CALLISTO is a reusable VTVL demonstrator propelled by a small 40 kN Japanese LOX-LH2 rocket engine. It is being developed jointly by the German Aerospace Center (DLR), the French Space Agency (CNES), and the Japanese Aerospace Exploration Agency (JAXA).

Ariane 6 is a European expendable launch system developed by ArianeGroup on behalf of the European Space Agency (ESA). It replaces the Ariane 5, as part of the Ariane launch vehicle family. The stated motivation for Ariane 6 was to halve the cost compared to Ariane 5, and increase the capacity for the number of launches per year.