<P> After the end of the Gemini program, the Soviets Union began flying their second - generation Zond manned spacecraft in 1967 with the ultimate goal of looping a cosmonaut around the Moon and returning him immediately to Earth . The Zond spacecraft was launched with the simpler and already operational Proton launch rocket, unlike the parallel Soviet manned Moon landing effort also underway at the time based on third - generation Soyuz spacecraft requiring development of the advanced N - 1 booster . The Soviets thus believed they could achieve a manned Zond circumlunar flight years before a U.S. manned lunar landing and so score a propaganda victory . However, significant development problems delayed the Zond program and the success of the U.S. Apollo lunar landing program led to the eventual termination of the Zond effort . </P> <P> Like Zond, Apollo Moon flights were generally launched on a free return trajectory that would return them to Earth via a circumlunar loop in the event that a Service Module malfunction failed to place them in lunar orbit as planned . This option was implemented after an explosion aboard the Apollo 13 mission in 1970, which is the only manned circumlunar loop mission flown to date . </P> <Table> <Tr> <Th> U.S.S.R mission </Th> <Th> Mass (kg) </Th> <Th> Booster </Th> <Th> Launched </Th> <Th> Mission goal </Th> <Th> Payload </Th> <Th> Mission result </Th> </Tr> <Tr> <Td> Cosmos - 146 </Td> <Td> 5,400 </Td> <Td> Proton </Td> <Td> 10 March 1967 </Td> <Td> High Earth Orbit </Td> <Td> unmanned </Td> <Td> Partial success--Successfully reached high Earth orbit, but became stranded and was unable to initiate controlled high speed atmospheric reentry test </Td> </Tr> <Tr> <Td> Cosmos - 154 </Td> <Td> 5,400 </Td> <Td> Proton </Td> <Td> 8 April 1967 </Td> <Td> High Earth Orbit </Td> <Td> unmanned </Td> <Td> Partial success--Successfully reached high Earth orbit, but became stranded and was unable to initiate controlled high speed atmospheric reentry test </Td> </Tr> <Tr> <Td> </Td> <Td> </Td> <Td> Proton </Td> <Td> 28 September 1967 </Td> <Td> High Earth Orbit </Td> <Td> unmanned </Td> <Td> Failure--booster malfunction, failed to reach Earth orbit </Td> </Tr> <Tr> <Td> </Td> <Td> </Td> <Td> Proton </Td> <Td> 22 November 1967 </Td> <Td> High Earth Orbit </Td> <Td> unmanned </Td> <Td> Failure--booster malfunction, failed to reach Earth orbit </Td> </Tr> <Tr> <Td> Zond - 4 </Td> <Td> 5,140 </Td> <Td> Proton </Td> <Td> 2 March 1968 </Td> <Td> High Earth Orbit </Td> <Td> unmanned </Td> <Td> Partial success--launched successfully to 300,000 km high Earth orbit, high speed reentry test guidance malfunction, intentional self - destruct to prevent landfall outside Soviet Union </Td> </Tr> <Tr> <Td> </Td> <Td> </Td> <Td> Proton </Td> <Td> 23 April 1968 </Td> <Td> Circumlunar Loop </Td> <Td> non-human biological payload </Td> <Td> Failure--booster malfunction, failed to reach Earth orbit; launch preparation tank explosion kills three in pad crew </Td> </Tr> <Tr> <Td> Zond - 5 </Td> <Td> 5,375 </Td> <Td> Proton </Td> <Td> 15 September 1968 </Td> <Td> Circumlunar Loop </Td> <Td> non-human biological payload </Td> <Td> Success--looped around Moon, returned live biological payload safely to Earth despite landing off - target outside the Soviet Union in the Indian Ocean </Td> </Tr> <Tr> <Td> Zond - 6 </Td> <Td> 5,375 </Td> <Td> Proton </Td> <Td> 10 November 1968 </Td> <Td> Circumlunar Loop </Td> <Td> non-human biological payload </Td> <Td> Partial success--looped around Moon, successful reentry, but loss of cabin air pressure caused biological payload death, parachute system malfunction and severe vehicle damage upon landing </Td> </Tr> <Tr> <Td> </Td> <Td> </Td> <Td> Proton </Td> <Td> 20 January 1969 </Td> <Td> Circumlunar Loop </Td> <Td> non-human biological payload </Td> <Td> Failure--booster malfunction, failed to reach Earth orbit </Td> </Tr> <Tr> <Td> Zond - 7 </Td> <Td> 5,979 </Td> <Td> Proton </Td> <Td> 8 August 1969 </Td> <Td> Circumlunar Loop </Td> <Td> non-human biological payload </Td> <Td> Success--looped around Moon, returned biological payload safely to Earth and landed on - target inside Soviet Union . Only Zond mission whose reentry G - forces would have been survivable by human crew had they been aboard . </Td> </Tr> <Tr> <Td> Zond - 8 </Td> <Td> 5,375 </Td> <Td> Proton </Td> <Td> 20 October 1970 </Td> <Td> Circumlunar Loop </Td> <Td> non-human biological payload </Td> <Td> Success--looped around Moon, returned biological payload safely to Earth despite landing off - target outside Soviet Union in the Indian Ocean </Td> </Tr> </Table> <Tr> <Th> U.S.S.R mission </Th> <Th> Mass (kg) </Th> <Th> Booster </Th> <Th> Launched </Th> <Th> Mission goal </Th> <Th> Payload </Th> <Th> Mission result </Th> </Tr>

When was the last time america went to space