LANDING SITE

At the dawn of the ‘space age’, despite centuries of telescopic observations very little was known for certain about the Moon. For example, there were competing theories for how the craters were made, and the origin of the smooth dark plains that together cover 30 per cent of the visible surface was disputed. Because the Moon’s axial rotation is synchronised with its orbital motion around Earth, we can never view its far side. When the Soviet Union sent a spacecraft beyond the Moon in October 1959 and transmitted photographs of its far side, this was revealed to be virtually devoid of dark plains, thereby posing the mystery of why there should be such a dichotomy. One thing was certain: the Moon represented a new frontier to be explored.

Initial reconnaissance

When NASA initiated the Ranger project in December 1959, this was intended to serve as the flagship for its reconnaissance of the Moon. The first two missions in August and November 1961 were to test the spacecraft’s basic systems in the deep space environment, but the Agena rocket stages failed and stranded their payloads in low ‘parking orbit’. Nevertheless, the Jet Propulsion Laboratory (JPL) decided to proceed with the second batch of spacecraft, whose plunging dive to the Moon was to be documented by a television camera and, just prior to hitting the surface, the spacecraft was to release a shock-resistant ‘hard landing’ capsule that contained a seismometer. Unfortunately, Ranger 3’s Agena overperformed and the spacecraft missed the Moon by 20,000 nautical miles. On the next attempt the trajectory was so accurate that Ranger 4 hit the Moon, but by then an electrical fault had already crippled the spacecraft. Ranger 5, which missed the Moon by 420 nautical miles, was also disabled by a power failure. In December 1962, with its best result being an inert spacecraft striking the Moon, the project was at risk of cancellation. After a review of spacecraft assembly procedures, NASA redefined the project’s goals: the next batch of vehicles would have only the television package, and their single objective would be to gain close-up pictures of the lunar surface in order to assess whether this was capable of supporting the weight of a spacecraft. The location of the target was constrained by flight dynamics considerations. The initial television view was to match the best telescopic pictures, and the spacecraft was to execute a near-vertical dive in order to reduce ‘smearing’ in the final phase, which required a target in the western hemisphere. Unfortunately, the television on Ranger 6 was disabled by an electrical arc at launch, but this did not become evident until the system failed to start as the vehicle neared the Moon. The project’s luck changed on 31 July 1964, when Ranger 7 dived into the Sea of Clouds. Its final image showed detail only a few feet across – an improvement in resolution by a factor of a thousand over the best telescope. The terrain was fairly soft and rolling, with none of the jagged features portrayed by science fiction. A set of shallow ridges suggested that the dark plain of the ‘sea’ was a lava flow, but this was disputed. The presence of boulders indicated the surface was likely to support a spacecraft. Although an automated craft might well come to grief by setting down on a rock or in a crater, there were evidently many open spaces and an Apollo crew ought to be able to manoeuvre to a safe spot on which to set down. As Apollo’s dynamical constraints favoured eastern sites, on 20 February 1965 Ranger 8 took a shallow trajectory that crossed the central highlands en route to the Sea of Tranquility, east of the lunar meridian. Although this approach increased the surface coverage, it also created substantial smearing in the final frames. Satisfied that the dark plains would support the weight of an Apollo spacecraft, NASA released the final probe to the scientists, and on 24 March 1965 Ranger 9 was sent to dive into Alphonsus, a 60-nautical-mile-diameter crater having a central peak and a flat floor displaying interesting rilles and ‘dark halo’ craters that appeared (to some researchers) to be volcanoes. For the first time, the television was fed to the commercial networks, which broadcast it with the banner ‘LIVE FROM THE MOON’. JPL had hoped to reinstate a ‘hard landing’ instrument package and mount a series of follow-on flights, but funding was denied. Originally intended to be the primary means of studying the Moon, the project had been overtaken by the incredible pace of events following President John F. Kennedy’s challenge to send astronauts to the Moon.