NASASpaceFlight.com has an intriguing article on the subject of SpaceX’s plans for future super heavy lift vehicles, heavier even than the Falcon Heavy (which is planned to have three Falcon 9 first stages strapped together) — the Falcon X and Falcon XX would be more powerful than even the Saturn V, and would likely require a new engine. The Merlin engine is very much state-of-the-art for kerosene burners, but the propellant does have its limits, and the engine isn’t robust enough for the many restarts over a long maintenance-free period that would be needed during a Mars mission. So what are they planning?
Well, surprisingly, it appears that this time instead of perfecting a very reliable, tried-and-true combustion cycle and propellant combination, they’re considering treading new ground with a full-flow staged cycle methane/LOX engine, with a novel turbopump design that would greatly improve longevity and safety. It’s very ambitious, and could be the answer . . . but have they finally bitten off more than they can chew? The answer will likely come when they start test-firing the Raptor engine. It’s not clear when that would be, but they’re in the process of modifying a test stand at Stennis Space Center to supply the methane/LOX combination. So, probably sooner rather than later. Exciting. 😉