Ares I-X Trajectory Reconstruction: Methodology and Results

The Ares I-X trajectory reconstruction produced best-estimated trajectories of the flight-test vehicle ascent through stage separation and of the first- and upper-stage entries after separation. The trajectory-reconstruction process combines onboard, ground-based, and atmospheric measurements to produce the trajectory estimates, using an iterated extended Kalman filter algorithm. The Ares I-X vehicle had a number of onboard and ground-based sensors that were available, including inertial measurement units, radar, air data, and weather balloons. However, due to problems with calibrations and/or data, not all of the sensor data were used. This paper describes the methodology and results of the trajectory-reconstruction process, including flight-data preprocessing and input uncertainties, trajectory-estimation algorithms and dynamic models, output transformations, and comparisons with preflight predictions. The results of the reconstruction indicate nominal vehicle performance that is well within the range of expected dispersions based on preflight Monte Carlo analysis.