In addition to the Prometheus reusable rocket engine program, European officials are pursuing a program named Callisto that aims to developing a reusable booster. SpaceNewsreports:
The French and German space agencies (CNES and DLR, respectively) have for the past two years collaborated on a scaled-down rocket that would allow Europe to practice different aspects of recovery and reuse. Callisto’s first flight is planned for 2020.
Callisto officials said the goal of the program is not to create a new vehicle in 2020 — the Ariane 6 is scheduled to debut that same year — but to establish a base of knowledge for future launch vehicles that could, maybe, be reusable.
“Prometheus and Callisto are two key elements of our future launcher preparatory roadmap,” Jean-Marc Astorg, head of CNES’s Launch Vehicles Directorate, told SpaceNews. “Prometheus is a new engine to equip Ariane 6 evolutions or brand-new launchers, and Callisto is developed to learn about reusability in Europe, which we have not done before. We are lacking an experience by operation of recovering a vehicle and reflying it. This is exactly what we would like to do with Callisto.”
Around 1 to 2 percent of Ariane 6’s 3.6-billion-euro ($4.3 billion) development budget is spent on Callisto, Astorg said, describing it as a “modest approach.” Callisto is still in a preliminary design phase, he said, with a full decision on the realization of the demonstrator anticipated this June.