The Soviet deep-space Zond probes consisted of two types of spacecraftÑan interplanetary series (1962Ð65) and a lunar flyby and return series (1968Ð70). Zond, or sonde, means "probe" in Russian and is related to the English term sounding rocket. A series of embarrassing failures in the Mars and Venera planetary probes that were launched from 1960 to 1963 prompted Soviet space officials to launch probes to Mars and Venus under the project name Zond, in order that subsequent failures would not be connected with any particular planet. Zond 1 was launched toward Venus on Apr. 2, 1964, and Zond 2 was launched toward Mars on November 30 of the same year. Both probes, however, failed in flight because of electronics problems. Consequently, Zond 3 was launched on July 18, 1965, to check out the design of the spacecraft. As Zond 3 passed the Moon, it took 25 photographs of the far side. It subsequently relayed television images from greater and greater distances as it entered a solar orbit. Beginning in 1967, Soviet space engineers launched a series of modified Soyuz capsules toward the Moon in preparation for a manned circumlunar flight. However, three spacecraft (Cosmos 146, launched Mar.
10, 1967; Cosmos 154, launched Apr. 8, 1967; and an unnumbered Zond, launched Nov. 22, 1967) failed either to achieve or to leave a preliminary Earth orbit. These failures frustrated Soviet plans to mark the 50th anniversary of the Bolshevik Revolution by sending a cosmonaut to the Moon in 1967. Zond 4, launched on Mar. 2, 1968, followed a deep-space trajectory that missed the Moon widely, but Zond 5, launched on Sept. 14, 1968, and Zond 6, launched on Nov. 10, 1968, both made successful passes around the Moon and safe landings back on Earth seven days after being launched. A manned flight, however, was evidently canceled following the surprisingly rapid successes of the U.S. Apollo program. Two additional unmanned circumlunar flybys (Zond 7, launched Aug. 8, 1969; and Zond 8, launched Oct. 20, 1970) took color photographs of the Earth and the Moon. Both also returned safely, with the latter being recovered from the Indian Ocean.