There’s renewed interest in fusion energy in the wake of the successful release of over 1.3 megajoules of energy at the National Ignition Facility (NIF). NIF has been attempting to achieve successful fusion ignition by bombarding pellets with nearly 200 high-powered lasers within their Inertial Confinement Fusion (ICF) research device.
Fusion energy — the energy released by the fusion of smaller atoms into larger ones — is the same energy that powers the sun, and is being hotly pursued by organizations all over the world. While developing fusion power used to be seen as the province of large institutions, like NIF and ITER, a growing number of private startups are exploring potential fusion technologies, including Canada’s own General Fusion in Burnaby, BC. These technologies can differ tremendously from the familiar institutional fusion technologies like the NIF’s ICF or ITER’s Tokamak. This growing interest is fueling speculation about which technology (or technologies) may actually succeed in true fusion ignition.
This explosion of interest in fusion resembles the explosion in new space-based technology, and particularly in novel launch and propulsion systems. Successfully harnessing fusion power itself could revolutionize propulsion in space, allowing for much shorter travel times to the Moon, to Mars, and even farther.
But will it happen? Could a technology like General Fusion’s actually succeed in driving space travel? And if not, are there other lessons to be learned from General Fusion about how fusion may play a role in space?
The answer is … ”it’s complicated.”
General Fusion’s technology is both novel and familiar
General Fusion is the leading example of the explosion in private Fusion companies. Founded by physicist and engineer Dr. Michel Laberge, General Fusion is the Canadian example of the different startups that are trying to make fusion a reality. While they don’t have the resources of the big international fusion organizations like ITER, they are amassing significant amounts of private interest and funding. And because they aren’t as big as these International organizations, they are more free to explore technologies and approaches that stand far outside the current institutional focus on Tokamak reactors and the ICF.
General Fusion’s approach to fusion is different from their institutional contemporaries. While their reactor, like all fusion reactors, uses intense energy and pressure to fuse atoms together and harness the resulting energy to generate heat and electricity, they don’t use either lasers (like the ICF) or a tokomak’s doughnut-shaped magnetic containment design. Instead, as Laberge explained to a Schulich audience in 2019, it’s “a mix between the two.”
Their reactor looks almost deceptively low-tech. The reaction chamber is a rotating cylinder containing whirling liquid metal. Magnetized plasma is injected into the chamber inside the metal, and thousands of precisely timed pistons compress the metal into a sphere, then keep compressing the metal down on the magnetized plasma until it fuses. Upon reaching fusion ignition, the metal will absorb the neutrons released by the fusion and rapidly heat up. Once the reaction is complete, the hot liquid metal is pumped to a heat exchanger, where it’s used to power a turbine that generates electricity and powers the pistons.
Each cycle is projected to take less than a second.
This may seem entirely theoretical. It’s not. General Fusion is already in the process of building a demonstration plant in the UK. In 2017, they brought Christofer Mowry aboard as their Chief Executive Officer, and Mowry has an extensive history in the energy production industry. They’ve received over $300 million in investment. And, in a statement to SpaceQ, they said that they have become “the world’s most advanced private fusion venture [with] more than 140 employees.”
They also said that their “MTF technology takes a practical approach to fusion energy, maximizing the use of existing industrial Technologies”. That may be the key to understanding their impact on fusion in space.
How Would Fusion Propulsion Work?
How does fusion affect space travel, though? How could it be used for propulsion? In a conversation with SpaceQ, SpaceRyde propulsion engineer (and fusion propulsion fan) Balin Moher explained how this could work.
Moher has had a long interest in fusion propulsion as the means by which we could travel throughout the solar system and between the stars, and said that it was a big reason why he decided to become a propulsion engineer. He believes that “if we can turn fusion energy into kinetic energy, the future of space travel becomes much, much brighter.” Yet, like most engineers, he’s a realist. So when asked about fusion propulsion, he gave a realistic assessment.
One point that Moher made is that fusion-based terrestrial launches may not be realistic. While fusion drives would revolutionize travel in space, he said that “it’s never going to be enough to fight gravity … or air resistance.” We’ll still need chemical propulsion systems for launching from Earth.
The benefit of a fusion drive is that, once it starts, it just doesn’t stop. Chemical rockets need a constant and sizable supply of propellants, while a fusion drive barely needs any at all compared to the amount of thrust it creates. So the specific impulse of a fusion drive would be absolutely enormous; a fusion engine could consistently accelerate for such a long amount of time that an interplanetary flight would take far, far less time than one propelled by chemical rockets.
He went on to discuss the two realistically foreseeable means by which fusion propulsion would operate: through electric power generation and a “direct fusion” drive. The first type would use a fusion reactor to generate electricity, and then use that electricity to power an electric thruster. The thruster side is “already done”, he’s said; various types of ion thrusters (like the common gridded ion thruster or the Hall thrusters used by SpaceX’s Starlink satellites) have become common workhorses for moving spacecraft around.
The difficult part would be building a fusion reactor that would work in space. As of yet, few companies are even attempting it.
Mohar said that a “more promising” possibility is the “direct fusion drive” being produced by another private fusion firm: Princeton Satellite Systems, which is working on the project with the Princeton Plasma Physics Laboratory. Unlike the toroidal tokamak design or General Fusion’s liquid metal sphere, the direct fusion drive uses a linear array of magnets surrounding a cylindrical chamber, with stronger magnets at the ends. A fusion region at the centre of the cylinder holds spinning HE-3 and deuterium plasma heated by what PSS calls a “novel radio frequency heating mechanism” which creates a current in the plasma.
The RF-heated plasma becomes hot enough to fuse, while cooler plasma is directed around the hot plasma region. Fusion products lose energy, join the plasma flow, and are passed to the back of the rocket, where (according to PSS) they “pass through the scrape-off layer heating up the plasma there, and that plasma shoots out the nozzle generating thrust.” The heat is also used to generate the electrical power needed for the coils, the RF heater, and other devices aboard the spacecraft.
Of course, there is a theoretical third option: using nuclear explosions. This dates back to the 1950s-era Project Orion, which theorized the use of pulsed nuclear bombs to propel starships. Moher laughed at the notion, saying “NASA scientists dreamed up some wacky stuff in the sixties,” before explaining that it wouldn’t really be viable. Not only would it be politically unfeasible to launch large quantities of nuclear material into space — fusion bombs still need fissile material to ignite — but the destructive capacity of the bomb would make it difficult to design an engine that could channel its force without disintegrating. The gamma radiation from the bomb would likely kill everyone aboard, too, unless the craft was extremely long.
(Moher admitted that he wasn’t as familiar with the original “pusher plate” design, which uses an enormous plate attached to the rear of the craft that absorbs the detonations and “pushes” the craft forward. When asked, he raised the question of how the plate could possibly keep from disintegrating. He also noted that gamma radiation would still be a huge issue.)
So while there have been some attempts to revive the concept, notably the University of Washington/MSNW magneto-inertial fusion driven rocket proposal in 2013, it’s very unlikely to see the light of day.
Could General Fusion’s tech work in space?
So assuming for the moment that we aren’t trying to build a bomb-driven vessel, and that the goal is to have a fusion plant sustaining an electric propulsion system, could one of these General Fusion energy plants be used in space, perhaps to drive electric propulsion?
GF said that it wasn’t a focus, but they weren’t ruling it out. In their statement to SpaceQ, they said that “when our founder Dr. Michel Laberge was first introduced to fusion, he was interested in space. But his mission was to solve climate change with a practical and economical approach to commercial fusion.”
Yet, while he was intrigued by GF’s technology, Moher’s initial reaction was a flat “no.” He didn’t see any way it would work.
He said it was a question of weight. All of these ground-based fusion plants are enormous and heavy. Trying to haul all that mass into space would be so costly in terms of time, money and energy that it wouldn’t ever be worth it, and they can’t be realistically scaled down. That’s a major reason why Princeton’s direct fusion drive is getting so much attention: it’s smaller than most, around the size of a minivan. (Its creators are already promoting it as a compact terrestrial energy solution as well.)
Returning to a key point from GF’s statement, though, opens up some possibilities. GF said that one of their key advantages is that they use known technology that is comparatively easy to manufacture. Instead of costly and delicate lasers, or precisely manufactured and complex electromagnetic coils, GF’s reactor relies on comparatively simple technology: a cylindrical cavity, some liquid metal, and a whole lot of digitally controlled steam-driven pistons to shape the metal. Nothing too exotic, outside of perhaps the plasma injectors, the electronics and the liquid metal, which also could be feasibly launched.
That may suggest that in-situ resources might be an option. If it’s just a whole lot of steel and other easily-manufactured materials, why bring them from Earth when you can just create and use them in space? Surely a lunar additive manufacturing facility could handle making some pistons. Even if some components must be launched from Earth, the heavy components might not be. Even the steam for the pistons is created by the generator, and the water for the generator could be acquired in-situ from lunar regolith or asteroid resources.
Moher allowed that the use of in-situ resources might be a possibility; that “if the reactor were already up there, it could conceivably work.” He still believes that it’s far less likely to see use than Princeton’s solution, though, assuming for the moment that both successfully achieve ignition. You still have the issues of getting materials that aren’t easily found in space, of managing the generator, and of removing excess heat — a serious challenge in space. And all that’s to say nothing of the issue of compressing spinning metal under acceleration.
So while it’s not impossible, the use of a GF-style reactor in space just doesn’t seem likely.
The GF Approach, but not necessarily GF Technology
Instead, what GF really brings to the table is their focus on using simple and robust tools to get the job done. While their specific fusion solution may not see use on a spacecraft, their attitude is another story. Any attempt to build workhorse power generation in space — aside from the omnipresent solar panels — will likely need to focus on robust solutions that use materials that can be procured in situ. Delicate and exotic mechanisms may look impressive, especially on paper, but the solutions are just as likely to be the orbital equivalent of creating fusion with pistons and spinning metal.
What it also shows is that the private sector’s contribution to space technology isn’t a fluke or an accident. Fusion technology, like space technology, has been seen as the province of national governments and international institutions for decades. Yet, right here in Canada, we’re seeing rapid growth in space-focused companies (like Moher’s employer SpaceRyde) and in novel energy startups like General Fusion.
So while these companies don’t have the same kind of resources as major institutions, they have the opportunity to be far more agile, eclectic and practical than major institutions. Most will fail, but some may succeed. It might be a company like General Fusion, in its quest for piston-squeezed fusion. It might be a company like Princeton Satellite Systems that is bent on creating a small fusion reactor that can be used for space-based propulsion. It may even be a company that doesn’t yet exist.
No matter who succeeds, this ecosystem of agile and eclectic companies, if supported, will make it far more likely that fusion energy and fusion propulsion will no longer be some distant dream, but will become a reality in our lifetimes.