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Mission Profile

Name (pre-launch in parentheses) GEOTAIL
International Designation Code 1992-044A
Objectives Research on structure and dynamics of the earth's magnetotail
Participation in ISTP (International Solar-Terrestrial Physics)
Launch Date July 24, 1992
Location Cape Canaveral (Florida, U.S.A.)
Launch Vehicle Delta 2
Configuration Weight 1,009 kg (at launch)
Shape Cylinder of 2.2m diameter and 1.6m height
Equipped with two 6m-long extendable masts for magnetic sensor and four 50m-long antennas

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Orbit Altitude Perigee 57,000 km, Apogee 200,000 km
Inclination 29°
Type of Orbit Double lunar swing-by
Scientific Instruments
  1. Magnetic field monitor
  2. Electric field monitor
  3. Two sets of plasma monitors
  4. Two sets of high-energy particle monitors
  5. Plasma wave instrument
Operation For the first two years, the satellite was planned to orbit and perform double lunar swing-bys to observe the magnetotail's far region (80 to 220 times the radius of the earth) while keeping apogee in the earth's night side. In mid-November, 1994, the apogee was lowered to a point 50 times the earth's radius and, on February, 1995, even further to 30 times the earth's radius to study the process of magnetotail sub-storms near the earth. The perigee was set to about 10 times the earth's radius and orbital inclination to the ecliptic plane was set to be -7° so that the apogee of the satellite would be positioned in the magnetotail's neutral plane around the winter solstice.

The above orbit was a great success and the region of 10 to 220 times the earth's radius of the magnetotail was closely investigated. In addition, due to the orbit arrangement, GEOTAIL was able to pass close by the boundary plane of the magnetosphere in the day side when the satellite's perigee was also in the day side. In June 1997, the perigee was slightly lowered to 9 to 9.5 times the earth's radius in order to increase the probability that GEOTAIL would be positioned just inside the magnetosphere's boundary plane in the day side. The orbit of 9 times (perigee) and 30 times (apogee) the earth's radius allowed us to study the magnetosheath, bay-shape shock wave and its upstream area in detail.
Results We found several important clues in the plasma sheet, the source of aurora electrons, to explain why the aurorae suddenly brighten on a global scale. Cooperating with other nation’s satellites, we also discovered many new facts concerning the location and timing of magnetic reconnection, an explosive energy-release phenomenon.