Japan's Geostationary Meteorological Satellite (GMS) system was originally developed by NASDA relying heavily on the US GOES design and is now jointly run by NASDA and the Japan Meteorological Agency. The American firm of Hughes is the prime contractor, working for Japan's NEC Corporation. Four GMS spacecraft have been launched since 1977, the last in September, 1989. GMS-3 (August, 1984) is available for backup operations at 120 degrees E, while GMS-4 is located in the primary position at 140 degrees E. As with all national satellites, GMS spacecraft are also known by a specific Japanese name, in this case, Himawari, meaning "sunflower." GMS-5, the final satellite in the series, is scheduled for launch by the H-II booster in 1995.
GMS-4 is a spin-stabilized (100 rpm) spacecraft with an on-orbit mass of approximately 325 kg, a diameter of 2.1 m and a height (after apogee kick motor separation) of 3.4 m (Figure 4.69). Solar cells applied to the exterior of the spacecraft bus generate up to 300 W. and the overall design life is five years. Hydrazine thrusters maintain the desired geostationary position and counteract perturbations attempting to alter the vehicle's inclination.
The major Earth-oriented instrument is the Visible and Infrared Spin Scan Radiometer (VISSR), "used to obtain visible and infrared spectrum mappings of the Earth and its cloud cover with a specially designed optical telescope and detector system" (Reference 581). Visible images are collected in the 0.50-0.75 µm band with a resolution of 1.25 km, and the infrared signatures are taken in the 10.5-12.5, µm band with a 5.0-km resolution. Thirty minutes are required to obtain a full Earth image consisting of 2,500 narrow strips. A separate payload, called the Space Environment Monitor (SEM), measures the flux of solar protons, alpha particles, and electrons.
While outwardly almost identical to GMS-4, GMS-5 will host a more sophisticated VISSR with one visible band (0.55-0.9 µm) and three IR bands (10.5-11.5, µm, 11.5-12.5 µm, and 6.5-7.0 µm). The relative visible and IR resolution will remain unchanged. The height of the spacecraft will increase slightly to 3.5 m as will the on-orbit mass of 338 kg. In place of the SEM, an experimental COSPAS-SARSAT transponder will be carried (Reference 582).
581. Geostationary Meteorological Satellite-4 [HIMAWARI-4], technical brochure distributed by NASDA, 1991.
582. Geostationary Meteorological Satellite-5 [HIMAWARI-5], technical brochure distributed by NASDA, 1991.