Roush Fenway Racing is developing an inline-six engine for United Launch Alliance’s Integrated Vehicle Fluids program. The goal of the program is to simplify ULA’s Vulcan rocket upper stage propulsion system by reducing the number of liquids to just hydrogen and oxygen. To accomplish this goal they are using a 600 cc flat-head inline-six engine. The engine has a compression ratio of 6.5:1, 8,000 RPM redline and produces 26 horsepower. The final design will weigh less than 50 kg and be around 27.5″ (700 mm) long. They initially looked at using air-cooled Wankel rotary engines but it did not produce enough waste heat. The waste heat is needed for vaporizing liquid hydrogen and oxygen for tank pressurization. They also choose the inline-six design because of the multi-cylinder dependability, intake gas flow, smooth power delivery, elimination of heavy flywheel, and power overhead for future growth.