Until 50 years ago today, we had never seen exactly what the Moon's surface looked like. As the Space Race heated up, NASA launched the first Ranger probe in 1961, intending to capture photographs and scout the way forward for a human landing. But a rocket on Ranger 1 failed to fire, sending the craft falling back into Earth's atmosphere with its mission uncompleted. This pattern would continue for three years and five more frustrating missions.

Finally, in 1964, Ranger 7 made it to the Moon. On July 31st, at 9:08AM ET, it returned the image above, capturing the Alphonsus and Ptolemaeus craters (on the right) and the lunar "Sea of Clouds." Over the next 17 minutes, it would send back 4,316 images, returning the last one less than 3 seconds before crashing into the Sea of Clouds' northern rim, according to NASA. The Universities Space Research Association has a collection of photographs from all the successful Ranger missions, which would end with Ranger 9 in 1965; by NASA's estimate, the whole Ranger series was carried out four around $170 million (presumably not adjusted for inflation.)

Besides the photo collections, the USRA page also includes reports on each mission from NASA's Jet Propulsion Lab, and NASA has mission summaries for all of the Ranger missions on its site. In honor of the mission, it's also posted a 30-minute documentary on Ranger 7, including archival footage. It may not be the the most famous Moon mission, but without it, the "giant leap for mankind" couldn't have gotten off the ground.