Ranger 4 
Two NASA spacecraft are orbiting the Moon in tandem right now, skimming low above the surface to map the Moon’s gravity and probe its interior. The feat is particularly impressive when you consider that the United States couldn’t even hit the Moon until 50 years ago.
The Army and Navy launched a series of small probes designed to fly near the Moon, but many of them never even got into space. None came closer than about 36,000 miles.
The first program designed to hit the Moon was known as Ranger. The craft were supposed to snap pictures before slamming into the lunar surface. The early missions also carried a small set of instruments to listen for moonquakes.
Ranger 3 was the first to take aim at the Moon, but it missed by a wide margin.
Next up was Ranger 4, and it did hit the Moon, on April 26th, 1962. But because of a computer glitch it never opened its solar panels, so it didn’t take any pictures or other readings. And it didn’t even hit the Moon in the correct hemisphere -- it hit the farside, not the side that faces Earth.
The next two Ranger missions also failed. The first success didn’t come until 27 months after Ranger 4.
After that, though, the successes piled up in a hurry. In fact, exactly 10 years after Ranger 4 hit the Moon, three astronauts were headed home from the Moon after the next-to-last Apollo mission -- a mission made possible in part by a craft that did nothing more -- and nothing less -- than hit the Moon.
Script by Damond Benningfield, Copyright 2012