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Like humans, spacecraft also go to a cemetery when they die, only this one isn't in a
memorial park.
It's here, this super remote spot in the Pacific Ocean that's actually known as the
spacecraft cemetery.
It's the farthest point on the globe from any human civilization, which means it's
the safest place to have hot metal falling from the sky.
Humans have purposefully crashed hundred of spaceships at this spot.
Which is super cool, and kind of sad.
The old adage of "what goes up must come down" applies to things in space, too.
Granted, not all of them.
A spacecraft launched with enough velocity on the right trajectory won't come back
to Earth, but things in Earth orbit will.
Like China's prototype space station, Tiangong-1, that's expected to fall back to Earth late
in March or early April of 2018.
The unusual thing here is, it's going to do it out of control!
Which raises the question of what happens when spacecraft die and have to home.
We have to do something with this old equipment, because most of the time they're going to
come down no matter what we do.
Satellites and space stations orbit because their speed — about 17,500 miles per hour
— balances against the pull of gravity.
The higher the orbit, the more stable it is, too.
That's because low-Earth orbit isn't a perfect vacuum.
There's no hard line where our atmosphere ends.
Instead, it gradually peters out meaning there's a thin veil of molecules that extends to where
some satellites do orbit.
Those molecules create drag, slowing the satellites until they can't keep up the fight against
the pull of gravity and they reenter the atmosphere.
This also happens in the region where the International Space Station orbits — about
200 miles above the planet.
So, to keep satellites in orbit we need to boost them continually.
Small bursts of speed kick satellites and stations up just enough to offset the drag
of the upper atmosphere.
Since most satellites and space stations are designed with a limited lifetime, mission
planners have figure out how to bring them home before they're even launched.
When they're ready to die, retrorockets fire against the direction of travel slow
the payload deliberately and start a reentry into the atmosphere, where most small satellites
just burn up.
But, there is another scenario.
If a satellite or space station is dead or nearly out of fuel, things can get a little
more complicated.
Without power, engineers can't control the deorbit burn to bring it down in predictable
place.
They have to cross their fingers and hope that it won't fall over a city.
This is exactly where we are with Tiangong-1.
Engineers dealing with the station CAN map its orbit and predict when it might come down,
but they can't predict every atmospheric disturbance that will affect where exactly
it lands.
The station itself is about 34 feet long and weighs close to 19,000 pounds (8.5mt).
A fair bit of it is expected to burn up on reentry, but large pieces could reach Earth.
That mass falling fast could do some damage, fatal damage if it hits a person!
But it's a slim chance.
Luckily, most of the planet is ocean, and there are more unpopulated areas than cities
in the world, so you shouldn't really have to worry.
Leftover spacecraft are a big deal, burning up or crashing is nice, because otherwise
they just hang out and get in the way of new missions or maybe future vacations!
Learn more here.
Satellites orbiting too high to bring home are put into a graveyard orbit some 22,400
miles up, where they'll be out of the way.
Thanks for watching!
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