Novel Approach to Mitigating Communication Blackout during Hypersonic Flight

Hypersonic vehicles traveling greater than Mach 4 produce plasma sheaths around the vehicle due to the viscous flow and associated heating of the air. This plasma sheath blocks radio communication with the vehicle for RF signals below the local plasma frequency, known as communication blackout. We propose to use a combination of multiple plasma models and experiments to show that excitation of surface plasma waves are a viable method to partially solve the communication blackout problem. We will use a fluid model developed at TechX called USim to accurately model the plasma environment surrounding a hypersonic vehicle and show that non-uniformities, or “dips”, in the plasma density allow for EM waves to be coupled to or from the outer surface of the plasma. Similar simulations have already been performed (https://arc.aiaa.org/doi/10.2514/1.A33122) which provides a good foundation for future research related to this project. We will then import the simulation data from USim into  VSim, a 1D/2D/3D EM PIC code also developed at TechX, to model the propagation of EM waves through the plasma dips and along the surface of the plasma. In VSim, we will model the plasma using a 3D dielectric model in order to simulate the propagation of EM waves through the plasma dips which form in the entire 3-dimensional sheath surrounding the hypersonic vehicle.  The dielectric constants will be computed directly from USim output by interpolating USim data onto the VSim grid. As a cross-validation, we will also use FEKO, an antenna and EM code, to model the propagation of EM waves through the plasma dips and along the surface of the plasma. Finally, preliminary experimental work will be performed at CU Denver to verify the formation of surface plasma waves when an EM wave is excited via a loop antenna and measured with a spectrum analyzer. The experimental setup will involve a microwave plasma discharge in a low pressure glass vessel with the shape approximating a hypersonic plasma sheath.