Design of fuel-saving lunar captures using finite thrust and gravity-braking

The emergence of microsatellite missions leaving low Earth orbits to pursue the exploration of the solar system is currently leading the development of new techniques of mission analysis. In fact, the small size of these satellites affects the performance of the propulsion systems, in particular because of the limited mass budget available for propellant stowage. This work focuses on the analysis of lunar microsatellite missions, proposing a method to design fuel-saving lunar captures. The solution is aimed at establishing the capture conditions taking advantage of the gravity-braking effect of the Moon, before injecting the spacecraft into a lunar capture orbit. The maneuvers are developed in the form of guidance laws, implemented based on primer vector theory and on the definition of a quasi-integral of motion for the elliptic restricted 4-body problem. The method is verified, by means of numerical analysis, on a 6U CubeSat equipped with a monopropellant thruster and considering deployment conditions compatible with microsatellite lunar missions. The achievement of lunar capture in a few days from the deployment, with propellant usage on the order of tenths of grams, corresponding to ΔV on the order of some meters per second, indicates the suitability of the method to expand the possible profiles of microsatellite missions to the Moon.