International X-ray Observatory

The International X-ray Observatory (IXO) was a cancelled X-ray telescope that was to be launched in 2021 as a joint effort by NASA, the European Space Agency (ESA), and the Japan Aerospace Exploration Agency (JAXA). In May 2008, ESA and NASA established a coordination group involving all three agencies, with the intent of exploring a joint mission merging the ongoing XEUS and Constellation-X Observatory (Con-X) projects.

Source: Wikipedia — International X-ray Observatory (CC BY-SA 4.0)