An experience in the investigation of a radio communications system for a reentry vehicle on the plasma flight trajectory portion

Abstract

Consideration is given to the experimental investigation of the original method of providing radio communications with the reentry vehicle along the trajectory section when the vehicle is surrounded by plasma of the ionized shock layer. The method suggests the location of antennas, placed in special containers, ahead of the front of the shock wave generated near the vehicle. Along with the measurements of ionization near the container, the thermal protection of the container and its pylon and the influence of the remote antennas on the vehicle’s aerodynamics are analyzed. Introduction Radio communication during the vehicle reentry in the Earth’s aGosphere is a vital challenge posed by the practice of space flights. Radio communication is known to be affected by plasma formations occurred near the vehicle at high flight velocities which attenuate strongly radio signals or even absorb them totally, thus resulting in blackout of communication between the vehicle and relevant tracking stations. To provide radio communication with the vehicle, the project developer must choose between various techniques of plasma screening. In this case, it is important to understand basic advantages and disadvantages of every possible technique. These techniques involve: l selection of communication band; l arrangement of antennas on the vehicle and organization of radio communication through zones with minimum electron concentrations near the vehicle (for example, through the leeward region to a relay satellite); l use of “spectral windows” at antenna locations which are produced, for example, by injectiqn of electrophilic fluids, injection of a cold gas, interaction of near-vehicle plasma with strong magnetic fields. The present report contains the results of complex investigations of basic problems related to the development of the system of radio communication through plasma during the vehicle reentry. The system is based on the arrangement of radiating and receiving antennas, placed in a streamlined container t Head of Branch. * Deputy Head of Lkpartment, Member AIAA. I Leading Scientist. of relatively small sizes, ahead the shock wave front near the vehicle. In this case, the gas ionization level near the antenna container depends on the isolated flow conditions over this container. With a small radius of the antenna container nose bluntness, ionization around the container can be reduced significantly down to the level which provides the’ capability of direct radio communication of the vehicle with ground tracking stations over centimetric and decimetric bands of electromagnetic waves. In the USSR, this technique of radio communication with the vehicle was suggested in the 1970’s by Yu. Khodatayev, a specialist of the “Energy” SRC. To study the prospects of its practical implementation, complex investigatidns of basic scientific/technical problems associated with possible application of such remote antenna assemblies @A) were carried out at TsAGI. During the preparation of the report, the authors made a decision not to include the results of the modem CFD-analysis. The investigation results given here are based to a great extent on laboratory experiments. The basic investigations were carried out in the following areas: 0 influence of the RAA configuration, angle of attack of the I&4 in flow, and the RAA nose cooling system using the distributed cold gas injection on the ionization levels; l influence of the RAA on the vehicle’s aerodynamic characteristics. l peculiarities of heat transfer over the RAA container pylon and possible application of its active heat protection using distributed cold gas injection. Peculiarities of nonequilibrium ionization in the shock layer near RAA During the flight of a hypersonic vehicle in the dense atmospheric layers, the shock layer contains considerable concentrations of free electrons formed in the course of nonequilibrium physical-chemical processes taking place in the high-temperature air. The interaction of electromagnetic waves with electrons in the shock layer can result in deterioration or total blackout of radio communication along some vehicle flight trajectory . segments. Simple estimation of such flight segments can ” be made using the well-known criterion o,o,~~~.‘, where o is the radio signal frequency, op is the plasma frequency, n, is the electron concentration. The flight trajectories for Copyright