After six failed Ranger missions, the program was under threat. Ranger 7, launched on July 28, 1964, worked perfectly. Its six television cameras began transmitting when the spacecraft was about 2,100 kilometers above the Moon and continued until impact. The final images showed craters less than a meter across, far smaller than anything visible from Earth. They helped NASA choose landing sites for Apollo and showed that the lunar surface was firm enough to support a spacecraft.
The Ranger program was designed to fly spacecraft straight into the Moon, taking pictures all the way down. Its early flights were plagued by rocket failures, missed trajectories and dead cameras, and Ranger 6, in February 1964, reached the Moon with its cameras silent. Congress held hearings, and the Jet Propulsion Laboratory, which ran the program, was under intense pressure.
Ranger 7 lifted off from Cape Kennedy on July 28 aboard an Atlas-Agena rocket. Three days later, on July 31, its cameras switched on as it fell toward a plain in the Sea of Clouds. At JPL in Pasadena, engineers watched the signal come in. The final frame, taken about 488 meters (1,600 feet) above the surface, was cut off at impact.
The pictures revealed a landscape of craters within craters, rounded and softened, and smaller than anyone had expected. The astronomer Gerard Kuiper, a mission scientist, said the images showed the surface to be solid enough to walk on. The impact site was later named Mare Cognitum, the Known Sea. Rangers 8 and 9 followed in 1965.
Key people: William H. Pickering, Gerard Kuiper