Customarily, the direction in which the high-gain antenna points is referred to as the “fore” (also, +z) direction,
whereas the direction towards the “bottom” of the spacecraft is referred to as the “aft” (also -z) direction.
Note that most of the time, the spacecraft is, in fact, traveling in the aft direction, as the HGA is pointing in
the general direction towards the Earth, in a direction opposite to the direction of travel (especially in deep
space).