Characteristics Of Terahertz Wave Attenuation In Plasma Sheaths Enveloping Reentry Vehicles

A hypersonic vehicle used to be surrounded by a dense plasma sheath while moving in near space.The temperature would be extremely high because of the friction between the surface of the vehicle and the air near it.Such a dense plasma could cut off the propagation of communication signals.As a result,the communication breaks and the so-called�blackout' occurs.The loss of communication could lead to significant risks to hypersonic vehicles.Unfortunately,there is not a general solution to the blackout problem so far.This article mainly uses terahertz communication and low-frequency communication to analyze the possibility of mitigating the blackout problem.In this research,the plasma sheath of the flight is seen as a dynamic fluid,its spatial structure and coefficients are significantly affected by flight conditions.This research focuses on the influence of flight speed which is one of the flight conditions.The transmission of terahertz and low-frequency signals in the plasma sheath were analyzed based on the model with hydrodynamic theories.Finally,an estimation model and some potential measures to mitigate the impact of the blackout were proposed based on the above.First,this article analyzes the value and importance of mitigating the blackout problem.The research process and the current situation of black countries in the world were introduced,too.Then,this article describes the basic characteristics of the plasma sheath and the reasons or advantages of using terahertz communication and low-frequency communication.Besides,a function between the flight speed and the electron density and the electron collisions frequency along the signal transmission path was found.Then,the terahertz signals attenuation with the frequency of three atmospheric window frequencies in different flight speeds were calculated.Based on the above,the fast estimation model was proposed.We can get the terahertz signals attenuation without solving the hydrodynamic model.At last,this article analyzed the transmission of low-frequency signals in the plasma sheath with the transmission matrix method.Especially,the relationship between the transmission coefficient of low-frequency signals and the antenna position,flight speed,and signal frequency were analyzed.Through the research of this article,the details were more clear when we use THz and LF communications to mitigate the blackout.This research proves the importance of the flight speed and the antenna position to the signals attenuation,and also provides a convenient and effective method to analyze the blackout problem using an estimation model.It has laid the foundation for further research on the mitigation of blackout problem in the future.