Hypersonic Vehicle Telemetry Blackout Analysis

During certain hypersonic flight regimes, shock heating of air creates a plasma sheath, resulting in telemetry attenuation or blackout. The severity of the signal attenuation is dependent on vehicle configuration and orientation, flight trajectory, and transmission frequency. With the promise of airbreathing hypersonic vehicles looming on the horizon, telemetry solutions must be found to address safety considerations for flight testing (that is, flight termination and/or catastrophe analysis). This attenuation phenomena are investigated with a focus on the nonequilibrium plasma sheath properties (electron concentration, plasma frequency, collision frequency, and temperature) for a range of flight conditions and vehicle design considerations. Trajectory and transmission frequency requirements for airbreathing hypersonic vehicle design are then addressed, with comparisons made to both shuttle orbiter and Radio Attenuation Measurements C-II reentry flights. The effects of an applied magnetic field normal to the plasma interface are shown over a range of flight conditions. It is shown that a combination of vehicle shaping effects, high transmission frequency, and an applied right-hand circularly polarized magnetic field (less than 1 T) show promise toward mitigating the telemetry blackout.