NASA's Deep Space Network (DSN) is a world-wide network of large antennas and communications facilities. Components of this network are located in the U.S., Spain and Australia. Its primary function is to support interplanetary space missions. Secondary applications include radio and radar astronomy observations and support for certain low-orbiting satellite missions. While this network is operated by the Jet Propulsion Laboratory (JPL), there are other deep space networks that are operated by Europe, Russia, China, India and Japan.

DSN's three deep-space communications facilities are placed about 120 degrees apart around the Earth, allowing continuous observations of almost any area of space as the Earth rotates. The domestic facility is the Goldstone Deep Space Communications Complex near Barstow, California. The Spanish facility is near Madrid. And, the Australian complex is near Canberra. These facilities are located in places that shield against radio frequency interference, in other words, isolated mountainous areas.

The DSN is essential to solar system exploration spacecraft, because it provides two-way communications links between Earth and planetary probes as they travel to planets such as Mars Jupiter and Saturn. Not only are data and images received via the DSN, but commands are sent from the network to individual spacecraft in order to implement course corrections and to control functions onboard the vehicles, even as they travel hundreds of millions of km from home.

All of the huge DSN antennas must be high-gain, steerable parabolic antennas. In addition, they must use frequencies that have been set aside for deep space use by the International Telecommunications Union (ITU). The frequency bands for deep space are for use at distances of over two million km from the Earth's surface. Thus, missions to the Moon and Earth-Sun Lagrangian points, L1 and L2, are considered near space and cannot use the deep space frequency bands.

An interesting footnote in DSN history is the fact that this network also supported communications and tracking functions for the Apollo lunar missions. Although primary responsibility for Apollo flights was held by the Manned Space Flight Network, the DSN provided redundancy and additional capability for communications and tracking of both the lunar orbiter and the lander at the same time.