Deep Space Communications Complexes
The DSN consists of three Deep Space Communications Complexes, each located on a different continent. There is a complex at Goldstone in Southern California's Mojave Desert, another near Madrid, Spain, and a third near Canberra, Australia. The sites are far from heavily populated areas so that the very faint signals from distant spacecraft are not contaminated or obscured by radio interference from such sources as power lines, radio and television stations, and household and industrial appliances.
Each complex consists of several deep space stations equipped with large, steerable parabolic reflector antennas and ultrasensitive receiving systems. The "flagship" antenna of the DSN is 70 meters (230 feet) in diameter - there is one at each of the three complexes. Expanding mission requirements and technology advancements have led to development and commissioning of newer 34-meter (112-foot) diameter high-efficiency and beam waveguide antennas at all three complexes.
The DSN's Earth-based communications network is an essential component for controlling a spacecraft's operating modes, loading and reprogramming the onboard computers, navigating the spacecraft to its destination, and sending scientific data back to Earth. The two-way communications link between Earth and the spacecraft consists of two typs of data; uplink and downlink (telemetry). Uplink includes commands, which are coded instructions sent from Earth to control the spacecraft's operating modes, and new mission software. Telemetry (downlink) consists of science information "housekeeping" status data sent from spacecraft back to earth. The link itself is used to generate information about the position of the spacecraft.
To provide for continuous communications if the spacecraft requires it, the complexes are located to compensate for Earth's daily rotation by being situated approximately 120 degrees apart in longitude. This arrangement provides an 8- to 14-hour view of the spacecraft at each complex plus suitable overlap for transferring contact with the spacecraft from one complex to the next.
The activities of the three complexes are coordinated and monitored at the Deep Space Operations Control Center at JPL.