A novel and simple analytical technique referred to as transmission line analogy is developed and modified to study the transmission properties of the perpendicular polarized wave and the parallel polarized wave obliquely incident on the reentry plasma sheath. Based on the transmission coefficients, the effects of the plasma sheath on the polarization property of obliquely incident electromagnetic (EM) waves are studied. Taking the GPS navigation right hand circularly polarized wave as an example, the influences of incident angle and plasma parameters, including the electron density and the collision frequency on the EM wave’s polarization property are studied. Numerical results indicate that the larger the incident angle and the lower the collision frequency is, the worse the deterioration of the polarization property. In addition, the polarization property deteriorates most seriously when the cutoff frequency of the peak electron density is closest to the frequency of the EM waves.

Effects of Reentry Plasma Sheath on the Polarization Properties of Obliquely Incident EM Waves

Vehicles flying at hypersonic velocities within the atmosphere become enveloped in a "plasma sheath" that prevents radio communication, telemetry, and most importantly, GPS signal reception for navigation. This radio "blackout" period has been a problem since the dawn of the manned space program and was an especially significant hindrance during the days of the Apollo missions. An appropriate mitigation method must allow for spacecraft to ground control and ground control to spacecraft communications through the reentry plasma sheath. Many mitigation techniques have been proposed, including but not limited to, aerodynamic shaping, magnetic windows, and liquid injection. The research performed on these mitigation techniques over the years will be reviewed and summarized, along with the advantages and obstacles that each technique will need to overcome to be practically implemented. A unique approach for mitigating the blackout communications problem is presented herein along with research results associated with this method. The novel method involves the injection of ceramic metal-oxide particulate into a simulated reentry plasma to quench the reentry plasma. Injection of the solid ceramic particulates is achieved by entrainment within induced, energetic cathode spot flows.

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Review of Leading Approaches for Mitigating Hypersonic Vehicle Communications Blackout and a Method of Ceramic Particulate Injection Via Cathode Spot Arcs for Blackout Mitigation

When a hypersonic vehicle reenters the Earth's atmosphere, plasma sheath generated by its collision with ambient air affects the electromagnetic (EM) wave propagation. To understand such effects is very important for the design of communication, telemetry, and satellite navigation systems. In this paper, the transmission coefficient of the plasma sheath is investigated using the finite-difference time-domain (FDTD) method. The moving-window (MW) technology is employed to reduce the massive computational resources required by the large model. Results show that the MW-FDTD requires much less computational resources, as compared to the full FDTD simulation. Investigation on a hypersonic vehicle's plasma sheath shows that more EM energy could pass through the plasma sheath at the tail of the hypersonic vehicle. There is a certain frequency band with serious EM attenuation, which should be avoided when designing the communication system.

Simulation of Electromagnetic Wave Propagation Through Plasma Sheath Using the Moving-Window Finite-Difference Time-Domain Method

Radio blackout that occurs during hypersonic reentry flight is an important issue for the operation of the vehicle. Since the radio blackout problem is caused by a high plasma number density around a vehicle, it is necessary to manipulate the plasma to allow communication. We suggest a configuration of an E B layer as a reentry blackout mitigationmethod.ThesuggestedE Blayerconfigurationwithatwo-dimensionalmagnetic fieldissimulatedusing thethermalized potentialmodelandthePoisson-like modelin ordertoillustrate theeffectiveness of thisapproachas amitigationmethod.Thenumericalmodelusesamagnetohydrodynamicsapproximationandissolvedusinga finite volumemethodwithaRiemannsolver.Theresultsofthenumericalmodelareassessedusingavailableexperimental results.Astrongplasmadensityreductionisobtainedwhenthehighelectricandmagnetic fieldsareappliednearthe cathode. The manipulated plasma region provides a possibility to communicate through a plasma layer during a reentry blackout.

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Modeling of electromagnetic manipulation of plasmas for communication during reentry flight

This paper investigates the dynamic effects of the reentry plasma sheath on electromagnetic wave propagation from the viewpoint of communication. Both the spatial turbulence and the temporal variation of the plasma electron density are included in our model, and the transmission matrix method is employed to investigate the interactions between the plasma and the electromagnetic wave. The simulation results indicated that because of the nonlinear property of plasma, the amplitude variation caused by the plasma sheath has a lognormal distribution, while the phase fluctuation is Rayleigh distributed. Moreover, with a higher relative variation intensity, the probability density function curves become more decentralized, indicating larger channel dynamics of both amplitude variation and phase fluctuation. The power spectrum broadening phenomena caused by the plasma sheath are also investigated and discussed.

S. D. Fergason

Papers

Causes and mitigation of radio frequency (RF) blackout during reentry of reusable launch vehicles