Plasma electron density measurement around hypersonic flight experiment vehicle

The hypersonic: flight experiment (HYFLEX) vehicle, which was a joint project for a hypersonic flight experiment between the National Aerospace Laboratory and the National Space Development Agency of Japan, was successfully launched from the Tanegashima Space Center by a J-1 rocket on 12 February 1996. The plasma electron density at the windward surface of the HYFLEX vehicle was measured using reflectometers, which are nonintrusive measurement devices. The reflectometer employs a phenomenon in which the radio waves are reflected from the plasma layer when the plasma density increases and exceeds a certain value. For comparison, the plasma density could also be calculated from a numerical analysis by real-gas computational fluid dynamics. It was difficult, however, to verify a real-gas computational fluid dynamics code using ground facilities, Here the flight data were compared with the calculations using a numerical simulation of the interaction between the radio waves and calculated plasma electron density. Also, this technique was applied to a prediction of the intensity of telemetry received at the Ogasawara Downrange Station during the flight of HYFLEX, These simulations agreed well with respect to the intensity of reflected and received radio waves, which is related to the plasma electron density measured during the flight. However, an interesting discrepancy remained in the timing of the reflection peak and blackout occurrence.