Depends on what you want to learn about, a degree in astrophysics or aeronautial engineering prepares you for many different possible jobs. I'm in a somewhat similar situation, maybe this will help:

(DISCLAIMER: I am not an aerospace engineer by training)

Calculus:

You'll definitely need to be very comfortable with single variable calculus and vector calculus up to partial derivatives, vector calculus integrals (Green, Stokes, Gauss) will definitely help. I wouldn't learn that from a book, try MIT's OCW, there is a calculus course covering all that. Learn the basic about ODEs, and be comfortable around PDE notation.

Linear Algebra:

In some sub-disciplines such as control and signal processing you'll also need to be very comfortable with linear algebra, so that all those matrices and stuff don't get in the way when learning modern control/DSP. I definitely recommend Prof. Strang's course in OCW for this. Try to at least be comfortable with simple ODEs before starting it. Linear algebra also helps a lot with Physics.

To get more into lineal algebra maybe you can read Linear Algebra Done Right if you want to learn more about Hilbert Spaces, and then maybe Shilov for tensors... those two books should be optional...

Software:

You don't need to be fast or maybe even know how to solve complex integrals in pen and paper. Try to complement learning calculus, differential equations and linear algebra with learning Matlab/Simulink and Mathematica. I can't even find a word to emphasize how much Matlab/Simulink is used in aerospace engineering...

Dynamics:

Learn classical mechanics, lots of it. Be confortable with rigid body dynamics in 3D. This is the best reading guide I know about, oriented to game development, but also useful for simulation and control: http://chrishecker.com/Physics_references Code simulators, visualizations, etc... Know what rotation, nutation and precession are, when and how they happen, etc...

From that list I have read a little of Goldstein and some Symon. If you find this books too hard, don't follow the guide but instead jump directly to the Feynman lectures (if you want to read) or Physics I from OCW (Prof. Lewin course, really really good).

Physics II from OCW can also help, maybe.

Space:

Once you are not scared with simple problems from all the previous subjects and can solve them, and can understand complex ones you should have no trouble following the first chapters (about dynamics, orbital and attitude maneuvering, etc) of some classical but real space books, for example:

SMAD by Wertz, a really classical book for space engineering courses. You should really be able to read it cover to cover but its not a very specific book and more oriented torwards missions management. Sometimes it gets boring because of it lack of details.
http://www.amazon.com/Introduction-Space-Dynamics-Aeronautic...
http://www.amazon.com/Spacecraft-Dynamics-Control-Practical-...
http://www.amazon.com/Modern-Spacecraft-Dynamics-Control-Mar...

You can also browse here: http://astrobooks.com/ and see if you find something particularly interesting. I really would like to recommend a more engaging approach and less boring books, but this is the best that I can come up with now.

After you can comfortably read the first chapters of those space books you should really choose what to focus into. Dynamics, Simulation, Finite Element Analysis, Mechanics/Thermal engineering, Signal Processing, Control... then learn the basics of that discipline and then try to apply it to space exploration or spacecraft design. Each of this disciplines would need their own reply and reading list I guess... some require more physics than rigid body dynamics, like fluid dynamics or thermodynamics, electromagnetism, etc...

Also, as usual, try to have fun but still be disciplined about reading/learning.