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D'Amario and Edelbaum (ref.27) have studied trajectories to L2, originating tangentially to the lunar surface in low lunar orbit. Such trajectories are those of concern for transport of lunar material. Their work was performed in the circular restricted three-body problem. The results are shown in figure 5-30.

The trajectories fall into two classes: "fast" transfers e. and "slow" transfers. The latter involve looped trajectories and transfer times over 200 hr. While they lead to arrival at L2 with velocities of only 100 m/s, approximately, they appear quite sensitive to small errors at launch and so are not of interest. The "fast" transfers involve transfer times under 100 hr and arrival velocities of approximately 200 m/s. Sensitivities of such orbits may be studied, at least when orders of magnitude only are of concern, by considering the transfer trajectories as conic sections in the two-body problem. A dynamic equilibrium may be sought between acceleration due to gravity and acceleration due to momentum flux. The equilibrium is unstable; nevertheless, the stationkeeping requirements associated with stabilizing the equilibrium may be much less than those associated with nulling out a momentum flux by continuous thrusting.

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