Autonomous navigation of distributed spacecraft using intersatellite laser communications

This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Thesis: Ph. D. in Space Systems, Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2020Cataloged from the PDF of thesis.Includes bibliographical references (pages 149-157).Autonomous navigation refers to satellites performing on-board, real-time navigation without external input. As satellite systems evolve into more distributed architectures, autonomous navigation can help mitigate challenges in ground operations, such as determining and disseminating orbit solutions. Several autonomous navigation methods have been previously studied, using some combination of on-board sensors that can measure relative range or bearing to known bodies, such as horizon and star sensors (Hicks and Wiesel, 1992) or magnetometers and sun sensors (Psiaki, 1999), however these methods are typically limited to low Earth orbit (LEO) altitudes or other specific orbit cases. Another autonomous navigation method uses intersatellite data, or direct observations of the relative position vector from one satellite to another, to estimate the orbital positions of both spacecraft simultaneously.The seminal study of the intersatellite method assumes the use of radio time-of-flight measurements of intersatellite range, and a visual tracking camera system for measuring the inertial bearing from one satellite to another (Markley, 1984). Due to the limited range constraints of passively illuminated visual tracking systems, many of the previous studies restrict the separation between satellites to less than 1,000 kilometers (e.g., Psiaki, 2011), or simply drop the use of measuring intersatellite bearing and rely solely on obtaining a large distribution of intersatellite range measurements for state estimation (e.g., Xu et al., 2014). These assumptions have limited the assessment of the performance capability of autonomous navigation using intersatellite measurements for more general mission applications.In this thesis, we investigate the performance of using laser communication (lasercom) crosslinks in order to achieve all necessary intersatellite measurements for autonomous navigation. Lasercom systems are capable of measuring both range and bearing to a receiving terminal with greater precision than traditional methods, and can do so over larger separations between satellites. We develop a simulation framework to model the measurements of intersatellite range and bearing using lasercom crosslinks in distributed satellite systems, with consideration of varying orbital operating environments, constellation size and distribution, and network topologies. We implement two estimation algorithms: an extended Kalman filter (EKF) used with Monte Carlo sampling for performance analyses, and a Cram~r-Rao lower-bound (CRLB) computation for uncertainty analyses.We evaluate several case studies modeled off of existing and planned constellation missions in order to demonstrate the new capabilities of performing intersatellite navigation with lasercom links in both near-Earth and deep-space orbital applications. Performance targets are generated from the current state-of-the-art navigation capabilities demonstrated by Global Navigation Satellite Systems (GNSS) in Earth-orbit, and by radiometric tracking and orbit estimation using the Deep Space Network (DSN) in deep-space orbits. For Earth-orbiting applications, we simulate a relay satellite system in geosynchronous orbit (GEO) inspired by current optical communications missions in development by both ESA and NASA, and Walker constellations in LEO inspired by the upcoming mega-constellations for global broadband internet service, such as those proposed by SpaceX and Telesat.In both case studies, we demonstrate improved navigation performance over the current state-of-the-art in GNSS receiver technologies by using intersatellite measurements from lasercom crosslinks. Monte Carlo simulations show median total position errors better than 3 meters in LEO, 12 meters in GEO, and 45 meters in high-altitude or highly-eccentric orbits (HEO), showing promise as an alternative navigation method to GNSS in Earth-orbiting environments. We also simulate current and future Mars-orbiting missions as examples of deep-space applications. In one case study, we create an ad-hoc constellation comprised of low-altitude Mars exploration orbiters modeled off of current Mars-orbiting missions. In a second case study, we focus on a high-altitude constellation proposed for dedicated Earth-to-Mars networked communications.Again, in both case studies, we demonstrate improved navigation performance over the current state-of-the-art in DSN radiometric orbit solutions by using intersatellite measurements from lasercom crosslinks. Monte Carlo simulations show stable median total position errors better than 25 meters for Mars-orbit, which demonstrates a notable improvement both spatially and temporally versus DSN orbit estimation, mitigating the large cost and time constraints associated with DSN tracking. These results demonstrate the promise of using lasercom intersatellite links for autonomous navigation, offering enhanced performance over current state-of-the-art capabilities, and a greater applicability to missions both near Earth and beyond.by Pratik K. Dave.Ph. D. in Space SystemsPh.D.inSpaceSystems Massachusetts Institute of Technology, Department of Aeronautics and Astronautic