A series of four Japanese exospheric satellites launched by the Institute of Space and Astronautical Science as part of the International Magnetospheric Study. All four were deigned to designed to investigate the aurora and aurora-related phenomena and Earth’s upper and middle atmosphere.

Exos-A (Kyokko). A 1-metre-wide cylindrical satellite launched by an Mu-3 rocket on 4 February 1978 at the Uchinoura Space Center in Kagoshima. The 126-kg satellite carried a tape recorder that stored 160 minutes of data at 512 bits per second.

Exos-B (Jikiken). A 92-kilogram polyhedron satellite launched by an Mu-3 rocket on 16 September 1978 at the Kagoshima Space Center, to make coordinated observations with Exos-A in its studies of Earth’s auroras. The satellite carried a seven-instrument package to investigate correlated mechanisms between particle fields and plasma turbulence.

Exos-C (Ohzora). A 210-kg polyhedron satellite launched by an Mu-3 rocket on 14 February 1984 at the Kagoshima Space Center, which carried 11 experiments to perform remote sensing of Earth’s middle atmosphere.

Exos-D. See Akebono.