  Thirty-six million miles separated the Earth from Venus at encounter. Communicating with Mariner II and tracking it out to this distance, and beyond, represented a tremendous extension of man’s ability to probe interplanetary space. The problem involved:
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 FACILITYThe National Aeronautics and Space Administration has constructed a network of deep-space tracking stations for lunar and planetary exploration 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 Table 1. Deep Space Instrumentation Facility Stations
The stations are equipped with receiving and tracking instruments so sensitive that engineers estimate that they can detect radio-frequency energy equivalent to that radiated by a 1-watt light bulb at a distance of approximately 75 to 80 million miles. Such energy received at the antenna would measure about 0.00000000000000000002 watt (2 × 10?²). The amount of power received at the antenna during Mariner’s encounter with Venus has been calculated at about 0.000000000000000001 of a watt (1 × 10?¹8). If a 100 percent efficient storage battery were charged with this amount of energy for some 30 billion years, the battery would then have stored enough energy to light an ordinary 1-watt flashlight bulb for about 1 second only. Furthermore, Goldstone engineers estimate that, if Mariner II had continued to function in all its systems and to point its directional antenna at the Earth, useful telemetry data could have been obtained by the DSIF stations out to about 150 to 200 million miles, and tracking data could have been secured from as far as 300 to 400 million miles. Construction of the DSIF net was begun in 1958. The Goldstone station was ready for the Pioneer III mission in December of that year. In March, 1959, Pioneer IV was successfully tracked beyond the Moon. Later in 1959, Pioneer V was tracked out to over 3 million miles. Goldstone participated in the 1960 Project Echo communication satellite experiments and the entire net was used in the Ranger lunar missions of 1961-1962. The Goldstone station performed Venus radar experiments in 1961 and 1962 to determine the astronomical unit more precisely and to study the rotation rate and surface characteristics of the planet. Following the launch of Mariner II on August 27, 1962, the full DSIF net provided 24-hour-per-day tracking coverage throughout the mission except for a few days during the cruise phase. The net remained on the full-coverage schedule through the period of Venus encounter on December 14. THE GOLDSTONE COMPLEXThe tracking antennas clustered in a 7-mile radius near Goldstone Dry Lake, California, are the central complex of the DSIF net. Three tracking sites are included in the Goldstone Station: Pioneer Site (DSIF 2), Echo Site (DSIF 3), and Venus Site. The Venus Site is used for advanced Pioneer Site has an 85-foot-diameter parabolic reflector antenna and the necessary radio tracking, receiving, and data recording equipment. The antenna can be pointed to within better than 0.02 of a degree. The antenna has one (hour-angle) axis parallel to the polar axis of the Earth, and the other (declination) axis perpendicular to the polar axis and parallel to the equatorial plane of the Earth. This “polar-mount” feature permits tracking on only one axis without moving the other. The antenna weighs about 240 tons but can be rotated easily at a maximum rate of 1 degree per second. The minimum tracking rate or antenna swing (0.250686486 degree per minute) is equal to the rotation rate of the Earth. Two drive motors working simultaneously but at different speeds provide an antibacklash safety factor. The antenna can operate safely in high winds. The Pioneer antenna has a type of feed system (Cassegrain) that is essentially similar to that used in many large reflector telescopes. A convex cone is mounted at the center of the main dish. A received signal is gathered by the main dish and the cone, reflected to a subreflector on a quadripod, where the energy is concentrated in a narrow beam and reflected back to the feed collector point on the main dish. The Cassegrain feed system lowers the noise picked up by the antenna by reducing interference from the back of the antenna, and permits more convenient location of components. The receiving system at Pioneer Site is also equipped with a low-noise, extremely sensitive installation combining a parametric amplifier and a maser. The parametric amplifier is a device that is “pumped” or excited by microwave energy in such a way that, when an incoming signal is at its maximum, the effect is such that the “pumped-in” energy augments the original strength of the incoming signal. At the same time, the parametric amplifier reduces the receiving system’s own electronic noise to such a point that the spacecraft can be tracked twice as far as before. The maser uses a synthetic ruby mixed with chromium and is maintained at the temperature of liquid helium—about 4.7 degrees K or -450 degrees F (just above absolute zero)—and when “pumped” with a microwave field, the molecular energy levels of the maser material are redistributed so as to again improve the signal amplification while lowering The antenna output at Pioneer is a wide-band telemetering channel. In addition, the antenna can be aimed automatically, using its own “error signals.” At both the Pioneer and Echo sites at Goldstone, however, the antenna is pointed by a punched tape prepared by a special-purpose computer at JPL and transmitted to Goldstone by teletype. Pioneer Site has a highly sensitive receiver designed to receive a continuous wave signal in a narrow frequency band in the 960-megacycle range. The site has equipment for recording tracking data for use by computers in determining accurate spacecraft position and velocity. The instrumentation equipment also includes electronic signal processing devices, magnetic-tape recorders, oscillographs, and other supplementary receiving equipment. The telemetered data can be decommutated (recovered from a signal shared by several measurements on a time basis), encoded, and transmitted by teletype in real time (as received from the spacecraft) to JPL. Echo Site is the primary installation in the Goldstone complex and has antenna and instrumentation facilities identical to those at Pioneer, except that there is no maser amplifier and a simpler feed system is used instead of the Cassegrain. However, Echo was used as a transmitting facility and only as a stand-by receiving station during the Mariner mission. Echo has a 10-kilowatt, 890-megacycle transmitter which was utilized for sending commands to the Mariner spacecraft. In addition, the site has an “atomic clock” frequency standard, based on the atomic vibrations of rhubidium, which permits high-precision measurements of the radial velocity of the spacecraft. A unit in the Echo system provides for “readback” and “confirmation” by the spacecraft of commands transmitted to it. In a sense, the spacecraft acknowledges receipt of the commands before executing them. Walter E. Larkin manages the Goldstone Station for JPL. THE WOOMERA STATIONThe Woomera, Australia, Station (DSIF 4), managed by William Mettyear for the Australian Department of Supply, has essentially the same antenna and tracking capabilities as Goldstone Echo Site, but it has no provisions for commanding the spacecraft. A small transmitter is used for tracking purposes only. The station is staffed and operated by the Australian Department of Supply. The Mobile Tracking Station (DSIF 1) follows the fast-moving spacecraft during its first low-altitude pass over South Africa. Station 5 of the DSIF is located near Johannesburg in South Africa. DSIF 4, at Woomera, dominates the landscape in Australia’s “outback.” Woomera, like Johannesburg, is capable of receiving tracking (position and velocity) data and telemetered information for real-time transmission by radio teletype to JPL. THE JOHANNESBURG STATIONDSIF 5 is located just outside Johannesburg in the Republic of South Africa. This station is staffed by the National Institute of Telecommunications Research (NITR) of the South African Council for Scientific and Industrial Research and managed by Douglas Hogg. The antenna and receiving equipment are identical to the Goldstone Echo Site installation except for minor details. The station has both transmitting and receiving capability and can send commands to the spacecraft. Recorded tracking and telemetered data are transmitted in real time to JPL by radio teletype. MOBILE TRACKING STATIONThe Mobile Tracking Station (DSIF 1) is a movable installation designed for emplacement near the point of injection of a space probe to assist the permanent stations in early acquisition of the spacecraft. This station is necessary because at this point the spacecraft is relatively low in altitude and consequently appears to move very fast across the sky. The Mobile Tracking Station has a fast-tracking antenna for use under these conditions. DSIF 1 was located near the South African station for Mariner II. It has a 10-foot parabolic antenna capable of tracking at a 10-degree-per-second rate. A 25-watt, 890-megacycle transmitter is used for obtaining tracking information. A diplexer permits simultaneous transmission and reception on the same antenna without interference. The equipment is installed in mobile vans so that the station can be operated in remote areas. The antenna is enclosed in a plastic dome and is mounted on a modified radar pedestal. The radome is inflatable with air and protects the antenna from wind and weather conditions. These stations of the DSIF tracked Mariner II in flight and sent commands to the spacecraft for the execution of maneuvers. The telemetry data received from the spacecraft during the 129 days of its mission were recorded and transmitted to JPL, where the information was processed and reduced by the computers of the space flight operations complex. |
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