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You can get a $100 60-day credit on a new Linode account at linode.com/scishow. What’s a surefire way to know  your rocket has reached the Moon?

Well, if it’s 1916, and you’re one of the founding fathers of modern rocketry, you might propose a bunch  of magnesium flash powder which would go off after  your rocket crashed into it. No, seriously. After some  experiments, Robert Goddard concluded it’d take just 6.2 kilograms of the  stuff to be quote “strikingly” visible.

Unfortunately, a flash of light  isn’t much communication beyond “Hey! I got here.” But  Goddard was on to something. A bunch of light is how we communicate  through the vacuum of space.

But scientists have spent over a century working out what kind of light works best. And one day, astronauts might  even use lasers to phone home. [INTRO] At the turn of the 20th century,  decades before most people thought it was even possible  to launch stuff into space, scientists wondered how we could  communicate with other worlds. They knew sound couldn’t travel through a vacuum, and outer space was very nearly a vacuum, so building a cosmic megaphone to shout at the universe was completely out of the question.

The answer was electromagnetic  radiation, a.k.a. light. After all, we’ve got a big ball  of plasma in the sky reminding us that light can traverse the vacuum of space. But what you and I typically think  of as light is just one tiny band in the middle of the electromagnetic spectrum.

Over here rocking the longest  wavelengths and lowest frequencies, you’ve got radio and microwaves. Hovering on either side of visible  light is infrared and ultraviolet. Then your x-rays and gamma rays are up here with the shortest wavelengths  and highest frequencies.

These are all light. Most  are just invisible to us. And by the 1930s, everyone from  scientists to early morning shock DJs were using certain frequencies in the radio band of that spectrum to send  messages around the world.

They didn’t need line of sight  because the radio waves were bouncing off of a layer in the  atmosphere called the Heaviside layer. Today we know it’s a section of the ionosphere. But that means they couldn’t be used  for interplanetary communications.

They wouldn’t go through Earth’s atmosphere. Lucky for scientists, they found  a subset of radio waves that could make it into space: the  ones with the highest frequencies. And while we haven’t exchanged  any radio messages with aliens, we do use those frequencies for  all kinds of space communication, from keeping in contact  with astronauts on the ISS, to deep space spacecraft.

Ever wonder how we get those  amazing high-resolution images from the James Webb Space Telescope, or send instructions to  spacecraft like New Horizons, on the other side of the Solar System? Yep. It’s all radio.

But there’s a problem. Radio waves are kinda crap in terms  of how fast you can transmit data. The longer the wavelength of light, the less information you can transfer per second.

And remember, the radio band  has the longest wavelengths of the entire electromagnetic spectrum. So when New Horizons flew by Pluto in 2015, it took over 15 months to get all  the data it collected back to Earth, at the painfully slow rate  of 1 kilobit per second. We’re communicating across billions  of kilometers of near empty space, but that feat might still not impress some people used to fiber optic cables  and cat-6 ethernet cables.

And that’s not the only  disadvantage our radio signals have. They spread out as they go. The farther out a spacecraft  is, the weaker its signal, and the harder it is to pick up  its call home, or vice versa.

Radio has served us well for so long, but if humanity wants to continue  expanding our space-based activities, our system is going to need a bit of an upgrade. And what sounds like more  of an upgrade than lasers? While the concept of space  lasers may evoke visions of spaceship battles and death stars, scientists want to use them to  transmit data.

Not destruction. The lasers we’re talking about  here are called optical lasers, but most aren’t actually using  optical, or visible, light. They’re using near-infrared, which is a little bit longer  as far as wavelengths go.

But they’re still way shorter than radio waves, so you can transmit a lot more data per second. Plus, since the whole point of lasers is to create a tightly focused beam of light, an optical space laser signal maintains  its strength at greater distances. Scientists have been testing their  space laser tech intermittently over the past half century.

Back in 1968,  as part of the Surveyor 7 mission, they demonstrated that a spacecraft on the Moon could detect a laser shining  all the way from Earth. Not quite the same as shining a laser pointer near your cat across the  room, and maybe not as cute, but a very important proof of concept. It took a few decades, but two-way  laser communication was eventually tested in the 1990s, using the Japanese  Space Agency’s ETS-VI satellite.

And in 2013, NASA used laser light  to deliver not just a message, but an image of the Mona Lisa to  the Lunar Reconnaissance Orbiter. But tests beyond the Earth-Moon  system are still upcoming. That’ll be the job of NASA’s  upcoming Psyche mission.

Currently scheduled to launch in  October 2023, the spacecraft will carry the Deep Space Optical Communications  Experiment on its journey to the asteroid Psyche, in the  belt between Mars and Jupiter. In the meantime, you can find plenty of optical space lasers in Earth’s orbit. Satellite constellations like Starlink use them so the satellites can talk amongst each other.

As humans continue to push the  boundaries of space exploration and venture deeper into the Solar System, our need for faster and  better communication through deep space will continue to grow. One day, space lasers may replace radio entirely. And hey, maybe someone will eventually  try using a proper visible laser to send pulses of information from the Moon, evoking Goddard’s magnesium flashes.

I don’t know about you, but I know  the first message I’d beam back. A little ditty from 1987. Because in my ideal future,  Rick-Rolls are back in style.

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