Well, aerospace is space engineering with an aeronautical flavour, while mechatronics (space) is space engineering with a mechatronic flavour. Generally, both do the basic aero courses, and space courses, and aerospace has more aeronautical aspects, and mechatronic has more mechanical/electronic/mechatronic aspects to it.
AFAIK, in first semsester of first semester, the two degrees have identical courses/units of study.
If you want to know more, a good place to go is the 2005 USyd faculty of engineering handbook - it outlines the units of study for all engineering courses, and offers good info for comparing the two courses.
Regards
Antarctic