When Heidi Fearn, a theoretical physicist at California State University, Fullerton, returned from sabbatical in 2012, she found a surprise in the laboratory adjoining her office: a man, an old man named James F. Woodward. Fearn knew him from around—he was a professor of science history and an adjunct professor of physics. With white hair and eyes perpetually peering over the top of his glasses, he fit the part. Still, she thought, “What the heck is this guy doing in my back room?” He was, it turns out, being shuffled around spacetime: The university had recently commandeered Woodward’s office for a newly created Gravitational Wave Physics and Astronomy Center. The institutional authorities had transferred him into this relatively unused spot. At first, Fearn viewed him as an intruder, but soon her perspective shifted. Woodward was researching a fringe topic—one way outside Fearn’s normal purview. She specialized in quantum optics, how light interacts with matter—a much more mainstream subject than Woodward’s interest: a hypothetical form of spacecraft propulsion so powerful that—if real—it could potentially push our species out to the stars. Or so he claimed. Fearn, whose shaved head and smirk suggest constant skepticism, was not so sure. “I wasn’t really convinced that what he was doing was correct,” she says. When she walked by every day, what Fearn saw resembled a Physics 101 lab experiment more than a futuristic propulsion system. Woodward’s setup had a bolted-down balance with a metal cage on one side, wires running to and fro, and counterweights on the other side. “You can create some very large gravitational effects just by pushing on stuff,” Woodward promised her—specifically, the stuff inside the metal box. He claimed he could induce tiny, ultraquick variations in an object’s mass, making it lighter and then heavier. And then, by tugging and shoving it back and forth strategically as its mass changed, he could create thrust. He showed her little blips on the output graph, each a vroom. Right, Fearn thought. But she side-eyed that graph daily. “Every time I walked past, the blip seemed to get bigger and bigger,” she says. Eventually Woodward asked if she wanted to help. She had tenure, and she liked Star Trek, so “Yeah, sure,” she said. Working together since then, the odd couple has been developing MEGA: the Mach effect gravity-assist drive. And although it is still on the outer limits of mainstream science, it has gained credibility. Three other labs have seen similar thrust from copycat setups, and MEGA has netted two of NASA’s most competitive grants. These are not just any grants, though. They come from the agency’s spaciest department: the NASA Innovative Advanced Concepts (NIAC) Program, which funds research that would be “huge if true.” In 2017 and 2018 advanced propulsion—sending more mass through more space in less time using less fuel than traditional rockets—has accounted for around 20 percent of the awards. These projects range from really exotic to merely eccentric, but they all diverge from the traditional path and aim for somewhere new. The NIAC grants are trying to remedy the fact that propulsion has stood relatively still since the mid-1900s. Most spacecraft use chemical propellants, the space version of gasoline. In conventional rockets, these chemicals combine and react with one another to heat up and expand. Too big for their chamber’s britches, they shoot out the back of the craft, creating thrust. Thrust is simply using force in one direction to create an equal force in the opposite direction. When you push into the wall of a swimming pool, thrust is what pushes you back. Fuel, though, is heavy and inefficient. To get truly huge thrust, a vehicle would need to carry so much gas that it would never get off the ground. For missions to other solar systems or even travel within our solar system at a much quicker pace, chemical fuel is just not going to cut it. “There’s only so much energy in those propellants,” says John Brophy of NASA’s Jet Propulsion Laboratory (JPL). He leads another NIAC-funded project called A Breakthrough Propulsion Architecture for Interstellar Precursor Missions. “It doesn’t matter how smart you are, how big a nozzle you make, you can’t beat that problem,” Brophy notes. A few deep-space projects, like NASA’s Dawn mission to the asteroid belt, have instead used electric propulsion. Such systems typically use electric power to accelerate charged particles, which can then shoot from the rocket at speeds up to 20 times faster than traditional fuels. But these, too, have been stuck in a rut. “It turns out that almost all the electric thrusters that have been invented were invented in the 1950s and 1960s,” says Dan M. Goebel, a senior research scientist at JPL. “It’s like there almost hasn’t been a new idea since then.” NIAC, though, is all about new ideas. The program functions as NASA’s venture capital arm, in that it supports technologies that might pan out, big-time. “Crazy” stuff, according to Jason Derleth, NIAC’s program executive. “What I mean by ‘crazy’ is something nobody is thinking about,” Derleth says. Something 10 times better than current technology, swooping in to push on the sluggish status quo. In start-up-world-speak, this would be called “disruption.” As an example, Derleth cites the work of Philip Lubin of the University of California, Santa Barbara. A few years ago Lubin proposed a project nicknamed Starchip Enterprise: a tiny satellite equipped with a “light sail” (a new iteration of an idea that predates the project). From Earth orbit, powerful lasers would shoot toward the sail. When they hit, the sail would reflect the light, and its momentum would thrust the spacecraft forward. NIAC awarded Lubin grants in 2015 and 2016, and he now works with a project from the Breakthrough Initiatives to send a laser-powered light sail to the closest star. This is the good kind of crazy, which NIAC likes. “It’s just crazy enough that it might work,” Derleth says. “NIAC is for going up to the edge of science fiction but not crossing over.” He adds, “We do our best to not cross over.” But the gap between science and fiction is fractional, at these low “technology readiness levels” (TRLs), a rating system NASA uses to assess how mature an innovation is. The solar panels on its Mars InSight lander rate a TRL 9, meaning already out in space, working. NIAC, though, seeks TRLs 1, 2 and, sometimes, 3—early-stage projects that need more baking before they are deployed in the real world. Around 200 groups typically submit NIAC Phase I proposals every year, and the agency okays just 15 to 18. With $125,000 apiece, scientists get nine months to do “a quick turn of the crank to see if something is really feasible,” Derleth says. If no deal breakers pop up, researchers can apply for the $500,000 Phase II grant. “It is one of the hardest proposals to write, with the lowest win rate in aerospace,” he says. “I consider these folks to usually be the cream of the crop.” Eight of the 47 projects funded in the past two years and three Phase II selections have dealt with advanced propulsion. But NIAC is taking a gamble on every project—hoping at least some represent a true outside force, something that can push propulsion in a new direction. “This has not been an exploration guided by genius and profound insight,” Woodward says one February day over a video conference call. He and Fearn are sitting in the office that has become their joint headquarters, where a box of tissues sits next to a pair of forceps. Fearn’s office, empty, shows on a screen, forest-tall metal bookshelves bungee-corded together in the background. Together—as Fearn proclaims the project belongs to Woodward and Woodward protests with equal and opposite force—they describe how MEGA might work. It begins with inertia. It is a simple principle, one you experience every day: the tendency of things to keep moving in the same direction they already are or to stay stopped if they are standing still. But scientists lack a solid explanation for why inertia exists. It just kind of ... is. In the late 1880s Austrian physicist Ernst Mach came up with the seed of one idea: inertia is the result of all the gravitational influence of all the matter in the universe. Anything inside a spacecraft engine, then, feels a gravitational pull from nearby stuff as well as that billions of light-years distant. And an object’s mass will change a bit every time it accelerates or decelerates relative to all that stuff. Other physicists around the same time, including Benedict Friedlaender and August Föppl, held similar relativistic ideas. But Albert Einstein is actually the one who named this “Mach’s principle,” after reading Ernst Mach’s earlier musings on the subject. More modern physicists—including the late Donald Lynden-Bell, who in 1969 first proposed that the centers of galaxies contain supermassive black holes—have taken up the cause. As a student, Lynden-Bell became intrigued by the idea, and his adviser gave him a 1953 paper by physicist Dennis Sciama, who articulated the most complete version of Mach’s idea. Sciama’s work is what inspired Woodward, too. Although Lynden-Bell maintained interest throughout his career, it was a side project; he subscribed to a research philosophy almost the opposite of Woodward’s: “Doing bread-and-butter science, straightforward extensions of what is known in order to elucidate new phenomena, is the main job,” he wrote in 2010. “We should not spend all our time groping at great problems that may be beyond our capacity.” Woodward disagrees, hewing more to a “go big or go home” ethos. And so he has continued to try to apply Mach’s principle to spacecraft engines. Engineer Marc Millis, who used to head NASA’s Breakthrough Propulsion Physics Program, sees promise here. “Unlike other claims, the [Mach effect thruster] ... is rooted in open questions in physics,” he says. The idea of a thruster based on Mach’s principle goes like this: By deforming an object, you accelerate its innards (imagine crumpling a piece of paper—when you crush it, you are moving its parts). And when you accelerate something, you change its energy. If you change its energy—according to Einstein’s revelation that E = mc²—you change its mass. If you change its mass, you affect its inertia. And if you mess around with inertia, you are messing with how the object relates to the entire rest of the universe. What this means, in a practical sense, is hard to say. But Woodward and Fearn have tried to bring these ideas down to earth. Inside their space drive is a clamped-together stack of “piezoelectric disks,” ceramics that expand and contract (like pieces of paper crumpling and uncrumpling) when shocked with a voltage. Some of that acceleration changes the internal energy of the disks, which then changes their mass: They grow heavier, lighter, heavier, lighter. If you pull on them when they are light and shove them away when they are heavy, you get thrust—without having to use any fuel. “Picture yourself standing on a skateboard with a 10 pound brick attached to you via a bungee cord,” wrote Woodward’s former graduate student, Tom Mahood, in an attempt to make this all slightly understandable, which was posted on his Web site in April 2012. “If you throw the brick away from you, you and the skateboard will move in one direction, and the brick will head in the opposite direction.” Thrust! It is not a perfect analogy, Woodward points out—but he admits he has never been able to come up with a physical metaphor that both makes sense and is totally correct. It sounds sketchy, and some scientists believe it violates the principle of conservation of momentum, but some studies (and Woodward and Fearn) disagree. Yet the idea caught the attention of Gary Hudson, president of the Space Studies Institute, a California-based organization once headed by famed theoretical physicist Freeman Dyson. The group set up an Exotic Propulsion Initiative in 2013, with first funds going toward Woodward and Fearn. Woodward soon began sending copies of his setup to people at other labs, so they could try to replicate the thrust. And Fearn and Lance Williams, then a scientist at Aerospace Corporation, a federally funded research and development center in El Segundo, Calif., suggested that the Space Studies Institute run a workshop for advanced propulsers. Because Williams lived in Colorado and knew it was a pretty place to hole up even if all the participants reneged on their RSVPs, the group settled on Estes Park in the fall of 2016, when aspens on the steeply pitched mountainsides turn the red-orange-fire color of (conventional) rockets. The conference’s motto, “Bury the Hatchet,” urged cooperation between competitors, and the meeting even had an official lapel pin: a hatchet and shovel crossed into an X. On the first day, Hudson stood before the gathered crowd, wood paneling and white boards behind him. “In the past, our work has been very solidly grounded in engineering and physics,” he said, “and of course exotic propulsion is a pretty controversial subject.” But, he went on, it has intrigued him for a long time. Science-fiction writer Arthur C. Clarke once told him that if he wanted to get far from this planet—and come back—he needed one thing: “A physicist who will give you a straight answer to the question, ‘What is inertia?’” “I remembered those words,” Hudson said. “The first physicist I encountered who gave me a straight answer was Jim Woodward.” And as the conference tripped along, others’ results seemed to—at least to some degree—back up Woodward and Fearn’s measurements. They showed thrust from the MEGA setup when the thruster was turned on and not when it was turned off. On the third day, Nembo Buldrini of FOTEC Research and Technology Transfer, an Austrian engineering firm, stepped to the front of the room. He usually evaluates the effects of electric thrusters, but a few years before, Woodward had sent him a Mach effect device. Buldrini brought up a plot showing his results, side by side with Woodward and Fearn’s. “The first thing that is evident is the shape of the curve,” he said. Indeed, both showed a dip when the device turned on, a constant thrust while it was powered up, and then an offset spike when it switched off. The thrust numbers differed by an order of magnitude—perhaps, Buldrini said, a problem of calibration. Perhaps not. (Woodward also notes that differences in the balance equipment could account for differences in magnitude.) Two other groups had similar data with similar thrust patterns. Martin Tajmar of the Technical University of Dresden had only preliminary results, but George Hathaway, an electrical engineer who runs his own consulting firm, had more data. During his presentation, he wore no shoes—only socks with rainbow-colored Einstein faces splashed all over them. His lab, he said, had done its work on antiseismic tables, to make sure the planet’s shaking did not mess up off-Earth travel results. And the thrust held up. After the workshop’s early-stage replications, NIAC took notice and gave Woodward and Fearn a 2017 Phase I grant. Which is not, of course, to say either that the thrust is definitively real and not some systematic error—or that, if it is real, the Mach effect causes it. In 2018 Tajmar presented a paper as part of his SpaceDrive project, an initiative to try to replicate, or rule out, fantastic(al) propulsion claims. And, in fact, that study showed anomalously high thrusts—meaning the blips might not be thrust at all but an error or some other phenomenon. At the Space Studies Institute’s 2018 workshop, a software engineer named Jamie Ciomperlik presented a simulation showing how vibrations in the system could masquerade as oomph. In May 2019, moreover, Tajmar published another SpaceDrive paper online, and when he subtracted out other effects that may masquerade as thrust, there was no thrust to see. “Our results challenge the validity of the genuine thrust claim on the Mach Effect thruster,” Tajmar says. “But further research is needed to definitely confirm that.” Woodward says he believes the setup was not configured correctly. The team plans to present new data later this year, and Tajmar says that even if the thrust returns, he does not think the underlying theory is correct. Millis tends to agree—both that teams could be seeing a false positive and that, if not, the device is not necessarily demonstrating the Mach effect. In some ways, though, the underlying theory matters less than the empirical demonstration. As Lance Williams said during the 2016 propulsion workshop, “If you can levitate a cannonball in front of us, we don’t care what the theory is.” “Skeptical doubt is healthy, and the only way to resolve doubt is irrefutable evidence,” says Millis, who recently spent three months at Tajmar’s lab chasing that evidence. “Despite the replications, [the thrust] still might turn out to be a common measurement artifact,” he says. “Then again, it may be a genuine new phenomenon.” Although the science is far from settled, MEGA’s Phase I results impressed NASA enough that the agency gave the group a Phase II grant in 2018. Woodward and Fearn’s experiment is the most exotic of NIAC’s propulsion grants. And not all the other researchers who have NIAC funding agree that “exotic” is the way to go. Brophy’s A Breakthrough Propulsion Architecture for Interstellar Precursor Missions is pinning its hopes on lasers. Similar in some ways to Lubin’s light-sail lasers, Brophy’s lasers will shoot from orbit, beaming light to panels that—like solar panels—turn it into electric power. That electricity feeds into a propulsion system pumped full of lithium. The voltage whacks electrons off the lithium atoms, leaving them with a positive charge. An electric field then accelerates them and routes them out the back of the spacecraft. Brophy wants it to travel 20 times faster than the Dawn spacecraft’s ionic propulsion system—whose development he led—for a speed of around 200 kilometers per second. But the project is still a moonshot. The team is not sure it can point the laser accurately enough or that it can assemble such a big laser array in space or make light-converting panels that generate the necessary 6,000 volts. “That’s why it’s a perfect NIAC study,” Brophy says. “[NIAC experiments are] intentionally right at the ragged edge of whether they are feasible or infeasible.” And some are trying to break away from the electric trajectory altogether. Another NIAC project is targeting an antimatter engine by “cooling down” positrons, which have the same mass as electrons but the opposite charge. In their natural state, these antimatter particles are hotter than the surface of the sun, making them hard to work with and store. But cooled down, they can be kept and controlled and—as this project does—smashed into electrons. The resulting gamma rays could fuel a fusion reaction that then propels the spacecraft. Another idea braids a beam of neutrons and a beam of laser photons so that the particles do not spread out, or diffract, as they travel through space. The neutron beam corrals the photons by refracting them, or bending their path, and the laser beam’s electric field “traps” the neutrons. The team claims a beam made with a 50-gigawatt laser, shot onto a sail on the spacecraft, could accelerate a one-kilogram probe on a 42-year mission to the nearest star system. And then, of course, there are nukes. Robert Adams of NASA’s Marshall Space Flight Center has a NIAC project called Pulsed Fission-Fusion (PuFF), which combines two nuclear strategies. “The only way we’ve developed anything fusion-related is with a fission trigger,” he says—in other words, using an easier-to-make fission reaction to create conditions extreme enough to kick-start fusion. But a fission-fusion trigger is a lot like a bomb, so Adams started to dream up systems that could not be repurposed by a criminal, and he happened on a concept called the Z-pinch. If you generate an electric current in a plasma (in this case, made of lithium), you can use the magnetic field it induces to compress, or pinch, something—in this case, a target made of uranium and deuterium-tritium. The squished uranium goes critical, and its fission energizes the deuterium-tritium enough to start fusion. Fusion makes neutrons, which get involved in more fission, which raises the thermostat and therefore the fusion rate. The two-stage explosion has the power of a few kilograms of TNT. Nothing to end the world with—but enough that, applied steadily and with a bunch of parallel devices, a 25-metric-ton craft could get to Mars in 37 days (compared with the nine months or so it takes with a chemical engine). In 2018, after applying for it five times, Adams finally got a Phase II grant. You can think of Adams’s biggest problem in terms of a Twinkie. Try to squeeze the Twinkie—that fission-fusion target—uniformly. Impossible! The spongy yellow bread bleeds down into the white filling; the filling squirts out the sides. In PuFF, that leakage means squished-away energy, leaving you without enough to rev up fusion. In the past, that issue was the end of the path for researchers. “They gave up on it and started going down these other roads,” he says. None of those roads, though, have led to giant leaps in space propulsion. A historical parallel to Adams’s project provides a lesson about one reason propulsion has stalled. From 1958 to 1964 the military and NASA spent $11 million ($93 million in today’s dollars) on an effort led by Freeman Dyson to develop a nuclear-based propulsion system named Orion, very similar to PuFF. The project’s motto? “Mars by 1965, Saturn by 1970.” It was not quite military, but it verged on too explosive for NASA, so both organizations wavered in their commitment. Finally, it became a no-go when, in 1963, the U.S. signed the Nuclear Test-Ban Treaty, illegalizing necessary experiments. “This is the first time in modern history that a major expansion of human technology has been suppressed for political reasons,” Dyson said at the time. Merit, then, is not the only factor that determines which technologies become reality. Whatever we send to space comes from Earth, where there are laws, unburied hatchets, poorly understood physics and unknown unknowns that seem too risky to put on a costly spaceship. These are among the factors that lead to proverbial inertia—the tendency to keep using the same technologies and keep going the same way we have been going. But that outside kick to point the field in a new direction could come at any moment. The jury is still out on MEGA, and the concept is still a long way from being useful, if it ever will be at all. The current devices provide just a small push—counted in “micro newtons”—an apple exerts orders of magnitude more force on a kitchen counter. And the apple is not going anywhere near Alpha Centauri. But every shove has to start somewhere. With the Phase II grant, Fearn and Woodward hope to increase their thrust and place multiple devices in parallel so that they add up to something usable. And then, with whatever funding they hope to get next, they will launch a mini satellite, equipped with a mini MEGA drive. With it, they will try to change the satellite’s orbit, showing that the Mach effect can act on the real world. This year NIAC opened a new funding line—Phase III awards totaling $2 million. The two 2019 awards went to space mining and prospecting projects, helping the agency achieve its solar system exploration goals. In the future, though, awards may look deeper into space and farther into the future—at projects like MEGA, provided its results pan out. But first, Fearn says, “NASA is making sure this isn’t some spurious thing that a couple of people in southern California are wasting their time on”—that it is, in fact, the good kind of crazy.