Significant research has addressed solar-sail transfers in heliocentric settings, whereas planet-centered transfers have received comparatively little attention. However, most solar-sail missions flown to date have operated in Earth-centered orbits and are likely to continue to do so, highlighting the importance of planet-centered sailing in the future of this new and promising technology. This work fully characterizes the co-planar multi-revolution circular-to-circular (MC2C) transfers, which enable motion between co-planar circular orbits and are therefore regarded as one of the “simplest” possible planet-centered solar-sail transfers. Using an indirect optimization approach, the performance of the MC2C transfers (i.e., achieved radius change in a fixed transfer time) is computed for various initial sun-orbit geometries. As a result, the best and worst transfer geometries (which depend on the illumination conditions of the orbital plane) are identified, enabling the construction of the performance envelopes that relate radius change to transfer time. These envelopes provide a simple graphical tool to obtain such metrics without having to optimize a single trajectory, greatly enhancing the workflow during early mission design. Through dimensional analysis, the envelopes are generalized to any sail design and any planet in the solar system, broadening their applicability. Finally, the explanation of the physical mechanisms behind the best and worst geometries is provided through new concepts that are unique to solar sailing, like the “growth vector”. This explanation lies the foundation for the study of future, more complex planet-centered solar-sail transfers. ... Read more