How the Lunar Space Tug can support the cislunar station

The Lunar Space Tug is a sustainable transportation system able to rendezvous with a target body in Low Earth Orbits environment, assess its current position, attitude and operational status, capture the target and move it to the Cislunar space where the Lunar Orbital Platform-Gateway will be settled. Thanks to the adoption of an electric Propulsion Subsystem based of Hall Effect Thruster clusters, the Lunar Space Tug can save fuel to the detriment of much longer transfer time to deliver the unmanned cargo to the cislunar Gateway. Since the Lunar Space Tug has been conceived to be reusable, one of the main issue is related to the on-orbit refueling to sustain the Lunar Space Tug during its operational lifetime. Each mission scenario shall take into account the effects related to refueling operations according to mission requirements and constraints. Considering the whole mission scenario in which the Lunar Space Tug will operate, this paper focuses on mission analysis and conceptual system design, including typical systems budgets, like transfer duration, Delta v, mass and power. Moreover, according to the transfer duration and the needs of the Lunar Orbital Platform-Gateway, a preliminary trade-off analysis has been accomplished to investigate the possibility of using a fleet of Lunar Space Tug instead of a single tug, taking onto account safety, reliability, costs and operations issues. The identified optimal configuration is then compared with the current reference option, i.e. the NASA Space Launch System adopted as cislunar delivery vehicle.