Category Archives: Fusion Propulsion

Fusion Rockets for Planetary Defense

Glen Wurden, Ph.D., of Los Alamos National Laboratory in NM gave this presentation on using fusion powered rockets to intercept comets and large asteroids. The talk was at the Max Planck Institute for Plasma Physics, in Greifswald, Germany on Oct. 16, 2015 home of the Wendelstein 7-X (W7-X), Stellarator fusion project. Scroll to the bottom for a PDF version and to see the LANL TedTalk video on “Why Did the Dinosaurs Need Fusion Rockets Too?”

Download the slide presentation for this talk

Watch the video

Fear of Fusion: What if It Works?

(This article from the LA Times was published in 1989, and has been posted here 26 years later)

LA Times April 19, 1989| PAUL CIOTTI | Times Staff Writer

When two scientists announced last month in Utah that they had achieved room-temperature nuclear fusion, the news shot through the halls of science like a scalded cat. “It was,” one Berkeley physicist said, “like seeing your car suddenly jump on the roof.” It was that unexpected and stunning.

But now that the first waves of astonishment, wonder and euphoria have passed, a few scientists, environmentalists and ecological activists have begun to have more troubling thoughts. For one thing, they say, even if desktop fusion really works–a matter still very much up in the air–it is unclear that the power produced will be as cheap or clean as many have suggested it might be.

And even if it were, given society’s dismal record in managing technology, the prospect of cheap, inexhaustible power from fusion is “like giving a machine gun to an idiot child,” Stanford biologist Paul Ehrlich says.

Laments Washington-based author-activist Jeremy Rifkin, “It’s the worst thing that could happen to our planet.”

Inexhaustible power, he argues, only gives man an infinite ability to exhaust the planet’s resources, to destroy its fragile balance and create unimaginable human and industrial waste.

The Power to Pollute

That fusion itself may be a clean energy source, especially in comparison with fossil fuels, is beside the point.

Not all pollution is caused by burning fuel; there are many other pollutants that fast-growing industrial societies throw into the atmosphere–compounds from rubber tires, fumes from drying paint, and hundreds of other byproducts of industrial processes. And clean-burning, non-polluting, hydrogen-using bulldozers still could knock down trees or build housing developments on farmland.

A mere technological change in fuel sources also does nothing to change man’s attitude toward nature–what UC Berkeley physicist John Holdren calls the “pave the planet and paint it green” mentality.

In addition, Holdren says, despite the claims made, there is no guarantee that fusion will necessarily be a clean process; in some circumstances it can produce deadly neutron radiation and poisonous tritium. Worst of all to some observers, its cheap inexhaustible energy would let the planet support many more people than its current population of 5.2 billion. And this, they say, would be a crowded Earth, without forests, wilderness, open space or the chance for solitude. What would the planet be like without “psychological space?” asks Richard Charter, a coastal lobbyist and environmentalist who notes that many of the aberrations and turmoil of inner cities can be blamed on “just plain crowding without hope.”

In the euphoria over fusion power, UC Berkeley anthropologist Laura Nader says, many people just assume that cheaper, more abundant energy will mean that mankind is better off, “and there is no evidence for that.” Between 1950 and 1970, Nader says, there was “a doubling of energy use,” while at the same time, quality of life indicators all declined.

“The Age of Progress is really an illusion,” Rifkin says. Far more people–800 million–go to bed hungry today than at any time in history. “There has never been a previous example of that. And yet we continue to delude ourselves with the illusion that this is the Age of Progress.”

No Panacea

Stanford’s Paul Ehrlich says he has no problem with the notion of cheap, clean, inexhaustible power, per se, which could be a tremendous boon to mankind.

The problem: Industrialized societies, so far, have not used power wisely. The world’s limited supply of fossil fuels is rapidly vanishing up smokestacks and out tail pipes. Rifkin cites a 1985 University of New Hampshire study showing that 88% of the Earth’s oil and gas reserves will be depleted by 2025.

And even if fusion turns out as well as it has been promoted, Ehrlich says, it won’t be a panacea. Most problems in the Third World, for example, are social, political or economic, not technological, he says. “The idea that you can solve the human dilemma with a single technological breakthrough is incorrect.”

For the foreseeable future, much of the world will remain involved in small-farm agriculture and it’s unclear how fusion power would alter that life style.

Fusion proponents, he notes, also estimate that commercial applications of their work are at least 20 years off. And it will be 30 years beyond then before fusion power has significant impact. In this sense, says Ehrlich, fusion is irrelevant because, he asserts, the world will have long since succumbed to over-population, famine, global warming and acid rain.

What About Solar Power?

The current unqualified euphoria for fusion also concerns Barry Commoner, director of the Center for the Biology of Natural Systems at Queens College in New York.

Fusion fuel cycles: What they are and how they work

VisionOfEarth BY BEN HARACK – NOVEMBER 10, 2010

As part of our series on nuclear fusion power, this post is going to look at fusion fuel cycles.

Fusion fuel cycles are the different ways that fuel nuclei can be combined to make heavier elements. It is convenient to think of them as analogous to chemical reactions, which have reactants, products, and some energy absorbed or released. We are only considering reactions that are exothermic (they release energy).

Proton-Proton Chain

The proton-proton chain starts with a reaction in which two protons fuse. After fusion we are left with a deuterium nucleus (isotope of hydrogen that has one proton and one neutron), a positron, a neutrino, and 0.42 MeV of energy. An “eV” is an electronvolt, a useful unit of energy for nuclear physics. Written out, the reaction looks like this:

Understanding the source of the sun’s energy was a problem for physicists in the past. Temperatures are not high enough in the center of the sun for protons to overcome the coulomb barrier if analyzed using classical mechanics. With the application of quantum mechanics, physicists began to understand that the protons in the sun are quantum tunneling in order to undergo fusion.

Quantum tunneling, for those of you who are new to the concept, is a term describing the ability of quantum particles to end up located in places that they should not have been able to get to according to classical mechanics. This is because they can ‘tunnel’ through barriers with some probability. The key concept is that a quantum particle seems to be able to cross any barrier. Although the greater the barrier, the lower the probability is that the particle will successfully tunnel. In the case of the proton-proton repulsion (since both are positive), there is a very substantial barrier to be overcome.

Proton-Proton Chain Image from WikiMedia Commons

Proton-Proton Chain Image from WikiMedia Commons

This is one of the fusion reactions that powers the sun. This is a very ‘slow’ process in the sun. A given proton would have to wait an average of 109 years to undergo fusion with another proton1. This is primarily because the energy and density conditions in the core of the sun are not sufficient to overcome the coulomb barrier without quantum tunneling. Another contributing factor to the improbability of this process is the fact that it relies on a weak nuclear interaction.

Weak interactions are in general much less likely than strong interactions. This means that even if one of the protons ends up tunneling through the coulomb barrier to be beside another proton, the chances that they will fuse are still very low.

People familiar with atomic physics may know that a double proton system is not allowed by the laws of nuclear physics as we understand them. So this double proton state only exists for an extremely small amount of time. One of the protons needs to undergo a weak interaction to become a neutron, so that they can form a stable state of proton + neutron, which is deuterium.

Despite its slow rate, this is the dominant energy source in our sun, and in stars of similar or lighter mass. In our sun, hydrogen is converted to helium primarily through the proton-proton chain.

What is the net effect of the entire process? Four protons are turned into a helium nucleus (also known as an alpha particle), a few neutrinos, and 26.73 MeV of energy. There are multiple pathways that this reaction can take after the first step. We presented here the reaction pathway that is most common in our sun.

Unfortunately the proton-proton cycle is completely infeasible for fusion reactors on the earth. Even in the center of the sun (at very, very high pressures and temperatures) the power density created by proton-proton fusion is very small. Estimates have placed its power density at a value that is actually about one quarter the power density of the heat created by a living human being.2 Similarly low power densities apply to the next solar fusion cycle we look at, the CNO Cycle.

CNO Cycle

CNO Cycle from WikiMedia Commons

CNO Cycle from WikiMedia Commons

If our sun was 1.5+ times larger, we would instead see a dominant reaction in the form of the CNO cycle. CNO stands for Carbon-Nitrogen-Oxygen. The heavy nucleus, which changes character between carbon, nitrogen, and oxygen due to the nuclear reactions, acts as a catalyst. The heavy nucleus is transformed during the cycle, but is not consumed in the cycle.

This is also known as the Carbon Cycle. This is problematic because it may cause some confusion with the earth’s carbon cycle.

The net effect of once around the CNO cycle is to turn four protons into: an alpha particle, two positrons, some gamma rays, and neutrinos. The net energy released in one cycle is 26.8 MeV, but we also released positrons which are going to be immediately annihilated when they encounter an electron. This raises the net energy released to 27.8 MeV.

Deuterium-Deuterium (D-D)‏

Now we are looking at nuclear fusion fuel cycles that have a real possibility of being used for terrestrial power generation. For D-D, the fusion reaction rate peaks at a temperature of 15 keV, which may be attainable in terrestrial reactors. This number will be useful for comparison to the next few processes we look at.

Deuterium is available in large quantities in the earth’s oceans even though it only represents a small fraction of all hydrogen on earth (about 0.0156%)3. This is a fuel source that we can rely on for a very long time into the future, assuming that we can make it work in the first place. It is important to keep in mind that hydrogen is the most common element in the universe.

Two processes occur with equal probability:


What are the advantages of D-D fusion? These fusions are strong interactions for which the conditions are relatively easy to create. We also only have to worry about one fuel that is relatively easy to acquire.

The helium that is produced can also fuse with a deuterium. We look at this case later on. D-He has a much higher peak reaction rate energy, so it is much less likely to fuse in a plasma that has been optimized for D-D fusion. This reaction also produces tritium, which can also be burnt in a second-stage fusion reaction since the minimum energy for D-T fusion is even lower than it is for D-D.

Deuterium-Tritium (D-T)

Tritium is a hydrogen atom with two neutrons. It is the heaviest isotope of hydrogen. D-T fusion is the following process, wherein it releases a helium-4 nucleus and a high energy neutron:

D-T has some properties that make it more desirable than D-D.

  1. Even higher cross section than D-D. This means that when the ions interact closely, there is a higher probability of a D-T reaction than a D-D reaction. This leads to a reduced Lawson criterion, which means that the conditions of fusion are easier to accomplish.
  2. Reaction rate peak at 13.6 keV, which is even lower than the 15 keV for D-D.

However, there are some associated disadvantages:

  1. Blanket of Lithium required for breeding tritium. Tritium does not occur naturally on the earth, we need to make it out of other things. The way to usually do this is a blanket of lithium that gets bombarded with neutrons from the reactions. Lithium bombarded with neutrons will produce tritium, which can then be used as fuel. This is however an interesting technical difficulty. Also, tritium presents some nuclear proliferation concerns.
  2. Neutron carries off 80% of energy. This means that only 1/5th of the total fusion energy even has a chance of staying in the plasma. Attaining ignition will be fairly difficult. Also, the radiation flux of neutrons from one of these reactors would be very intense. This introduces design difficulties for possible reactors.

This is considered the most likely fuel cycle for use in tokamak reactors since it has the lowest temperature requirements of the terrestrial fusion fuel cycles. Muon-catalyzed fusion can be done at lower temperatures. When we look at it in detail later on, we will look at how it is currently impossible to build a muon-catalyzed fusion reactor.

How can we avoid the serious neutron radiation problems inherent in these fuel cycles? It turns out that there are some fusion reactions that produce very few neutrons. We will look at some of them now.

Deuterium-3Helium (D-He)‏

In this fusion reaction, deuterium is fused with helium-3, the lightest isotope of helium.

D-He fusion has some interesting advantages over D-T:

  1. This reaction is aneutronic. That is, the main pathway for the fusion creates no neutron radiation. Some neutrons would be produced due to side reactions of D-D for instance. However, with the dramatically reduced neutron radiation, this could mean much less expensive shielding will be required for the reactor.
  2. Direct conversion is possible. Direct conversion, which we will go into more depth on later, is the process of extracting energy from fast-moving charged particles and turning it directly into electricity. There is no ‘heating’ stage, where we heat up a coolant like water and run it through steam turbines. Direct conversion may allow for very high efficiencies (>90%) compared to thermal conversion (40-50%). For a complete look at how this is possible, see our introduction to direct conversion.

Disadvantages:

  1. Helium-3 is quite hard to acquire currently. I have actually talked to researchers in condensed matter physics who have had a very difficult time getting any helium-3 in the last few years. Creating helium-3 is not that easy right now. We can currently get some of it as a product from fission reactors. This is because tritium produced in fission reactors naturally decays into helium-3 after some time. There are also ambitious plans floating around to go to the moon and mine the helium-3 that has been rained down on the surface due to the solar wind.4
  2. Reaction rate peaks at 58 keV, a very high temperature compared to D-D and D-T.

The acquisition of Helium-3 is problematic enough that consideration of another aneutronic fusion fuel cycle is warranted.

p-11B

Proton-11Boron is another interesting candidate, and the last fuel cycle that we will look at in this article.

It has some very notable advantages over its counterparts:

  1. Aneutronic. Even fewer neutrons will be produced with this reaction than with D-He. This is a reaction ‘clean’ enough that it may not pose any notable neutron radiation risk. Neutronicity of this reaction has been estimated at around 0.001. This means for every thousand fusion reactions, there will be one neutron emitted.
  2. Direct conversion possible, just as with D-He, because all of the products are charged particles.
  3. Very great fuel availability. Fuel is easy to find and there is lots of it.

There is only one major disadvantage to this fuel cycle, but it is a big one. The reaction rate peaks at an energy of 123 keV! This is a very high energy, so high in fact that many people consider this fuel cycle to be a dead end in terms of research.

There are, however, some proposals for reactors which we will discuss in later posts that might be able to reach energies this high. This would be preferable, since if we can design a reactor to use an aneutronic fuel cycle with direct conversion, we would be well on our way to an energy source for the next millennium.

You might be wondering how boron-11 can break up into three helium-4 nuclei. This looks like fission, where a heavier nucleus is broken up into smaller pieces. This is however not the case. What actually happens is the proton and boron-11 fuse, forming an unstable carbon-12 nucleus. This nucleus then decays to three alpha particles. The reason this is energetically possible is because helium-4 is one of the most stable isotopes in the universe. For a more in-depth discussion of this phenomena, see the Wikipedia article on Nuclear binding energy.

Next we will look at a reaction that is not another fuel cycle, but a way to catalyze one of the above fuel cycles.

Muon-catalyzed fusion

What is a muon? Imagine an electron that is about 200 times as heavy as a normal electron, and decays away into other particles after only about 2.2 milliseconds. When a muon instead of an electron is orbiting a nucleus, it does so at about 1/200th the distance that an electron does. This has the effect of lowering the coulomb barrier substantially. This means that fusion can be accomplished at much lower temperatures. In fact, it lowers the minimum temperatures so much that fusion can easily occur at room temperature. In fact, muon-catalyzed fusion experiments are often conducted with the fuel elements frozen into a solid block at -270ºC, within a few degrees of absolute zero.

However, we cannot use muon catalyzed fusion for power production unless we solve a couple major problems. The first is ‘alpha sticking‘. As mentioned before, an alpha particle is a helium nucleus. This means that it has two protons and two neutrons. Thus it has a net charge of +2. This means that the attraction between the muon and the alpha will be higher than between the muon and a proton. This causes the muon to stick to alpha particles rather strongly. Since alpha particles don’t undergo fusion under these conditions, it means that the muon is then essentially lost, since it will decay after only ~2.2ms.

Additionally, a heavier fuel ion such as boron-11 will likely have several electrons around its nucleus. This would mean that the effect of a single muon would be a lot less than it is with hydrogen (which only has one positive charge). Heavier fuels are thus not helped substantially by muon catalyzation.

The best catalyzing achieved so far is about 100 fusions per muon. New research indicates that 200-333 catalyzed fusions per muon may be possible. The problem is that the theory says we probably need about 500 fusions before being attached/decaying because of their energetic cost of production.

In order to utilize muon-catalyzed fusion, humans need to develop an energetically cheap source of a very large number of muons. Currently the energy cost per muon is around 6 GeV, far more than the net energy gained from its catalyzed fusions. Unfortunately this technique doesn’t really work with multiple electron atoms. We would need a LOT of muons, far more than is generally considered feasible.

We have seen some references to new and interesting developments in the area of high efficiency muon production from pion interactions. However, we haven’t seen the science on which these claims are made. It is very unlikely that muon-catalyzed fusion is anywhere near being economical, even if relatively large leaps are made in producing the muons.

With that, we conclude this installment of our nuclear fusion power post series. Stay tuned for our next publication, which will look into the details of exactly how we hope to create machinery that can contain plasma and extract fusion energy from it.

MagLIF with DT cryo layer could achieve ten thousand times net gain nuclear fusion and it would be very good for fusion space propulsion

NextBigFuture.com

The cheapest, smallest reactors will emerge from the so-called magneto-inertial fusion (MIF) parameter space. This physics regime is a hybrid between the low density magnetic confinement and beyond solid density inertial confinement. Many of the smallest proposed fusion propulsion systems are in fact MIF systems, consistent with this recent study. (The Case and Development Path for Fusion Propulsion by Jason Cassibry, Ross Cortez, Milos Stanic)

Among the various MIF confinement schemes, we observe that pulsed z-pinch based approaches have potentially solved many of the perceived problems associated with instabilities, and that breakeven systems may require only ~60 MA of current. Such a current level is only a factor of 3 away from current capabilities at the Sandia Z Machine and a factor of 30 away from a new pulsed power facility being reassembled at the University of Alabama in Huntsville in collaboration with NASA MSFC and The Boeing Company. We offer a potential development path to a TRL 9 flight system, including potential side experiments that can be done to help pay for the development and upgrades to facilites.

* Magnetic fields can make laboratory fusion easier
* Magnetically driven targets driven by pulsed power drivers are energy efficient and could be a practical and cost effective path to significant fusion yields over 100 megaJoules per pulse. Z today couples ~0.5 MJ out of 20 MJ stored to MagLIF target (0.1 MJ in DD fuel)

The pulsed z-pinch approach is perhaps the most direct route to development of fusion propulsion.

Z-pinch yields have been found to scale as ~I^4, where I is the current supplied by the pulsed power system.

5 to 10% of the implosion energy will be transferred to the central hotspot.

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SOURCES – Sandia National Lab, University of Alabama

Aneutronic Nuclear Fusion Reactor + Engine Proposal

Here is some brief theory behind Aneutronic Fusion, a form of nuclear fusion which produces no harmful neutron radiation, eliminating the need for heavy shielding in energy plants and spacecraft engines. The reaction can be initiated under a picosecond laser pulse which is aimed at a metal target producing protons which can fuse with Boron atoms in the molecular lattice of the fuel substance. The alpha particles generated from this reaction can be converted directly to an electrical current using alpha voltaics. Due to the reaction being initiated by the laser beam, all radiation emitted stops as soon as the laser is switched off allowing for the highest level of control for a nuclear reaction.

Due to the nuclear test ban treaty, nuclear propulsion spacecraft engines have never been deployed in space, creating a huge set back in our ability to reach deep space. Aneutronic fusion, if viable, could act as a loophole around the test ban treaty as it is impossible for this technology to be used as a weapon as no harmful radiation is generated.

Other plans for nuclear propulsion engines include gas core electromagnetic fission reactors which could generate high levels of ultraviolet photon pressure to propel a spacecraft, however such a technology would not be viable until the late 21st century.

Helium-3, Lithium-7 and Boron-11 are the isotopes which can be fused with protons to produce energy.

in p-11B fusion the proton and boron-11 nucleus are fused and form a short-lived excited state of a carbon-12 nucleus, sometimes called a Hoyle state in the Triple-Alpha fusion cycle. The unstable carbon-12 Hoyle state then decays by gamma decay into beryllium-8 and an alpha particle. Beryllium-8 then decays by gamma decay into two helium nuclei.

the p-11B fusion reaction requires the most energy, however 11B has a large cross-section for alpha particles and the reaction gives off 3 alpha particles for every 1 consumed, so in principle a critical mass for fusion can be reached.

The p –7Li reaction has no advantage over p –11B, given its somewhat lower cross section. But this is mitigated by having double the power output.

Helium-3 is an ideal potential aneutronic fusion fuel, however it is only present in very low quantities on the Earth and requires nuclear fission reactions to make it, which removes the purpose of a self-sustaining fusion energy industry altogether. The far side of the Moon, Mercury, Mars and gas planets such as Jupiter and Saturn have the largest quantities of Helium-3 in the solar system, so space exploration is required to make Helium-3 fusion possible. Hence Helium-3 is most likely to be a second or third generation nuclear fuel.

Therefore Boron-11 is currently the best isotope on earth for studying the aneutronic fusion reaction process and to design a nuclear reactor/engine around the principle, at least until lunar mining gets underway which may not be until mid to late 21st century. Therefore the development of these principles should continue with 11B aneutronic fusion research so the technology exists to use Helium-3 when a system exists to have it on tap from the moon.

China is going to mine the Moon for helium-3 fusion fuel

extremetech.com By John Hewitt on January 26, 2015

China’s Chang’e lunar probe dynasty is already having a great year. The Chang’e 3 lunar lander surpassed all expectations last week to emerge from its 14th hibernation while the Chang’e 5-T1 just completed its transfer from the Earth-Moon Lagrange Point 2 into a stable orbit around the Moon. Chang’e 3’s main mission was only to take spectrographic and ground penetrating radar measurements, but the Chang’e 5 missions will bring back the first samples containing the actual prize — fusion-ready helium-3.

One of the main reasons helium-3 is sought as a fusion fuel is because there are no neutrons generated as a reaction product. The protons that do get generated have charge, and can therefore be safely contained using electromagnetic fields. Early dreamers imagined that Saturn or Jupiter would be the ideal places to try and get their hands on some helium-3, but it now appears that the Chinese have set their sights on the Moon.

Although the Sun dispenses ample amounts of helium-3 wherever it blows, the Earth is largely shielded from this windfall by its own magnetic field. The little we do have is mostly generated by various terrestrial processes like cosmic ray bombardment and even relic sources from leftover nuclear warheads. The Moon, on the other hand, is a far more concentrated depot with up to five million tons conveniently embedded in its top surface layer.

If you are thinking that panning the entire surface of the Moon might not be a sound business model, consider that helium-3 would probably not be the only payoff expected. Just as extraction of rare earth metals on our own planet is often piggybacked on a larger iron ore harvest, the Moon would offer a lot in the way of other primary raw materials like, for example, titanium.

While the West might justify its own inaction on the helium-3 front in terms of old space treaties or lunar conservation, excuses like this are probably laughable to a country like China who now actually is going and getting their own lunar helium-3. The real hurdles they face are not the bureaucratic red tape or even the logistics of a mass space and mining effort, but rather the physics of helium-3 fusion itself. In other words, is helium-3 necessarily the best way to do fusion?

There are a couple of possibilities for helium fusion here. If you can excuse the jargon for a moment, the temperatures required for a 21H (hydrogen) plus 32He (helium) reaction are significantly higher than conventional deuterium-tritium fusion. This process can still result in a few of those pesky neutrons so it may not be ideal. The alternative reaction, fusion of 32He with itself requires even higher temperatures to overcome the double positive charges on each helium. It therefore remains to be seen what is the best path forward in fusion. Other issues like how best to extract the energy once generated also loom. For example, it may be advantageous to directly drive electrical turbomachinery using charged protons without any heat conversion — although the claimed efficiencies of 70% would need to be fully vetted.

One thing we do know is that we need more helium-3 now. Our own DHS, for example, had hoped to detect the telltale neutron emissions of plutonium smuggled in shipping containers, but it was stalled for the lack of an affordable helium-3 source in our post-nuclear weapons economy. Getting this precious helium from the Moon will undoubtedly be difficult. The realization that it will take significant manpower — actual boots on the lunar surface — I think for now is inescapable in planning future missions. Mining, even if it is barely subsurface, will always be risky. Robots will have their place for sure, but they can not replace our versatility on the moon if they cannot even replace men at mines here.

Nuclear Fusion Rocket Could Reach Mars in 30 Days

space.com April 10, 2013

A concept image of a spacecraft powered by a fusion-driven rocket. In this image, the crew would be in the forward-most chamber. Solar panels on the sides would collect energy to initiate the process that creates fusion.
Credit: University of Washington, MSNW

Nuclear fusion, the energy source that fuels the sun and other active stars, could one day propel rockets that allow humans to go to Mars and back in 30 days, researchers say.

Fusion-powered rockets promise to solve problems of deep-space travel that have long plagued plans for manned missions to Mars — long journeys, high costs and health risks, among them. Scientists at the University of Washington and a space-propulsion company named MSNW say they are getting to closer to creating a feasible fuel for travel to other planets.

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

Previous estimates have found that a roundtrip manned mission to Mars would require about 500 days of space travel. Slough, who is president of MSNW, and his colleagues calculated that a rocket powered by fusion would make 30- and 90-day expeditions to Mars possible. The project is funded in part through NASA’s Innovative Advanced Concepts Program and received a second round of funding under the program in March.

For comparison, past NASA studies have centered on Mars flights that would take two years to complete, and could cost $12 billion just to launch the fuel needed for the mission, according to Slough’s team.

Nuclear fusion occurs when the nuclei of two or more atoms combine, resulting in a release of energy. The sun and other stars convert this energy into light, and the same process gives hydrogen bombs their destructive power.

But to use fusion to power a manned spacecraft, a more controlled process is needed.

The fusion driven rocket test chamber at the UW Plasma Dynamics Lab in Redmond is a proving ground for fusion-powered rockets.

The fusion driven rocket test chamber at the UW Plasma Dynamics Lab in Redmond. The green vacuum chamber is surrounded by two large, high-strength aluminum magnets. These magnets are powered by energy-storage capacitors through the many cables connected to them. Image added April 10, 2013.
Credit: University of Washington, MSNW

Lab tests by Slough and his team suggest that nuclear fusion could occur by compressing a specially developed type of plasma to high pressure with a magnetic field. A sand-grain-sized bit of this material would have the same amount of energy as current rocket fuel, the team says.

To get this fuel to propel a rocket to Mars, the team says a powerful magnetic field could be used to cause large metal rings (likely made of lithium) to collapse around the plasma material, compressing it to a fusion state, but only for a few microseconds. Energy from these quick fusion reactions would heat up and ionize the shell of metal formed by the crushed rings. The hot, ionized metal would be shot out of the rocket nozzle at a high speed. Repeating this process roughly every minute would propel the spacecraft, the researchers say.

Slough said the design is fairly straightforward. The next step of the team’s work is to combine each of the isolated tests they’ve already completed successfully into a final experiment that produces fusion using this technology.

“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,” Slough said in a statement.