When spacecraft are sent to orbit other planets, the main thrust is all at the beginning when leaving the origin planet's orbit. The trajectory is calculated so that the spacecraft will enter orbit of the destination planet. A retro burn using the main thruster, and small course corrections to enter the orbital entry window are made using maneuvering thrusters. There isn't a range restriction after leaving the origin planet's orbit. The factors are speed, distance and time. I think the range restriction should be removed, but for the sake of speeding things up the time to travel from one