Now there is a race on to develop alternatives to existing fuels like RP-1 and UDMH, and liquid methane appears to be in the lead. Several new rocket engines, including SpaceX's Raptor and the European Space Agency's Prometheus engine, have been designed to use this gas as a fuel because it has a higher performance than other fuels, meaning the rocket can be smaller and produce less soot when it's launched. Its lower cost means the price of a rocket launch can be reduced, too.
