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 L-4 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. (C) 2015 COSPAR. Published by Elsevier Ltd. All rights reserved.