Study on Air Film Approach in Reentry Blackout Mitigation

Abstract

Communication blackouts are among the most severe problems in the atmospheric reentry phase. Flight data are lost because the plasma gas generated by aerodynamic heating interrupts telecommunications. Therefore, mitigation methods are necessary to improve the accuracy of the landing-site prediction. In this study, we demonstrated the effectiveness of a air film, which is a thin insulating coolant layer on the surface, as a novel mitigation method. Here, we show that a gas injection system can reduce the reentry blackout. The coupled approach with computational fluid dynamics and a frequency-dependent finite-difference time-domain method resolved the plasma flow properties and electromagnetic propagation around the test model in the arc-heated wind tunnel L3K in DLR (German Aerospace Center). The numerical results indicated that the injected nitrogen gas formed an insulating air film layer on the surface. The thin layer advected backward, maintaining a low temperature without ionization, and covered the object in the wake region. The electromagnetic waves propagated and reached a distant area because the electron density was low inside. This means that the air film layer acted as a propagation window for the telecommunication waves. Thus, communication blackouts can be avoided because electromagnetic waves can be transmitted through the air-film layer. It can be concluded that the air film effect, developed as a thermal protection technique, is a novel mitigation scheme for reentry blackouts.