In Aerospace Engineering involves made of different disciplines. Some of the them set the basics, others are always used. Yet, like in any other profession, some topics are only used in some specializations.
The two most important subjects are Math and Physics. You have to deal with complex equations in Aerospace Engineering problems. Math skills helps you solve the equations. Physics helps you understand the meaning of the equations.
Math and Physics are building blocks. Yet, other disciplines are also important. For example, Aerospace Engineering requires knowledge in Chemistry, Materials, Communications, Structures, Fluid Mechanics.
Aerospace Engineering can be very different depending on the specialization. For instance, the areas of specialization include Satellite Engineering, Orbital Analysis, Satellite Communications.