Study Of Electromagnetic Wave Propagation In Spacecraft Plasma Sheath

The spacecraft will experience the well-known “blackout” problem when itre-entry into the Earth’s atmosphere, which results in communication failures betweenthe spacecraft and the ground control center. The reason is that a plasma sheath isformed near the spaceraft, which severely affects the propagation of the incidentelectromagnetic wave and cause severe electromagnetic wave attenuation. For example,the re-entry capsule of Shenzhou-9spacecraft experiented a blackout for4minutes. Thespacecraft will lose all communications including GPS (Global Positioning System)signals, date telemetry, voice communication and so on when it enters the blackoutphase. The blackout introduces significant problems related to the mission success ornot, vechile tracking, electric countermeasure capability and so on. The blackoutproblem is becoming more and more important with the rapid development of theaerospace.The altitude and time for blackout are related to the aerodynamic shaping, reentryspeed, angle of attack, altitude of the spacecraft, communication frequency and so on.Gernerally speaking, the blackout occurs when the strength of electromagnetic wavereaches the receiver is lower than its threshold. It is important to study the properties ofelectromagnetic wave propagation in spacecraft plasma sheath for soving the blackoutproblem.The properties of electromagnetic wave propagation in spacecraft plasma sheathhave been studied with theoretical and experimental method in this dissertation:1. The properties of electromagnetic wave propagation in plasma have been studiedwith theoretical method in this dissertation. The electromagnetic wave propagation inplasma has been studied with the analytical solution, WKB method andthree-dimensional FDTD method. The dependence of plasma density, plasma collisionfrequency, thickness of plasma, electromagnetic wave frequency and the angle ofincidence on electromagnetic wave propagation is presented. The results with differentmethods have been compared with each other and the scope of analytical, WKB and FDTD methods have been analyzed.2. The properties of electromagnetic wave propagation in plasma have been studiedwith experimental method. The properties of L-band, S-band, Ka-band, W-band andTHz (terahertz)-band electromagnetic wave propagation in plasma have been studiedexperimentally with shock tube and plasma torch, and the experimental results accordwell with the FDTD and electromagnetic software ones. The results indicate thatincreasing the electromagnetic wave frequency (for example, using THz wave) is analternative and effective method to solve the reentry blackout problem.3. The effects of plasma on the performance of antenna are given. The effects ofplasma density, collision frequency and the thickness of plasma on the radiationperformance of L-band, S-band, C-band and X-band antenna have been studied. It isfound that the effects of same plasma parameter on different band antenna are not thesame. The return loss becomes large, the direction of the main lobe has been changedand the gain at0°reduced with increasing plasma density or thickness. The return lossbecomes small, the gain at0°first increase and then decrease for L-band and S-band,while the return loss becomes large, the gain at0°decrease for C-band and X-band.The effects of the plasma density or thickness on the performance of antenna arereduced with higher band.4. The analysis of RAM C (Radio Attenuation Measurement C) flight has beengiven. The effects of RAM C plasma sheath on the performance of L-band, S-band,C-band and X-band antenna under different height have been given. The properties ofVHF-band, L-band, S-band, C-band and X-band electromagnetic wave propagation inRAM C plasma sheath have been computed with the FDTD method, and the altitudeand time for blackout have been estimated. The FDTD results match well with the flightones. The results indicate that increasing the electromagnetic wave frequency is aneffective way to shorten the altitude and time for blackout.