Sound Space

August 2022 Science Snacks Newsletter

by Marianne Dyson

No one can hear you scream in space. They can’t hear you laugh or cough or clap your hands, either.

Sound is defined as vibrations that travel through a gas, liquid, or solid (e.g. the floor of the apartment upstairs) that is heard when those vibrations “shake” the eardrum of a person or animal.

iphone speakers
Sound is a vibration that travels through a gas, liquid, or solid. Play a song or video on your cell phone and hold your finger near one of the speakers (look for the row of holes at the bottom shown in the photo) to feel the air vibrating. Marianne Dyson photo, 2022.

So despite the loud booms of spacecraft exploding in movies, explosions in space are silent. However, secondary sound effects may be heard. Debris striking a hull or window of a spacecraft might cause a vibration inside that generates sound. Astronauts onboard the space shuttle reported hearing loud bangs as the metal structure of the vehicle shook during jet firings. A spacewalker banging on the hatch could be heard by those inside. Would touching helmets together work? Probably not much, considering the thickness of the glass, but combined with lip reading, it might help!

But wait—people on the ground talk to astronauts in space all the time. How can they do that?

Radio waves are not sound waves. Radio is a band of electromagnetic waves of a frequency between 3 kilohertz to 300 gigahertz [NASA reference]. Radio, just like visible light and x-rays and other frequencies of electromagnetic waves, travels at the speed of light in a vacuum.

Humans cannot hear radio waves directly. (Human eyes “see” electromagnetic waves in the visible light 1015 Hz range.) But clever humans have learned how to convert the energy in a radio wave into vibrations that create sound waves that human and animal ears can sense.

Humans can generally hear sound waves between 12 Hz and 20 KHz. [Reference] Other animals such as dogs, cats, and especially bats can hear higher frequencies, and some, including whales, much lower frequencies than humans. [Reference]

The way an astronaut communicates with Mission Control is to speak into a microphone that converts the vibrations in the air made by her voice into radio waves. Those waves are (after being converted to the proper frequency and chopped into bits for transmission by a computer) sent through the vacuum of space, the atmosphere of Earth, and to a receiver on the ground that distributes the waves to the various devices that convert the radio waves back into sound such as flight controller headsets, someone’s cell phone, or amplified speaker boxes in school auditoriums. A response likewise is converted to radio and back into sounds that the astronaut hears in her headset or through a speaker in a spacecraft or spacesuit.

Author wearing headset
Noise-canceling headsets (shown worn by the author) convert radio to sound while protecting the wearer from hearing loss. Frequent exposure to loud sounds (more than 60 min. above 60% volume/day) or to sounds greater than 165 decibels (a gunshot at close range), can cause permanent damage to the inner ear. [Reference]  Marianne Dyson photo, 2022.

But even at the speed of light, it takes time for the signals to travel back and forth in space—so be prepared for a time lag between questions and answers. As I noted in a previous blog, this time lag almost caused us to hang up on an astronaut who called our house from space!

Because aircraft and spacecraft cockpits are noisy, some sounds, like “d” and “t” are hard to distinguish from each other, especially considering various accents. To avoid confusion, the aviation and space community employ an aviation alphabet to spell out each letter of a word. So instead of spelling out “dot” as “dee oh tee” which might sound like DoD or tot or even pot, in aviation/space speak, it is “Delta Oscar Tango.”

I hope your brain enjoyed this science snack. In case you didn’t hear, that’s Sierra November Alpha Charlie Kilo!

Writing and Speaking About Space

I’m happy to announce I have a short story, “The Power of Apollo (16)” and science article in the September/October 2022 issue of Analog Science Fiction and Fact Magazine (and my name is on the cover!). Single print copies can be found at bookstores and newsstands. Electronic subscriptions are available via Amazon.

Want to live in space? Listen to the Big Picture Science podcast (also broadcast on NPR Science Fridays), “Building a Space Colony.” I’m quoted during the first segment which is followed by a segment with Author Emily St. John Mandel and another with John Adams of Biosphere 2.

Texas friends: I hope to see you at FenCon in Dallas September 16-18, 2022. Stop by my autograph table to get signed copies of Shuttle Mission Control, Fly Me to the Moon, A Passion for Space, and my newest children’s title, Up in Space. Autographed books can also be ordered through Thank you for your support!