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Science Fiction has long written about this communication technique in vacuum: Astronauts touch their helmet against another astronaut's helmet, so that sound will transmit through that physical connection and they can to talk to each other without needing electronic communication devices (Example screencap from The Expanse). But is there a source that real astronauts have ever done this?

Googling "astronauts touching helmets" and "astronaut helmet-to-helmet" mostly yields verifications that it is indeed possible. The only real world mention I could find is from the US Navy diving manual: "The two divers need only touch helmets to talk with each other".

Edit: To clarify why I asked: Multiple Redditors claimed that this has happened in real life, but of course this is all hearsay: Comment 1, Comment 2

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    $\begingroup$ Unless there was an emergency situation, such a communication method would not be required inside a space craft during a mission. This then reduces the question to how many times have multiple astronauts conducted an EVA, or EVA conditions such as an open cargo area on the Space Shuttle, at the same time & were they in close proximity to one another be able to communicate in such a manner. $\endgroup$
    – Fred
    Jun 25, 2022 at 3:12
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    $\begingroup$ @Fred there would be no reason to use this method unless the EVA radio comm failed, and at least on US missions, I don't think it ever has. Also on most US EVAs the helmets have thermal / protective fabric or other structures over a large part of the helmet which might prevent this from working. My guess is that this has never been done on a US EVA but it would be an enormous task to prove that... $\endgroup$
    – Organic Marble
    Jun 26, 2022 at 13:05
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    $\begingroup$ Was this solid-borne sound transfer ever tested in a vacuum chamber on Earth? $\endgroup$
    – Uwe
    Jun 26, 2022 at 17:37
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    $\begingroup$ If this has ever been tested it would have been as a backup communication method, I suspect. Proving a negative is hard, however... $\endgroup$
    – PearsonArtPhoto ♦
    Jun 27, 2022 at 15:32
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    $\begingroup$ @Uwe vacuum might not be necessary for the test. If they can't hear each other before touching and suddenly they can hear each other when touching, then it works and air vs vacuum outside doesn't matter. The only time that vacuum would be necessary is if they could already hear each other before touching. $\endgroup$
    – uhoh
    Jun 27, 2022 at 17:32

1 Answer 1

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As the only practical reason for touching helmets would be to have a private conversation, it would be something that would be unlikely to be reported and be known about. It could only have happened with spacewalks. For the Apollo lunar work, it's unlikely they could bend over enough to touch helmets, the mid-body section of their suits were very stiff.

The question is a form of logical error known as an "Irrefutable Hypothesis."

However, touching helmets certainly could have been done as exploratory science - simply to test whether it could work if needed. But we don't have any evidence of that having happening. Also it'd be fascinating to see a test of the children's use of two tin cans connected with a string to communicate. Since the energy of the vibrating string is partially dampened by the resistance of the atmosphere, the "two can and string telephone" should work better in space, where there is no such impedance.

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    $\begingroup$ Your answer could be improved with additional supporting information. Please edit to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers in the help center. $\endgroup$
    – Community Bot
    Jun 15 at 12:49
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    $\begingroup$ "...the only practical reason..." another practical reason would be to test the technique in case radio communication is lost - electrical problem, radiation damage... I think the idea that one can be certain there is only one practical reason is itself illogical. $\endgroup$
    – uhoh
    Jun 15 at 16:12
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    $\begingroup$ I suspect the helmet-touch method would result in very faint, probably incomprehensible amounts of sound transfer, and in any case hand gestures are a more reliable way to communicate in the case of a radio outage. The scuba diving signs should be perfectly functional in space. $\endgroup$
    – Darth Pseudonym
    Jun 15 at 18:20

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