Slice of History - Marking 60 Years Since Ranger 9’s Launch

Ranger 9, the last craft of the series, launched 60 years ago on 21 March 1965! The craft was designed to image and impact Alphonsus, a large crater about 12 degrees south of the lunar equator. The probe was timed to arrive when lighting conditions would be at their best. The Atlas- Agena B booster injected the Agena and Ranger 9 into an Earth parking orbit at 185 km altitude. A 90 second Agena 2nd burn put the spacecraft into lunar transfer trajectory, which was followed by the separation of the Agena and Ranger 9. The initial trajectory was highly accurate; uncorrected, the craft would have landed only 650 km north of Alphonsus.

Ranger 9 reached the Moon on 24 March 1965. Unlike its predecessors, this Ranger pointed its cameras directly in its direction of travel, yielding stunning photographs of the lunar surface. Transmission of 5,814 good contrast photographs was made during the final 19 minutes of flight.

Millions of Americans followed the spacecraft's descent via real time television coverage of many of the F-channel images from both cameras A and B. These pictures showed the rim and floor of the crater in fine detail.

A panel of scientists presented some preliminary conclusions from Ranger 9’s mission at a press conference that same afternoon. Crater rims and ridges inside the walls, they believed, were harder and smoother than the moon’s dusty plains, and therefore were considered likely sites for future manned landings. Generally, the panel was dubious about landing on crater floors because they were solidified volcanic material potentially incapable of supporting a spacecraft. Data from the mission dramatically improved scientists’ understanding of the Moon’s mass and led to the discovery that the Moon’s center of mass is displaced from its geometric center. CL#25-0622

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