Antenna arraying combines the signals received by multiple antennas at different locations to function as a single large antenna. Arraying is commonly used to improve reception of weak signals. The technique is beneficial in deep space communications where the signal transmitted by a spacecraft becomes very weak as it travels across vast interplanetary distances.
When a spacecraft's signal reaches Earth, it is spread over a wide area, so a single antenna only intercepts a small part of it. Arraying allows more of the weak signal to be captured and enables higher data rates.
The Deep Space Network first used arraying for missions in the early 1970s. Experiments with a prototype arraying system for the 1979 Voyager encounters at Jupiter and the Pioneer 11 encounter with Saturn told engineers a great deal about how to gain increased sensitivity. All three DSN complexes then made intensive use of arrayed configurations for the Voyager encounters with Saturn in 1980 and 1981.
By the time Voyager 2 flew by Uranus in 1986, the DSN was combining signals from up to four antennas. For the spacecraft's Neptune encounter three years later, the DSN combined signals from Australia's Parkes Radio Telescope into the Canberra complex, and combined signals from the 27 antennas of the Very Large Array (VLA) in New Mexico into the Goldstone array.
A Triumph for Galileo
The Galileo mission to Jupiter employed arraying in 1996 and 1997 to increase the amount of science data that mission, with its crippled high-gain antenna, could return. For Galileo, the DSN arrayed up to five antennas from three tracking facilities on two continents (specifically, Goldstone, Canberra and Parkes).
The result for Galileo was improved data return by a factor of three, compared to that of a single 70-meter (230-foot) antenna. Arraying, plus advances in data compression and encoding techniques, helped make Galileo so successful that its mission was extended to more than a dozen years of valuable observations of Jupiter and its moons.