The prospects for realizing a magnetohydrodynamic (MHD) bypass hypersonic airbreathing engine are examined from the standpoint of fundamental thermodynamic feasibility. The MHD-bypass engine, first proposed as part of the Russian AJAX vehicle concept, is based on the idea of redistributing energy between various stages of the propulsion system flow train. The system uses an MHD generator to extract a portion of the aerodynamic heating energy from the inlet and an MHD accelerator to reintroduce this power as kinetic energy in the exhaust stream. In this way, the combustor entrance Mach number can be limited to a specified value even as the flight Mach number increases. Thus, the fuel and air can be efficiently mixed and burned within a practical combustor length, and the flight Mach number operating envelope can be extended. In this paper, we quantitatively assess the performance potential and scientific feasibility of MHD-bypass engines using a simplified thermodynamic analysis. This cycle analysis, based on a thermally and calorically perfect gas, incorporates a coupled MHD generator-accelerator system and accounts for aerodynamic losses and thermodynamic process efficiencies in the various engin components. It is found that the flight Mach number range can be significantly extended; however, overall performance is hampered by non-isentropic losses in the MHD devices.Litchford, R. J. and Cole, J. W. and Bityurin, V. A. and Lineberry, J. T.Marshall Space Flight CenterTHERMODYNAMIC CYCLES; THERMODYNAMICS; THERMODYNAMIC EFFICIENCY; MAGNETOHYDRODYNAMICS; MAGNETOHYDRODYNAMIC GENERATORS; TURBOFAN ENGINES; HYPERSONICS; SUPERSONIC COMBUSTION RAMJET ENGINES; AERODYNAMIC HEATING; COMBUSTION CHAMBERS; EXHAUST GASES; GAS STREAMS; FLIGHT ENVELOPES; MACH NUMBER; THRUST