Experimental verification of pulsed electrostatic manipulation for reentry blackout alleviation

Spacecraft entering the Earth's atmosphere from space are enveloped by a plasma layer containing highly mobile electrons that cause attenuation of electromagnetic waves, often leading to a loss of command, communication and telemetry signals, which is commonly referred to as the “blackout period”. The blackout period may last up to several minutes, and is a major contributor to the landing error ellipse. In the context of human spaceflight, this may also present a significant safety hazard. A new method called Pulsed Electrostatic Manipulation (PEM) was recently proposed to circumvent the communications blackout by applying strong electronegative voltage pulses from electrodes placed on the reentering spacecraft. Through two dimensional Particle-In-Cell (PIC) simulations, a reduction in electron density of up to three orders of magnitude in the vicinity of the electrode was demonstrated. These simulations were performed on the electron time scale (~ nanoseconds), with emphasis on the interactions of the plasma with the insulation surrounding the electrode. In January 2016, a preliminary experimental campaign was conducted at the DLR L2K arc-heated facility in Cologne, Germany to verify the efficacy of PEM in reducing the electron density in a hypersonic plasma, in order to allow for the transmission of electromagnetic waves, thereby restoring communications during the blackout. We discuss the experimental setup for these tests - ranging from the design of the model, including the communication system, to the implementation of experimental protocols. Further, we share data for the attenuation caused by the presence of plasma between the receiving and transmitting antenna, and the effect of the applied high voltage pulses (up to 2.5 kV) over short periods of time (~ 10 microseconds) on the attenuation. Several unexpected effects have been observed in the voltage response of the electrode, including inductive spikes, stray capacitive effects, and Paschen breakdown of the gas inside the test stand. No measurable change in the attenuation profile was observed for pulses with voltage up to 2.5 kV. This is consistent with the results obtained from a Hybrid-PIC Boltzmann Electron (HPBE) simulation of the experimental setup, which are presented in this work. These simulations also show an increase in window duration with the use of surface treatments that minimize the absorption of charge on the electrode insulation. We finally present design changes planned for future tests with higher voltage pulses based on the data obtained from simulation results and from the preliminary tests.