As Carl Sagan once said, "The sky calls to us. If we do not destroy ourselves, we will one day venture to the stars." And our first emissaries to the stars will be robotic probes. These interstellar probes will be largely autonomous, but we will want to communicate with them. At the very least, we will want them to phone home and tell us what they've discovered. The stars are distant, so the probes will need to make a very long-distance call.

Currently, we communicate with space probes throughout the solar system via the Deep Space Network (DSN). This is a collection of antenna stations located around the world. Each station has one large 70-meter dish and several smaller dishes. Such large radio dishes are necessary because the signals from a space probe are rather faint, and they grow fainter with increasing distance.

When we start sending probes to other stars, we're going to need an interstellar communication network.