Recalibration of Flush Air Data System (FADS) on Pressure Port/Sensor Failures

Flush Air Data sensing System (FADS) forms a mission critical sub system in future reusable space transportation systems. FADS makes use of surface pressure measurements from the nose cap of the vehicle for deriving the air data parameters of the vehicle like angle of attack, angle of sideslip, Mach number, etc. These parameters are used by the control and guidance system of the vehicle for reentry flight management as well as for subsequent mission phases upto landing. The on board algorithm makes use of calibration coefficients derived from wind tunnel data to achieve better accuracy in the estimated air data parameters. In the event of faults in FADS due to port blockages or pressure sensor failures, recalibration is essential for achieving the desired accuracy of air data estimates. This paper describes recalibration of FADS using surface fit method in the event of pressure port blockage or sensor failures. The method is based on the storage of coefficients of a 4th order surface fit corresponding to the wind tunnel calibration data and recalibration using these polynomial coefficients.