This was the first U.S. attempt to impact a probe on the lunar surface. The Block 2 Ranger spacecraft carried a TV camera that used an optical telescope that would allow imaging during descent down to about 15 miles (24 kilometers) above the lunar surface. The main bus also carried a 94 pound (42.6 kilogram) instrument capsule that would separate at about 13 miles (21.4 kilometers) altitude and then independently impact on the Moon.

Protected by a balsa wood outer casing, the capsule was designed to bounce several times on the lunar surface before coming to rest. The primary onboard instrument was a seismometer. Because of a malfunction in the Atlas guidance system (due to faulty transistors), the probe was inserted into a lunar transfer trajectory with an excessive velocity. A subsequent incorrect course change ensured that the spacecraft reached the Moon 14 hours early and missed it by 22,862 miles (36,793 kilometers) on Jan. 28, 1962.

The central computer and sequencer failed and the spacecraft returned no TV images. The probe did, however, provide scientists with the first measurements of interplanetary gamma ray flux.

Ranger 3 eventually entered heliocentric orbit.


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

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