DENPA, also known as REXS (Radio-wave Exploration of the Solar System), was a Japanese scientific satellite launched by the Institute of Space and Astronautical Science (ISAS), which later became part of JAXA (Japan Aerospace Exploration Agency). The primary purpose of the DENPA (REXS) mission was to study radio waves in space, particularly focusing on solar radio emissions and their interactions with the Earth's ionosphere. The mission aimed to enhance the understanding of the space environment and solar-terrestrial interactions.