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The Moon: Miracle in Sound

4 minute read

WITH remarkable clarity, the words reached the earth from a quarter of a million miles away in space. “Houston,” the distant voice announced, “Tranquillity Base here. The Eagle has landed.” Though somewhat overlooked in the drama of the lunar landing, the intricate electronics systems that brought Neil Armstrong’s voice back from the moon were almost as much of an engineering triumph as the rocketry that carried him there.

The long, electronic link with the earth started with tiny microphones carried inside the astronauts’ space helmets. Their voices were fed from the mikes into a small, 3-ft.-sq. box directly behind them in the lunar module. Despite its deceptively simple appearance, the 100-lb. package was the heart of the LM’s communications system. Known as a signal processor, it accepted the astronauts’ voices as well as 900 other signals—telemetric data on heartbeats, for example, pressure readings in the cabin, data from the computers—and imposed them on a single “carrier” frequency of 2,282.5 megahertz. An amplifier increased the signal’s power from half a watt to 20 watts, the strength of a small ham-radio transmitter. The 26-in. dish antenna, perched atop the LM, then beamed the signal to earth.

Traveling at the speed of light, the signal was picked up 1.3 sec later by the huge radio telescope at Goldstone, Calif., which has a dish-shaped antenna 210 ft. in diameter. Next, the signal was relayed to Goddard Space Flight Center near Washington, D.C., where the message was broken down into its individual parts and routed to Mission Control in Houston. The astronauts’ voices then traveled via ordinary telephone lines to radio and TV stations in New York for rebroadcast throughout the U.S. and the world. In one of the longest roundabout routes in the history of radio, Goldstone also relayed the voices back into space where they were picked up by Mike Collins in the command ship, some 70 miles above their source on the lunar surface. The reason for the round trip of nearly half a million miles: Collins was in direct radio line with the LM for only 15 minutes during each two-hour orbit of the moon.

Precise Synchronization

The system became still more complex after the astronauts stepped out of the LM and onto the moon. No longer hooked up with the cabin, Armstrong carried in his backpack a 61-lb. unit consisting of two transmitters and three receivers. The portable outfit sent his voice back to the LM, which then rebroadcast it to the world. Once Edwin Aldrin emerged from the cabin, he picked up Armstrong’s voice directly by means of a backpack receiver of his own. Aldrin’s voice, in turn, was broadcast to Armstrong by a tiny FM transmitter. It was Armstrong’s backpack equipment, however, that converted Aldrin’s voice back to a standard AM frequency, combined it with his own signal and fed it into the lunar module, which converted it back into FM for transmission to the earth. The intricate AM-FM system linking the two astronauts was devised to save the weight of an extra receiver in the LM.

The electronic wizardry was all the more impressive because the same carrier that transmitted voice signals to earth was made to handle TV as well. Although voices went to Goldstone, NASA technicians found that another 210-ft. dish antenna in Parkes, Australia, provided the best reception for the TV signal. From Parkes the signal was relayed overland to Sydney, flashed to the Moree Earth Station 200 miles to the north, beamed up to the Intelsat communications satellite 22,300 miles above the Pacific Ocean, relayed to Jamesburg, Calif., passed by microwave ground signal and coaxial cable to Houston and finally transmitted to New York for distribution to individual television sets. In spite of the separate systems and the incredibly circuitous routes, both sight and sound arrived in precise synchronization in millions of homes around the world.

The next lunar show should be even more spectacular. The $400,000-camera abandoned by Armstrong and Aldrin on the surface of the moon could transmit only in black and white. In the months ahead, NASA hopes to have ready a color camera capable of withstanding the extremes of lunar temperatures for the Apollo 12 flight in November.

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