SpaceX intends to build a methane/liquid oxygen (Lox) engine, said founder Elon Musk, in a shift away from the highly refined kerosene rocket propellant (RP-1) that has powered the company’s previous engines.

Speaking at the Royal Aeronautical Society in London, SpaceX chief executive and lead rocket engineer Musk said Lox and methane would be SpaceX’s propellants of choice on a mission to Mars, which has long been his stated goal.

SpaceX’s initial work will be to build a Lox/methane rocket for a future upper stage, codenamed Raptor.  The design of this engine would be a departure from the “open cycle” gas generator system that the current Merlin 1 engine series uses. Instead, the new rocket engine would use a much more efficient “staged combustion” cycle that many Russian rocket engines use.

Musk says that methane fuel has performance, cost and storage advantages over alternatives and could even be extracted from the Martian atmosphere for use in landing and ascent stages.

Although methane is known to be a better fuel for reusable engine operations in not having significant coking (carbon deposit) problems that kerosene has, Musk noted that this was not a main driver for the choice.

“The energy cost of methane is the lowest and it has a slight Isp (specific impulse) advantage over kerosene,” said Musk, adding that “it does not have the pain-in-the-ass factor that hydrogen has”.  Hydrogen, another commonly used fuel, has storage and handling difficulties and the problem of hydrogen embrittlement.

Musk confirmed that he would not be seeking collaboration with the Russians, despite their lead in this technology, before adding however that “we might hire a few”.  Musk also ruled out working with China, noting that they did not seem to want collaboration anyway.