures electric fields over the range 0.5 Hz to 400 kHz, and magnetic fields over the range 1 Hz to 10 kHz. Triaxial magnetic search coils are utilized in addition to a pair of electric dipole antennas. The instrument contains two sweep-frequency receivers (12 Hz to 400 kHz and 12 Hz to 6.25 kHz), a multichannel analyzer (5.6 Hz to 311 kHz for the electric antenna and 5.6 Hz to 1.0 kHz for the magnetic coils), a low frequency waveform receiver (0.01 to 10 Hz), and a wideband waveform receiver (10 Hz to 16 kHz). 24) 25) 26)
EPIC (Energetic Particle and Ion Composition Experiment):
PI: R. McEntire, APL, Johns Hopkins University, instrument sponsored by NASA. Objectives: measurement of the charge, mass, and energy of ions. Study of the relative importance of ion sources and mechanisms for acceleration, transport and loss of particles, the formation and dynamics of magnetospheric boundary layers. - The EPIC instrument is actually composed of two separate sensor and processing assemblies: 27) 28)
• STICS (Supra-Thermal Ion Composition Spectrometer). Objective: Measurement of ions. STICS 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 30 - 230 keV/charge. It uses an electrostatic analyzer with a geometry factor of 0.05 cm2 sr, time of flight and energy analysis.
• ICS (Ion Composition Subsystem). The objective is to measure mass and energy properties of energetic ions with energies of less than 50 keV to 3 MeV. ICS uses a pair of collimators with sweeping magnets to reject electrons, followed by TOF and energy analysis, with a geometry factor of 0.2 cm2 sr. A thin foil/solid state detector electron telescope measures electrons higher than 30 keV.
Figure 7: Diagram of the EPIC instrument elements (image credit: JHU/APL)
Figure 8: View of the STICS component of the EPIC instrument (image credit: JHU/APL)
Figure 9: Illustration of the ICS component of the EPIC instrument (image credit: JHU/APL)
Figure 10: EPIC sensors elevation FOV (Field of View) geometries (image credit: JHU/APL)
CPI (Comprehensive Plasma Investigation):
PI: L. A. Frank, University of Iowa, instrument sponsored by NASA. Objectives: measurement of the 3-D plasma in the Earth's magnetotail. The plasma data will be correlated with the magnetic field, plasma waves, electric particles, and auroral imaging data to determine magnetotail plasma dynamics.
Instrument: measurement range of 1 eV - 50 keV for the Hot Plasma and Ion Composition Analyzer, and 150 eV - 7 keV energy/unit charge for the Solar Wind Analyzer. Plasma parameters, including heat flux and field-aligned current density, are measured. 29) 30)
The instrument contains three sets of quadrispherical analyzers with channel electron multipliers. These three obtain 3-D measurements for hot plasma and solar wind electrons, for solar wind ions, and for positive-ion composition measurements. The positive-ion composition measurement includes five miniature imaging mass spectrometers at the exit aperture of the analyzer, and covers masses from 1 to 550 u/Q at 100 eV, and 1 to 55 u/Q at 10 keV. The hot plasma analyzer measures electrons and ions in the range 1-50,000 eV/Q. The solar wind analyzer measures ions from 150 to 7,000 eV/Q. Sequencing of the energy analyzers and mass spectrometers, and other control functions, are provided by two microprocessors.
Figure 11: Front view of CPI (image credit: University of Iowa)
7) “New Japanese Spacecraft to Study Solar Flares, Effects of Sun on Earth”, Aviation Week and Space Technology, Aug. 27, 1990, pp. 76-81
8) M. Fehringer, F. Rüdenauer , W. Steiger, “Space-Proven Indium Liquid Metal Field Ion Emitters for Ion Microthruster Applications,” 33 rd AIAA Joint Propulsion Conference, July 6-9, 1997, Seattle, WA, USA
9) “Geotail: 20 Years of Science and Still Going Strong,” NASA, July 27, 2012, URL: http://www.nasa.gov/mission_pages/sunearth/news/geotail-20th.html
10) Information provided by Robert M. Candey of NASA/GSFC, Greenbelt, MD, USA
12) Toshio Terasawa, “GEOTAIL Satellite - Detailed Story of Astronomical Gammay-ray observation,” URL: http://www.isas.jaxa.jp/e/forefront/2005/terasawa/02.shtml
13) “GEOTAIL Instruments and Initial Results,” Foreword by A. Nishida, Journal of Geomagnetism and Geoelectricity, ISSN 0022-1392, Vol. 46, No 1, 1994, p. 3
16) A. Nishida, K. Uesugi, I. Nakatani, T. Mukai, D. H. Fairfield, M. H. Acuna, “Geotail mission to explore earth's magnetotail,” EOS (AGU), Vol. 73, No. 40, p. 425, 428, 429, Oct. 1992
17) K. Tsuruda, H. Hayakawa, M. Nakamura, T. Okada, A. Matsuoka, F. S. Mozer , R. Schmidt , “Electric Field Measurements on the GEOTAIL Satellite ,” Journal of Geomagnetism and Geoelectricity, Vol. 46, 1994, p. 693-711, URL: http://www.darts.isas.jaxa.jp/stp/geotail/jgg_efd.pdf
18) Y. Kasaba, H. Hayakawa, K. Ishisaka, T. Okada, A. Matsuoka, T. Mukai, Y. Takei, “Evaluation of DC electric field measurement by the double probe system aboard the Geotail spacecraft,” Advances in Space Research, Vol. 37, Issue 3, 2006, pp. 604-609
19) S. Kokubun, T. Yamamoto, M. H. Acuna, K. Hayashi, K. Shiokawa, H. Kawano, “The GEOTAIL Magnetic Field Experiment,” Journal of Geomagnetism and Geoelectricity, Vol. 46, No 1, 1994, pp. 7-21, URL: http://www.darts.isas.jaxa.jp/stp/geotail/jgg_mgf.pdf
20) T. Doke, M. Fujii, M. Fujimoto, K. Fujiki, T. Fukui, F. Gliem, W. Guttler, N. Hasebe, T. Hayashi, T. Ito, K. Itsumi, T. Kashiwagi, J. Kikuchi, T. Kohno, S. Kokubun, S. Livi, K. Maezawa, H. Moriya, K. Munakata, H. Murakami, Y. Muraki, H. Nagoshi, A. Nakamoto, K. Nagata, A. Nishida, R. Rathje, T. Shino, H. Sommer, T. Takashima, T. Terasawa, S. Ullaland, W. Weiss, B. Wilken, T. Yamamoto, T. Yanagimachi, S. Yanagita, “The Energetic Particle Spectrometer HEP onboard the Geotail spacecraft,” Journal of Geomagnetism and Geoelectricity, Vol. 46, No 1, 1994, pp. 713-733,
21) T. Doke, N. Hasebe, T. Hayashi, K. Itsumi, J. Kikuchi, M. N. Kobayashi, K. Kondoh, H. Shirai, T. Takashima, T. Takehana, Y. Yamada, T. Yanagimachi, J. Yashiro, “Observation of galactic cosmic ray particles by the HEP-HI telescope on the GEOTAIL satellite,” Advances in Space Research, Vol. 23, Issue 3, 1999, pp. 487-490
22) MPAe contribution: The Geotail HEP-LD instrument; URL: http://mirage.mps.mpg.de/en/projekte/geotail/index_print.html
23) T. Mukai, S. Machida, Y. Saito, M. Hirahara, T. Terasawa, N. Kaya, T. Obara, M. Ejiri, A. Nishida, “The low energy particle (LEP) experiment onboard the Geotail satellite,” Journal of Geomagnetism and Geoelectricity, Vol. 46, No 1, 1994, pp. 669-692, URL: http://www.darts.isas.jaxa.jp/stp/geotail/jgg_lep.pdf
24) I. Nagano, S. Yagitani, H. Kojima, Y. Kakehi, T. Shiozaki, H. Matsumoto, K. Hashimoto, T. Okada, S. Kokubun and T. Yamamoto, “Wave form analysis of the continuum radiation observed by GEOTAIL,” Geophysical Research Letters, Vol. 21, N25, 1994, pp. 2911-2914
25) H. Matsumoto, I. Nagano, R. R. Anderson, H. Kojima, K. Hashimoto, M. Tsutsui, T. Okada, I. Kimura, Y. Omura, M. Okada, “Plasma Wave Observations with GEOTAIL Spacecraft,” Journal of Geomagnetism and Geoelectricity, Vol. 46, No 1, 1994,
27) D. J. Williams, R. W. McEntire, C. Schlemm II, A. T. Y. Lui, G. Gloeckler, S. P. Christon, F. Gliem, “Plasma Wave Observations with GEOTAIL Spacecraft,” Journal of Geomagnetism and Geoelectricity, Vol. 46, No 1, 1994, pp. 39-58
28) “GEOTAIL Spacecraft Mission Energetic Particles and Ion Composition Instrument (EPIC), Ground-Based Data Conversions and Corrections,” Version 1.5, Nov. 12, 2006
30) L. A. Frank, K. L. Ackerson, W. R. Paterson, J. A. Lee, M. R. English, G. L. Pickett, “The Comprehensive Plasma Instrumentation (CPI) for the GEOTAIL Spacecraft,” Journal of Geomagnetism and Geoelectricity, Vol. 46, No 1, 1994
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates.