12 astronauts landed on the moon between 1969-1972 as part of the Apollo missions, including Neil Armstrong and Buzz Aldrin in 1969 who were the first to walk on the moon. Animals like monkeys and dogs were early passengers in rockets and space flights during the 1950s and 1960s to test the effects of space travel. Rocket propellants undergo chemical reactions to produce thrust by ejecting hot gases. The Soviet Union's Luna 2 was the first man-made object to land on the moon in 1959.