Aerospace engineers may develop new technologies for use in aviation, defense systems, and spacecraft. They specialize in designing different types of aerospace products like commercial and military aircraft. They may also specialize in remotely piloted aircraft like drones. Aerospace engineers often become experts in more than one field. For example they can become an expert in aerodynamics, thermodynamics, celestial machines, flight mechanics, propulsion, acoustics, and guidance and control systems.
In short, aerospace engineers design primarily aircraft, spacecraft, satellites, missles. Also they test prototypes to make sure that they function according to their design.
Aerospace engineers typically specialize in either aeronautical engineering and astronautical engineering.
Aeronautical engineers work with aircraft. They are involved primarily in designing aircraft and propulsion systems and in studying the aerodynamic performance of the aircraft and construction materials. They work with the theory, technology, and practice of flight within the earth's atomosphere.
Astronautical engineers however work with science and the technology of spacecraft and how they perform inside and outside the earth's atmosphere.
Aeronautical and Astronautical engineers face different environmental and operational issues in designing their craft. However the two fields overlap a great deal due to their dependence of the basics of physics.