Alec Gallimore: “What you're seeing is this energetic blue-greenish plasma that comes
out of the thruster.
It really looks like science fiction.
In the end, we're supplying electricity through a wire and an inert gas and we turn it into
this beautiful plasma that's moving at tremendous velocities that's providing thrust that may
one day send people to Mars.”
Chemical rockets are the workhorses of the space age, and they’ve had a pretty standard
formula for the past 60 years.
Get millions of pounds of liquid or solid fuel into a rocket, light it on fire with
an oxidizer, and then the speed of the propellant shooting out the back gives the rocket enough
thrust, or kick, to get into space.
This works great for escaping Earth’s gravity.
But if we want to get to Mars, chemical rockets have hit their their performance limit.
We need new propulsion systems that can rapidly shoot a spacecraft across interplanetary distances,
while using less propellant at the same time.
That’s where the X3 comes in.
As part of NASA’s NextStep program, the X3 is an entirely new space engine that’s
all electric.
Alec Gallimore: “Electro-propulsion devices have the equivalent of 10 times the propellant
efficiency of a chemical system.
To give you an example, a chemical rocket tops out at around 40,000 mph.
An electric system can go over 100,000 mph and in fact, NASA is working on a project
to design one that can actually achieve a velocity of 500,000 mph.
And at that speed you cover a distance between the Earth and the Moon in about 30 minutes.”
Here at the University of Michigan’s Plasmadynamics and Electric Propulsion lab, engineers and
students are working on the X3, a type of electric propulsion design called a Hall thruster.
Alec Gallimore: “Hall effect thrusters are really a kind of a very ingenious propulsion
system.
We take a propellant, in some cases an inert gas like xenon.
We put a huge amount of energy into it, creates a high temperature plasma, charged particles
of electrons and ions, and then we can use electromagnetic fields to shoot out the plasma
at very high speeds.
So they're very simple in design, complex though in operations and very, very efficient.”
Hall thrusters aren’t just a thing of the future.
There are actually hundreds of satellites above you right now using electric propulsion
to stay in position.
But this technology hasn’t been used for manned missions yet, because the amount of
thrust they’re capable of generating is just too low, which means slower acceleration
and a longer trip to Mars.
So, we need more thrust.
Ben Jorns: “Traditional Hall thrusters that work in space operate between one and six
kilowatts.
Now the X-3 comes in and trying to scale Hall effect thruster technology, into a new power
operator machine.
So going from six kilowatts to 100 or 200 kilowatts.
And the advantage of that is if you go to higher power, you can generate higher thrust.
And therefore have higher acceleration.
Instead of using one channel, which a traditional hall thruster has three channels, so you take
all those engineering requirements and you multiply it by a factor of three.”
For these engines to be used in space one day, testing is critical, and these labs are
uniquely equipped for the challenge.
Alec Gallimore: “Sitting behind me is what's called ‘The Large Vacuum Test Facility’
the LVTF.
It has one of the highest pumping speeds in the world, which means it's able to have a
very low pressure while it's operating a large flow rate.
And we use it to simulate space.
We have 19 cryogenic pumps, that remove all the air and all the gasses from the chamber
so we can have a more realistic environment to test these thrusters.
Students run experimental campaigns in the LVTF.
One student might be trying to analyze the life of a thruster.
Another person might be trying to understand how the electrons from the cathode make their
way to the channel.
A successful test is often when you find something unexpected that ultimately leads you to having
a better understanding of the device you're testing.
And that happens quite a bit.”
But the X3 is too powerful for even the LVTF, and at this point, only NASA’s Glenn Research
facility can handle its testing at full capacity.
Alec Gallimore: “A typical thruster may weigh 10 pounds, this thing weighs 500 pounds.
So just designing and building all the components of this mega-scale thruster was a challenge
that we took on.
Last year was a blockbuster year for the X3.
It set records for Hall thrusters for the highest power level at over 100 kilowatts
of power.
The highest level of thrust and actually the highest amount of current being passed through
any type of Hall current thruster.”
These engineering achievements are key, because electric propulsion is going to be a central
part of our future in space.
Alec Gallimore: “NASA is working on developing a sort of a 20 year game plan.
The idea is that we've been in the International Space Station now for more than a decade and
that has been a great.
But the next step would be something like a space station around the Moon.
We would have an outpost around lunar orbit to test new technologies that would be needed
to have humans live in space.
Hall thrusters are playing a really important role in this...it's baseline is to have a
bank of four Hall effect thrusters around because they want to be able to move around
this space station and actually demonstrate the ability to use electric propulsion of
this kind with a human attended spacecraft.”
The X3 is likely two incarnations away from being flight ready, but the work happening
here is all about demonstrating new principles for how to design electro-propulsion engines.
Ultimately, future space travel will use a combination of chemical and electric propulsion
to travel through space.
And it’s projects like the X3 that make a future mission to Mars even more possible.
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