Robust multisensor fusion for autonomous spacecraft navigation during final approach for mars entry, descent, and landing

Abstract

An integrated navigation scheme for autonomous spacecraft operation during the final approach phase of a Mars entry, descent, and landing (EDL) mission is considered. Optical camera-based observations of natural celestial bodies are aided by X-ray pulsar signal time of arrival (TOA) measurements to provide accurate three-dimensional position and velocity solutions. Once the proposed navigation system is initialized, it operates with no need for assistance from man-made assets on the ground or in orbit, providing complete autonomy. As a reference for the research community, a catalog of 41 X-ray pulsars that are deemed most promising for navigation purposes is presented. The list builds on top of the work of previous researchers and contains the expected range measurement error margins from each source together with the relevant parameters used to compute these error margins. This catalog is utilized in an optimization-based technique for selecting the best $j$ pulsars for navigation from among a candidate list of $k$ pulsars wherein, geometry and measurement accuracy are jointly considered. Afterward, measurements from the optical sensors and data from the chosen pulsars are fused in a distributionally robust nonlinear optimization-based filtering framework. The proposed robust navigation filter provides significant resilience under severe measurement outliers which cause non-Gaussian noise behavior that subsequently results in the degradation of navigation performance. The results of the pulsar selection algorithm as well as the robust sensor fusion scheme are illustrated on a simulated final approach trajectory of the Mars Science Laboratory (MSL). The pulsar selection algorithm is further deployed on an embedded platform to demonstrate potential onboard implementation. A new robust approach to image processing for planet/moon centroid and apparent diameter extraction is also provided with actual mission images used to validate the concept. Although this research takes Mars landing as a case study, the methods developed herewith can be used for other interplanetary missions, asteroid landings, and as an aid to spacecraft rendezvous and docking applications.