Startup Astro Mechanica is developing what it calls a turboelectric-adaptive jet engine that shifts from turbofan to turbojet to ramjet mode as it accelerates from a standing start to a projected Mach 6. This is achieved by using a dual turbine approach. One turbine acts as an turbogenerator. The second turbine acts as the propulsion unit. The turbogenerator powers an electric motor that controls the compressor of the second turbine. The motor can change speeds to keep the fan turning at the ideal RPM for a specific flight mode. In turbojet and ramjet modes, the inlet is narrowed to compress the air and eliminate bypass. The turbogenerator is commercially available, while the propulsion unit is built by the company. A key innovation is that electric motors have dramatically increased their power density so that the weight of the motor is no longer prohibitive.