Distance to the Sun during the closest approach for ISD particles with β = 1.6 and Q/m = 0, i.e. their closest distance to the Sun projected on a plane. The axes show the original position of the ISD particles in AU, in the ISD frame, while the numbers in the contour lines show their closest approach distances. The dotted lines are the reference case where β = 1 and Q/m = 0 (particles fly in straight lines, so the dotted contour lines are circles). The particles are “pushed away” by solar radiation pressure force, so less space is needed on the starting grid to investigate a certain area in the solar system.