Star Trek fans take note: Have a seat before you read the next sentence or prepare to swoon.
University of Alabama-Huntsville (UAH) aerospace engineers working with NASA, Boeing and Oak Ridge National Laboratory are investigating how to build fusion impulse rocket engines for extremely high-speed space travel.
“Star Trek fans love it, especially when we call the concept an impulse drive, which is what it is,” says team member Ross Cortez, an aerospace engineering Ph.D. candidate at UAH’s Aerophysics Research Center.
Stay seated Trekkies, because there’s more.
“The fusion fuel we’re focusing on is deuterium [a stable isotope of hydrogen] and Li6 [a stable isotope of the metal lithium] in a crystal structure. That’s basically dilithium crystals we’re using,” Cortez says, referring to the real-world equivalent of the fictional element used to power Star Trek’s Starship Enterprise.
While this engine, if produced, wouldn’t generate a fraction of the velocity as the faster-than-light warp drives envisioned in the TV shows, books and movies, it could produce speeds that exceed other not-science-fiction-based systems that rocket scientists are investigating.
Their ultimate goal is to develop a nuclear fusion propulsion system by 2030 that can spirit spacecraft from Earth to Mars in around three months—about twice as fast as researchers think they could go with a nuclear fission engine, another scheme that is being investigated but has not yet been built.
Their current design has a spacecraft with the impulse engines being built in low Earth orbit, so the thrusters and ship wouldn’t need to cope with the atmosphere or achieving escape velocity. That doesn’t mean it would be a lightweight when fully assembled, though. Cortez says the craft could tip the scales at almost 500 tons.
Major problems to solve
There’s a big gap between hopes and goals, though. For decades, nuclear fusion researchers have worked to harness the huge amounts of energy generated from slamming atoms together so hard they fuse. Their efforts have led to scientific progress, but the goal of getting more energy out of a fusion reaction than what is required to smash them together at amazingly high speeds has so far proven elusive.
Last week, Sandia National Laboratory investigators said they are getting closer to “break-even,” the holy grail of research that will see the same amount or more energy released from a nuclear fusion reaction than that which was put in.
“We’re interested in deep-space exploration,” says Dr. Jason Cassibry, a UAH engineering professor and the head of the research team. “Right now humans are stuck in low Earth orbit, but we want to explore the solar system. We’re trying to come up with a system that will demonstrate break-even for thermonuclear propulsion.”
To really start getting around the solar system, spacecraft will need to go much faster than they do now.
According to astronomy professor Courtney Seligman, the next date Earth will be closest to Mars after the team’s 2030 objective will be in May 2031, when the two planets will be 51.4 million miles apart. For the team’s fusion-powered spacecraft to reach the red planet in three months at that point, it would have to travel at almost 24,000 miles per hour, or about 10 times the muzzle velocity of a bullet fired from an assault rifle.
(conceptual diagram of the team’s fusion impulse engine. Image courtesy Ross Cortez/UAH)
Z-pinch fusion and magnetic nozzles
To hit this phenomenal speed, the researchers are investigating something called z-pinch fusion as a source of propulsion. Cortez says the technique takes a cylindrical array of super-thin lithium wires and puts a massive electric current through them. The electricity—millions of amps are being sent through the wires in 100 nanosecond pulses, which could produce 3 terawatts of output power—creates a magnetic field around the array and vaporizes the wires to form plasma. The magnetic field pinches the plasma until it collapses on a core of deuterium and lithium, which they hope will cause its atoms to fuse and result in a massive release of energy.
“What we’re aiming for is to get enough compression and heat in the z-pinch implosion to cause the fusion fuel to react,” Cortez says. “With the energy that would release, we could get millions of pounds of thrust out the back of this thing—on the order of Saturn-V-class thrust.”
After achieving the proper speed, the engines would be shut down and the craft would coast to its target.
Besides figuring out the fusion problem, another obstacle to their goal is how to contain and direct the resulting energy to generate thrust—no small task because the reaction would create temperatures in the millions of degrees Celsius, enough to vaporize any known material. To solve this problem, part of the team is working on another line of research, which seeks to develop a “magnetic nozzle.” This would use directed magnetic fields to guide the energy out of the engine.
“We’re facing some pretty heavy problems to getting this thing working; it won’t be a cinch,” Cortez says. “But we’re very ambitious and we’ve got a lot of great ideas. Put enough bright people to work on it and you’re going to get gold or, in this case, fusion.”
But even if they don’t reach their objective of developing the z-pinch fusion propulsion system, the group’s work will likely be useful in the global effort to develop terrestrial fusion reactors as a source of clean, limitless energy.
The major hurdles have not yet shaken Cortez’s optimism, because he keeps thinking of what success might mean: “How could I not stay interested? With this work, eventually, I might have the chance of seeing Jupiter up close or help humanity colonize Mars.”
(UAH doctoral candidate Ross Cortez assembles a device that generates massive bursts of electricity for fusion propulsion research.)
Top Image: A conceptual model of the University of Alabama-Huntsville’s fusion impulse propulsion spacecraft. Courtesy Ross Cortez/UAH.