Investigation of an RF plasma afterglow with a cathode-spot driven quenching method for spacecraft reentry blackout mitigation

Summary form only given: communications blackout, which is experienced by spacecraft re-entering the atmosphere at hypersonic velocities, is caused by the formation of a dense plasma envelope produced by shock heating. Communication signals at frequencies below the plasma cutoff frequency cannot propagate through this layer. Methods suggested for mitigating blackout have included aerodynamic shaping, magnetic windows, and the use of quenchants to reduce plasma densities. The Gemini 3 mission in 1965 successfully used water as a quenchant to cool the reentry plasma and increase communication signal strength. Techniques for mitigating communications blackout are currently being developed. The investigation of a novel system for plasma quenching by dispersing fine particulate in a plasma has been performed. Cathode-spot plasma plumes are utilized to disperse particulate into the afterglow of a pulsed overhead radio-frequency (RF) plasma. These particles will collect a net negative charge as they travel through the overhead plasma, reducing the electron density of the afterglow plasma. Measurements of the overhead plasma afterglow with and without particulate dispersal via Langmuir probes have been obtained. Full current-voltage profile measurements at several time delay increments of the afterglow allow comparison of electron densities with and without particulate dispersal. The reduction in electron density due to particle dispersion has been verified and results in lowering the cutoff frequency, theoretically allowing for the transmission of radio-communication waves through this quenched plasma. The results and measurements from this study are presented and discussed below.