Rangers 1 and 2 were test missions. Rangers 3, 4, and 5 carried a capsule, containing a seismometer, which was intended to be jettisoned and then decelerated by retrorocket in order to make a rough but survivable landing. However equipment failures dogged the first six missions, some of them blamed on heat-sterilization procedures meant to destroy microbes and thus avoid contaminating the Moon. Because of these failures, NASA announced that henceforth unmanned lunar landing spacecraft, including Rangers and Surveyors, would be assembled in clean-rooms and treated with germ-killing substances to prevent contamination without damaging sensitive electronic components.
The final three flights of the series, Ranger 7, Ranger 8, and Ranger 9, were a complete success, returning a total of more than 17,000 photos with a resolution of 0.25–1.5 meters. Ranger 9 was equipped to convert its signals into a form suitable for showing on domestic television, and brought images of the Moon into ordinary homes. Millions of Americans, following live TV coverage of the final descent of Ranger 9, saw a series of pictures, starting with three flat craters – Ptolemaeus, 137 km (85 miles) in diameter, Alphonsus, 80 km (50 miles) across, and Albategnius, 96 km (60 miles) wide. As the spacecraft drew closer to the Moon's surface, the area photographed became large in scale and focused on the crater Alphonsus. Pictures remained sharp and clear as little as 600 meters from the surface, and then the screen suddenly went black as the probe smashed into the floor of Alphonsus. The final picture was returned when the spacecraft was just two-tenths of a second from impact. Ranger 9 completed its mission comes just 24 hours after the launch of Gemini 3.
The Ranger program was followed by Lunar Orbiter and Surveyor.
Related entry Moon, unmanned spacecraft
Related categories SATELLITES AND SPACE PROBES
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