[♪ INTRO]
Despite our best efforts, satellites aren’t
always the most predictable.
Sometimes, they just up and reboot.
Or, occasionally, they misbehave for some
unknown reason.
As you might expect, these failures are a
pain for scientists.
Like, come on! We’re trying to explore the universe out
here.
But, if nothing else, we can take comfort
in the fact that
we at least understand where some of these
errors come from.
In one 1980s study, engineers made a map of
where many anomalies happened
for two satellites, and they found something
really weird:
The vast majority of them happened in a region
above South America and the Atlantic Ocean.
This region is known as the South Atlantic
Anomaly.
And it’s one of the most dangerous near-Earth
areas of space, for satellites and humans.
The story of the Anomaly starts with the Sun.
All the time, electrically-charged particles
from the Sun’s atmosphere
stream off at supersonic speeds.
Some of that material zooms by Earth, and
when it does,
it interacts with our planet’s magnetic
field, because,
well, that’s just what charged particles
tend to do.
Some of the material gets directed into our
atmosphere and causes the auroras,
and some of it leaves the system.
But most importantly for this story, some
of that solar material
gets trapped by the magnetic field and contributes
to the Van Allen radiation belts:
ring-shaped regions around Earth full of very
high-energy particles.
Despite the name, they’re not actually radioactive;
space scientists use the term “radiation”
differently than, say, doctors do.
But in general, engineers would still like
to launch satellites
so they never encounter these belts.
Because those charged particles can pass right
through a satellites’ computers,
causing hiccups known as single-event upsets.
The particles can hit a computer chip and
change its memory;
basically, flipping signals from “on”
to “off,” or vice versa.
And that can cause anything from bad data
to severe malfunctions or crashes.
The problem is, depending on where you want
to put your satellite,
the radiation belts aren’t always easy to
avoid.
Because despite what you might be picturing,
they’re not perfectly centered around Earth.
They’re a little skewed. Imagine you’re looking down at the North
Pole.
You can start by picturing the belts as a
ring around the Earth’s equator.
Now, push that ring a little closer to Earth
on one side, near North and South America.
Then, tilt it a bit, so it gets closer to
the Earth near South America,
and a bit further away near North America.
On average, that’s what the belts actually
look like.
They’re like this because Earth’s magnetic
field
is tilted and shifted away from Earth’s
geographic rotation axis,
meaning the magnetic poles don’t line up
with our geographic ones.
Scientists think that’s because the magnetic
field is generated by Earth’s core not rotating
exactly the same as the rest of the planet.
Because of this, there’s a region near South
America,
stretching from around 15 to 45 degrees south
latitude,
where the inner radiation belt is unusually
close to Earth.
Typically, the belt is at least a few thousand
kilometers above the surface,
but here, it’s only about 600 kilometers
up.
That region is the South Atlantic Anomaly.
And there, the inner belt is low enough to
affect and damage satellites.
Now, it might seem like the obvious solution
is to just not launch satellites that pass
over South America. But it’s not that easy.
For one, sometimes we want satellites there!
But even when it’s not necessary,
it’s really hard to avoid this region because
of how orbits work.
Orbits are symmetric around the equator,
so if you want a satellite to pass over a
certain latitude in the northern hemisphere,
it will also have to pass over the same latitude
in the southern hemisphere.
So, if you want your satellite to fly over
somewhere specific,
like NASA’s facility in Maryland at about
40 degrees north,
your satellite will also have to pass over
40 degrees south.
Right through the South Atlantic Anomaly.
Because of this, low, Earth-orbiting satellites
often end up
traveling through this spot for a few minutes
every day.
And as they do, they encounter those high-energy
particles
and the potential problems that come with
them.
One way to protect spacecraft from this is
to shield them with physical barriers.
But since those can get heavy and therefore
expensive to launch,
we’ve had to find other workarounds.
A common, and clever, one is to give a satellite
multiple computers that can vote.
For instance, you might have three computers
all running exactly the same code getting
exactly the same information.
And if at least two of them agree on an action,
the satellite will do that.
So, if one computer glitches, the mission
will be okay.
This type of system wasn’t invented just
for the Anomaly,
but it still saves us a lot of trouble.
But there’s another problem, too:
Because we currently launch most equipment
and crew from Russia and its high latitudes,
the International Space Station also orbits
through the Anomaly.
That’s bad news, because high-energy particles
can damage our DNA.
So as we get exposed to more of them,
the probability of getting cancer and other
diseases goes up.
NASA attempts to limit astronaut’s exposure
to this as much as they can.
And thanks to things like physical shielding
and careful spacewalk planning, they do a
good job.
But if we didn’t know about the Anomaly…
things could be a lot worse.
Exploration would be easier if the radiation
belts were all
nice and perfectly centered, but hey, that’s
not the hand we’ve been dealt.
Instead, we’ve had to get creative with
our engineering.
And I like to think that that’s made us
better explorers.
After all, when we someday venture beyond
near-Earth space,
we’ll have to deal with all kinds of particles
like this.
So, at least we can figure out the basics
close to home.
Thanks for watching this episode of SciShow
Space!
If you enjoyed it and want to learn more about
satellites,
you can watch our episode about how these
things get and stay in orbit.
And if you have questions for us, we’d love
to hear them.
You can leave us a comment below or if you’re
a patron,
you send us a quick question in our patron
inbox over at Patreon.com/SciShow.
[♪ OUTRO]
