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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, RickRolls are back in style.
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[OUTRO]