Transcript: Public interest in the space program and its cost probably peaked in the late 1960s with the Apollo program. In a series of six launches twelve astronauts set foot on the moon and brought back a few hundred kilograms of moon rocks. The program was cancelled in 1972. Thereafter, NASA turned to exploration of the solar system using unmanned probes. Both the Russians and the Americans sent probes to Venus and Mars, and by the end of the 1970s probes had been sent to explore all the planets of the solar system except Pluto. The result of all this activity was a burst of innovation in the field of planetary science.