Picture Album of the
DEEP SPACE NETWORK

70-Meter Antenna Conversion Project

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Voyager's successful encounters with Jupiter and Saturn demonstrated the feasibility of encounters with Uranus and Neptune. However, the spacecraft communications systems would not be capable of significant science or imaging data return without enhancement of the ground system. Studies initiated in 1980 indicated that two directions could be followed: (1) extend the 64-meter antennas at the Mars subnet to 70 meters or (2) enlist the assistance of the great radio observatories of the world to combine the signals of their antennas with those of the network. The decision to extend the antennas was based on technology and economics and on the fact that the resulting enhanced sensitivity would improve array performance with existing 34-meter antennas.

From December 1982 to August 1988 the three 64-meter antennas of the Mars subnet at Goldstone, Spain, and Australia were extended to 70 meters. This effort included the design, fabrication, and installation of the structural modifications to support the additional diameter; additional counterweight; a new, high-precision surface; a new, low-profile quadripod; and a larger, high-precision subreflector.

To minimize the time that the antennas would be out of service, the quadripod, subreflector, surface panels, and new rib assemblies for the outer half of the reflector structure were prefabricated. Six months of downtime was required to strip off the old structure, reinforce the remaining structure, install the new modified structural elements, perform the necessary alignments and tests, and measure performance.

The quadripod was preassembled and aligned on the ground, then placed on the antenna as a single assembly, as seen in the upper left. This photo shows the antenna in Spain, with all of the outer portion of the reflector structure removed. The photo in the upper right shows one of the rib subassemblies being prepared for installation on the antenna at Goldstone. Several rib subassemblies have already been installed on the antenna in the background. The 18-story scaffold at Goldstone was the largest freestanding scaffold ever built in the United States and included an elevator to transport people and equipment. The antenna structure was rotated as each subassembly was positioned so that the workers had a place from which to work.

The photo in the lower left shows the crane positioning one of the rib subassemblies at the Australian antenna. With the new precision-bonded panels installed and aligned, the overall accuracy of the radio frequency optical system is 0.6 millimeters (0.023 inches) root-mean-square.

The photo in the lower right shows the subreflector being machined. A new subreflector design was required because of the larger main reflector and because the main reflector was to be "shaped" rather than parabolic. This cast aluminum subreflector is 7.8 meters (25.6 feet) in diameter and weighs 6000 kilograms (13,200 pounds). The asymmetrical surface is machined to an accuracy of 0.15 millimeters (0.006 inches).

The average improvement in performance of the three stations of the subnet is over 2 decibels at X-band. This very significant performance increase was vital for the return of science data during Voyager's successful encounters with Uranus and Neptune. It also extended the useful range of communications for Pioneer 10 from about 50 astronomical units to about 60 astronomical units at S-band. The increased sensitivity enhances both radio science and planetary radar experiments. The completed antenna near Madrid is shown in the center photo.

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