Computational Approach to Evaluating the Characteristics of an Onboard Antenna with Complex Thermal Protection

Onboard antennas of the returned spacecraft are protected from aerodynamic heating by a radio-transparent heat-resistant heat shield. Electrical characteristics of heat shield under conditions of high-temperature heating significantly change. Superheated layer of molten heat shield by its electrical characteristics become close to the properties of conducting materials. This leads to significant losses of radiation power of the onboard antenna. The losses become so great that they are commensurate with the losses in the plasma shell surrounding the spacecraft. Taken together, these losses lead to disruption of radio communication on the descent trajectory. To eliminate such a situation, radio illumination of the onboard antenna in conditions of aerodynamic heating is necessary. We consider the design of an onboard antenna of complex design, when the heat shielding is made of two components. The melting temperature of the central part of the heat shield (rod) is lower than the melting temperature of the peripheral part (sleeve). It is assumed that the rod is cooled by fracture product vapor, which eliminates the melting of the outer surface of the rod. In this case, the electromagnetic wave emission occurs mainly through the rod. The carried out theoretical studies showed the possibility of radio illumination of on-board antennas of returned spacecraft by cooling a part of outer surface of heat shield and eliminating its melting in this part.