On July 20, 1969, Apollo 11 astronauts Neil Armstrong and Buzz Aldrin planted the US flag on the Moon. The image of Aldrin standing with the flag is one of the indelible images of that great day. But over the years, one question has vexed space buffs – what happened to the flag? In his book Return to Earth, Aldrin says that when the Lunar Module’s Ascent stage lifted off from Tranquility Base, he saw the flag topple over. Since no one could confirm what happened, it remained a mystery ... at least, until now. On July 27, NASA announced that its Lunar Reconnaissance Orbiter Camera (LROC) had solved the puzzle of the fate of the Apollo lunar flags.
Whether or not the Apollo 11 flag fell over is a well-known episode in space history. In one of his novels, science fiction author Sir Arthur C. Clarke had a bit about future conservationists debating whether to put the flag back up or leave it lying ... but it isn’t the only flag left by the astronauts with a question mark over it. The fate of all the Apollo flags was in doubt until now. The cross piece on one flag pole that holds the flag upright in the lunar vacuum broke when the Apollo 12 astronauts put it up, so they were having trouble from the start. Others were seen in videos of lunar lift-offs flapping furiously in the rocket backwash. Whether or not they subsequently toppled was unknown.
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Even whether they still existed was a question. All six of the flags left by Apollo were made of nylon and the lunar surface isn’t very friendly to nylon. With the intense heat and hard UV radiation, at the very least the flags would have soon bleached white. After four decades, the polymers in the fabric could have broken down completely and disintegrated into ashy threads.
Then along came LRO. Launched on June 18, 2009, the spacecraft was one of the first sent to mark NASA’s return to the Moon. Its mission was to carry out low altitude reconnaissance. The high resolution images sent back to Earth would be used for looking for landing sites for future missions and to carry out a detailed survey of the polar regions and their potential ice deposits, vital to future lunar colonies. One side benefit was that it allowed scientists and the public their first look at old lunar landing sites, especially those from Apollo.
The images sent back of the sites were like nothing seen previously. The Lunar Module’s Descent stage, the experiments, Lunar Rover tracks and even footprints were visible. Then the LROC team realized that they had the means to solve the flag mystery. By comparing images of the sites taken at the same angle at different times of day, they could compare them, and the shifting shadows would reveal the height and shape of objects on the ground (see the video below). When they applied this to the Apollo sites, there were what looked like the flags ... at five of them. The sixth, Apollo 11, had no flag. It looks as though Aldrin was right.
One question that remains is if the flags themselves still exist or just the poles with what looks like flags. The poles and cross pieces are certainly standing there and images show something like a flag shape, but the resolution isn't high enough to show them clearly. One possibility is that the “flag” may be a combination of pole and cross piece, plus a patch of footprints left by the astronauts when setting it up.
That, however, is a question for another day.