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Tracking Stations

Tracking Stations

One of the key elements of spaceflight is the ability to track spacecraft and obtain telemetry that informs ground controllers of the condition of spacecraft and crew. Ground-based "tracking stations" play a key role in these functions, providing tracking and data acquisition services for vehicles in deep space and high Earth orbit and for certain missions in low Earth orbit . These networks of ground stations also supply launch and emergency communications for human missions in space and tracking and data acquisition for aeronautics, balloons, and sounding rocket programs.

The early years of the space age were marked by the creation of integrated networks of tracking stations that dotted the globe. Tracking ships were also built to provide additional coverage across oceans. In addition, special aircraft were deployed around the world to track various spacecraft. For the National Aeronautics and Space Administration (NASA), the launch of the Tracking and Data Relay Satellite System significantly reduced the number of stations needed to track space missions. Nevertheless, tracking stations still play a very important part in space activity. Today, the Ground Networks Program has responsibility for managing the tracking stations that comprise NASA's Space Flight Tracking and Data Network (STDN) and the Deep Space Network (DSN), the latter of which is supervised by the Jet Propulsion Laboratory (JPL).

For over thirty years elements of the STDN have supported robotic scientific missions as well as the human spaceflight program. Today, the STDN complex of tracking stations at Merritt Island, Florida, and on Bermuda provides real-time voice, telemetry (data), and command communications to the space shuttle, and furnishes launch support for expendable launch vehicles . The Merritt Island tracking facility contains thirteen antennas that track or point directly at the radio signals transmitted from a moving space vehicle. A ranging signal transmitted to the spacecraft establishes the distance by how long the two-way trip takes.

NASA's Deep Space Network is the largest and most sensitive scientific tracking and communications system and the most precise radio navigation network in the world. Its principal responsibilities are to support interplanetary spacecraft missions and radio and radar astronomy observations. The forerunner of the DSN was established in 1958, when JPL, then under contract to the U.S. Army, deployed portable radio tracking stations to receive telemetry and track the orbit of Explorer 1, the first successful U.S. satellite. Since 1958, the DSN has provided support for more than seventy robotic Earth-orbiting, lunar, and planetary spacecraft.

The DSN is comprised of three complexes located in Australia, Spain, and Goldstone, California. Located around the world approximately 120 degrees apart in longitude, the facilities allow continuous coverage of distant spacecraft or interplanetary objects. Each station has one antenna 70 meters (230 feet) in diameter, plus several smaller ones, with the antennas capable of transmitting and receiving data from interplanetary and Earth-orbiting spacecraft. The antennas can be operated separately or can be combined together electronically (in a process called "arraying") to form a larger aperture (essentially an enormous virtual dish) to receive very weak signals from distant or impaired missions (such as the Galileo spacecraft).

The DSN stations have the capability to acquire, process, decode, and distribute data from deep space probes and Earth orbiters while also sending signals to control the activities of spacecraft. The DSN has also contributed to our knowledge of the solar system through radio frequency experiments performed between spacecraft and the DSN radio science system. Experiments have allowed scientists to characterize planetary atmospheres and ionospheres, planetary surfaces, and rings.

From the late 1950s to the early twenty-first century, the mission of Earth-bound tracking stations has expanded from tracing the paths of satellites to include space research and communication, command, and navigation of spacecraft beyond low Earth orbit. Tracking stations will continue to have a major role in space activities and will have their capabilities upgraded as more spacecraft are launched and technical demands grow.

see also Navigation (volume 3); Tracking of Spacecraft (volume 3).

John F. Kross

Bibliography

Cortright, Edgar M., ed. Apollo Expeditions to the Moon. Washington, DC: National Aeronautics and Space Administration, 1975.

Lewis, Richard S. Appointment on the Moon. New York: Viking Press, 1968.

Oberg, James E. The New Race for Space. Harrisburg, PA: Stackpole Books, 1984.

Shelton, William R. Man's Conquest of Space. Washington, DC: National Geographic Society, 1975.

Internet Resources

Deep Space Network. Jet Propulsion Laboratory. <http://deepspace.jpl.nasa.gov/dsn/>.

"Office of Space Communications: Program Overview." National Aeronautics and Space Administration. <http://www.hq.nasa.gov/office/spacecom/GndNet.html>.

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