The Networks Division of Goddard Space Flight Center, Greenbelt, Md., is responsible for operating, maintaining and controlling the space flight tracking and data network, which consists of the space network and ground network for providing tracking, data acquisition and associated support. The network is operated through NASA contracts and interagency and international agreements that provide staffing and logistic support for space missions. The Networks Division also operates the Network Control Center and NASA Ground Terminal. The division is responsible for testing, calibration and configuring network resources to ensure network support capability before each mission. It coordinates, schedules and directs all network activity and provides the necessary interface among GSFC elements and other agencies, centers and networks.

The STDN, controlled by the NCC at Goddard, is composed of the White Sands Ground Terminal and NASA Ground Terminal in White Sands, N.M.; the NASA Communications Network, Flight Dynamics Facility and Simulation Operations Center at GSFC; and the ground network. These elements are linked by voice and data communication services provided by Nascom. The prime operational communications data are formatted into 4,800-bit blocks and transmitted on the Nascom wide-band data and message switching system. Other communications are transmitted by teletype and facsimile facilities.

The Tracking and Data Relay Satellite system will consist of two Tracking and Data Relay satellites in geosynchronous orbit (130 degrees apart in longitude), an on-orbit spare, and a ground terminal facility (located at White Sands). The TDRS can transmit and receive data and track a user spacecraft in a low Earth orbit for a minimum of 85 percent of its orbit. TDRSS telecommunication services to and from the user's control and data processing facilities operate in a real-time, bent-pipe mode.

The White Sands Ground Terminal contains the ground terminal communications relay equipment for the command, telemetry, tracking and control equipment of the TDRSS. The NASA Ground Terminal is colocated with WSGT. The NGT is managed and operated by the Networks Division and, in combination with Nascom, is NASA's physical and electrical interface with the TDRSS. The NGT provides the interfaces with the common carrier, monitors the quality of the service from the TDRSS, and remotes data quality to the NCC.

Goddard's ground tracking stations for various communications are located throughout the world:

Also supporting the STDN are several instrumented United States Air Force aircraft, referred to as advanced range instrumentation aircraft, that are situated upon request at various locations around the world where ground stations cannot support space shuttle missions.

The various antennas at each STDN site accomplish a specific task, usually in a specific frequency band. Functioning like giant electronic magnifying glasses, the larger antennas absorb radiated electronic signals transmitted by spacecraft in a radio form called telemetry.

The Nascom Division at Goddard is responsible for providing an operational telecommunication network for all NASA programs and projects. The Nascom network is a worldwide complex of communications services, including data, voice, teletype and television systems that are a mixture of government-owned and leased equipment as well as leased services. Nascom is responsible for the operations, maintenance and testing required to provide optimum service to the users. The major switching centers in Nascom are located at GSFC; the Jet Propulsion Laboratory in Pasadena, Calif.; Cape Canaveral, Fla.; Canberra, Australia; and Madrid, Spain.

This communication network is composed of telephone, microwave, radio, submarine cables and communication satellites. These various systems link the data flow through 11 countries of the free world with 15 foreign and domestic carriers and provide the required information between tracking sites and Johnson Space Center (Houston, Texas) and Goddard control centers. Special wide-band and video circuitry is used as needed. GSFC has the largest wide-band system in existence.

Included in the equipment of the worldwide STDN are numerous computers located at the different stations that control tracking antennas, handle commands and process data for transmission to the JSC and GSFC control centers. Shuttle data from all the tracking stations are funneled into the main switching computers at GSFC and rerouted to JSC without delay by domestic communications satellites. Commands generated at JSC are transmitted to the main switching computers at GSFC and switched to the proper tracking station for transmission to the space shuttle.

If NASA's JSC Mission Control Center should be impaired for an extended period of time, an emergency control center would be established at NASA's ground terminal at White Sands and manned by NASA JSC personnel.

A station conferencing and monitoring arrangement allows various traffic managers to hold conferences with as many as 220 different voice terminals throughout the United States and abroad with talking and listening capability at the touch of a few buttons. The system is redundant, which accounts for its mission support reliability record of 99.6 percent. All space shuttle voice traffic is routed through this arrangement at GSFC.

Communication satellites electronically connect the Earth stations and permit transmission of 10 to 20 times more data. Ground terminals for domestic communications satellites are situated at JSC; Kauai, Hawaii; Goldstone, Calif.; Kennedy Space Center. Florida; NASA's Dryden Flight Research Facility, California; GSFC, Greenbelt, Md.; and White Sands, N.M.

The tracking station at Ponce de Leon Inlet, Fla. (near New Smyrna Beach), provides support during powered flight because of attenuation problems from the solid rocket booster motor plume.

The existing worldwide ground stations provide coverage for approximately 20 percent of a satellite's or spacecraft's orbit, limited to brief periods when the satellite or spacecraft is within the line of sight of a given tracking station.

A new era in space communication began with the STS-6 mission in April 1983, when the first Tracking and Data Relay Satellite was deployed. TDRS-A was the first of three identical satellites planned for the system. The TDRS system was developed after studies in the early 1970s showed that a telecommunication satellite system could support the projected scientific and application mission requirements better than ground stations and also could halt the spiraling cost of upgrading and operating a worldwide network of tracking and communication ground stations.