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Getting the picture from the Lunar Orbiter series | Looking Up

Having discussed the Ranger missions and the Surveyor missions in the past few weeks, we’re now moving on to the final set of information-gathering missions that NASA used to figure out if landing on the moon were even possible. The Lunar Orbiter missions were intended to map the surface of the moon in preparation for the Apollo moon landings, considering our view from an Earth-based telescope just wasn’t good enough to make out the detail needed.
There were five Lunar Orbiter missions and (spoiler alert) they were all extremely successful. We had learned a lot from the failures of earlier missions and, well, it’s just a heck of a lot easier to put a spacecraft in orbit than to carefully land it on an alien world without breaking anything.
Scientists had been prepared to only get by with one successful orbiter to make the Apollo landing, so having all five go off flawlessly was an unexpected boon. NASA managed to photograph 99 percent of the moon’s surface at a decent resolution, taking a lot of guesswork out of the calculations for the manned missions. Thanks to these photos, they knew the astronauts would be able to look out their capsule window as they headed down for a landing and see the surface conditions in order to avoid hazards such as crevices and large rocks. Related Articles

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The first three Lunar Orbiter series were put into low orbit and photographed 20 potential landing sites that had been picked from previous Earth-based examination. One of these, in Mare Tranquillitatis (the Sea of Tranquility), was the eventual landing site for Apollo 11, the first manned mission to the moon.
Because these first three missions were such an unqualified success, NASA was able to use Lunar Orbiter 4 and 5 for other scientific research. Both orbiters were put into high polar orbits, which allowed nearly the entire surface of the moon to be photographed between the two of them. Lunar Orbiter 4 took the majority, getting images of nearly 95 percent of the far side of the moon and the entirety of the near side. Lunar Orbiter 5 mopped up, completing the far side coverage and getting even higher resolution photos of some additional sites NASA was interested in after seeing the first pass photos.
These photos, and the information garnered from the Ranger and Surveyor missions, allowed scientists to use several criteria to select their ideal landing site. They wanted a location that was smooth, without many craters, and had an approach path that was unhindered by either tall hills or deep craters that might throw off the altitude instruments of the Apollo lander. They also wanted a flat area, with a slope of less than 2 degrees. There were other considerations that weren’t based on the data gathered as well, such as the lighting conditions at the time of the launch and a location that would allow for the most fuel efficiency and the best return trajectory.
All sorts of other undertakings have expanded out of these three series of missions and those that came after, and not just in NASA. Both Russia and China and now Israel have launched spacecraft whose initial premises emerged from knowledge gained by early U.S. probes of the moon.
Although we mostly hear and think about the more famous missions, such as Apollo 11, I think it’s so important to remember our missteps and how much background data gathering we had to do before that important mission could take place. We couldn’t have accomplished it without the Ranger, Surveyor and Lunar Orbiter missions paving the way.
LOOKING UP THIS WEEK: Mars is joined by Mercury in the western sky until an hour or so after sunset, when Mercury sets. In the predawn mornings, look for a bright Venus with Saturn above it, rising as Venus sinks toward the sun. Jupiter will remain above both planets, brighter than Saturn but outshined by Venus in that southeast sky before sunrise. The moon is currently a waxing gibbous and will be full on Wednesday.
Marisa Stoller can be reached at or on Twitter @MarisaStoller.

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