Advanced navigation and guidance for high-precision planetary landing on Mars
Several international missions scheduled for years 2011--2013 have as objective a Mars surface sample return to Earth. In order to gather samples of high scientific quality, these missions require precise landing at preselected locations on Mars. Since the previous missions on Mars have flown unguided and highly inaccurate atmospheric entry, a new generation of landing systems must be developed. It was demonstrated by Wolf et al .,  that the most efficient way to increase the landing accuracy is achieved during the atmospheric entry by steering the vehicle trajectory in order to eliminate the dispersions caused at entry and accumulated during the hypersonic phase. Thus, the research project proposed here will investigate the problem and bring advances on atmospheric entry navigation, guidance and control techniques applied to atmospheric entry on Mars. The state-of-the-art revealed several limitations on the current techniques such as the lack of proper navigation system and the inability to guide the trajectory efficiently in presence of disturbances and entry conditions uncertainties. On the theoretical side, the nonlinear state estimators required for navigation use algorithms that are a heavy computational burden for the onboard processor. Following these limitations, the research presented in this document is conducted along three paths: estimation theory, entry navigation techniques and entry guidance techniques in order to investigate on advances to achieve high precision landing. After an in-depth investigation of the theoretical background required to understand the atmospheric entry dynamics, a number of issues are addressed and the following substantial contributions regarding Mars atmospheric entry navigation and guidance are achieved. (C1) A theoretical improvement of the unscented Kalman Filter by merging two variants in the literature. The resulting technique has the advantages of both former algorithms. (C2) Four navigation concepts using inertial measurement units and radio ranging from reference beacons (known and unknown) for complete state estimation, atmospheric density estimation and vehicle aerodynamics estimation. (C3) The successful application of the unscented Kalman filtering to atmospheric entry for both state and parameter estimation. (C4) The development of two analytical predictor-corrector guidance techniques for atmospheric entry. The first uses two constant flightpath angle segments in order to meet the terminal altitude, velocity and downrange requirements. The second is based on a single density-proportional flightpath angle segment. These contributions have been reported in three conference papers and one scientific journal.
- Génie – Thèses