How did the Apollo astronauts toss their spacesuits overboard?

Hint: They kept the most important part.

PLSS backpacks
The Apollo 17 astronauts photographed one of their PLSS backpacks, unceremoniously dumped on the lunar surface at mission's end. NASA

Sometimes a little knowledge can be a dangerous thing, no matter how good your reasoning skills. Take the following question from Gianni Berati in Italy, who writes: "I have read that [Apollo 11 astronauts] Armstrong and Aldrin, after their extravehicular activities on the moon, had to throw off everything superfluous onto the lunar surface, even the lunar suits, in order to get the lunar module (LM) lighter. Is that true? How could they do that without a depressurized LM cabin?"

Berati is correct—the LM cabin did not have a safe area where unclad astronauts could seek refuge from the vacuum when they opened the hatch. Before going outside, they had to first put on spacesuits, then depressurize the entire landing craft. After a moonwalk they reversed the process, only taking off their suits when the LM pressure had been brought back up to normal. The next generation of moon lander will rectify this, adding an airlock as a "mud room" where astronauts can enter and exit while others lounge unprotected inside the craft.

So how did the Apollo astronauts manage to throw their spacesuits overboard? For an answer, the good folks at NASA's history office directed me to the Apollo Lunar Surface Journal, which explains in detail the unceremonious discarding of equipment onto the lunar surface. It turns out Berati is only partly right. The lunar explorers did not ditch the suits themselves, but rather the 84-pound Portable Life Support Systems (PLSS). The PLSS units, worn like backpacks, supplied enough air for four hours on the surface.

Armstrong, standing inside the LM in his space suit, opened two valves to bring the cabin pressure down to zero, then opened the hatch to the outside. The astronauts took the boxy PLSS packages, which they'd detached from their suits, and pitched them out the door with gloved hands (later lunar explorers found it more effective to use their feet).

"We didn't have any problems," Aldrin recalled during a technical debriefing. "I didn't notice you (Neil) had any difficulty giving the packages the heave-ho. I think each PLSS bounced once on the porch before it went down." (The "porch" was a lip of the LM jutting out just outside the hatch.)

Seismic sensors left on the surface by the astronauts even recorded the thumps of the gear hitting the moon. As Mission Control radioed to the two explorers: "We observed your equipment jettison on the TV, and the passive seismic experiment recorded shocks when each PLSS hit the surface" Armstrong responded, "You can't get away with anything anymore, can you?"

Examples of the PLSS gear and an unused Apollo lunar lander can be found at the National Air and Space Museum in Washington D.C. The real ones, of course, are now lunar litter.

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