Crazy Engineering: Ion Propulsion for the Dawn Mission

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Hey guys, this is Mike Meacham at the Jet Propulsion Laboratory and this is an episode of Crazy Engineering.

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Here at JPL, we have to solve problems that nobody's ever solved before and sometimes the solutions can seem a little crazy.

Today we're going to talk about this bad boy, an ion thruster. What's so special about an ion thruster? What makes it different and how does it help us get through the solar system? Let's go talk to an expert.

Alright guys, we found our expert. This is Marc Rayman.

Hi Mike.

Marc, where are we?

We're at a vacuum chamber here at JPL where we test ion engines like this one and we have three just like it on the Dawn spacecraft. It's out in the main asteroid belt between Mars and Jupiter.

Can you explain what makes an ion thruster different than other kinds of thrusters?

Sure, well first, let's remind ourselves how a regular rocket engine works.

You take a gas and you heat it up, or you put it under pressure and you push it out of the rocket nozzle, and the action of the gas going out of the nozzle causes a reaction that pushes the spacecraft in the other direction.

With ion engines, instead of heating the gas up or putting it under pressure, we give the gas xenon a little electric charge, then they're called ions, and we use a big voltage to accelerate the xenon ions thru this metal grid and we shoot them out of the engine at up to 90,000 miles per hour. And they're going out so fast that each individual ion gives a relatively large push back on the spacecraft.

So, if I'm the spacecraft could you push me as hard as I'm going to feel from one of these thrusters.

I can try.

Okay, I'm ready. I can take it.

(Blows air)

I barely felt that.

That's right, the engine pushes on the spacecraft as hard as this single piece of paper pushes on my hand.

In the zero gravity, frictionless, environment of space though, gradually the effect of this thrust builds up.

At full throttle, it would take Dawn four days to accelerate from zero to sixty miles per hour.

Wow that's a slow car, isn't it?

It is, but instead of thrusting for four days, if we thrust for a week or a year or as Dawn already has, for almost five years, you can build up fantastically high velocity.

It's what I like to call acceleration with patience.

Why is that a good thing? What's the tradeoff? What can Dawn do that other spacecraft cannot do?

The ion engine gives us the maneuverability to go into orbit and after we've been there for awhile, then to leave orbit and go on to another destination and do the same thing.

In 57 years of space exploration, Dawn is the first mission targeted to orbit any two extraterrestrial destinations. It wouldn't be possible without ion propulsion.

For two centuries, this has been just a little smudge of light against the stars.

Dawn got to spend 14 months at Vesta and turned it into a whole new complex, fascinating, alien world.

Marc, where are we right now? This is the Dawn mission control room at JPL. This is where we control the spacecraft from; we tell the spacecraft where to point the thruster, what throttle level to use and that's how we guide the spacecraft through the solar system.

And we're on to the next location, which is Ceres.

That's right, the dwarf planet, in fact the first one ever discovered we're going to get into orbit very soon and the pictures are going to be coming into this very room.

Very cool! Stay tuned for those photos and stay tuned for some more Crazy Engineering.

It's going to be cool.

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