Callisto is a demonstrator designed to conduct flight testing and mature the complex technologies required to return a launcher to Earth, as well as refurbishment operations between flights, and to precisely cost an operational European launcher with a reusable first stage (it is not intended to become an operational launcher). Standing for “Cooperative Action Leading to Launcher Innovation in Stage Toss-back Operations”, Callisto is a project being pursued with the Japan Aerospace Exploration Agency (JAXA) and the German space agency DLR. A large number of international contractors are also contributing to the experiment, among them ArianeGroup and Mitsubishi Heavy Industries.
