Most games lose relevance after a few years, but the indie rocket-building game Kerbal Space Program is a bit different. It’s a glitchy, 10-year-old underdog of a game with a cult following of programmers, engineers, astronaut candidates, and your typical lay explosion enthusiasts, and it has a unique and active community of modders who’ve been fixing bugs, adding new features, and generally keeping the game fresh for nearly a decade.
In the game, you are the omniscient director of a space program composed of literal little green men (and beloved little green woman Valentina Kerman—we see you, trailblazer) that you send skyward in spacecraft of your own design. It often feels like watching those blurry old videos of rockets launching only to come straight back down in an explosion of fiery schadenfreude: you feel a little bit frightened, a little bit sadistic, and you really want to try it again.
Art imitates life
One of the most prolific Kerbal modders is Chris Adderley, Nertea in the game, who is an engineer at the Canadian space company MDA by day, designing ground-based systems that retrieve data from spacecraft. But in his off time, Adderley gets into the pilot’s seat himself. He started playing Kerbal Space Program soon after its release, and in 2013 started building his first mod for the game—a pack of spare parts, including a xenon fuel tank and a magnetoplasmadynamic thruster (just try saying that three times fast).
Since then, he’s designed dozens of additional mods, including a Mark IV Spaceplane and space station add-ons like centrifuges and inflatable habitats.
“I build stuff that I’d like to see us as a species build in the future,” says Adderley.
Recently, Addlerley decided to take some of the most plausible far-future theoretical rocket engine concepts and build them in the game—introducing a way for gamers to try out these sci-fi concepts in a simulated environment that can teach us how they might actually work, on a more practical level, in the future.
Adderley combed through dozens of scientific papers that outlined theoretical blueprints for these ultra-advanced propulsion systems, looking for those that were most realistic.
“Everybody tries to sell their project as the propulsion system of the future,” says Adderley. “You need to kind of think a little bit critically about what people have hand waved.”
He crunched the numbers, considered how much power a specific engine would need, how to deal with the heat produced, and how you’d harness the energy to propel the virtual rocket further. “That was superfun, which might be a supernerdy statement, but you know.”
In the end, he built out 13 different engine concepts, including fusion engines—like The Expanse‘s Epstein drive is theorized to be—fission engines, and antimatter rockets.
Though we don’t yet have the technology to implement these specific-impulse demons, there is some real world value in being able to simulate advanced engines in a low-stakes environment. In fact, it’s such a great sandbox that engineers at SpaceX and the Jet Propulsion Laboratory have used Kerbal graphics in their presentations. In 2018, NASA released Open MCT, a telemetry data visualization software designed for operating spacecraft, to the public on Github. It’s costly and time-consuming to test these systems on real spacecraft, so some participants ran their programs through Kerbal instead.
For Sumontro Sinha, an aerospace engineer and fusion researcher at the Propulsion Research Lab at the University of Alabama in Huntsville, Kerbal is the go-to for testing out new ideas and training new engineers.
“Instead of Powerpoint slides and pages of equations, just make the ship and see how it works,” he says. “If it works in Kerbal, then it has a good chance of working in real life.”
The spherical tokamak fusion engine is based on the fictional spaceship in 2001: A Space Odyssey, sans HAL the killer AI. Adderley found the actual science behind it in a NASA study, in which the paper’s lead author, Craig Williams, says NASA funded a number of projects focused on developing advanced propulsion systems. Williams’ team designed an engine that uses the energy produced by a fusion reaction to generate thrust. Fusion occurs naturally in the interior of stars like our sun, where lightweight atoms are superheated to the point where their electrons and neutrons decouple and neutrons, normally repellant to one another, fuse together and produce massive amounts of energy. One of the biggest challenges in producing this energy on Earth is that you need a way to confine the resultant plasma and harness its power.
One way to do this is with a tokamak, a device that generates a donut-shaped magnetic field that keeps the superheated plasma in place. In Williams’ engine prototype, this tokamak would be nearly spherical—more like a donut hole. The exhaust produced would propel the vehicle to over 166,000 mph, taking passengers to Jupiter in just under 4 months. To put that into perspective, the deep space probe Voyager is traveling away from our solar system at 35,000 mph.
When Williams’ paper came out in 2001, the authors wrote that the capability to produce this type of engine might be 30 years out. Now that it’s 2021, Williams is revising his estimate. “We’re probably not any closer,” he says. His paper came out in an era of enthusiasm for advanced propulsion, but much of that zeal has waned until recently. “You can’t really make much progress when there’s no active program going on, “ he says. “Until you start the clock again, that 30-year projection will just keep moving forward.” Bummer. But in the decades between now and humanity’s era of two-week Saturn vacations, you can still try out your own digital version of Williams’ engine.
Ride the nuclear lightning
The Afterburner fission fragment rocket engine is based on another NASA-funded engine concept study from 2011 that utilizes the energy created in nuclear reactions to propel a spacecraft forward. Reactors filled with Americium, a highly radioactive rare material that is a byproduct of uranium-driven nuclear reactions, generate fission products that flow down a chamber. This chamber is injected with hydrogen gas, which gets intensely excited when it meets up with the fission fragments and generates a plasma that is funneled through a powerful magnetic nozzle as thrust.
With this breakthrough, a round trip to Mars would take 292 days, including a 60-day stay on the planet. While the engine is slower overall than a fusion engine would be, it’s far closer to what we’re technologically capable of at present.
“The nuclear thermal rocket is a technology that is getting developed, and it’s already been demonstrated,” says Jason Cassibry, who leads the Propulsion Research Center at the University of Alabama in Huntsville. In April, DARPA selected three contractors to demonstrate the first phase of a nuclear thermal rocket, and NASA and the DOE put out a call for similar preliminary designs in February. Cassibry says fission fragment and nuclear pulse engines are not far behind, but they have additional engineering hurdles to face, including figuring out how to divert all that energy away from the hull of the spacecraft so it doesn’t burn up in space.
This story originally appeared on wired.com.