American Flag
Detail from Apollo 12 photo AS12-47-6983 showing the deployed flag and its shadow. The latch failed on the pivot designed to hold the top edge of the flag out perpendicular to the pole on a supporting rod, so the flag hung limp. The photo was taken at about 1455 UTC on 19 November 1969. The Sun's elevation was 9.2 degrees. Platoff describes the flag as being 5 by 3 feet (1.5 by 1.0 meters). Because the supporting rod is close to vertical, we can estimate that the part of the pole above ground is about 7 feet (2.1 m) tall and that the bottom of the flag is about 2 feet (0.6 meters) off the ground. On level ground, the far end of the shadow would be about 13 meters from the pole. The bottom of the flag is about 0.5 m above the surface and its shadow would be about 3 meters from the pole.
Text & image: NASA
Do the Apollo flags remain where they were planted or have they fallen or have they disintegrated after four decades of exposure the lunar environment?
Current Thinking
A variety of recent media articles report current thinking on the condition of the flags. Here is a sampling:
Reichhardt, Tony, Finding Apollo, Air and Space, Smithsonian Institution, September 2008.
The (Apollo 11’s) flag is probably gone. Buzz Aldrin saw it knocked over by the rocket blast as he and Neil Armstrong left the moon 39 summers ago. Lying there in the lunar dust, unprotected from the sun’s harsh ultraviolet rays, the flag’s red and blue would have bleached white in no time. Over the years, the nylon would have turned brittle and disintegrated. … Dennis Lacarrubba, whose New Jersey-based company, Annin, made the flag and sold it to NASA for $5.50 in 1969, considers what might happen to an ordinary nylon flag left outside for 39 years on Earth, let alone on the moon. He thinks for a few seconds. “I can’t believe there would be anything left,” he concludes. “I gotta be honest with you. It’s gonna be ashes.”
Chow, Denise, On the Moon, Flags & Footprints of Apollo Astronauts Won't Last Forever, Space.com, September 2011
Based on the new (LRO) images, that mystery may remain unsolved, but (LRO Camera Principal Investigator, Dr. Mark) Robinson is skeptical that the flags are intact, if they are still there. The moon's extreme heat and ultraviolet conditions would probably destroy the nylon flags over time, he explained. "Personally, I would be surprised if there's anything left on them," Robinson said. "You know how [if] you leave a flag out over summer, how it starts to fade. Now, imagine the extreme UV environment on the moon, and the hot and cold cycling, and it's been 40 years — so if the flags are still there, they're probably in pretty rough shape."…. (Robert Pearlman, an expert on space history and collectibles, and editor of collectSPACE.com said) "We didn't design a special American flag to go to the moon to last thousands of years. They literally sent out a secretary to the nearby Sears and bought an off-the-shelf flag and modified it. The natural disintegration of the flag's material in the harsh conditions on the moon's surface is to be expected."
Axelrod, Jim, What happened to the American flags on the moon?, CBS News, July 2011.
(Historian Anne Platoff) believes the first two (flags) from Apollo 11 and 12 did not survive the ignition gases of the lunar liftoff … "It wasn't the intention for the flag material itself to last. It was just to be there during the event - the landing and departing from the moon. We didn't have a requirement that the flag, the U.S. flag, had to withstand all the environments for eons". Made from nylon just like the ones at a dime store, though ordered off the shelf from a government supply catalogue, Annie Platoff's theory is they are probably darkened and maybe more than a bit tattered. "I would guess, over time, 40 years, the combination of sun-rot and micro-meteor impact is probably devastating. I mean it's not a pretty picture to paint. The only way you're going to test these theories is to go back to the Moon and look at the flag," Platoff says.
Finally, Lunar Scientist Paul Spudis, in a July 2011 blog posting, writes:
For forty-odd years, the flags have been exposed to the full fury of the Moon’s environment – alternating 14 days of searing sunlight and 100° C heat with 14 days of numbing-cold -150° C darkness. But even more damaging is the intense ultraviolet (UV) radiation from the pure unfiltered sunlight on the cloth (modal) from which the Apollo flags were made. Even on Earth, the colors of a cloth flag flown in bright sunlight for many years will eventually fade and need to be replaced. So it is likely that these symbols of American achievement have been rendered blank, bleached white by the UV radiation of unfiltered sunlight on the lunar surface. Some of them may even have begun to physically disintegrate under the intense flux.
"Bleached", “disintegrated”, “ashes”, “rough shape”, and “tattered”. Intuitively, experts mostly think it highly unlikely the Apollo flags, could have endured the 42 years of exposure to vacuum, about 500 temperature swings from 242 F during the day to -280 F during the night, micrometeorites, radiation and ultraviolet light, some thinking the flags have all but disintegrated under such an assault of the environment.
Lunar Reconnaissance Orbiter Camera images
Fortunately the outstanding high-resolution images from the Lunar Reconnaissance Orbiter camera of the Apollo sites enable us to see if any of the flags still cast shadows. Examining the detailed images by themselves (i.e. separately) provide a somewhat ambiguous impression of the flags. It is known the astronauts walked around the flag poles a great deal and disturbed the regolith (lunar dirt) so the appearance in any one image can give the illusion of the location of the flag only or perhaps what appears to be the flag pole itself.
When a person looks at a shadow, they normally expect it to start at the object casting the shadow that starts at the object and extend out to a distance that depends upon the elevation of the Sun and the slope of the ground on which the shadow falls. In the case of a flag supported by a thin pole, the shadow of the pole starts at its base, but the nearest part of the flag shadow is some distance away from the pole, unless the Sun is near the zenith.
Apollo 11
In August 2011, the author combined LROC images of each Apollo site taken at roughly the same orientation (i.e. spacecraft-to-lunar surface site angle) but with different Sun angles to show the travel of shadows. Combined with knowledge of the Apollo site maps which show where the flag was erected relative to the Lander, long shadows cast by the flags at three sites - Apollo 12, Apollo 16, and Apollo 17 - show that the these flags are still “flying”, held aloft by the poles.
On page 239 in his book, Return to Earth, Buzz says that, during the liftoff from the Moon, "There was no time to sight-see. I was concentrating intently on the computers, and Neil was studying the attitude indicator, but I looked up long enough to see the flag fall over." As expected, there is no indication of a flag shadow in Apollo 11 LROC images. Figure 3-15 from the Apollo 11 Preliminary Science Report shows the location where the flag was deployed. The second and third frames in the animation shows ground disturbed by the crew between the MESA and the TV camera. The flag was deployed in that area.
Apollo 12
Animation made from five LROC images of the Apollo 12 landing site, ordered from sunrise to sunset, and showing the changing length and location of the shadow cast by the U.S. flag erected by the crew. The frames are: (1) M131806467LC, Sun 8 degrees above the eastern horizon; (2) M114104917RC, 32 degrees, east; (3) M137699517LC, 59 degrees, west; (4) M117650516RC, 9 degrees, west; (5) M132983773RC , 6 degrees, west. LROC images courtesy NASA/GSFC/Arizona State University.
The Apollo 12 moon landing occurred on November 19, 1969. The crew spent 31.5 hours on the lunar surface before returning to lunar orbit. A U.S. flag was erected early in EVA-1. As indicated in an overall discussion of the six flags left on the lunar surface, there are questions as to whether the flag material has survived 40-plus years in the lunar environment or whether any of the flag poles had fallen, either during the Lunar Module liftoff or anytime afterward. This article resolves this issue for Apollo 12.
Al Bean told Houston that he hammered the lower section of the pole about "a foot" into the ground. The location is marked in Figure 10-50 from the Apollo 12 Preliminary Science Report. and is about 7 meters out from the MESA, halfway between the plus-Z (west) and plus-Y (north) struts.
Detail from AS12-48-7152, taken by Al Bean on his way back to the LM at the end of the EVA-2 traverse. Pete Conrad went ahead of Bean to start the close-out. The flag is on the right and the erectable S-band antenna in the center. The antenna is connected to the MESA by a 20-foot (6 m) cable. The dish is 3 meters across and the height of the supporting tripod is about 2 meters.
During Apollo 12 preparations for LM liftoff, the RCS hot-fire check blew over the S-Band antenna:
140:12:11 Conrad: Here you go, Houston, with roll, pitch, and yaw (tests of the RCS).
140:12:14 (CapCom Gerry) Carr: Roger, Pete. (Static; Long Pause) Intrepid, Houston.
140:12:53 Conrad: (To Houston) Don't panic! We just blew over our S-band erectable (with the exhaust from the RCS), and we're up on our steerable.<p>
140:13:02 Carr: Roger. I was just going to tell you, Pete, we lost some of the data on that fire check.
Because of the tripod attached to the bottom of the dish and the transmitter mast at the top, the antenna probably ended up on its side, supported by the ends of two or three ribs and by either one or two of the tripod legs or the transmitter. It may well have remained mechanically connected to the MESA by the cable. Photo AS12-48-7163 was taken out the LMP's window after EVA-2 and shows most of the S-band shadow, with the densest part of the shadow cast by the hardware at the top of the tripod and the converging ribs at the center of the dish. Further discussion can be found in the Apollo 14 flag page.
Detail from LROC image taken with the Sun 59 degrees up from the western horizon.
This stack displays the five LROC images details used to make the animation at the top of the page. The vertical yellow lines approximate the east-west location of the flagpole. In the early morning images at the top of the stack, the flag shadows start from points west of the flagpole and end farther west. The situation is reversed for the late afternoon images at the bottom of the stack. The vertical red lines approximate the east-west location of the S-band antenna. With the antenna on its side, its shadow will be 'attached' to the antenna.
What is really being seen in these five images is the flag shadow itself and not the flag pole shadow. The flag pole is only about 7/8ths of an inch in diameter. LRO cameras can at best see down to 0.45 meters (1.5 feet) which is the equivalent to one pixel width in the images and .55 meters (1.8 feet) which is equivalent to one pixel of height. This resolution is just good enough to see the drooped flag shadow (estimated to be from 6 inches to 1.5 feet). Even if the drooped flag is narrower than the .45 meter resolution, since one pixel of the camera’s optics is an average over an entire area of coverage, the flag’s shadow can substantially dim a large fraction of this area and, on average, reduce the pixel illumination even though it cannot blacken it completely.
The shadows cast by the flag reach fairly far. The astronauts indicate the Apollo 12 landing site is fairly flat. If the slope was significant tilted toward East or West, the shadows would be elongated or shortened depending on the direction, as would be the case for slight craters and hills along the shadow path. Assuming the flag is 2.1 m from the ground to the top of the pole and on a flat surface, for the near sunrise image (8 degree elevation), the shadow tip would be 15 meters from the flag pole base (which is not visible in these images due to the small diameter of the flag pole); for the near sunset image (6 degree elevation), the shadow tip would be 20 meters) from the flag pole base. Due to the unsupported shape of the flag, a precise comparison of predicted versus actual shadow lengths is not possible, as well as derivation of flag height from shadow length.
Finally, note that in the morning images at the top of the LROC stack, the S-band dish shows up as a bright spot because sunlight reflecting off the mesh. In the afternoon images, the dish is fainter, suggesting that the tripod is pointing east and the transmitter mast is pointing west.
All text & images: NASA
Apollo 11 astronauts plant flag on the moon on July 20, 1969