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  • [ ♪ Intro ♪ ]

  • We humans have become pretty good at sending things to space.

  • But once a spacecraft is up there, moving it around can be trickier -- especially if it's tiny.

  • The fiery rocket launches we know and love involve engines that are just too powerful

  • for something like a toaster-sized CubeSat once it's in space.

  • These little probes and satellites sometimes just need gentle nudges instead of big shoves.

  • But, unlike traditional rocket engines, these spacecraft do need engines that can keep nudging

  • for years or decades without running out of fuel.

  • And one promising new way of accomplishing that is called electrospray propulsion.

  • It nudges spacecraft with tiny, charged droplets, and it's already quietly passed rigorous

  • tests on one of the most sensitive probes we've got.

  • All rocketry is based on our old friend Isaac Newton's third law of motion, which says

  • that forces always come in pairs.

  • One way or another, fuel gets pushed out of the back of the rocket.

  • And when the rocket pushes back on the fuel, the fuel also pushes forward on the rocket

  • -- so the spacecraft moves.

  • That's true whether the rocket uses explosions or squeezes air out of a balloon.

  • Huge, traditional rockets -- the kind that get things off the Earth -- are a lot closer

  • to the explosions side, and use energetic chemical reactions.

  • But these engines can deliver more power than a lot of tiny probes need, and they can go

  • through their fuel faster than we'd like for long-term, low-maintenance missions.

  • This is where electrospray propulsion comes in.

  • It's a type of ion engine, which uses strong electric fields to push electrically charged

  • atoms called ions out of the back of the ship.

  • These engines can be tiny and efficient.

  • Like, thrusters the size of quarters can work continuously for weeks at a time.

  • They can do this by providing way smaller forces than chemical engines and go through

  • their fuel a lot more slowly.

  • And that's perfect for something like a CubeSat — a lightweight, mini-satellite

  • that needs to gather data from orbit for a long time.

  • There are actually a few types of ion engines already, and one was even used for the Dawn

  • mission to the asteroid belt.

  • But these engines are a little different than electrospray ones.

  • Traditionally, ion engines work by relying on a bunch of individual atoms for thrust.

  • The atoms are pushed out the back, and the craft moves forward.

  • But electrospray engines use tiny, charged droplets of liquid -- or groups of atoms -- for

  • thrust instead.

  • Those liquids might be something like molten salts, although engineers are still trying

  • to find the best materials for the job.

  • Some thrusters might even use mixtures of liquids, which scientists sometimes call a

  • colloid”, so they're also sometimes known ascolloid thrusters”.

  • One major benefit of these engines over other kinds of ion propulsion is that they're

  • a lot easier to control and fine-tune.

  • If you only need a little force for your spacecraft, it's a lot easier to create a smaller droplet

  • of liquid than it is to control a bunch of individual atoms.

  • This kind of control is perfect for some of today's smallest satellites, like CubeSats

  • or the even tinier nanosatellites, which usually don't have any propulsion systems of their own.

  • Usually, they just stay in space until the atmosphere drags them back down.

  • But as methods like electrospray become cheaper, easier, and more widespread, we'll start

  • seeing CubeSats that can stay in space almost indefinitely.

  • And the good news is, research into these engines has recently picked up.

  • Because as people have started imagining the kinds of things we could do with a lot of

  • small, inexpensive, Earth-orbiting satellites, electrospray propulsion has seemed even more important.

  • Like, with a bunch of satellites like this, you could have internet access or phone signals

  • everywhere on Earth.

  • Governments would also have an easier time monitoring things like nuclear arms treaties,

  • and scientists would have an easier time tracking something like climate change.

  • And, of course, fleets of small, exquisitely sensitive satellites and probes would help

  • astronomers, too.

  • We might not even have to wait very long before this technology is ready to go.

  • The European Space Agency's LISA Pathfinder probe tested electrospray engines between

  • 2015 and 2017.

  • LISA was a proof-of-concept for a planned team of probes that will hopefully search

  • for gravitational waves -- ripples in space caused by super-dense objects moving around.

  • Gravitational waves are unimaginably tiny, so probes looking for them will have to be

  • super sensitive to have any shot at success.

  • LISA's engines and other stabilizers had to be able to move or turn the ship by the

  • width of a single strand of DNA and then stop without jolting -- and they needed to keep

  • that precision up for hours or even days at a time.

  • And with eight electrospray engines on board, LISA achieved all of its ridiculously precise goals.

  • Now, electrospray engines won't suddenly become the only engine out there.

  • We'll still need bigger engines to get satellites off of Earth, and to push around larger spacecraft.

  • But as they're improved and refined over the next decade or two, we'll probably see

  • them on a lot more of the Earth-orbiting satellites -- and space-based observatories -- that make

  • our lives easier.

  • So hopefully we'll have a lot more to say about them soon.

  • Thanks for watching this episode of SciShow Space!

  • If you'd like to learn about another kind of experimental engine -- one that could get

  • humans to Mars in just over a month -- you can watch our episode all about the VASIMR engine.

  • [ ♪ Outro ♪ ]

[ ♪ Intro ♪ ]

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A New Way to Move Tiny Spacecraft | Electrospray Propulsion

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    林宜悉 posted on 2020/03/30
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