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.

The problem of how to optimally transfer between two planet-centered orbits using solar sails remains nearly unexplored. Most of the existing body of knowledge focuses on (blended) locally optimal control laws, often considers open-ended trajectories instead of orbital transfers, or tackles specific mission scenarios, leaving insight into the general transfer problem unexplored. In this work, we present the first step in the comprehensive study of optimal solar-sail transfers around planetary bodies by analyzing the simplest conceivable transfer, the planar circular-to-circular (C2C) transfer. The considered C2C transfer spans only one orbital revolution, which may constitute the future building block of more complex multi-revolution trajectories. The optimized control law maximizes the change in orbital radius within the C2C transfer, where the achieved radius change is used as the performance metric. The results show that the C2C performance (i.e., the ability of the solar sail to transfer) depends on the illumination conditions of the orbital plane and the ratio of the sail’s characteristic acceleration to the local gravitational acceleration. Maximum performance is achieved when the orbital plane is perpendicular to the Sun-planet line, where the transfer structure resembles that of a C2C transfer conducted with an ion drive. Furthermore, by using the ratio as the scaling parameter, the results presented in this paper allow to easily compute the C2C performance for a wide range of mission scenarios around any planetary body, providing a new tool for early mission design.