A Japanese satellite for solar X-ray studies, launched in 1981 February; before launch it was known as Astro-A. It carried high-resolution soft X-ray spectrometers and hard X-ray instruments which obtained the first images of solar flares at energies above 25 keV (wavelengths shorter than 0.05 nm). Observations ended in 1982 October.

http://www.isas.jaxa.jp/e/enterp/missions/hinotori.shtml Mission page at Japan Aerospace Exploration Agency.