Reentry

In the earliest days of the space program, it was noted that a communication blackout period occurs during hypersonic and space vehicle flight that directly relates to the re-entry plasma formed by these vehicles; this is commonly referred to as the “re-entry problem.”  This communication problem remains largely unsolved at the present time, although a wide variety of schemes have been proposed, including modification of the plasma fluid, the application of strong magnetic fields, excitation of plasma waves that couple to external electromagnetic waves, and recently, nonlinear coupling to external waves.  None of these methods have proven entirely successful to date, though work in this area remains active.  Of crucial importance in addressing this problem is a detailed understanding of the plasma that develops around the vehicle under a wide variety of conditions that depend on neutral density, and hence on altitude.  The scope of plasma physics over the range of relevant altitudes is quite broad and must include aspects of air chemistry, surface ablation physics and possible collective plasma phenomena.  No comprehensive models to date have been presented and only scant experimental data regarding this diverse range of plasma conditions has been made available.