0:00:07.400,0:00:10.906
When you picture a spaceship,[br]you probably think of something like this,

0:00:10.906,0:00:13.414
or this, or maybe this.

0:00:13.414,0:00:15.017
What do they all have in common?

0:00:15.017,0:00:19.456
Among other things, they're huge[br]because they have to carry people, fuel,

0:00:19.456,0:00:22.758
and all sorts of supplies, [br]scientific instruments,

0:00:22.758,0:00:26.414
and, in rare cases, planet-killing lasers.

0:00:26.414,0:00:31.231
But the next real-world generation [br]of spacecraft may be much, much smaller.

0:00:31.231,0:00:35.403
We're talking fit-inside-your-pocket tiny.

0:00:35.403,0:00:40.708
Imagine sending a swarm of these[br]microspacecraft out into the galaxy.

0:00:40.708,0:00:43.215
They could explore [br]distant stars and planets

0:00:43.215,0:00:46.331
by carrying sophisticated [br]electronic sensors

0:00:46.331,0:00:50.027
that would measure everything[br]from temperature to cosmic rays.

0:00:50.027,0:00:51.792
You could deploy thousands of them

0:00:51.792,0:00:54.886
for the cost of a single [br]space shuttle mission,

0:00:54.886,0:00:57.229
exponentially increasing [br]the amount of data

0:00:57.229,0:01:00.058
we could collect about the universe.

0:01:00.058,0:01:02.364
And they're individually expendable,

0:01:02.364,0:01:04.715
meaning that we could send them [br]into environments

0:01:04.715,0:01:08.468
that are too risky [br]for a billion dollar rocket or probe.

0:01:08.468,0:01:13.421
Several hundred small spacecraft[br]are already orbiting the Earth,

0:01:13.421,0:01:14.960
taking pictures of outer space,

0:01:14.960,0:01:16.436
and collecting data on things,

0:01:16.436,0:01:19.868
like the behavior of bacteria [br]in the Earth's atmosphere

0:01:19.868,0:01:23.177
and magnetic signals that could help[br]predict earthquakes.

0:01:23.177,0:01:28.477
But imagine how much more we could learn[br]if they could fly beyond Earth's orbit.

0:01:28.477,0:01:32.393
That's exactly what organizations,[br]like NASA, want to do:

0:01:32.393,0:01:36.334
send microspacecraft [br]to scout habitable planets

0:01:36.334,0:01:41.161
and describe astronomical phenomena[br]we can't study from Earth.

0:01:41.161,0:01:45.924
But something so small can't carry [br]a large engine or tons of fuel,

0:01:45.924,0:01:48.841
so how would such a vessel propel itself?

0:01:48.841,0:01:53.744
For microspacecraft, it turns out, [br]you need micropropulsion.

0:01:53.744,0:01:55.602
On really small scales,

0:01:55.602,0:01:58.597
some of the familiar [br]rules of physics don't apply,

0:01:58.597,0:02:02.934
in particular, everyday [br]Newtonian mechanics break down,

0:02:02.934,0:02:06.982
and forces that are normally negligible[br]become powerful.

0:02:06.982,0:02:11.089
Those forces include surface tension[br]and capillary action,

0:02:11.089,0:02:13.698
the phenomena [br]that govern other small things.

0:02:13.698,0:02:19.412
Micropropulsion systems can harness[br]these forces to power spacecraft.

0:02:19.412,0:02:21.636
One example of how this might work

0:02:21.636,0:02:26.251
is called microfluidic [br]electrospray propulsion.

0:02:26.251,0:02:28.214
It's a type of ion thruster,

0:02:28.214,0:02:32.686
which means that it shoots out[br]charged particles to generate momentum.

0:02:32.686,0:02:36.338
One model being developed at NASA's[br]jet propulsion laboratory

0:02:36.338,0:02:39.485
is only a couple centimeters [br]on each side.

0:02:39.485,0:02:40.813
Here's how it works.

0:02:40.813,0:02:46.199
That postage-stamp sized metal plate[br]is studded with a hundred skinny needles

0:02:46.199,0:02:50.631
and coated with a metal [br]that has a low melting point, like indium.

0:02:50.631,0:02:53.589
A metal grid sits above the needles,

0:02:53.589,0:02:57.579
and an electric field is set up[br]between the grid and the plate.

0:02:57.579,0:03:00.752
When the plate is heated,[br]the indium melts

0:03:00.752,0:03:04.966
and capillary action draws [br]the liquid metal up the needles.

0:03:04.966,0:03:08.116
The electric field tugs [br]the molten metal upwards,

0:03:08.116,0:03:10.910
while surface tension pulls it back,

0:03:10.910,0:03:14.210
causing the indium to deform into a cone.

0:03:14.210,0:03:16.428
The small radius of the tips [br]of the needles

0:03:16.428,0:03:21.181
makes it possible for the electric field[br]to overcome the surface tension,

0:03:21.181,0:03:22.589
and when that happens,

0:03:22.589,0:03:28.790
positively charged ions shoot off at[br]speeds of tens of kilometers per second.

0:03:28.790,0:03:33.828
That stream of ions propels the spacecraft[br]in the opposite direction,

0:03:33.828,0:03:35.941
thanks to Newton's third law.

0:03:35.941,0:03:38.926
And while each ion [br]is an extremely small particle,

0:03:38.926,0:03:42.734
the combined force of so many of them[br]pushing away from the craft

0:03:42.734,0:03:46.339
is enough to generate [br]significant acceleration.

0:03:46.339,0:03:49.356
And unlike the exhaust [br]that pours out of a rocket engine,

0:03:49.356,0:03:53.373
this stream is much smaller[br]and far more fuel efficient,

0:03:53.373,0:03:57.745
which makes it better suited[br]for long deep-space missions.

0:03:57.745,0:04:01.366
These micropropulsion systems[br]haven't been fully tested yet,

0:04:01.366,0:04:04.513
but some scientists think that they[br]will provide enough thrust

0:04:04.513,0:04:07.690
to break small craft out of Earth's orbit.

0:04:07.690,0:04:11.707
In fact, they're predicting that thousands[br]of microspacecraft

0:04:11.707,0:04:14.013
will be launched in the next ten years

0:04:14.013,0:04:18.065
to gather data that today [br]we can only dream about.

0:04:18.065,0:04:21.402
And that is micro-rocket science.