The identical U.S. interplanetary probes Voyager 1 and 2 were designed to explore the outer, giant planets of the solar system and their satellites. Voyager 1, launched from Kennedy Space Center on Sept. 5, 1977, made its closest approach to the cloud tops of Jupiter (272,000 km/170,000 mi) on Mar. 5, 1979, and to those of Saturn (126,000 km/78,000 mi) on Nov. 12, 1980. Voyager 2, launched on Aug. 20, 1977, on a slower and longer trajectory, made its closest approach to Jupiter (640,000 km/400,000 mi) on July 9, 1979, and to Saturn (101,000 km/63,000 mi) on Aug. 25, 1981. Voyager 1 then headed on a trajectory taking it above the plane of the solar system toward interstellar space. Voyager 2 sped toward an encounter with the planet Uranus, making its closest approach (80,000 km/50,000 mi) on Jan. 24, 1986. The probe then headed toward Neptune, making its closest approach to that planet (5,000 km/3,100 mi) on Aug. 25, 1989. It, too, then headed toward interstellar space, on a trajectory below the solar system's plane. Voyager data suggest that the "edge of the solar system"Ñthe heliopause, or outer limit of the Sun's magnetic influenceÑlies from 82 to 130 astronomical units out from the Sun. On Feb. 17, 1998, when it reached 70 astronomical units from the Sun, Voyager 1 exceeded the record of Pioneer 10 to become the most distant object to have been launched from Earth.The SpacecraftThe central part of each 815-kg (1,797-lb) Voyager is a 10-sided aluminum framework ring, about 45 cm (18 in) high and 179 cm (70 in) across. The ring contains 10 electronic packaging compartments and surrounds a titanium sphere filled with hydrazine propellant for the 16 maneuvering thrusters. Above the ring is a high-gain antenna dish, 3.7 m (12 ft) in diameter, capable of transmitting and receiving at two frequencies in the S and X bands. Each spacecraft is powered by 3 radioisotope thermoelectric generators.The scientific equipment on each probe comprises a radio transmitter and 10 experiment packages, most of them located on the scan platform boom. Voyager's optical scanners include a pair of television cameras, an infrared radiometer and interferometer-spectrometer, an ultraviolet spectrometer, and a photopolarimeter.
The 4 particle and field detectors measure interplanetary plasmas, low-energy charged particles, cosmic rays, and magnetic fields. Each probe also carries 4 magnetometers, plus a pair of 10-m-long (33-ft-long) antennas for studying planetary and plasma radio emissions.ResultsBoth Voyager probes have carried out their functions with great success during their planetary encounters, the results of which are described in the separate entries on the planets and their major satellites. Voyager 2, in particular, which was designed to operate at peak performance only through its Saturn encounter, required extensive reprogramming in order to maintain adequate data transmission as its distance from the Earth continued to increase. One change in performance was a process called data compression, which reduced by more than 50% the number of bits of data required to transmit an image. Because the probe had to pass through the tilted plane of Uranus's satellite system at great speed, it also had to be reprogrammed for rotation of the craft while the camera shutter remained open. NASA also employed two or more of its Deep Space Network antennas to reinforce the very faint signals from Voyager 2Ñroughly equivalent to the wattage of a refrigerator lightbulb.Messages to Extraterrestrial CivilizationsBecause of the remote possibility that either probe might be recovered by some extraterrestrial civilization, scientists attached to both probes an identical gold-coated record. Encoded there are 117 pictures of Earth and of human beings, greetings in 54 different languages, and a 90-minute selection of the world's music.