When the CSIRO's Parkes telescope was commissioned in 1961, it was the most advanced and most sensitive radio telescope in the world. It incorporated so many innovative design features, that it was recognised very early on, to be a near-ideal instrument for tracking spacecraft in deep space, that is, far from the Earth.
In 1960, a year before the telescope's construction was completed, NASA proposed included it in its fledgling Deep Space Network (DSN) - the network of tracking antennas NASA was planning for tracking spacecraft at the planets. The offer was knocked back, but the CSIRO did agree to make the telescope available whenever a strong and reliable signal was required at critical moments in NASA's upcoming planetary missions.
Consequently, Parkes tracked Mariner 2, the first ever interplanetary spacecraft, when it flew by Venus in December 1962. It followed up in 1965, when it tracked Mariner 4 at Mars and received the first ever closeup pictures of the Martian surface.
Indeed, the Parkes telescope was so successful, that it became the model for NASA's large tracking antennas, which were all initially 64-metres in diameter, like Parkes. This network of large antennas was not completed until the early 1970's by which time the Apollo program was nearing its end.
These early missions proved to be the prelude to the main event. In October 1968, the then Director of the Parkes Observatory, John Bolton, was visiting colleagues in the United States, when he was invited to a dinner party. At the dinner were high ranking personnel from NASA's Jet Propulsion Laboratory. During the course of the dinner, John was asked if he could make available the Parkes facility for reception of signals from the Apollo 11 spacecraft, particularly during the most critical phases of the mission when the Lunar Module (LM) was on the lunar surface.
The historic nature of the mission, combined with the fact that human lives were at risk in space, convinced both Edward 'Taffy' Bowen, the Chief of CSIRO's Radiophysics Division, and John Bolton to support the mission. Following high level representations in early 1969, Cabinet level meetings approved the Parkes Observatory's involvement in the upcoming Apollo 11 mission.