The Ground Stations

Communications Complexes

       Every U.S. space mission is designed to allow continuous radio communication with the spacecraft. Continuous 24-hour coverage for several in-flight deep space missions requires several Earth-based antenna stations at locations that compensate for the Earth's daily rotation. Because Earth is rotating at 0.004 degrees per second, all celestial bodies, including planetary spacecraft, rise in the east, travel slowly across the sky and set in the west.

       The network's complexes in Spain, Australia and California are located approximately 120° apart in longitude, which provides an 8 to 14 hour view period at each location which is suitable for overlap for transferring the spacecraft signal from one complex to the next.

       To shield against radio-frequency interference, each complex is located away from population centers in semi-mountainous, bowl-shaped terrain. The Australian complex is located 40 kilometers (25 miles) southwest of Canberra near the Tidbinbilla Nature Reserve. The Spanish complex is located at the Robledo de Chavella in the El Escorial region of central Spain, about 60 kilometers (37 miles) west of Madrid. The Goldstone complex is located inside the boundaries of the U.S. Army's Fort Irwin National Training Center in the Mojave Desert, approximately 72 kilometers (45 miles) north of the city of Barstow. The operations control center for the DSN, the Space Flight Operations Facility, is located at JPL's main facility in Pasadena, California.

       Each complex consists of four deep space stations equipped with large parabolic reflector antennas and ultrasensitive receiving systems. Each DSN station is comprised of the following antenna arrays:

• 0ne 70-meter-diameter (230-foot) antenna. These are the largest and most sensitive DSN antennas, and are capable of tracking spacecraft traveling more than 16 billion kilometers (10 million miles) from Earth. The giant antennas collect and amplify signals as weak as one 100-millionth of one 100-billionth of a watt, or approximately one thousand billion times weaker than a commercial television signal arriving at a home. The surface of the 70-meter reflector must remain accurate within a fraction of the signal wavelength, meaning that the precision across the 3,850-square-meter (4,600-square-yard) surface is maintained within 1 centimeter (0.4 inch). The dish reflector and its mount -- which move in the azimuth, or horizontally, as well as in elevation -- weigh nearly 2.7 million kilograms (8,000 tons).
• One 34-meter (110-foot) standard antenna which was originally constructed as a 26-meter (85-foot) antenna and later extended to 34 meters in preparation for missions to the outer planets. The mechanical design of the standard antenna is identical to that of radio astronomy antennas developed in the 1950s, in that the mount and pointing system is designed to track planetary spacecraft at the Earth's rotation rate (0.004° per second).
• There are also 34-meter high-efficiency antennas at each station. These antennas incorporate more recent advances in antenna design and mechanics. The mount is an azimuth-elevation type and operates in both axes at up to 0.40° per second. The reflector surface is precision-shaped for maximum signal capability.
• The other antennas at the DSN sites are 26-meters (85- feet) in diameter. Originally built to support the crewed Apollo missions to the Moon between 1967 and 1975, they are currently used for tracking Earth-orbiting satellites, most of which are in orbits 160 to 1,000 kilometers (100 to 620 miles) above Earth. The two-axis mount allows the antenna to point low on the horizon to pick up fast-moving Earth orbiters as soon as they come into view. The maximum tracking speed is 3° per second. The Earth orbiter schedule often includes receiving telemetry from as many as 15 satellites per day.
• Each station also maintains one 13-centimeter-diameter (5-inch) omnidirectional antenna that receives signals from Navstar satellites in the Defense Department's Global Positioning System (GPS). The DSN's navigation activities use GPS signals to measure Earth platform characteristics needed for generating deep-space navigation data and determining precise near-Earth satellite orbits.
• At the Goldstone station, there is an additional 9-meter-diameter (30-foot) antenna designed and primarily used for communicating with Earth-orbiting satellites, which have receiving and tracking requirements that are basically different from deep-space missions.

(Information provided by Deep Space Network - JPL)