Use of GNSS signals to reconstruct the shape of the plasma sheet surrounding the re-entry vehicles

During the re-entry phase the strong deceleration generates a plasma layer surrounding the vehicle. The resulting, undesired communication blackout has long been a topic of research: modern computational fluid dynamics simulations can help in determining the ionized shield’s shape, yet real measurements are important. This paper proposes a novel measurement technique based on stable radiofrequency signals coming from well-known directions, as the ones provided by satellite navigation systems. These signals can be sampled and recorded onboard and then processed with a software receiver to exactly define their strength, their disappearance and then their return after the blackout phase. The distribution of GNSS sources, currently in excess of 140, ensures that a rich number of directions could be investigated, providing relevant information about the shape and the behavior in time of the plasma layer. A preliminary evaluation of the technique, considering a coarse fluid dynamics simulation and the analysis of GNSS visibility conditions, is presented, showing the interest of the proposed approach. To be remarked that the possible implementation of the technique onboard a re-entry vehicle should require a limited equipment, with GNSS antennas probably already present on board for the guidance and navigation function, and a data sampler/ recorder. The after-flight use of a software receiver would then provide accurate findings.