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Ranger 4 Preparations Technicians prepare the Ranger 4 spacecraft for launch. An impact absorbing sphere made of balsa wood sits atop the spacecraft, painted with a saw-tooth pattern to maintain thermal balance during its mission to the Moon. The sphere contained a lunar seismometer, which was to rough land just south of the equator on the rim of the Ocean of Storms and measure "lunarquakes."

The master clock in Ranger 4's computer failed during flight and the spacecraft did not respond to commands. It crashed into the far side of the Moon on April 26, 1962. Despite the failure to return information, the use of balsa wood was an important precursor in the design of other rough landings on extraterrestrial bodies, particularly Mars. Aerobraking, gliding, impact absorption, parachuting, and retro rockets have all been considered.