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Ranger 4 was the first American spacecraft to reach another celestial body, in this case, the Moon. Like its predecessor, also a Block 2 spacecraft, it was designed to transmit pictures in the final 10 minutes of its descent to the Moon and to roughland on the lunar surface a balsa wood capsule (25.6 inches or 65 centimeters in diameter) that, among other instruments, carried a seismometer.

A power failure in the central computer and sequencer stopped the spacecraft’s master clock, preventing the vehicle from performing any of its pre-planned operations, such as opening its solar panels.

Drifting aimlessly and without any mid-course corrections, Ranger 4 impacted the Moon on its far side at a velocity of about 5,965 miles per hour (9,600 kilometers per hour) at 12:49:53 UT April 26, 1962. Impact coordinates were 15.5° south latitude and 229.3° east longitude.

Although the spacecraft did not achieve its primary objective, the Atlas Agena-Ranger combination performed without fault for the first time.

Source

Siddiqi, Asif A. Beyond Earth: A Chronicle of Deep Space Exploration, 1958-2016. NASA History Program Office, 2018.

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