NASA Orion Flush Air Data Sensing System Feasibility Determination and Development

Abstract

Exterior probes are not viable options for the Orion crew capsule air data system due to the extreme aero-thermal environment on re-entry. The Air Force Academy Department of Aeronautics was tasked by the NASA Johnson Space Center Aeroscience and CFD Branch in December, 2011, to determine the feasibility of implementing a Flush Air Data Sensing (FADS) system, which would provide air data state flight parameters for the Orion spacecraft. The proposed Orion FADS system consisted of nine pressure ports on the capsule heat shield. FADS systems have been implemented on several aircraft nose cones in the past; however, application to the Orion presented a unique feasibility challenge due to the large radius of curvature of the heat shield versus the relatively low radius of curvature of aircraft nose cones, offsets in the pressure port arrays from the symmetrical centerlines, extreme orientations, and irregular and asymmetric heat shield geometries. Algorithm logic was developed, based on differential pressures from these ports, to predict angle of attack, sideslip, Mach number, and static pressure. Development of the system included creation of appropriate algorithms and scaled wind tunnel testing. Initially, a calibration procedure was implemented to characterize four experimental FADS correction parameters for the Generation II Orion Parachute Test Vehicle (PTV-2) based on computational fluid dynamic predictions and wind tunnel results. These calibration parameters were incorporated in a solution algorithm and used in post-flight analysis to reduce the air data state from the actual NASA PTV-2 drop test. The calibration procedure was then repeated for the Orion Exploration Flight Test-1 (EFT-1) vehicle in anticipation of the first orbital flight of the Orion program in November, 2014. Several independent wind tunnel cases, not used to build calibration tables for the EFT-1 vehicle, were evaluated to test the accuracy of the solution algorithm’s determination of air data state. The final product had average error of 0.06 o in α prediction, 0.24 o in β prediction, 0.579% in Mach number prediction, and 2.67% in prediction of P∞. These results indicated that implementation of a FADS system on the Orion was feasible and provided a reliable approach for determination of the Orion air data state.