Fusion Power, or Creating A Star On Earth
And what it means for space travel
Energy production today is a battlefield. It’s a competition between the grime and pollution of fossil fuels, the unreliability of solar and wind power, and the looming towers of nuclear plants and their dangerous waste. With the world’s energy consumption growing each year and the planet straining under our use of coal and oil, an innovative source of energy for our cities is quickly becoming a necessity. That’s what makes fusion power so attractive; it promises to provide all the energy we need reliably, cheaply, and, most exciting of all, in an environmentally safe way with zero carbon emissions. It would be the ultimate source of power for our booming civilizations here on Earth and our craft setting out to explore the solar system. Even catastrophes at a fusion reactor would result in little more than the plasma expanding and cooling, with no chances of a huge, endangering explosion.
And it’s not impossible. Fusion is what drives every star dotting the endless skies — including our gorgeous, broiling sun. At its core, hydrogen is fused into helium and eventually escapes as electromagnetic radiation. That is, two hydrogen atoms are rammed together and produce a helium atom as a result. But the fusion of one element into another is not as easy as it sounds. Because both protons have the same charge, the only way to overcome their natural repellence is to bring them close enough together that they fuse. The sun is able to do this because of its immense mass (it claims 99.8% of all matter in our solar system) and, consequently, the immense amount of gravitational force made available. The heat, the pressure, and the gravity are what make solar fusion possible.
That’s what makes fusion different from fission — while fission aims to split apart a heavier nucleus into two lighter ones, fusion brings together lighter nuclei into a heavier one. The fusion process means the resulting element has less mass and the remaining mass turns into energy. An enormous amount of energy. Our nuclear reactors today use fission, which unfortunately makes radioactive waste that lasts tens of thousands of years. Still, many see fission powered reactors as an improvement over fossil fuels since it’s less polluting than most other sources of energy and has helped us avoid 14 billion metric tons of carbon dioxide in the past 21 years. Nuclear power is affordable and provides about 20% of all electricity in the US.
But it’s not fusion. It’s not everything fusion promises to be.
But it turns out recreating conditions of the sun here on Earth isn’t going to be a straightforward task. One of the saddest jokes regarding fusion is that it’s the energy of the future…and always will be. This type of remarkable energy has been 30 years away for the past 8 decades now. But this time could be different. Physicists are feeling more confident than ever in their ability to problem-solve and there’s been a great number of breakthroughs in the last few years.
One of the problems they face is that the process requires temperatures in the hundreds of millions of degrees — temperatures up to 10 times higher than those at the core of the sun. Needless to say, no solid material could withstand that amount of heat and so scientists often use magnetic fields to hold up the scorching plasma during what’s known as magnetic confinement. Magnets then press the plasma into higher densities, but that means the atoms aren’t always stable enough to contain the energy. Plasma heated using lasers and ion beams require too much energy going into the system.
In short, the current goal of fusion research is to break even in terms of energy. Researchers want to get as much energy out as what they’re putting in. Up until now we’ve been working on a deficit where energy output is far less than energy input. The end goal, of course, is to get many times as much energy out as what we’re putting in.
Some new approaches are a hybrid of electrical and magnetic fields that beam atoms against a solid target until the atoms from the beam fuse together with those of the target. This process utilizes hydrogen since lighter elements produce more energy during fusion. The trick here is to minimize the number of atoms scattering and thus increase the amount of energy collected.
As far as a commercial reach for fusion goes, estimates range from 60 years from today to a mere 15 depending on who you ask. Researchers from MIT are confident they can have a fusion reactor on the grid as soon as 2033, though even that brings up the question of whether or not we can afford to wait so long for clean energy.
Instead of focusing too much on the technicalities of fusion power itself, I was very interested in what this kind of energy would mean for space exploration. It turns out that NASA is funding a fusion-powered rocket with hopes of a working prototype by 2020. If successful, fusion powered spacecraft would reach Mars twice as fast as anything we could send now. This means that instead of a trip to the red planet taking 7 months, it would only take a little over 3, greatly reducing the crew’s exposure to radiation, psychological strain, and weightlessness. Not to mention they would need much less food, fuel, and oxygen onboard. In fact, a small grain of aluminum would provide the equivalent power as a gallon of fuel does in today’s chemical rockets.
Fusion rockets would have a specific impulse of 130,000 seconds — 300 times greater than that of modern rockets. Specific impulse is a term that refers to the relationship between thrust and the amount of propellant used. In the case of chemical rockets, a specific impulse of 450 seconds means that a rocket can hold 1 pound of thrust from 1 pound of fuel for about 450 seconds. Fusion rockets would also allow for a bigger payload since not as much room is needed for fuel. Instead, magnets with lithium bands would push atoms together, resulting in fusion and energy to push the rocket forward. If the fusion rockets use hydrogen as a propellant, they could replenish their stock by collecting hydrogen from the surface of planets.
It’s a fast, much more efficient method of interplanetary travel. And the foundations for it are being built today. Projects like VASIMR act as steps on the path to fusion rockets. VASIMR is a plasma rocket that heats and expels the plasma to create thrust but, because fusion rockets will also use plasma, anything researchers can learn from this craft would help them in the design and creation of a fusion drive.
Recreating the power of a star is something that sounds uniquely human: a violent, tricky, seemingly fantastical goal. And yet achieving it would bring our civilization so much, both in terms of physical energy and introspection. How far can we truly advance, and can we reach the goals of our wildest ambitions?