Studying the solar corona is fundamental for understanding phenomena that affect satellite operations, such as solar flares, coronal mass ejections, and highly energetic particles. Because  solar corona is at least one million times fainter than the Sun, observations can be achieved by means of coronagraphs, which are optical instruments whereby a mask and other optical components occult the light coming from the Sun’s disk. However, both ground-based space-based coronagraphs are limited by stray light and vignetting effects that prevent access to the innermost layers of the Sun’s atmosphere (e.g., below 1.05 Sun radii).

Observation quality improves with a larger distance between the external occulter and the detector, which is why total solar eclipses offer unique opportunities for studying the corona of the Sun. Unfortunately, total eclipses are extremely rare events that typically last for a few minutes only (less than 7 minutes for all of the total eclipses in the 21st century). More recently, Proba-3 managed to image the corona of the Sun by means of two satellites in close formation (150 m baseline). At best, Proba-3 aims at imaging the corona of the Sun down to 1.1 solar radii.

A novel concept proposes to use natural bodies as occulting disks [1,2]. The idea is to place a satellite in proximity of the tip of the umbra cone generated by a celestial body, allowing high-resolution long-lasting observations of the inner sun corona. Baresi et al. advanced the Moon-enabled Sun occultation mission concept (MESOM), advocating the use of the Moon as a natural occulter. Synodic resonant periodic orbits were identified in the Sun-Earth-Moon system to enable repeated and prolonged inner corona observations once every synodic month [3]. The preliminary trajectory design of MESOM was presented in [4] using chemical propulsion, thereby demonstrating the ability of MESOM to image the corona of the Sun down to 1.02 Sun radii for up to 2 years with less than 700 m/s. Moreover, Herasimenka et al. proposed a preliminary analysis of a low-thrust MESOM concept in [5]. First, a rough estimation of the efficiency of the thrusters needed to enable such a mission Is performed, demonstrating its compatibility with the solutions available on the market. Second, a multiple-arc approach was used to fully optimize one observation cycle using electrical propulsion.

The current paper builds upon the demonstrated feasibility of the MESOM concept by proposing a fully optimized trajectory for a two-year mission scenario. To accurately model the system dynamics, we employ a full ephemeris model that capitalizes on SPICE kernels to compute the positions and velocities of celestial bodies throughout the mission timeline. Furthermore, the potential benefit of utilizing lunar flybys throughout the mission is explored. Lunar flybys can indeed offer a significant gravitational assist, which may improve the feasibility of low-thrust trajectories, especially in terms of minimizing fuel consumption for orbital size and inclination adjustments. Finally, a transfer from a Lunar Transfer Orbit (LTO) to the science orbit of MESOM is considered so as to address the whole trajectory design with low-thrust propulsion and quantify the total ?V budget of the MESOM low-thrust option.

[1]  S. Eckersley and S. Kemble, “Method of Solar Occultation,” Airbus DS Patent 9,676,500, 2017. 

[2] S.R.Habbal, H.Morgan, et al,“Probingthe Fundamental Physics of the Solar Corona with Lunar Solar Occultation Observations,” Solar Physics, Vol. 285, Sept. 2012, p. 9–24, 10.1007/s11207-012-0115-5. 

[3] N.Baresi, L.Green, H.Morgan, et al., “MESOM: A Moon-Enabled Sun Occultation Mission,” 31st IAA Symposium on Small Satellite Missions, IAC 2024, p. 100–120, 10.52202/078365- 0012. 

[4]  N. Baresi, D. Owen, A. Herasimenka, L. Green, H. Morgan et al., “Trajectory design and optimization of the moon-enabled Sun occultation mission,” Space Flight Mechanics Meeting 2025.

[5] A. Herasimenka, N. Baresi, L. Green, H. Morgan, et al.. "Low-thrust trajectory optimization for the Moon-enabled Sun occultation mission concept,” Astrodynamics Specialist Conference 2025.