How does NASA communicate with spacecraft?
Radio waves almost always travel through space in a straight line. There are two exceptions. One is that radio waves are pulled and turn slightly because of gravity when they pass by large masses. The other exception is that radio waves can be reflected by certain substances, like the way that light is reflected by a mirror. The angle at which a radio wave is reflected from a smooth metal surface (also called the angle of reflectance) is always equal to the angle at which it approached the surface (also called the angle of incidence). Take a look at the picture below.
Figure from NASA's Jet Propulsion Laboratory's publication: Basics of Space Flight Learner's Workbook. http://www-b.jpl.nasa.gov/basics/
Reflectance is used to great advantage in designing the antennas that collect radio signals.
What are radio waves?
How is data put on radio waves?
What could go wrong with communications?
What interferes with radio waves?
How does DS1's communications system work?
What kinds of antennas are there?
What are high and low gain?
How do you make a radio wave?