JCSAT-1B, known as JCSAT-5 before launch, is a geostationary communications satellite operated by SKY Perfect JSAT Group (JSAT) which was designed and manufactured by Hughes (now Boeing) on the HS-601 platform. It has a pure Ku band payload and was used to replace JCSAT-1 at the 150°East longitude. It covers Japan, Korea, most of China, Thailand, Vietnam, Laos, part of Indonesia, part of Malaysia, and Hawaii.

Equator-S is an element of the International Solar-Terrestrial Physics (ISTP) program. Spacecraft design, manufacturing, and testing were provided by the Max-Planck-Institut für Extraterrestrische Physik (MPE). The project was financially supported by DARA (Deutsche Agentur fur Raumfahrt Angelegenheiten).

The Equator-S objectives are to provide high-resolution plasma, magnetic, and electric field measurements in several regions not adequately covered by the existing ISTP missions, namely the low-latitude dayside magnetopause and its boundary layer, the equatorial ring current region, and the near-earth equatorial plasma sheet. These regions play key roles in our understanding of the global perspective of solar-terrestrial relations as well as the detailed plasmaphysical processes.