SciShow Space is supported by Brilliant.org.
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Thanks to its watery history and potential
for past life,
Mars has been fascinating people for decades.
So it’s no surprise that we’ve sent more
spacecraft there than any other planet.
We’re talking 45 missions.
Most other worlds have had just a small handful.
The problem is, around half of the probes
that have ever attempted to explore Mars
have either crashed or disappeared.
So as much as we want to understand the planet,
getting to its surface is no easy feat.
Mars’s unique atmosphere often gets the
better of us,
and it’s taken some creative
engineering to get to the ground.
Before Mars, the only places we’d ever landed
spacecraft were the Moon and Earth.
And while that did come with challenges, we
had strategies nailed down pretty well for both.
The hard thing about landing on Earth is that
our thick atmosphere creates extreme friction
and heat with incoming spacecraft.
But we’ve solved that problem with heat
shields, and besides, that thick atmosphere
also means parachutes work very well.
The Moon is kind of the opposite.
It has virtually no atmosphere, which gets
rid of the heat problem,
but it also means parachutes don’t work.
We have to use retro-rockets to land, little
rockets that fire underneath a spacecraft
to slow its descent.
Mars, meanwhile, is a whole different beast.
It comes with all the challenges of landing on Earth and the Moon,
but with none of the real benefits.
Its atmosphere is 100 times thinner than Earth’s,
meaning parachutes can’t grab onto enough
air to completely slow down the spacecraft.
But unlike the Moon, there’s also just enough
atmosphere to create problems.
Just like friction causes space rocks and
old satellites to burn up in Earth’s atmosphere,
a space probe entering Mars’s atmosphere
can get hotter than 2000 degrees Celsius.
That’s hot enough to melt iron, and just
about every other metal.
So the millions of dollars’ worth
of machinery we send to Mars
needs serious protection to
keep from being fried.
So, how do you get an expensive, heavy chunk
of metal, traveling tens of thousands of kilometers
an hour, to come gently to a stop on the surface
of another world?
A whole lot of creativity. And probably a good amount of coffee.
Every mission to land on Mars starts with
something called an aeroshell:
a special capsule that protects
its cargo against the heat.
Its outer layer is filled with a material,
called an ablator, that was invented in the
1970s for the first Mars landers:
the Viking missions.
It reacts with the Martian atmosphere in a
way that removes the heat
and leaves behind a trail of gas.
It gets so hot that it glows red, but inside
the capsule,
cargo stays a little cooler than room temperature.
Next, once friction has slowed things to about
1600 kilometers per hour,
a parachute opens, and part of the aeroshell is cast off.
Amazingly, engineers are still using a parachute
pretty similar to the one
designed for the Viking landers
more than 40 years ago.
It’s made of nylon and polyester, with tethers
made of the same material as bulletproof vests.
That makes it super strong and light, which
is really important, considering the craft
is still moving at supersonic speeds when
it deploys.
And while it isn’t enough to slow down a
spacecraft all the way, it does help.
After a few minutes, the parachute brings
the craft down to a few hundred kilometers
per hour, and it gets discarded along with
the rest of the aeroshell.
Now, this is where things get really creative,
and no type of mission has been exactly the same.
Engineers have had to come up with special
solutions to get each spacecraft on the ground.
For example, those 1970s Viking landers used
retro-rockets like on the Moon.
But there was always the possibility that
they’d botch a landing on uneven ground.
And while they were fine for landers, carrying
around a bunch of rockets would be a pointless
burden on the rovers we started sending to
Mars in the ‘90s.
So for the Pathfinder mission that landed
in 1997, which included the first experimental
rover, engineers tried a new method: a cluster
of airbags.
After slamming into the ground, this robotic
explorer bounced along for hundreds of meters.
And by bounced, I mean it shot several stories into the air
and moved as fast as cars on the
freeway before rolling to a stop.
But somehow, it worked.
In fact, it worked so well that scientists
used the same system to land
the more recent Spirit and Opportunity rovers.
Then, in 2012, things had to change again,
because airbags were out of the
question for the Curiosity rover.
It was nearly five times the mass of Spirit
and Opportunity,
so engineers came up with
their most epic solution yet.
They called it a sky crane.
Basically, it was a stage that used retro-rockets
to hover above the surface.
From there, it slowly lowered the rover on
a tether,
then cut itself free and flew off to crash-land nearby.
NASA’s next Mars mission, Mars 2020, will
use a similar strategy.
But who knows what kind of unique designs
we’ll see after that.
Oh, and in case this all isn’t complicated
enough, every single step of these landings
also has to happen completely automatically.
That’s because radio signals travel at the
speed of light, so they take at least eight
minutes to go from Earth to Mars and back,
which is longer than it takes to land.
And it’s not exactly easy to put a spacecraft
on autopilot in a world that’s still
really foreign and unpredictable.
The good news is, all these years of work
have been well worth it.
Besides preparing us for future exploration,
these landers have brought us closer to
knowing what Mars was like in the past.
That could help us figure out whether or not
it ever hosted life, and what it would take
to support human life one day in the future.
And it’s all thanks to some brilliant engineers
and organizations.
If you’ve ever dreamed of becoming an engineer
who lands spacecraft on other planets, you’ll
want to make sure you’re an expert on orbital
mechanics.
And conveniently, Brilliant has some courses
that can really help you out.
Once you’ve learned how orbits work,
you can even try their quiz about
how to send a spacecraft to Mars.
I like how Brilliant makes the physics easy
to understand,
and their visuals and diagrams are super helpful.
You can check it out at Brilliant.org/SciShowSpace,
and right now, the first 200 people to sign
up at the link will get 20% off of an annual
premium subscription to Brilliant.
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