Geometry of a close approach in the reference frame (x₁, x₃), where a gravitational acceleration effect is induced on the test masses, as described in Eq. (1). The blue line corresponds to the asteroid orbit, and the red line shows the LISA spacecraft. D corresponds to the magnitude of the shortest distance between the two orbits, and v presents the magnitude of the velocity of the asteroid when passing at the point of the shortest distance in its orbit.