These stations plus certain of the other satellite network stations have been equipped with digital telemetry and command equipment in order to be able to handle the more complex and larger satellites.

It has also been necessary to improve the tracking capabilities of the satellite network to meet the requirements of certain satellites which are outside the capabilities of the existing system which is known as minitrack (fig. 227).

The existing minitrack system derives its tracking data output by measuring the angular position of a satellite passing through its field of view. Data from several passes are required in order to compute reasonably accurate orbital parameters. This means that several hours will elapse before an accurate orbit can be determined. This system is acceptable for low and medium altitude satellites. It is not adequate for satellites in highly eccentric orbits, however, where the satellite is at extreme altitudes and moves so slowly through the field of view of the minitrack system that its angular position cannot be measured accurately enough to compute an accurate orbit. The system also is not adequate to provide the tracking information required to place a satellite into a synchronous orbit or to meet station keeping requirements.

This additional capability is being achieved with an improved tracking system which is able to determine range and velocity of a satellite. A special transponder is required aboard the spacecraft and, therefore, because of weight consideration, is used only on those satellites that require such support. The range and velocity system is being implemented at selected stations of the satellite network. They are Rosman, Australia, southern Africa, Alaska, and Chile.

Tracking and data acquisition support for the applications satellite programs (meteorological and communications) concerns itself with basic satellite network tracking, acquiring of engineering data, and also the specialized ground support needed to carry out the meteorological and communications experiments.

Since 1960 the TIROS meteorological program has been operating very successfully (figure 228). Two stations have been used to provide most of the support for read out of the meteorological portion of this program, one at the Pacific Missile Range and one at Wallops Island, Va., are still operating satisfactorily. The station in Fairbanks, Alaska, is now also supporting TIROS. NIMBUS, the R. & D. version of the next generation meteorological satellite, will use the facilities installed at Fairbanks, Alaska, and Rosman, N.C. It is also planned to launch future TIROS satellites into polar orbit and these will be supported by Fairbanks, Alaska, as well as Wallops Island. Orbital tracking is supplied by the minitrack system of the satellite network.

Communications satellites such as ECHO, RELAY, TELSTAR, and SYNCOM are supported by two general types of ground facilities (fig. 229). The first are those which participate in the communications experiments primarily for the conduct of tests which are designed for an orderly advancement of space communications technology. The second are the satellite network stations providing support by acquiring data regarding the status of spacecraft and by transmitting commands to the spacecraft for stationkeeping purposes. For example, the commands transmitted to SYNCOM II to adjust its

synchronous orbit were transmitted from stations operated by NASA. Figure 229 lists contractors, Government agencies, station locations, and foreign countries participating in the various communications satellite experiment programs. The sources of tracking and data acquisition support are also shown on figure 229. Injection into synchronous orbit and stationkeeping of the SYNCOM-type satellites requires the accuracy and rapidity of tracking which is available with range and velocity tracking.

Deep space network

The lunar and planetary space missions (fig. 230) include ORBITER, RANGER, and SURVEYOR, the trajectories of which extend out to the Moon approximately one-quarter million miles from the Earth, and MARINER and PIONEER with trajectories extending out to planetary distances. The deep space network will provide the tracking and data acquisition support required for these missions. The bottom of the figure shows the time periods when network support of each type of mission will be required to meet current flight schedules. The length of the bar for SURVEYOR project, for example, indicates that the network must be prepared to support SURVEYOR flights during approximately a 12-year period of time. The composite lunar and planetary schedule shown here indicates the simultaneity of requirements approaching for tracking and data acquisition by the deep space network. This results in a significant increase in workload for deep space network facilities.

Network construction is underway (fig. 231) to duplicate the capabilities of the existing stations at Woomera, Australia, and Johannesburg, South Africa, with the addition of 85-foot antenna facilities at Canberra, Australia, and Madrid, Spain, both locations falling within the approximately 120° longitude spacing needed for continuous deep space coverage. Two facilities are needed at each longitude to meet the ground support requirements for simultaneous lunar and planetary missions. The second 85-foot antenna facility for Goldstone, Calif., is already operational.

Looking ahead to advanced planetary exploration with unmanned spacecraft, a prototype 210-foot antenna system is also under construction in Goldstone, Calif. Present planning indicates that two additional 210-foot installations, one at each of the other longitude locations, will be required for supporting future missions which will orbit or land on the planets.

The research and development work necessary to prove each significant improvement in the deep space network capability is carried on at Goldstone, Calif., under the direction of the Jet Propulsion Laboratory located in Pasadena, Calif.

Manned space flight network

The original manned space flight network was established to support the MERCURY program. Facilities were installed at the sites listed in figure 232. For the forthcoming GEMINI program, the stations in Muchea and Woomera in Australia are being replaced by a single station at Carnarvon, Australia. It was determined