The Soviet Union's Zond (Russian for "probe") spacecraft series was designed to carry two cosmonauts around the Moon—that is, to conduct a circumlunar flight. Zond, also known as L-1, was a stripped-down Soyuz spacecraft. Modifications to the Soyuz design were designed primarily to reduce weight and included removal of various components, such as the third cosmonaut couch, a backup engine, and a backup parachute. Weight reduction was necessary so that Zond's chosen booster, a two-stage Proton rocket with a Block D third stage, could launch it around the Moon. In addition, Zond included a large radio antenna for communication across the 380,000 kilometers (235,600 miles) separating Earth and the Moon.
The Soviet Union conducted fourteen unpiloted Zond launches in three phases. The first four Zond tests aimed to prepare the vehicle for a piloted circumlunar flight to mark the fiftieth anniversary of the Communist Revolution in October 1967. The next six sought to prepare Zond to fly cosmonauts around the Moon before Apollo astronauts could orbit the Moon.
This phase ended with a launch failure in January 1969, a month after Apollo 8 orbited the Moon. Soon after, the cosmonauts in training for Zond flights were re-assigned. Of the remaining four Zond capsules, two served as automated probes and two as test payloads for the giant N1 Moon rocket.
Kosmos 146 (March 10-18, 1967) was a successful test of the Block D stage in Earth orbit. The Kosmos 154 (April 8-19, 1967) Block D failed to reignite in Earth orbit, so Soviet engineers could not test the Zond capsule's atmosphere re-entry. The third Zond Proton rocket suffered first-stage failure; emergency escape rockets blasted the capsule to safety (September 29, 1967). The fourth Zond also ejected following Proton second-stage failure (November 22, 1967). This marked the end of the first phase of the Zond program.
The name Zond had been used before in the Soviet space program. Zonds 1 through 3 were automated planetary probes unrelated to the piloted circumlunar program. The next Zond flight (and the first in the second phase of circumlunar program), therefore, was named Zond 4 (March 2-9, 1968). This spacecraft flew to lunar distance, but away from the Moon. Soviet controllers destroyed it during re-entry after it veered off-course. Two Proton launch failures (April 23, 1968 and July 14, 1968) followed. Zond 5 (September 14-21, 1968) flew successfully around the Moon, but landed off-course in the Indian Ocean. Zond 6 (November 10-17, 1968) also flew around the Moon, but the capsule's air escaped during return to Earth, and it crashed. It was, however, the first Zond to return to Soviet soil. Another Proton failure (January 20, 1969) ended Soviet plans to launch cosmonauts in Zond.
The next Zond rode the first N-1 (February 20, 1969), beginning the third Zond phase. The giant rocket caught fire and crashed, but the Zond capsule successfully ejected. The second N-1 exploded on its launch pad (July 3, 1969); again the Zond ejected. Zond 7 (August 7-14, 1969) was the most successful mission. It photographed the Moon's farside before landing safely in the Soviet Union. Zond 8 (October 20-27, 1970) flew around the Moon, but suffered control problems and landed off-course in the Indian Ocean, ending the unsuccessful Zond program.
see also Capsules (volume 3).
David S. F. Portree
Portree, David S. F. Mir Hardware Heritage. Houston, TX: NASA Lyndon B. Johnson Space Center, Information Services Division, 1995.
Siddiqi, Asif. Challenge to Apollo: The Soviet Union and the Space Race, 1945-1974. Washington, DC: NASA History Office, 2000.
Portree, David S. F. Mir Hardware Heritage. 1995. National Aeronautics and Space Administration. <http://spaceflight.nasa.gov/history/shuttle-mir/ops/mir/mirheritage.pdf>.