Japan and Geophysics
During 1993-1994 Japan continued to operate two spacecraft in Earth orbit dedicated to investigations of space plasma physics. EXOS-D (aka Akebono) was launched on 21 February 1989 by ISAS on a M-3SII booster into an elliptical orbit of 275 km by 10,475 km at an inclination of 75 degrees. Designed to make measurements of the Earth's electromagnetic fields, plasma, and waves while imaging the aurora, the 295-kg, spin-stabilized EXOS-D has "revealed how the configuration of the aurora is related to the bulk flow of plasma across the geomagnetic field and how the activity of the magnetosphere is controlled by the magnetic field in interplanetary space" (Reference 57). By 1 January 1995 the orbit of EXOS-D had decayed to 270 km by 8,400 km.
Joining EXOS-D in July, 1992, was the Geotail satellite, a joint US-Japanese endeavor to probe the Earth's geomagnetic tail with emphasis on magnetic and electric fields, plasma, and energetic particles. The 1,008-kg Geotail was placed into a highly eccentric Earth orbit by a Delta-2/PAM-D combination with an apogee of approximately 350,000 km. Lunar gravitational perturbations were then used to gradually alter the orbit to nearly 1.3 million km apogee by 1994. Spacecraft propulsion later lowered the apogee to about 320,000 km toward the end of 1994 with further apogee reductions planned for 1995. The diameter and height of Geotail are 2.2 m and 1.6 m respectively, but two 6-m-long, magnetometer-equipped masts were deployed after launch as were two 50-m-long wire antennas designed to measure electric fields and waves. The design life of Geotail is approximately four years (References 58-60).
Meanwhile, Japan's 1985 Sakigake heliocentric satellite continues to return data on the solar system medium and the Earth's magnetosphere.
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