1. The establishment of the spacecraft’s velocity and position relative to the Earth, Venus, and the Sun with high precision. 2. The transmission of commands to activate spacecraft maneuvers. 3. The reception of readable spacecraft engineering and scientific data from the far-ranging Mariner. The tracking network had to contend with many radio noise sources: the noise from the solar system and from extragalactic origins; noise originating from the Earth and its atmosphere; and the inherent interference originating in the receiving equipment. These problems were solved by using advanced high-gain antennas and ultra-stable, extremely sensitive receiving equipment. DEEP SPACE INSTRUMENTATION FACILITY The National Aeronautics and Space Administration has constructed a network of deep-space tracking stations for lunar and planetary exploration missions. In order to provide continuous, 24-hour coverage, three stations were built, approximately 120 degrees of longitude apart, around the world: at Goldstone in the California desert, near Johannesburg in South Africa, and at Woomera in the south-central Australian desert. [Illustration: _The three tracking stations of the Deep Space Instrumentation Facility are located around the world so as to provide continuous flight coverage._] These stations are the basic elements of the Deep Space Instrumentation Facility (DSIF). In addition, a mobile tracking station installed in vans is used near the point of injection of a spacecraft into an Earth-escape trajectory to assist the permanent stations in finding the spacecraft and to acquire tracking data. The control point for the DSIF net is located at JPL in Pasadena, California (see Table 1). The Jet Propulsion Laboratory has the responsibility for the technical direction of the entire DSIF net and operates the Goldstone facilities with assistance from the Bendix Corporation as a subcontractor. The overseas stations are staffed and operated by agencies of the Republic of South Africa and the Commonwealth of Australia. The DSIF net tracks the position and velocity of U.S. deep-space probes, issues commands to direct the spacecraft in flight, receives engineering and scientific data from the probes, and automatically relays the data to JPL in Pasadena, where it is processed by computers and interpreted. (In the tracking operation, a signal is transmitted to the spacecraft, where it is received and processed in a transponder, which then sends the signal back to the Earth. The change in frequency, known as the doppler effect, involved in this operation enables engineers to determine the velocity at which the spacecraft is moving.) _Table 1. Deep Space Instrumentation Facility Stations_ _Station_ _Location_ _Equipment_ _Functions_