WEBVTT

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When you picture a spaceship,
you probably think of something like this,

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or this, or maybe this.

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What do they all have in common?

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Among other things, they're huge
because they have to carry people, fuel,

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and all sorts of supplies, 
scientific instruments,

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and, in rare cases, planet-killing lasers.

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But the next real-world generation 
of spacecraft may be much, much smaller.

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We're talking fit-inside-your-pocket tiny.

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Imagine sending a swarm of these
microspacecraft out into the galaxy.

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They could explore 
distant stars and planets

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by carrying sophisticated 
electronic sensors

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that would measure everything
from temperature to cosmic rays.

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You could deploy thousands of them

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for the cost of a single 
space shuttle mission,

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exponentially increasing 
the amount of data

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we could collect about the universe.

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And they're individually expendable,

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meaning that we could send them 
into environments

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that are too risky 
for a billion dollar rocket or probe.

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Several hundred small spacecraft
are already orbiting the Earth,

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taking pictures of outer space,

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and collecting data on things,

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like the behavior of bacteria 
in the Earth's atmosphere

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and magnetic signals that could help
predict earthquakes.

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But imagine how much more we could learn
if they could fly beyond Earth's orbit.

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That's exactly what organizations,
like NASA, want to do:

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send microspacecraft 
to scout habitable planets

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and describe astronomical phenomena
we can't study from Earth.

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But something so small can't carry 
a large engine or tons of fuel,

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so how would such a vessel propel itself?

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For microspacecraft, it turns out, 
you need micropropulsion.

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On really small scales,

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some of the familiar 
rules of physics don't apply,

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in particular, everyday 
Newtonian mechanics break down,

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and forces that are normally negligible
become powerful.

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Those forces include surface tension
and capillary action,

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the phenomena 
that govern other small things.

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Micropropulsion systems can harness
these forces to power spacecraft.

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One example of how this might work

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is called microfluidic 
electrospray propulsion.

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It's a type of ion thruster,

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which means that it shoots out
charged particles to generate momentum.

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One model being developed at NASA's
jet propulsion laboratory

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is only a couple centimeters 
on each side.

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Here's how it works.

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That postage-stamp sized metal plate
is studded with a hundred skinny needles

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and coated with a metal 
that has a low melting point, like indium.

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A metal grid sits above the needles,

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and an electric field is set up
between the grid and the plate.

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When the plate is heated,
the indium melts

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and capillary action draws 
the liquid metal up the needles.

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The electric field tugs 
the molten metal upwards,

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while surface tension pulls it back,

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causing the indium to deform into a cone.

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The small radius of the tips 
of the needles

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makes it possible for the electric field
to overcome the surface tension,

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and when that happens,

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positively charged ions shoot off at
speeds of tens of kilometers per second.

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That stream of ions propels the spacecraft
in the opposite direction,

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thanks to Newton's third law.

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And while each ion 
is an extremely small particle,

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the combined force of so many of them
pushing away from the craft

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is enough to generate 
significant acceleration.

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And unlike the exhaust 
that pours out of a rocket engine,

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this stream is much smaller
and far more fuel efficient,

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which makes it better suited
for long deep-space missions.

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These micropropulsion systems
haven't been fully tested yet,

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but some scientists think that they
will provide enough thrust

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to break small craft out of Earth's orbit.

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In fact, they're predicting that thousands
of microspacecraft

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will be launched in the next ten years

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to gather data that today 
we can only dream about.

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And that is micro-rocket science.