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Communicating With Farthest Space
How the Deep Space Network receives radio broadcasts from the edge of the Solar System
Spring 2006 | Volume 21, Issue 4
“It’s like watching grass grow,” says Douglas Mudgway, a longtime engineer and now the historian of NASA’s Deep Space Network. “There’s not very much drama attached to a big antenna tracking a spacecraft millions of miles away. You can’t even see it move. There’s absolutely nothing to see except blinking red lights and guys sitting around drinking coffee and wishing they were somewhere else.”
However, millions of dollars, countless hours of human effort, and irreplaceable scientific knowledge all depend on those people sitting in that control room, monitoring the great antenna dishes outside that loom over the desert like ancient monuments. They’re at one end of an invisible line of communication stretching to the edge of infinity. All the magnificent visions of the planets that our unmanned explorers have brought us from the depths of the solar system, every bit of data collected by the Pioneers and Mariners and Voyagers and Cassinis, all of it first reached Earth as a whisper of photons caressing the face of an antenna dish. For more than 40 years now, maintaining that communication has been the mission of the Deep Space Network, a worldwide system that routinely traffics in the weakest, faintest, and longest-distance calls ever.
Before the space age dawned, in the late 1950s, the idea of sending messages between Earth and deep space was the stuff of science fiction and fringe obsessions. But it became obvious that some means of communicating with spacecraft would be needed. The first steps toward it were made by the military, which was working on intercontinental missiles and needed facilities for tracking and guidance.
In the early 1950s the California Institute of Technology’s Jet Propulsion Laboratory (JPL) was developing such facilities at the White Sands Missile Range for the Army’s Corporal and Sergeant missiles. A team of intensely dedicated engineers, led by Eberhardt Rechtin, created a network called Microlock, a series of ground stations featuring ingenious receivers that could compensate for the shifting frequencies transmitted by moving rockets with a technique known as the phase-locked loop. As perfected by Rechtin and his colleagues Richard Jaffe and Walter Victor, the phase-locked loop system would be the key for communicating to the edge of the solar system.
When America began sending satellites into orbit after the shock of Sputnik , in 1957, Microlock was hastily expanded to include tracking stations in San Diego, Cape Canaveral, Singapore, and Nigeria, from which it followed the Explorer satellites. Some of its equipment was far from sophisticated. “We used little hand-held machines to listen to the satellites,” Rechtin recalls.
But the equipment scaled up rapidly. By mid-1958, as the Pioneer space probes were being readied for America’s first attempts to reach the moon, Rechtin and his team were constructing an 85-foot aluminum parabolic dish on government property in the Mojave Desert in California. Named the Goldstone Pioneer station and built by the Blaw-Knox Company, of Pittsburgh, Pennsylvania, it became the first station of Microlock’s successor, which would be called the Deep Space Instrumentation Facility (DSIF).
The Pioneer station was essentially a radio astronomy antenna based on the Cassegrain system, a configuration already used in many optical astronomy telescopes. Incoming radio waves were reflected by a parabolic main dish to a secondary reflector above the center of the antenna, and the subreflector then bounced the signal down to the focal point of the big dish (reversing the process when the antenna was transmitting). Such a design allowed the antenna’s heavy, bulky electronic transmitting and receiving equipment to be conveniently mounted at the structure’s center of gravity. Modified by two JPL engineers, William Merrick and Robertson Stevens, the antenna used a precision servo-controlled drive mechanism to keep itself pointed at a moving spacecraft, while Rechtin’s supersensitive receivers sifted the spacecraft’s faint voice out of the background radio noise of the cosmos.