Verification of a Fully Numerical Entry Guidance Algorithm

The process, methodology, and results of a two year effort are presented in this paper on verification of an advanced entry guidance algorithm, called Fully Numerical Predictor-corrector Entry Guidance (FNPEG). FNPEG is a model-based numerical guidance algorithm capable of performing both direct (orbital or suborbital) entry and skip entry missions. Few vehicle-dependent adjustments are necessary, and no reference trajectory or mission-dependent planning is required. The algorithm is applicable to a wide range of vehicles with different lift-to-drag ratios and includes state-of-the-art capability to effectively control g load and damp out phugoid oscillations, without adversely affecting the guidance precision. FNPEG has undergone extensive testing and evaluation in the high-fidelity simulation environment for the Orion spacecraft at NASA Johnson Space Center. In this paper, the verification methodology and process are described. The metrics for verification are defined. Extensive testing and simulation results on FNPEG and the comparison with the primary entry guidance algorithm for Orion, PredGuid, are provided. The outcome of this effort has clearly demonstrated the capability, strong robustness, and excellent performance of FNPEG, even in the presence of dispersions and uncertainties significantly higher than the design level.