Rennilson's journey to the moon began 55 years ago in 1961, when he had a fresh degree focusing on optical physics, and was working at the Scripps Institution of Oceanography in San Diego. A friend told him NASA's Jet Propulsion Laboratory in Pasadena, Calif. needed people who knew optics. While Rennilson's wife was reluctant to leave San Diego, the couple moved and Rennilson found himself at the front line of the space race.
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That year was important in human spaceflight; Soviet cosmonaut Yuri Gagarin was the first human in space on April 12, with the United States' Al Shepard following just weeks later, on May 5. Then NASA's mandate got a push from President John F. Kennedy on May 25. He addressed Congress with a speech on "urgent national needs" that in part, ordered his country to "commit itself to achieving the goal, before this decade is out, of landing a man on the moon and returning him safely to the earth."
It was a tall order for the United States, which had 15 minutes of human spaceflight experience. This is where the Surveyor program and its predecessor, Ranger, became supremely important; they took pictures of the moon and also taught scientists what the surface was like, ahead of the Apollo program that did land humans on the moon on time, in 1969.
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Rennilson joined JPL's photoscience group that was responsible for all of the imaging characteristics of missions with cameras. Ranger carried "slow-scan" television cameras (meaning the images were read out at a slower rate than standard television at the time). The program endured six failures before successfully impacting Rangers 7, 8 and 9 on the moon as planned between 1964 and 1965. Those missions showed the first American close-up images of the moon.