Traveling through deep space is a hazardous undertaking and choosing the right engine can mean the difference between a fast, successful mission and a slow one with mounting dangers of radiation sickness, equipment failures and personal conflicts. A team of researchers from the University of Washington (UW) and Redmond, Washington-based MSNW are aiming to expand the options by developing a new fusion drive rocket engine that promises to make possible a manned spacecraft that could reach Mars and return to Earth in months rather than years.

There are a number of ways of getting to Mars, but the options are pretty limited if it includes having a crew on board. The obvious choice is chemical rockets. That’s how all space vehicles from Earth are launched and most are set on their trajectories. It’s a tried and trusted technology, but long ago reached the point of diminishing returns. Without getting into the maths, using chemical rockets would mean building a huge Mars ship that is mostly fuel with a tiny payload that will take years to complete the journey.


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Nuclear thermal rockets

One alternative is a nuclear thermal rocket that gets its power from splitting heavy atoms such as plutonium in more or less the same way as power plants do on Earth. These rockets have been under development since the 1940s, but none have ever been used on a space mission. There are a remarkable number of designs, from straightforward fission reactors that heat hydrogen as it passes through the core, to exotic gas core reactors.

With their greater power output and energy density, they hold the promise of more powerful engines and thus shorter journeys, but there are a lot of tradeoffs that offset the advantages – such shielding and larger tanks to accommodate lighter weight propellants. So in reality, even the most practical ones don’t reach much more than a 30 percent improvement over chemical rockets.

According to the research team, a nuclear thermal rocket Mars mission would require nine launches to put the Mars ship into Earth orbit at a cost of more than US$12 billion – and that doesn't include the rest of the budget for building the ship, exploring Mars or making the tea. The ship would weigh 848 tonnes (935 tons) and a round trip mission to Mars would take 4.6 years.

“Using existing rocket fuels, it’s nearly impossible for humans to explore much beyond Earth,” said lead researcher John Slough, a UW research associate professor of aeronautics and astronautics. “We are hoping to give us a much more powerful source of energy in space that could eventually lead to making interplanetary travel commonplace.”

Fusion Driven Rocket could be the answer

The team believes that they can do better using a Fusion Driven Rocket (FDR). As the name implies, it uses fusion, the fusing of light elements, as a power source instead of fission. There are a number of ways of causing fusion and here the Washington team is using a Field Reversed Configuration (FRC).

A FRC is a device for confining plasma on closed magnetic field lines without a central penetration. It uses huge electric capacitors powering an extremely powerful magnetic field with one million amps that causes large lithium metal foil rings to implode on a blob of ionized hydrogen plasma as it squirts into the engine. The metal foil squeezes the plasma for a few microseconds until fusion occurs. The magnetic field then channels the superheated, ionized metal out of the rocket nozzle at high velocity in a pulse of thrust.

It’s not a very smooth ride. The pulses come at one minute intervals, so the ship travels in a series of jolts rather than a constant thrust, but the Washington team believes that it can do the job and is very efficient with only a bit of material the size of a grain of sand producing as much power as a gallon (3.7 l) of chemical rocket fuel. According to the team, a Mars ship using the FDR engine would have a mass of only 134 tonnes (148 tons), need only one launch to put it into orbit, and could make the trip to Mars and back in 210 days with a 30 day stopover.

Currently, the team is working to develop individual components and then combining them into a working prototype of a whole engine. “I think everybody was pleased to see confirmation of the principal mechanism that we’re using to compress the plasma,” Slough said. “We hope we can interest the world with the fact that fusion isn't always 40 years away and doesn't always cost $2 billion.”

The results of the team’s work was presented last month at the 2013 NIAC Symposium.

The brief animation below shows how the fusion drive works.

Sources: University of Washington, MSNW

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