A series of space probes launched by the former Soviet Union for testing spacecraft equipment and flight techniques. Zonds 1 and 2 in 1964 were launched towards Venus and Mars to test long-distance communications, but contact was lost with both. Zond 3 in 1965 July took photographs of the parts of the Moon's farside not covered by Luna 3. Zonds 4–8 in 1968–70 were rehearsals for a planned manned Soyuz mission around the Moon and back that was cancelled after the success of Apollo.
Subjects: Astronomy and Astrophysics.