Methods of Changing the Halo Orbit of a Spacecraft in Order to Approach Asteroids

The paper presents possible options for changing the orbit of the spacecraft operating near the Sun–Earth libration point for the purpose of carrying out a close passage of asteroids approaching the Earth. Two methods of constructing transfer trajectories to one or more celestial bodies are proposed: transferring the spacecraft from the initial bounded orbit in the vicinity of the L2 Sun–Earth libration point to the required one in the same vicinity and taking it to the Earth along the trajectory of an unstable manifold. Examples are provided in which the asteroids Apophis and 1997 XF11 are chosen as targets, the trajectories of which will pass near the spacecraft in 2029 and 2028, respectively. It is shown that under the existing fuel cost restrictions, the spacecraft can be redirected to the targeted asteroids by the proposed methods. According to the calculations, in all cases the spacecraft does not leave the near-Earth space, and, therefore, during or after the passage of the asteroid, it can be used in solving other scientific problems.