Issued by the Russian agency for foreign trades, KNIGA, these covers were officially signed by cosmonauts of the 6 Vostok missions, postmarked In Moscow, USSR, January 10,1964 on the occasion of the 1964 Filatelic Programme.
Vostok 1 was the first manned space mission. Launched on April 12, 1961, Vostok 1 took Soviet cosmonaut Yuri Gagarin into space, the first human being to travel beyond the Earth's atmosphere and the first to orbit the Earth on a Vostok 3KA spacecraft. The mission lasted 1 hour 48 minutes and orbited the Earth once.
Vostok 2, launched on August 6, 1961, carried cosmonaut Gherman Titov into orbit for a full day in order to study the effects of a more prolonged period of weightlessness on the human body. Titov orbited the Earth over 17 times, and was the second human to orbit the Earth.
Vostok 3, launched on August 11, 1962, carried cosmonaut Andrian Nikolayev for a near fours days spaceflight in order to determine the ability of the human body to function in conditions of weightlessness and test the endurance of the Vostok 3KA spacecraft over longer flights.
Vostok 4 was launched a day after Vostok 3 on August 12, 1962, with cosmonaut Pavel Popovich on board - the first time that more than one manned spacecraft were in orbit at the same time.
Vostok 5, launched on June 14, 1963, was a joint mission with Vostok 6. It carried Valery Bykovsky on board and was originally planned to stay in orbit for 8 days. Bykovsky was ordered back to Earth after 5 days due to elevated levels of solar flare activity at that time. This remains today the record for the longest solo manned flight in Earth orbit.
Vostok 6, launched on June 16, 1963, was the first human spaceflight mission to carry a woman, cosmonaut Valentina Tereshkova, into space. During the mission, Tereshkova collected data on the female body's reaction to spaceflight. Her photographs of the horizon from space were later used to identify aerosol layers within the atmosphere. Vostok 6 was the last flight of a Vostok 3KA spacecraft.