Reducing RF blackout during re-entry of the reusable launch vehicle

Abstract

The Aerospace Corporation was tasked to assess radio frequency (RF) blackout phenomena caused by plasma generation around vehicles during reentry and presently known methodologies for mitigation of this condition inhibiting communications. The purpose was to understand these phenomena and mitigation approaches applicable to reusable launch vehicles (RLVs) used for commercial space. The viability and limitations of selecting frequency bands amenable to continuous communication in presence of plasma sheaths were assessed and mitigation recommendations provided. The ability to predict the ionized flow field for classes of vehicles most likely to emerge as hypersonic space transportation systems, with sufficient accuracy to identify the altitudes of blackout onset and recovery within reasonable bounds, has been demonstrated for altitudes greater than approximately 100 kft. This high-altitude regime is the most likely for future space transportation due to low g forces and low heat loads. For the lower, suborbital altitudes, many commercial RLVs will not be subjected to RF blackout because their relatively low velocities will not create conditions that generate plasma. Determination of the interaction of RF with a known ionized layer, including reflection, attenuation, refraction, high-power breakdown limits, and also effects of the plasma on the antenna characteristics, have been demonstrated successfully. Analytic codes are available to evaluate these phenomena. Approaches for mitigating the interruption of communications due to interactions of plasma electrons with RF signals are reviewed. The most promising are: aerodynamic shaping, injection of quenchants, use of magnetic windows, and use of high frequencies.