Reentry Plasma Sheath Research Articles

Effects of a reentry plasma sheath on the beam pointing properties of an array antenna

The reduction in the gain of an on-board antenna caused by a reentry plasma sheath is an important effect that contributes to the reentry “blackout” problem. Using phased array antenna and beamforming technology could provide higher gain and an increase in the communication signal intensity. The attenuation and phase delay of the electromagnetic (EM) waves transmitting through the plasma sheath are direction-dependent, and the radiation pattern of the phased array antenna is affected, leading to a deviation in the beam pointing. In this paper, the far-field pattern of a planar array antenna covered by a plasma sheath is deduced analytically by considering both refraction and mutual coupling effects. A comparison between the analytic results and the results from an electromagnetic simulation is carried out. The effect of the plasma sheath on the radiation pattern and the beam pointing errors of the phased array antenna is studied systematically, and the derived results could provide useful information for the correction of pointing errors.

Studies on the transmission of sub-THz waves in magnetized inhomogeneous plasma sheath

There have been many studies on the sub-terahertz (sub-THz) wave transmission in reentry plasma sheaths. However, only some of them have paid attention to the transmission of sub-THz waves in magnetized plasma sheaths. In this paper, the transmission of sub-THz waves in both unmagnetized and magnetized reentry plasma sheaths was investigated. The impacts of temporal evolution of the plasma sheath on the wave transmission were studied. The transmission of “atmospheric window” frequencies in a magnetized plasma sheath was discussed in detail. According to the study, the power transmission rates (Tp) for the left hand circular (LHC) and the right hand circular modes in the magnetized plasma sheath are obviously higher and lower than those in the unmagnetized plasma sheath, respectively. The Tp of LHC mode increases with both wave frequency and external magnetic field strength. Also, the Tp of LHC mode in both magnetized and unmagnetized plasma sheaths varies with time due to the temporal evolution of the plasma sheath. Moreover, the performance of sub-THz waves in magnetized plasma sheath hints at a new approach to the “blackout” problem. The new approach, which is in the capability of modern technology, is to utilize the communication system operating at 140 GHz with an onboard magnet installed near the antenna.

A 2-D FDTD Model for Analysis of Plane Wave Propagation Through the Reentry Plasma Sheath

A 2-D finite-difference time domain model was developed to analyze the wideband plane wave propagation characteristics in the reentry plasma sheath at the receiving antenna position. Because of the variation of the flow field, various inhomogeneous structures exist in the plasma sheath, such as electron density irregularities, large-scale ablation particles, and vortex electron density structures, which play important roles in refracting and distorting the electromagnetic wave signals. The proposed model directly included the effects of these inhomogeneous structures. The model used a $\pi $ -shaped total-field/scattered-field (TF/SF) boundary to introduce the plane wave source to the simulation domain. Based on the current density convolution (JEC) method and the phase matching principle, six 1-D auxiliary propagators were generated to obtain field values at the TF/SF boundary. The convolutional perfectly matched layer was implemented as the absorbing boundary condition of the auxiliary propagator. The efficiency and accuracy of the proposed method were validated by numerical examples.

Transmission properties and physical mechanisms of X-ray communication for blackout mitigation during spacecraft reentry

Recent advances in X-ray science have witnessed the X-ray communication (XCOM), a new revolutionary technology first proposed by NASA since 2007. In combination with the advanced modulated X-ray source, XCOM shows a promising prospect for helping to alleviate the occurrence of inevitable blackout communication by using the regular radio frequency (RF) signal, paving the way towards realizing real-time communication during spacecraft reentry into atmosphere. Here, we acquired the detailed information of electron density distribution of plasma sheath encountered during vehicle reentry through Computational Fluid Dynamics simulation. Based on these derived parameters, Finite-difference Time-domain method was employed to investigate the transmission properties of X-rays through the plasma sheath, and the results indicated that X-ray transmission was not influenced by the reentry plasma sheath at different reentry altitudes and spacecraft surface positions compared with RF signal. In addition, 2D Particle-In-Cell simulation was also adopted to provide deeper insight into the transmission properties and physical mechanisms of X-ray carrier propagating through the plasma sheath, and results showed that the transmission coefficient was over 0.994 and the observation of plasma channel effect was also an important signature, which was of great importance to X-ray propagating through the plasma sheath.

A Multiscale Model of Reentry Plasma Sheath and Its Nonstationary Effects on Electromagnetic Wave Propagation

During reentry, plasma sheath is affected by many flight factors, such as trajectory, velocity, angle of attack, and fluid turbulence. As a result, the plasma parameters are time-varied and nonstationary. The nonstationary effects of reentry plasma sheath on electromagnetic (EM) wave propagation are investigated in this paper. First, the factors that affect the plasma sheath are analyzed, and the plasma sheath variation is divided into three scales. A multiscale reentry plasma sheath electron density model is established. A compatible modeling method is proposed, and this method is proven effective. Finally, we analyze the effects of plasma sheath on EM wave at 1.57542, 2.2, and 5 GHz, which are generally used in GPS and telemetry, tracking, and command systems. Results show that the statistical parameters of complex transmission coefficients are time-varied and nonstationary.

Potential application of X-ray communication through a plasma sheath encountered during spacecraft reentry into earth's atmosphere

Rapid progress in exploiting X-ray science has fueled its potential application in communication networks as a carrier wave for transmitting information through a plasma sheath during spacecraft reentry into earth's atmosphere. In this study, we addressed the physical transmission process of X-rays in the reentry plasma sheath and near-earth space theoretically. The interactions between the X-rays and reentry plasma sheath were investigated through the theoretical Wentzel–Kramers–Brillouin method, and the Monte Carlo simulation was employed to explore the transmission properties of X-rays in the near-earth space. The simulation results indicated that X-ray transmission was not influenced by the reentry plasma sheath compared with regular RF signals, and adopting various X-ray energies according to different spacecraft reentry altitudes is imperative when using X-ray uplink communication especially in the near-earth space. Additionally, the performance of the X-ray communication system was evaluated by applying the additive white Gaussian noise, Rayleigh fading channel, and plasma sheath channel. The Doppler shift, as a result of spacecraft velocity changes, was also calculated through the Matlab Simulink simulation, and various plasma sheath environments have no significant influence on X-ray communication owing to its exceedingly high carrier frequency.

Characteristics of electromagnetic wave propagation in time-varying magnetized plasma in magnetic window region of reentry blackout mitigation

The “magnetic window” is considered a promising means to eliminate reentry communication blackout. However, the turbulence of plasma sheath results in phase jitter and amplitude turbulence of electromagnetic (EM) wave and may influence the eliminating effect. Therefore, the effect of fluctuating property of reentry plasma sheath on EM wave propagation when a magnetic field is used for eliminating blackout is investigated. For this purpose, a time-varying electron density model, which includes both temporal variation and spatial turbulence, is proposed. Hybrid matrix method is also employed to investigate the interaction between time-varying magnetized plasma and EM wave. The EM wave transmission coefficients in time-varying magnetized and unmagnetized plasmas are likewise compared. Simulation results show that amplitude variation and phase jitter also exist on transmitted EM wave, and the turbulent deviation increases as the degree of plasma fluctuates. Meanwhile, the fluctuation of transmitted EM wave attenuates at low-frequency passband and increases at high-frequency passband with the increasing magnetic field. That is, comparing with unmagnetized time-varying plasma, the fluctuation effect can be mitigated by using a magnetic field when the EM wave frequency is at low-frequency passband. However, the mitigating effect can be influenced by the nonuniformity of magnetic field.

Adaptive Multistate Markov Channel Modeling Method for Reentry Dynamic Plasma Sheaths

Channel modeling of a plasma sheath for hypersonic reentry vehicles is important in addressing reentry communication blackout issues. Given that the time-varying property of the transmission medium is caused by physical factors such as large-scale flight conditions variation, especially angle of attack, and small-scale fluid turbulence, a new adaptive multistate Markov channel modeling method is proposed to present the dynamic effects of reentry plasma sheaths on wireless channels. First, a quasi-Gaussian function mathematical model for the electron density of a dynamic plasma sheath is established according to the variation frequency of the dynamic physical factors. Then, the time-varying attenuation is calculated by combining the quasi-static Monte Carlo and uniform hierarchical analytical methods for nonuniform electronic density distribution. Finally, a hidden Markov model is employed to model the channel characteristics of the dynamic plasma sheath, and a reversible-jump Markov chain Monte Carlo algorithm is used to adaptively estimate the channel parameters of the multistate Markov channel. Simulation results show that the first-order statistical properties of the proposed channel are in good agreement with the calculated variable attenuation of radio waves, and this method has the adaptive capacity to estimate the number of multiple states and the channel parameters in each state without a need for manual setting.

Influences of Turbulent Reentry Plasma Sheath on Wave Scattering and Propagation**supported by the National Basic Research Program of China (No. 2014CB340205) and National Natural Science Foundation of China (Nos. 61301173 and 61473228)

The randomness of turbulent reentry plasma sheaths can affect the propagation and scattering properties of electromagnetic waves. This paper developed algorithms to estimate the influences. With the algorithms and typical reentry data, influences of GPS frequency and Ka frequency are studied respectively. Results show that, in terms of wave scattering, the scattering loss caused by the randomness of the turbulent plasma sheath increases with the increase of the ensemble average electron density, ensemble average collision frequency, electron density fluctuation and turbulence integral scale respectively. Also the scattering loss is much smaller than the dielectric loss. The scattering loss of Ka frequency is much less than that of the GPS frequency. In terms of wave propagation, the randomness arouses the fluctuations of amplitude and phase of waves. The fluctuations change with altitudes that when the altitude is below 30 km, fluctuations increase with altitude increasing, and when the altitude is above 30 km, fluctuations decrease with altitude increasing. The fluctuations of GPS frequency are strong enough to affect the tracking, telemetry, and command at appropriate conditions, while the fluctuations of Ka frequency are much more feeble. This suggests that the Ka frequency suffers less influences of the randomness of a turbulent plasma sheath.

Characterization of the Dynamic Effects of the Reentry Plasma Sheath on Electromagnetic Wave Propagation

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.

Effects of Pressure Variation on Polarization Properties of Obliquely Incident RF Waves in Re-Entry Plasma Sheath

Synthesizing the compressible turbulent flow theory and plasma electromagnetic (EM) theory together, a novel method connecting pressure variation and relative permittivity of re-entry plasma sheath is developed. Using this method and transmission line analogy, effects of pressure variation on polarization properties of obliquely incident EM waves at GPS frequency and Ka frequency is studied. Numerical results indicate that effects in different conditions are various. When electron density is lower than $10^{18}~\text{m}^{\mathrm {-3}}$ , influences of pressure variation are obvious at GPS frequency, while Ka frequency is feeble. For GPS frequency, effects enlarge with the increase in incident angle, but reduce with the increase in collision frequency and electron density. Ka frequency has more advantages on mitigating the disturbances of pressure variations in this situation. While in the opposite situation, influences are more remarkable at Ka frequency. Considering that GPS wave rapidly attenuates in the sheath when electron density is higher than $10^{18}~\text{m}^{\mathrm {-3}}$ and Ka wave does not, Ka frequency is an effective way to mitigate the blackout during the re-entry process after its shortcomings on polarization alteration have been carefully considered.

Effects of Reentry Plasma Sheath on Mutual-Coupling Property of Array Antenna

A plasma sheath enveloping a reentry vehicle would cause the failure of on-board antennas, which is an important effect that contributes to the “blackout” problem. The method of replacing the on-board single antenna with the array antennas and using beamforming technology has been proposed to mitigate “blackout” problem by many other researchers. Because the plasma sheath is a reflective medium, plasma will alter the mutual coupling between array elements and degrade the beamforming performance of array antenna. In this paper, the effects of the plasma sheath on the mutual coupling properties between adjacent array elements are studied utilizing the algorithm of finite integration technique. Results show that mutual coupling coefficients of array elements are deteriorating more seriously with the decrease of collision frequency. Moreover, when electron density and collision frequency are both large, plasma sheath improves the mutual coupling property of array elements; this conclusion suggests that replacing the on-board single antenna with the array antennas and using beamforming technology can be adopted to mitigate the blackout problem in this condition.

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

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 GPS Patch Antenna Polarization Property

A plasma sheath enveloping a reentry vehicle would affect performances of on-board antenna greatly, especially the navigation antennas. This paper studies the effects of reentry plasma sheath on a GPS right-hand circularly polarized (RHCP) patch antenna polarization property during a typical reentry process. Utilizing the algorithm of finite integration technique, the polarization characteristic of a GPS antenna coated by a plasma sheath is obtained. Results show that the GPS RHCP patch antenna radiation pattern distortions as well as polarization deteriorations exist during the entire reentry process, and the worst polarization mismatch loss between a GPS antenna and RHCP GPS signal is nearly 3 dB. This paper also indicates that measures should be taken to alleviate the plasma sheath for maintaining the GPS communication during the reentry process.

Analysis of the Impact of Plasma Sheath on GPS Antenna

The electromagnetic simulation software CST was used to analyze the effects of reentry plasma sheath on the GPS navigation antenna. The Impedance and radiation characteristics of antenna were studied on condition that the antenna was coated with uniform and nonuniform electron density distribution plasma sheath respectively. The results show that, the antenna coated with the uniform plasma sheath, the plasma electron density increasing, the antenna operating frequency moves to high-frequency and that the directivity decreases as well; when the antenna was coated with nonuniform plasma, with the higher electron peak density of plasma sheath, besides that the operating frequency also moves to high-frequency, the bandwidth stretches wide and the return loss reduces; the antenna radiation pattern distorts seriously at the electron peak density of 1018m-3.

An exact solution of the relativistic equation of motion of a charged particle driven by a circularly polarized electromagnetic wave and a constant magnetic field

An exact solution is found for the relativistic equation of motion of a charged particle driven by a circularly polarized electromagnetic wave and a constant magnetic field. The explicit expressions of particle position and velocity are obtained for certain initial conditions. The results are of interest to the interaction of the high-power laser with the magnetized plasma, electromagnetically pumped free-electron laser with a guide magnetic field, propagation of electromagnetic wave signals through a re-entry plasma sheath in the presence of a strong magnetic field, and magnetic confinement plasmas.

Comments on "The singular integral problem in surfaces"

The commenter questions the work of D.B. Miron (ibid., vol.AP-31, no.3, p.507-9, 1983) concerning the evaluation of the singular integral in the expression for the electric field at a point where electric current exists (e.g. reentry vehicle heatshields, plasma sheaths and wakes, charged-particle beams, semiconductors, biological tissues and other polarization media). The difficulty is caused by the nonintegrable R-3singularity of the irrotational part of the electric dyadic Green's function. In particular, the convergence of certain improper regularization integrals is called into question. D.B. Miron's rebuttal is presented

Progress in Reentry Communications

Considerable progress has been made in the past few years toward understanding and solving the spacecraft communications blackout problem caused by the reentry plasma sheath. A summary of the causes and effects of the reentry plasma sheath is presented, together with a discussion of reentry plasma diagnostic techniques, proposed methods of alleviating the communications blackout, and a review of the reentry flight experiments performed to better our understanding of the reentry plasma.

Amplitude modulation of electromagnetic waves by modulated magnetic fields: modified theory and application to communications during blackout

In this paper a modified theory of amplitude modulation by modulated magnetic fields has been developed. In contrast to earlier work, the present analysis does not impose any restriction on the values of the relevant parameters. The possibility of using this phenomenon for communications through rocket exhausts and re-entry plasma sheaths during the blackout region has also been analysed.

Laboratory simulation of reentry plasma sheaths

Laboratory simulation of reentry plasma sheaths