The project will establish a collaborative opportunistic navigation (COpNav) framework as a reliable, accurate, affordable, and maintainable positioning, navigation, and timing (PNT) system, mitigating the shortcomings of the current GPS-dependent PNT paradigm. We will achieve this by establishing new theory and algorithms as well as hardware and software prototypes to exploit terrestrial and space-based signals of opportunity (SOPs), demonstrating robust and accurate ground vehicle and unmanned aerial vehicle (UAV) navigation in GPS-denied situations. Our investigation is structured around the following questions: