Zond program
The Zond program was a series of Soviet unmanned space missions from 1964 to 1970 to test spacecraft intended for manned flights around the moon. While the lunar mission was the mission's primary goal from 1968 on, the first three missions of the program . However, it was only when the race to the moon intensified that missions 4 through 8 became the main test flights for manned circumlunar flight: the first three missions were intended to gather information about Venus and Mars. "Zond" is simply Russian for generic "probe" and covered different vehicle designs.
The Soyuz 7K-L1 spacecraft was used for the moon-aimed missions, stripped down to make it possible to launch around the moon from the earth. They were launched on the proton rocket which was just powerful enough to send the Zond on a free return trajectory around the moon without going into lunar orbit (the same as Apollo 13 flew in its emergency abort). It could have carried 1 or 2 Cosmonauts.
There were serious reliability problems with both the Proton rocket and the new Soyuz, but the test flights pressed ahead with some glitches. The September 1968 flight was the reason NASA flew Apollo 8 to the moon in December 1968 instead of the Earth orbital test which had been planned because the CIA knew what the Russians were planning to do. Had Apollo 8 not flown when it did, it is possible the Russians would have been the first to fly around the moon in late 1968 or early 1969.
Instrumentation flown on these missions gathered data on micrometeor flux, solar and cosmic rays, magnetic fields, radio emissions, and solar wind. Biological payloads were also flown and many photographs were taken.
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