Ariane 6 is a European expendable launch system currently under development by ArianeGroup on behalf of the European Space Agency. It is intended to replace the Ariane 5, as part of the Ariane launch vehicle family. The stated motivation for Ariane 6 is to halve the cost compared to Ariane 5, and double the capacity for the number of launches per year. Ariane 6 is designed with two core stages both powered by liquid hydrogen-liquid oxygen engines. The first stage has an improved version of the Vulcain engine already used on the Ariane 5, whilst the second stage has a newly-designed Vinci engine. Most of the initial lift-off thrust is provided by solid rocket boosters attached to the first stage: either two or four P120s, which are larger versions of the P80s used on the Vega rocket. Selection of the design concept was made by ESA in December 2014, favouring it over an alternative all-solid-fuel rocket option.