A hypersonic application of the fully sensor-less virtual air data algorithm

During a reentry flight, both accurate and reliable air data would be strongly desirable in order to better control, above all, the vehicle trajectory and the heat flux. Despite the very high inertial velocities experienced in this kind of flights, in the middle Terminal Area Energy Management (TAEM) phase the effects of wind velocity could arise as significant. So far, very complex and expensive devices were taken into account in order to get air data measurements in the hypersonic missions but they never presented high reliability, even after an extended calibration campaign. In this article, an adaptation to the hypersonic regime of the sensor-less Virtual Air Data (VAD) technology is reported. This technology was successfully flight tested in the second CIRA USV mission (2010), characterized by a flight envelope similar to an effective TAEM phase. This innovative approach suitably uses the inertial measurements and an approximate knowledge of the vehicle aerodynamics and of the Reaction Control System, without using any air data sensor. This algorithmic solution shows-by definition-a great fault tolerance capability improving significantly, at the same time, the air data estimation accuracy with respect to the largely adopted inertial estimation (zero wind assumption). Additional VAD benefits are represented by a considerable cost and weight saving in the vehicle design, key aspect for each Reusable Launcher Vehicle (RLV), and by the complete removal of both numerical and experimental calibrations.