Doppler Tracking

This study addresses the development of a methodology using the Doppler Effect for high-resolution, short-range tracking of small projectiles and vehicles. Minimal impact on the design of the moving object is achieved by incorporating only a transmitter in it and using ground stations for all other components. This is particularly useful for tracking objects such as sports balls that have configurations and materials that are not conducive to housing onboard instrumentation. The methodology developed here uses four or more receivers to monitor a constant frequency signal emitted by the object. Efficient and accurate schemes for filtering the raw signals, determining the instantaneous frequencies, time synching the frequencies from each receiver, smoothing the synced frequencies, determining the relative velocity and radius of the object and solving the nonlinear system of equations for object position in three dimensions as a function of time are developed and described here

Analysis of radiofrequency-based methods for position and velocity determination of autonomous robots in lunar surface exploration missions

The use of distributed systems has been disruptive in almost any industrial sector, from manufacturing to processing plants from environmental monitoring to vehicle control, and many more. It is therefore natural to assess the benefits that such an advantageous engineering paradigm could bring to space exploration. In recent years, we have been witness to the emergence of concepts such as fractionated satellite systems, formation flying, megaconstellations, and femtoswarms. Most of these space missions have evolved from the idea of a decentralization of processes that were formerly performed in platforms conceived as monolithic systems. The application of this concept to robotic systems is not new, and a great deal of scientific contributions on multi-robot systems exists, focusing on different aspects such as cooperative robotics, behavioural or reactive control, distributed artificial intelligence, swarm multi-agent systems etc. The intrinsic advantages of distribution (improved reliability and efficiency, higher robustness, etc.) has been boosted by the exponential growing of computational power density and a simultaneous miniaturization of technology, leading to smaller and more powerful robotic platforms, which could make a distributed robotic system, made of small robotic agents, a powerful substitute to classical large robotic platforms. This thesis proposes, in the framework of multi-robot systems, a localization method for robotic agents in planetary surface exploration scenarios based on RF range and Doppler frequency shift analysis. The relevance of spatial localization awareness in agents belonging to a distributed robotic system is defined in the context of the advantages of robotic exploration. Different range determination techniques and, specifically, the advantages of including Doppler Effect in the determination of the relative position within the robotic system deployed are considered and the strengths and weaknesses analysed accordingly. Special attention is devoted to the noise sources present in the lunar environment, related to a practical (i.e. non-ideal) implementation architecture and its influence on the system performance. From this point of view, we develop a theoretical model for localization accuracy estimation, generated from power spectrum characteristics, in accordance with the system architecture proposed, and consolidated with numerical simulations and a parametrical assessment on a set of real references of components playing a key role in the overall performance. The selected system architecture is then implemented in a representative set-up and tested under laboratory conditions. Algorithms used for carrier frequency generation and frequency measurement are developed, applied and tested in the hardware-on-the-loop breadboard. The results show that Doppler frequency component can be measured with the proposed architecture, yielding a high sensitivity in the determination of relative speed even at standard communication frequencies (UHF), and improving significantly at higher bands (S, C, etc.). This enables the possibility of adding relative speed to relative position determination via sensor fusion techniques, improving the response time and accuracy during navigation through the exploration scenario