In my previous blog post , I covered some of the technologies that sci-fi writers have predicted we’ll have in the future. I used some of the tech from the Star Trek universe as examples, since it wasn’t possible to cover all sci-fi tech in one post. One of those technologies is warp drive, which is one method for faster-than-light space travel. Since most of my first novel, The Lightning in the Collied Night, is set about 30 years from now and involves space travel, the discussion on warp drive led me to think, how will spaceships get around about 30 years from now? Based on what I’ve learned about the prospects forwarp drive becoming a reality, I don’t think spaceships will be using that any time soon. But what, then?

When I researched that question for my novel, I found an emerging spacecraft propulsion technology that fits my story: Quantum Drive. It’s a technology that’s progressed far enough for testing in space—although it hasn’t yet been successfully tested. But that’s okay—I’ve got about 25 years before it has to work for the spaceships in my novel. I like that it stretches the laws of physics but is still considered feasible for the near future. I also think the name sounds pretty cool.

When I researched spacecraft propulsion technologies for my book, I learned that there’s many other possibilities besides Quantum Drive. However, my story requires spacecraft that can travel pretty darn fast—about 20 percent of the speed of light, give or take. That narrows down my options significantly. I think the most likely candidates for my novel, from the technologies listed in the table referenced above, other than Quantum Drive are:

• Solar sails
• Photon rockets
• Antimatter rockets

I’ll discuss each of those technologies in turn.

Solar sails, as the name implies, use radiation pressure from sunlight on large surfaces. Because sunlight travels at the speed of light, that’s the theoretical top speed for a spaceship equipped with solar sails. “Theoretical” is the key word here. Notice in the linked article, the duration of a trip to one of the inner planets like Mars using a solar sail is estimated to take hundreds of days, and multiple years for outer planets like Jupiter. Sorry, that’s not fast enough for my purposes. However, if instead of sunlight the light from lasers or masers were used, it might be possible to achieve speeds from 11 percent to 50 percent of the speed of light. That’s more like it! Unfortunately, that approach is only theoretical and faces huge engineering challenges, such as the need to build large solar arrays near Mercury. I doubt that will be practical in the next 30-50 years. Now, there is one sure way to get enough solar energy to propel a craft with solar sails to near-light speeds: use the light from a nearby supernova. But I don’t think we want to see a supernova in our neighborhood anytime soon! On the plus side, solar sails are already being tested in space; NASA deployed a nine-meter solar sail recently.

Photon rockets use thrust from the momentum of emitted photons for their propulsion. The good news about photon rockets is that they’re based on established physics and technologies. And because they use light energy, the maximum speed of such ships is theoretically close to the speed of light. Ah, there’s that word “theoretical” again. Unfortunately, the actual maximum speed of a photon rocket powered by the most likely energy source that will be available in the next 30 years or so—a nuclear fission or fusion reactor—is much lower, perhaps only 0.02 percent of the speed of light… much too slow for interplanetary travel or the mission of the spaceships in my novel. There is potential for higher speeds using beamed laser propulsion, where the photons would come from lasers directed at the spacecraft. But it’s questionable whether that approach would work for long-distance voyages such as travel to the outer planets or beyond.

Antimatter rockets are powered by the energy created by the annihilation of antimatter. There are three types of antimatter rockets: those that directly use the products of antimatter annihilation for propulsion; those that heat a working fluid or an intermediate material which is then used for propulsion; and those that heat a working fluid or an intermediate material to generate electricity for some form of electric spacecraft propulsion system. (Note that it does not include using antimatter to power a warp drive; for a discussion on that, see my previous blog post .

Of those three options, the one that has the best potential for propelling spaceships at some significant fraction of the speed of light (that is, relativistic velocities) is the first one: channeling the products of antimatter annihilation through magnetic nozzles to create thrust. A couple of approaches have been theorized. The first involves a matter-antimatter giga-electronvolt gamma ray laser photon rocket that utilizes a relativistic proton-antiproton pinch discharge, where the recoil from the laser beam is transmitted by the Mössbauer effect to the spacecraft. (Whew! That’s a load of technobabble, isn’t it? At least it’s science-based technobabble.) The second approach is relatively new, and more iffy: convert hydrogen or deuterium into relativistic particles through laser annihilation. Theoretically, a spacecraft with such an engine could reach 94 percent of the speed of light, or 0.94 c. (Darn, there’s that word again—theoretical.) Although a relativistic particle reactor is being built at the University of Iceland, it’s unclear whether that method of propulsion will be ready to test in a spacecraft any time in the near future. Several challenges would have to be overcome first, including the immense cost of producing antimatter and the need for heavy shielding to protect the spacecraft and people inside it from the intense heat and gamma rays produced by antimatter annihilation.

I’ve focused here on propulsion technologies that could theoretically be available in the next 30 years or so to propel a spaceship at relativistic speeds, because that’s what I need for the story in my book. But there’s many other techniques that sci-fi writers use to have their spaceships get around. One of the most popular is faster-than-light travel, using approaches such as hyperdrive (Star Wars et. al.),  warp drive (Star Trek et. al.), FTL jump drive (cf. Battlestar Galactica), and traversing wormholes (many examples, including Babylon 5, Contact, Doctor Who, The Expanse, Farscape, the MCU, the Stargate universe, and the Star Trek universe.)

Another popular, and very old, mechanism in sci-fi for characters to travel great distances through space is the use of suspended animation, also called cryosleep. The idea of suspended animation dates back to the legends of King Arthur, fairy tales like Sleeping Beauty, Shakespeare’s works such as Romeo and Juliet, and early American fiction (Rip Van Winkle). In science fiction, suspended animation first appeared in the early 1800s in Rodger Dodsworth: The Reanimated Englishman by Mary Shelley. More recently, suspended animation was a key plot device in literature such as the Buck Rogers stories, several works by Arthur C. Clarke including his Space Odyssey series, and The First Immortal. Sci-fi films abound with suspended animation; some recent examples are Avatar, Interstellar, and Passengers. Cryosleep is also common in sci-fi TV shows such as Futurama, Lost in Space, and Star Trek (“Khaaaaaan!”). There’s been considerable research done on suspended animation, including hypothermic experiments with dogs and pigs. Another technique for long-distance space travel that’s often paired with suspended animation in sci-fi stories is the use of generation ships. On such spaceships, also called sleeper ships, crews would live there for at least several decades, such that they would comprise multiple generations. There’s several obstacles to generation ships, including the effect of cosmic rays on humans during a lifetime in space. Although this concept has been studied in depth, the many hurdles involved probably mean we won’t see such spaceships in the next 30-50 years at least.