nasa fusion jet

NASA Fusion Jet

The journey time from Earth orbit to Mars could be slashed from six

months to less than six weeks if NASA's idea for a nuclear

fusion-powered engine takes off.

The space-flight engine is being developed by a team led by Bill

Emrich, an engineer at NASA's Marshall Space Flight Center in

Huntsville, Alabama. He predicts his fusion drive would be able to

generate 300 times the thrust of any chemical rocket engine and use

only a fraction of its fuel mass.

That means interplanetary missions would no longer need to wait for a

"shortest journey" launch window. You can launch when you want.

The principle is to sustain an on-board fusion reaction and fire some

of the energy created out the back of the spacecraft, generating

thrust. Of course, harnessing fusion is no easy task. Scientists have

struggled to contain the super-hot plasmas of charged ions needed for

fusion reactions.

Bare nuclei

To achieve fusion, scientists heat the hydrogen isotopes deuterium and

tritium to at least 100 million kelvin. This strips electrons from the

isotopes, creating a plasma of bare nuclei. If this plasma is hot and

dense enough, the two types of nuclei fuse, giving off neutrons and

huge amounts of energy.

However, the plasma can only be contained by strong magnetic fields,

and creating containment fields that do not leak has proved very

difficult. What is more, no one has managed to generate a stable

fusion reaction that passes the "break-even" point, where the reaction

is generating more energy than it takes to sustain it.

Fortunately for Emrich, the reaction would not need to go far beyond

the break-even point to generate thrust. And containment is less of a

headache because you actually want some of the plasma to escape, he

says. "That's where the thrust comes from."

The problem is 100 million kelvin is not hot enough to generate

thrust. At that temperature, the fusion reaction only generates

neutrons, which are uncharged and therefore cannot be steered and

fired through a magnetic jet nozzle. To produce thrust, you need

charged particles.

Bold solution

Emrich is proposing a bold solution. He wants to use microwaves to

heat the plasma to 600 million kelvin, triggering a different kind of

fusion reaction that generates not neutrons but charged alpha

particles - helium nuclei. These can then be fired from a magnetic

nozzle to push the craft along.

Emrich has tested the idea with a scaled-down version using an argon

plasma. He found that he could get around many of the containment

problems by using a long, cylindrical magnetic field with powerful

magnets at each end (see graphic).

In a fusion drive, the fields at the end could easily be controlled to

release the highly energetic alpha particles and propel the craft.

If fusion researchers can ever achieve stable, break-even fusion,

Emrich believes a full-scale fusion drive - perhaps 100 metres long -

could be ready and waiting within two decades.

Nuclear fusion could power NASA spacecraft