Predicting The Evolution Of Rocket Engines

Evolution in animals and vehicles often favors larger size for longevity and range. However, the same trend does not hold for rocket engines. A comparison of historical and modern engines reveals a shift toward smaller, lighter designs in newer models like SpaceX’s Raptor 3. This counterintuitive trend is largely driven by increasing combustion chamber pressures, which allow for reduced chamber and nozzle size and weight. Using scaling laws, this study analyzes how combustion chamber pressure influences the mass of major engine components, including the combustion chamber, expansion bell, turbomachineries, and plumbing. While higher pressure leads to more compact and efficient combustion components, it demands heavier turbomachineries and more robust plumbing, creating a trade-off. Ultimately, there is a performance ceiling where the benefits of higher pressure are constrained by the turbomachinery design. Pushing beyond this point requires advances in turbomachinery technology, marking a new direction in engine evolution.