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  • SciShow Space is supported by Brilliant.org.

  • [ ♪ Intro ]

  • While traveling in space, one of the hardest things to do is, stop. Or change direction.

  • Without anything to push against or friction to slow things down, spacecraft need to do

  • all the hard work of changing their speed or path.

  • And sometimes they do that in ways you'd never expect: like by vaporizing Teflon.

  • They're called pulsed plasma thrusters, and they can use the same stuff that's on

  • your frying pan to make spacecraft zoom around the universe. And they've been doing it

  • since the 1960s.

  • To make basically any move in space, satellites rely on Isaac Newton's famous Third Law

  • of Motion, which is probably on a poster in every high school physics classroom: For every

  • action, there's an equal and opposite reaction.

  • Put another way: throw stuff backwards and you'll go forward.

  • In fact, you can boil down every rocket design, no matter how complicated, to this basic idea.

  • When thinking of a rocket, you might normally imagine what's called chemical propulsion.

  • That's thefire-coming-out-the-endkind, which uses a controlled explosion to

  • hurl material out the back of the rocket.

  • And once in space, another kind, electromagnetic -- or EM -- propulsion, also becomes available.

  • They aren't strong enough to get rockets off the ground, but they are great once you're

  • past most of Earth's atmosphere.

  • These rockets work kind of like railguns, accelerating charged particles, or ions, out

  • the back with electric or magnetic fields.

  • Today, we have all kinds of EM thrusters, but pulsed plasma thrusters, or PPTs, were

  • the first ones ever flown in space. They were used in 1964 on the Soviet Zond 2 mission to Mars.

  • Like some other engines, PPTs specifically use plasma to generate thrust, instead of

  • a random collection of ions. Plasma is a super hot substance made of charged ions, and it's

  • the fourth state of matter.

  • In some ways, it behaves kind of like a gas, because its atoms are pretty spread out. But

  • unlike the other states of matter, plasmas can be shaped and directed by electric and magnetic fields.

  • To generate its plasma, PPTs eat Teflon! Which is pretty awesome.

  • A pulsed plasma thruster places a block of Polytetrafluoroethylene -- what we know as

  • Teflon -- between a pair of metal plates.

  • Then, connected wires charge up those plates with electricity until it arcs through the

  • Teflon block, set off by a spark plug.

  • That arc delivers thousands of volts into the block, vaporizing the nearby Teflon and

  • ionizing it into a plasma.

  • The sudden burst of plasma effectively creates a circuit connecting the metal plates, which

  • allows electricity to flow like it's traveling through a wire.

  • One neat side effect of flowing electricity is that it generates a magnetic field. And

  • everything in the thruster is already arranged so that this field pushes the plasma out into space.

  • At this point Newton's third law springs into action, pushing the spacecraft in the

  • opposite direction of the departing particles.

  • And, huzzah, motion!

  • Well, the tiniest bit of motion.

  • A pulsed plasma thruster deployed by NASA in 2000 produced an amount of force equal

  • to the weight of a single Post-it Note sitting on your hand. Which might not seem that exciting,

  • but it has some big implications.

  • Like other forms of electromagnetic propulsion, these engines require a lot of electricity

  • to run, but in exchange they offer incredible efficiency with their fuel.

  • Pulsed plasma thrusters can produce up to five times more impulse -- or change in momentum

  • -- for every gram of fuel than a typical chemical rocket.

  • They do it very, very slowly, but they get the job done.

  • PPTs also offer exceptional simplicity and safety.

  • The onlymoving partis a spring that constantly pushes the Teflon block forward

  • and, without the need to store pressurized liquid or gas fuel, there's no chance of explosion.

  • So it makes sense then that pulsed plasma thrusters were so useful back in the 1960s.

  • Since then, their lack of power has meant that most spacecraft main engines have remained chemical.

  • And when companies really need some kind of EM drive -- like for the Dawn mission to the

  • asteroid belt -- they'll tend to choose more sophisticated designs.

  • But that doesn't mean we're done with these thrusters just yet.

  • Recently, their extreme simplicity has made them a natural fit for the most up-and-coming

  • field of exploration: CubeSats.

  • CubeSats are tiny, shoebox-sized satellites designed for simple missions and built on

  • the smallest of budgets -- often by research labs or universities.

  • Earth-orbiting CubeSats seem almost tailor-made for the strengths of pulsed plasma thrusters.

  • Lots of sunlight gives them ample electric power, but since they're so small, space

  • and weight are at an absolute minimum. And right now, most CubeSats typically don't

  • have any kind of propulsion system of their own.

  • So one solution is micro pulsed plasma thrusters, which can weigh just a few hundred grams and

  • measure under 10 centimeters on a side.

  • That might not sound like much, but even a tiny amount of thrust could double the useful

  • life of some kinds of CubeSats.

  • They'll likely need to undergo more testing and development before they're ready for

  • primetime, but someday, we could have a whole fleet of Teflon-eating satellites.

  • Not bad for the same stuff that coats our kitchen pans!

  • So I joked about Newton's third law of motion being etched into our brains earlier, but

  • when's the last time you really thought about good ole' Newton critically?

  • Brilliant.org has a whole section on Newton's Laws as part of their Classical Mechanics

  • course. And learning about pulsed plasma thrusters made me want to test how well I remember using

  • Newton's third law. So, imagine you're on a beautiful, frictionless lake. In your

  • own little boat. The sun is shining, there are birds in the air, there might be lilly

  • pads around you. And then you spot another boat, just like yours, a little bit bigger

  • across the lake, 30 meters away. And you know that your boat is 60 kilograms and actually

  • that's your friend, so you know that that boat weighs 90 kilograms. And you want to

  • bring the boats together so you can have a picnic. Luckily they're connected by a string.

  • So if your string is pulled with a constant force and your two boats meet up after 20

  • seconds, how far did your boat move? You probably don't even need to get into a boat to solve

  • this problem. I believe in you. You can go to Brilliant.org to check out this quiz and

  • a bunch of others like it and the first 777 people to sign up at brilliant.org/scishowspace

  • will get 20% off of their annual Premium subscription AND support SciShow Space - so thank you!

  • [ ♪Outro ]

SciShow Space is supported by Brilliant.org.

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