Plasma-Enhanced Hypersonic Performance Enabled by MHD Power Extraction

This paper reviews work underway on the development of new technologies that will enhance the performance of hypersonic vehicles through plasma-related processes and the utilization of MHD to provide the large power levels that are required to drive these processes. Three technologies are discussed for plasma-enhanced hypersonic performance. These include: (1) the use of off-body plasmas for drag reduction, steering, and enhanced inlet performance; (2) the use of surface or near-surface plasmas for mitigating local heating and controlling separation; and (3) the use of electron beam and plasma processes for controlling combustion for enhanced performance inside the engine and for local heat addition applications in other regions of the flow path. For realistic scale vehicles, the energies required for these applications exceed the present capability of on-board auxiliary power units, and, therefore, will require power to be generated directly from the hypersonic air passing over the vehicle or through the engine. In the high Mach number regime characteristic of re-entry vehicles, there is sufficient heating of the air to allow MHD power extraction using equilibrium ionization of alkali vapor seed material. By replacing a portion of the vehicle surface with a hollow core truss structure containing an embedded magnet coil, hundreds of kilowatts of power can be extracted during re-entry and used for vehicle control or other applications. At lower Mach numbers, MHD power extraction can be done downstream of the engine, then the temperature of the exhaust can be high enough to allow conductivity to be achieved with alkali seeding. This MHD generated power extracted from the flow aft of the engine can be used for plasma control upstream of the engine as well as for engine performance enhancement. Some aspects of this reverse energy bypass concept are analyzed in the paper, including plasma heating of the inlet flow that would allow elimination of the isolator, snowplow surface arcs for boundary layer and separation control, and electron beam and microwaves for initiation and control of combustion.