To achieve longer driving distances, planetary robotics missions require accurate localization to counteract position uncertainty. Freedom and precision in driving allows scientists to reach and study sites of interest. Typically, rover global localization has been performed manually by humans, which is accurate but time-consuming as data is relayed between planets. This paper describes a global localization algorithm that is run onboard the Perseverance Mars rover. Our approach matches rover images to orbital maps using a modified census transform to achieve sub-meter accurate, near-human localization performance on a real dataset of 264 Mars rover panoramas. The proposed solution has also been successfully executed on the Perseverance Mars Rover, demonstrating the practicality of our approach.