Starship Prototype Unveiled
380s for ISP for the Raptor vacuum engine seems durn good, considering the tradeoffs between hydrogen and methane.The most efficient engines we've flown, the RL-10 [0] (used on the Delta IV and Atlas rockets as part of the Centaur Upper Stage) and the RS-25 [1], (the Space Shuttle Main Engine) get around 450-460s for their specific impulse. These engines use liquid hydrogen and liquid oxygen. The issue with liquid hydrogen is twofold: it is not very dense, and to keep it from boiling away in liquid form, it needs to be really cold. So you need huge, insulated tanks to store it. Hydrogen is everywhere, but it's kind of a pain to use as rocket fuel.Merlin Vacuum [2], which is currently used on the Falcon vehicles gets 311s. The RD-0110 [3], used on the Soyuz gets 326s. These use RP-1, which is highly refined kerosene. It's super easy to work with. On earth. Where we have 200 years of infrastructure in place to support using hydrocarbons. It takes that infrastructure to refine it into a form that rocket engines can use without gunking up the works with unburnt carbon and other particulate crap.Raptor uses methane, which is kind of like a jack of all trades between density, efficiency, ease of processing, storage, and ease of use in engines. This is basically how SpaceX seems to operate: rather than optimizing a single part of the system (like trying to get the most efficient engine), they try to optimize from a systems level. I don't really know much more than that, because there hasn't really been a lot of stuff for civilians to read on methane engines. This is kind of the cutting edge of the second golden age of space exploration. This freaking rules, what a time to be alive.[0] https://en.wikipedia.org/wiki/RL10[1] https://en.wikipedia.org/wiki/RS-25[2] https://en.wikipedia.org/wiki/Merlin_(rocket_engine_family)[3] https://en.wikipedia.org/wiki/RD-0110