Starship Prototype Unveiled
380s for ISP for the Raptor vacuum engine seems durn good, considering the tradeoffs between hydrogen and methane.<p>The most efficient engines we&#x27;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 <i>really</i> cold. So you need huge, insulated tanks to store it. Hydrogen is everywhere, but it&#x27;s kind of a pain to use as rocket fuel.<p>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&#x27;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.<p>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&#x27;t really know much more than that, because there hasn&#x27;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.<p>[0] <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;RL10" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;RL10</a><p>[1] <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;RS-25" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;RS-25</a><p>[2] <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Merlin_(rocket_engine_family)" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Merlin_(rocket_engine_family)</a><p>[3] <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;RD-0110" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;RD-0110</a>