High Quality Content by WIKIPEDIA articles! The Advanced Telescope for High ENergy Astrophysics (ATHENA) is a proposed X-ray telescope. It is an ESA forking/rebooting of the International X-ray Observatory (IXO) project planned by NASA, ESA, and JAXA from about 2008 to 2011. In 2011, NASA pulled out. It was a candidate for the first (L1) L-class mission within the ESA Cosmic Vision Programme. It lost to the Jupiter Icy Moon Explorer. It may be a candidade for the next L-class mission.