What are satellites made of?
If you mean man-made satellites ... Traditionally the main
structure has been made of aluminum, although many now are some
sort of composite. Usually it's some sort of graphite
fiber-polycyanate face sheet over aluminum honeycomb, though it
varies a lot by manufacturer and application. Polycyanate is
preferred to epoxies for the matrix because it doesn't shrink as
much when it loses moisture. There's a lot of other stuff in there.
Propellant tanks are usually titanium, while other propellant
components like lines and engines are typically steel. Housings for
electronics are usually aluminum.