International efforts by the United States, the United Kingdom and Japan are underway for the joint development of SOLAR-B, an observatory satellite for the study of the impact of the Sun on Earth.

SOLAR-B is a successor to the orbiting solar observatory YOHKOH (SOLAR-A). Its launch, scheduled for 2006, is being coordinated by the United Kingdom, the United States and Japan. The satellite systems being developed by JAXA and the Mitsubishi Electric Corporation will accommodate a large solar optical telescope (SOT), an X-ray telescope (XRT), and an Extreme Ultraviolet (EUV) imaging spectrometer. The SOT is being jointly developed by the United States and Japan. Japan, represented by JAXA and the National Astronomical Observatory of Japan, is working on the telescope optics and the U.S. National Aeronautics and Space Administration (NASA) is developing the focal-plane package (FPP). For XRT, NASA will provide grazing-incidence mirror optics, while JAXA will provide the CCD camera. Development of the EUV Imaging Spectrometer is being led by the Particle Physics and Astronomy Research Council (PPARC) of the United Kingdom, with the support of NASA and JAXA. SOLAR-B will be launched by Japan's M-V-7 at the Uchinoura Space Center (USC).

The satellite mission's main scientific aim is to unravel some of the mysteries and mechanisms of the activities taking place in the solar corona.

The Sun is the only fixed star available for us to observe in detail. By focusing on it, scientists hope to get a better understanding of the mechanisms of various processes taking place in the Universe. SOLAR-B will carry a coordinated set of optical, X-ray, and EUV instruments that will perform highly accurate measurements of magnetic fields, electrical currents and velocity fields in the solar atmosphere and corona. The result will be an improved understanding of the mechanisms of solar explosions, which will in turn greatly help us predict how solar events affect Earth. The satellite's polar orbit will allow its instruments to stay in continuous contact with the Sun for nine months of the year. SOLAR-B will operate for at least three years.