Transfer orbits to the Earth-Moon triangular libration points

The particular positions and dynamics of the triangular libration points in the Earth-Moon system make them potential candidates for future space applications. Taking the leading L4 point as an example, this paper studies the transfer orbits to the vicinity of this equilibrium point. Two basic models are used: the circular restricted three-body problem (CRTBP) and the bi-circular problem (BCP). The order-three analytical solution of the motion around the triangular libration points in the CRTBP model is taken as the nominal orbit. Three different approaches are studied: direct transfer, transfer utilizing powered lunar gravity assist, and transfer utilizing the Sun's gravity. Lastly, low energy transfer orbits are extensively studied in the BCP model via a numerical approach. Our studies show that the total delta-v cost is considerably reduced if the Moon's gravity or the Sun's gravity can be used, at the cost of a longer transfer time. The delta-v cost and the time of flight (TOF) in our work are approximately: 3.90-4.40 km/s and 4-8 days for the direct transfer; 3.41-3.48 km/s and 18-52 days for the transfer utilizing powered lunar gravity assist; 3.33-3.40 km/s and 70-95 days for the transfer utilizing the Sun's gravity. For the low energy transfer orbits, the lower limit of the delta-v cost is around 3.10 km/s.