This episode was written and produced by Jack Higgins.

We've all heard the iconic recordings from the Apollo missions. But how exactly does NASA manage to run live audio between Earth and the moon? And how might we chat with astronauts on Mars and beyond? Featuring Astronaut Peggy Whitson, NASA Audio Engineer Alexandria Perryman, and Astrophysicist Paul Sutter.

MUSIC FEATURED IN THIS EPISODE

Are We Loose Yet Bodytonic
Algo Rhythm Natural by Sound of Picture
Gathering by Sound of Picture
If I Lost You (with Emily C Browning and Why the Face) by Ariza
Raining the Blues by Ernie Barton
Fragile Do Not Drop by Sound of Picture
Dirty Wallpaper by Lemuel
Roadside Bunkhouse by Truck Stop
Andromeda by Tony Anderson
Thumbscrew by Sketchbook 2
Night Vision by Sound of Picture
Vega by SVVN
Sequence by Greg Thomas

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View Transcript ▶︎

[music in]

With the rise of cell phones, it’s never been easier to get in touch. You just unlock your phone [SFX], tap a name [SFX], and in just a few seconds [SFX: Phone ringing], you can literally talk to someone on the other side of the planet [SFX: “Konnichiwa”]. We’re all used to it by now, but the technology that makes that call possible is pretty incredible.

When you initiate that phone call [SFX: phone dial], the antennae on your cell phone beams [SFX: laser sound] a radio signal [SFX: radio signal] to a nearby cell tower. The cell tower then sends this signal over a fiber optic line [SFX: electricity] to a switching center [SFX: switches and plugin sounds]. From there, the signal is connected to another cell tower [SFX: electricity], which then beams [SFX: radio signal] it to the phone of whoever you’re calling [SFX: hello].

That’s complicated enough, but what happens when you need to talk to someone who’s not even on this planet?

[SFX clip: Key sound SFX: Houston this is Neil, radio check...]

You're listening to Twenty Thousand Hertz.

[SFX clip: NASA: Neil this is Houston...]

[music out]

When you’re orbiting the Earth at over 17,000 miles an hour, communication gets really tricky.

[music in]

Alexandria: They use what's considered space to ground loops. It's radio frequency, and because they're moving around the earth so quickly, they have to bounce off of satellites in order for it to get transmitted down.

Alexandria Perryman is an audio engineer at the Johnson Space Center in Houston. Yep, the same Houston that the astronauts are always talking to...

[SFX: “Houston” montage]

When communication from a space mission reaches ground control, it’s Alexandria and her colleagues who broadcast the audio to the public.

Alexandra: We have the space to ground loops going, running, 24/7, and it's all being recorded.

Alexandria: And so what we do with our audio is clean it and put it out to the public live. So the same space to ground loops that the mission control was talking into, I have control of that to put it out on NASA TV and Facebook Live and use it for other things for the public to be able to hear.

Almost all of the audio that comes into mission control gets immediately rebroadcast.

Alexandria: When we're live on air, say we're doing a space walk what you guys are hearing is what we're hearing.

[music out]

The fact that we can run live audio between Earth and space is pretty mind boggling. One of the first things you’ll learn in physics class is that sound can’t travel in a vacuum.

Paul: Sound at its most simplest level is pressure waves, waves of varying pressure in a medium like air or water.

This is Paul Sutter. He’s an astrophysicist at Stony Brook University and the Flat Iron Institute in New York City.

Paul: As sound waves propagate out, you can watch microscopically, the little air molecules [SFX: wind and dust/debris] or water molecules [SFX: moving water, bubbles] scrunch together [SFX: sounds are sucked into center] when the wave hits a peak and then spread out as the wave hits a trough [SFX: sounds pan across stereo spectrum]. And we create those pressure waves by shoving air through our throat and vibrating our vocal chords [SFX: singing]. Those pressure waves travel through the medium into our ears and where they vibrate our eardrums [SFX: vibration]. The little air molecules next to our eardrums wiggle it back and forth, [SFX: electrical sounds] and that it translates into a signal that we interpret in our brains.

To create this ripple effect, sound waves have to have something to travel through.

[music in]

Paul: The key part of all this is that it requires a medium, so you need some sort of gas or fluid that can have a pressure in order to sustain sound waves.

But in the vacuum of space, there’s virtually no pressure at all, so those soundwaves have nothing to travel through.

Paul: So we have to transform our sound waves into something that can transmit through vacuum, and light can travel through a vacuum.

What we normally think of as “light” is really just the tip of the iceberg.

Paul: Light comes in many, many different kinds of wavelengths. Some of them we can see, like red or green or blue, and in many, many wavelengths that we can't see, like infrared or microwave or radio. And radio waves are pretty fantastic for transmitting through space. They can cut through a lot of interstellar dust pretty easily, and so radio waves are our preferred form of communication in space.

Once you transform a soundwave into a radio wave, you can send it over huge distances, through the air, under water, or, in the case of space, [music out] across an empty vacuum.

[SFX: Radio static/tuning]

If you ever listen to the radio in the car, you’ve probably had the strange experience of picking up two stations at once. [SFX: song 1 + song 2 playing at once with heavy radio static]

This happens because both stations are broadcasting at about the same frequency.

This interference usually goes away pretty fast as you drive farther away from one signal, and closer to the other one. [SFX: one song stutters and fades out while the other becomes more clear, then quickly ends like you turned off the radio]

But the signals going to and from space are much stronger than your local radio station. To reduce radio interference, different radio bands get designated for different types of communication. For instance, the International Space Station now uses four specific bands.

Peggy: Originally, we had two S-band communication systems. And now, we have four bands of communication, two on S-band and two on KU-band.

This is Peggy Whitson, the first female commander of the International Space Station, or ISS. The definitions of S-band and KU-band get pretty technical. The point is, the more radio bands you have to work with, the more lines of communication you have.

Peggy: If everybody's doing different experiments, we need more bands of communication so people can be talking to different team members.

These astronauts might be talking to mission control in the US, Japan and Germany all at once, meaning their radio signals are going all over the world. To make this possible, these transmissions have to go through a Tracking and Data Relay Satellite, also known as TDRS.

[music in]

Peggy: It's being transmitted into geosynchronous orbit, which is 22,000 miles out. There are half a dozen satellites that sit, different places around the planet and they rotate as the planet rotates, so they're always in the same place above the planet.

These TDRS satellites work almost like cell phone towers in space, transmitting messages between ground control and the astronauts in orbit. [SFX: Satellite beeping]

Peggy: [SFX: Peggy speaks as through a radio, panning left to right] And so, the signal gets sent to those satellites out there at 22,000 miles then it gets bounced back to us at 250 miles above the earth. But we're traveling at 17,500 miles an hour so we have to switch to different satellites as we're going around the world to maintain that communication.

All of this happens in milliseconds.

Peggy: I always think it's funny that it goes from the ground, out 22,000 miles then back to 250 miles above the earth before we actually hear it.

[music out]

Of course, the astronauts on the ISS aren’t always working. In their free time, they sometimes check in to see if anyone down on Earth wants to chat, using what’s called a “ham radio”. “Ham radio” essentially means “amateur radio,” and it covers any use of radio communication for non-commercial or unofficial purposes. Here’s astronaut Doug Wheelock using the onboard ham radio to talk to someone in Texas.

[SFX clip: Doug Wheelock: Whiskey Five Sugar Sugar Victor, we’ve got you loud and clear. Welcome aboard the International Space Station, number Alpha One Sugar Sugar.

Club Owner: Thank you for answering the call, Doug I just want you to know our club is 90 miles southeast of Houston and we’re looking forward to getting home, and maybe we can have dinner when you get back. Appreciate you answering the call. Whiskey Five Sugar Sugar Victor.]

[music in]

Now that the ISS has two extra radio bands to work with, they can use these extra channels for the more casual interactions.

Peggy: The ham radio is not used as much these days because we have four channels of com now. We do a lot of school talks nowadays to students, projecting our video, and they get direct com via the S-band or the KU-band assets on board the station.

For Alexandria, these school talks are some of the best days on the job.

Alexandria: I love the part where I'm doing a live interview with, say, that astronaut on the ISS and an elementary school. And they're communicating through Skype and I'm coordinating the audio through, just seeing the kids' faces light up when the astronaut floats across the screen. That moment, I was like, "I officially have the coolest job ever."

[SFX clip: Aiden: Hi, my name is Aiden. How would you describe the view from the International Space Station? Over!

Akihiko Hoshide: I can describe it in one word, and it is, “COOL!”]

Alexandria: These kids, they come there and they're dressed up as astronauts and they get to ask their question. And I'm the one who gets to push their audio through to the astronaut. And that may be a moment they think of for the rest of their life.

[music out]

The systems that make these transmissions possible are normally pretty reliable, but nothing’s perfect. A loss of signal, happens more often than you might think.

Alexandria: There are times we know that they're going to be in a dead zone for maybe two or three minutes.

Alexandria: It's just that their signal, because of the speed they're moving and before it's able to get to the next satellite, it's too much of a distance, then that would cause a dead zone to happen. That would cause their signal not to reach us.

Peggy says that getting a brief moment of radio silence isn’t always such a bad thing.

Peggy: Sometimes it's a relief [laughs].

But when you’re outside the ship doing an Extra Vehicular Activity, or an EVA, losing that voice over the headset can be pretty freaky.

[music in]

Peggy: It can be disturbing if you need to have the com. My worst scenario was actually during a spacewalk, and my EVA partner and I could hear each other, and I could hear the crew member that was in the space station, and the ground could hear us, but we couldn't hear the ground.

Typically, losing comms means, “Get back on board until we figure this out.”

Peggy: We would've normally end the EVA because we don't have com, but because Yuri on the station could talk to the ground, we had this kind of relay com going on, which was not going to work for the EVA, but still got us by long enough for the ground to figure out and get the communication systems configured.

[music out]

Talking with astronauts orbiting the Earth at 17,500 miles an hour is hard enough, but as humans go back to the moon, and then to Mars and beyond, communication will be exponentially harder.

[music in]

Paul: Both NASA and private companies like Space X have stated goals to step up lunar missions again, maybe we'll have a permanent lunar base, where crews are rotating in and out on a regular basis.

Paul: That will help us test out and prepare some of the technologies that we need to be able to send astronauts on a two year round trip mission to Mars.

Alexandria: Right now, if we were to go to Mars with the technology that we have, for me saying “Hello” and you saying “Hello” back, round trip, it would be about 40 minutes.

Alexandria: And you just cannot have that, because if something goes wrong while they're there, having to wait 40 minutes just before you can get an answer back is not very helpful at all.

As we head into a new era of space exploration, we’ll need to figure out ways to talk to people on other planets, and maybe, someday, in another solar system. That’s coming up, after the break.

[music out]

MIDROLL

[music in]

In the entirety of human history, we’ve only been able to reach space for 60 years. We’ve barely scratched the surface of this final frontier, and as we journey farther and farther from home, maintaining fast and reliable communication with Earth will be crucial.

Currently, the spacecraft orbiting the Earth are in constant radio communication with ground control [SFX: space comm montage].

These radio waves travel at the speed of light, which is 186 thousand miles per second. That’s fast enough that if we put TDRS satellites around the moon, we could talk to a lunar base with only a tiny bit of lag.

Peggy: If they are able to use TDRS, it would be pretty seamless. There might be a little bit of lag in the communication, just like a second.

[SFX: Testing 1 2 3… Houston, do you read me?]

[music out]

But if you go beyond our moon, real-time communication quickly becomes impossible, even with messages traveling at the speed of light.

Peggy: It's pretty amazing to think that I could be on Mars and say "Houston, I have a problem." And it'll be 40 minutes before they get back and say "What's up?"

NASA is already testing how communication could work for a Mars mission.

[music in]

Peggy: We actually found that something similar to texting is more efficient so that you could text something, go do you other thing, come back when it's convenient and get the answer and continue on.

Texting might work for routine updates and long term planning. But losing the human contact you get from interacting in real time would be a huge adjustment for astronauts on Mars.

Peggy: For psychological reasons obviously that's going to be a big difference, because right now we talk to family and friends. On the weekends we get a video conference. That's not going to happen. It's going to be a one way recorded message both directions, and so it's not like you're going to have a conversation anymore.

[music out]

To make real-time communication possible over such vast distances, we’ll need to be able to send a signal faster than the speed of light. Over the years, science fiction writers have come up with creative ideas for communicating, and travelling faster than lightspeed. One common concept is a wormhole.

Paul: Wormholes are theoretical objects that can act as shortcuts through space. If we had a wormhole, maybe you can just take a couple steps and immediately plant your foot on Mars.

In the movie Interstellar, the crew use a wormhole to jump to distant planets.

[SFX clip: Interstellar clip: “That wormhole lets us travel to other stars. Came along right as we needed it.”

“They’ve put potentially habitable worlds right within our reach.”]

Wormholes have been theorized for decades, but sadly, they’ve never been proven to exist.

Paul: As far as we can tell, we keep trying to cook up actually physical ways of building wormholes or having stable wormholes in our universe. Every time we do it, the universe concocts some reason why they can't exist.

So sending a radio signal through a wormhole to chat with your friend on Mars isn’t very likely.

Paul: If wormholes did exist, yes, you could potentially build one and send a message to Mars very, very quickly. But it looks like our universe doesn't allow wormholes to exist, but we don't know why. And that's a bit perplexing.

Another idea for communicating across space involves something called “quantum entanglement.”

[music in]

Paul: There's this idea in quantum mechanics called entanglement, where I can take two little particles and prepare them in a special way where their inherent quantum properties become mixed together, where in some sense, they're a single quantum object.

If two particles are entangled on the quantum level, knowing something about one particle let’s you reliably predict the state of the other one.

Paul: And this connection persists no matter how far away the particles are from each other. And what this means is that because they share a same state, if I change something about one particle, there will be a corresponding change in the other.

Let’s say you flip one entangled particle upwards. The other particle should theoretically flip up too, even if it’s lightyears away.

Paul: And the initial thought is like, "Oh, I can take that entanglement and I can use communication." Because I can take my little entangled particle and start wiggling it back and forth. And you're saying, "up, up, down, down, down, up, up, up," doing some sort of Morse code. And someone on the other side of the universe can be watching their particle and get the message. It doesn't work that way.

[music out]

The problem is that other forces can affect these particles, too. This would make it almost impossible to distinguish an actual message from random noise.

Paul: The only way I can verify whether this is just random quantum noise or this is a message that I'm getting, is to send a light signal, something that's limited by the speed of light.

Paul: No matter what, the spread of information, the spread of causality, is limited by the speed of light.

Of course, this also makes it really hard to connect with any alien species that might be trying to say hi.

[music in]

Paul: We saw it's 40 minutes round trip just to say hi to Mars, and that's the next nearest planet. A round trip for a “Hello” to our next nearest neighbor star is eight years. And that's just our nearest neighbor. The time and space scales in our galaxy are so incredibly immense and outside the experience of anything that we've ever experienced as a species.

Even sending a normal radio signal to a neighbor star would be pretty challenging. Throughout the universe, there are all kinds of natural reasons that we find radio waves. For instance, a “quasar” is a supermassive black hole surrounded by a giant field of gas. Supermassive blackholes [SFX: black hole rumble] are billions of times more massive than our sun. As the gas [SFX: gas] around a quasar gets pulled into the blackhole [SFX: suction], other particles get blasted [SFX: energy blast] outwards as electromagnetic radiation.

Much of this energy registers as visible light, making quasars some of the brightest objects in the universe. But some quasars also emit powerful radio waves. In fact, when astronomers first observed these objects using radio telescopes, they called them “quasi-stellar radio sources,” which was eventually shortened to “quasar.”

Because of all of the galactic radio noise made by quasars, sunspots, and even Jupiter’s ionosphere, any interstellar message we tried to send would get garbled pretty quickly.

Paul: Our own radio [SFX: Music fade out and white noise fade in] messages that we’ve blasted into the cosmos are just mixed with the general radio background. You can't even hear us from our nearest neighbor star, because we're not powerful enough.

So if any alien civilizations are out there listening, they probably can’t hear us.

Paul: We're not alone in the universe, but we might as well be.

[SFX: white noise out]

[music in]

While the challenges ahead may seem daunting, it’s these same challenges that will inspire future generations of space explorers.

Peggy: I was nine years old when the Apollo 11 landed on the moon and I thought, “Wow, cool job. I’d like to do that.” Of course, when you're nine, you want to do lots of things but it was one that stuck with me.

As long as curious people keep looking to the stars and wondering what’s out there, we’re going to keep chasing the next horizon.

Paul: I just love the magnitude, the timescales, the space scales. We get to watch stars being born and watch stars die. We get to watch galaxies collide. We get to watch the universe expand before our very eyes. This is stuff so far beyond our normal everyday Earthly experiences. It just draws me in every single time.

Twenty Thousand Hertz is hosted by me, Dallas Taylor, and produced out of the sound design studios of Defacto Sound. Find out more at defactosound.com.

This episode was written and produced by Jack Higgins. And me, Dallas Taylor. With help from Sam Schneble. It was story edited by Casey Emmerling. It was sound designed, and mixed by Soren Begin and Jai Berger.

Thanks to our guests Alexandria Perryman, Peggy Whitson and Paul Sutter.

Paul hosts a really cool podcast called Ask a Spaceman, which you can find right here in your podcast player.

Thanks to the team at NASA who make all of their audio and communications public, and thanks to the National Archives in DC.

Thanks to listener Dan Ray for coming up with the title for this episode. If you’d like to help us name episodes, and get bonus content like sneak previews and goofy sound design videos, then be sure to follow 20K on Facebook and Twitter, and subscribe to our subreddit, Reddit dot com slash R slash 20K.

Thanks for listening.

[music out]