5.15 How come the backpack antenna appears and disappears?

IN A NUTSHELL: It only “disappears” if you look at the low-resolution copies of the photographs. It doesn’t in the high-quality scans, but it becomes fainter. This is because it was a flat antenna and therefore it became almost invisible when it was edge-on to the camera or to the Sun.

THE DETAILS: The PLSS radio antenna, located at the top of the astronauts’ backpacks, seems to come and go in photographs taken moments apart. This is interpreted by some as evidence that the photographs were not taken in sequence and someone forgot to place the antenna consistently in the various photographs.

An example of the disappearing antenna is offered by photos AS11-40-5942 and AS11-40-5943 from the Apollo 11 mission, which show Buzz Aldrin as he carries the instruments to be left on the Moon.

The numbering of these photographs implies that they were officially taken in sequence. Yet the antenna is missing in the first one and distinctly visible in the second one.

Detail of photo AS11-40-5942: no antenna.

Detail of photo AS11-40-5943: the antenna is clearly visible.

Once again, this apparent inconsistency arises from one of the recurring mistakes of conspiracy theorists: using low-resolution copies instead of high-quality scans of the originals.

The first picture comes from the low-resolution online set of the Johnson Space Center and shows no antenna, but inspection of the high-resolution version of the photograph reveals that the antenna is actually present, even though it’s very faint.

Detail of a high-resolution scan of photo AS11-40-5942.

Why does it look so different in the two pictures? Because it’s not a traditional rod-like antenna: it’s a flat metal strip, as shown below.

Detail of the stowed VHF antenna of Charlie Duke’s spacesuit (Apollo 16). Courtesy of K.C. Groneman and D.B. Eppler, NASA Johnson.

Seen edge-on, i.e., when the astronaut is directly facing the camera or has his back to it, these VHF antennas are almost invisible against the black lunar sky. Seen from the side, they become clearly visible by reflecting the sunlight from a much wider surface.

In the first picture (5942), Aldrin is seen squarely from the back and therefore the antenna is edge-on to the camera. In the second picture (5943), the astronaut is turned sideways and so his antenna is showing its flat side to the camera.

In other pictures, such as AS11-40-5874 (the flag salute), the astronaut is seen from the side, but he’s facing the sun and therefore the antenna is edge-on with respect to the light source, so only its front edge catches the light, making it hard to see except in the high-resolution scans.