Hakucho was the first Japanese X-ray astronomy satellite; it was named "swan" in Japanese because one of the most powerful cosmic X-ray sources is Cygnus X-1. As in the case of many other X-ray satellites deployed around this time, Hakucho was designed to study and monitor transient (quick-changing) phenomena, with special emphasis on X-ray bursts in the energy range 0.1–100 keV. It was known prior to launch as Corsa-B. Hakucho stopped operating in April 1985.