The Radical Spacecraft That Could Send Humans to a Habitable Exoplanet

Solar One—part light sail, part laser system, part fusion reactor—can theoretically travel at 22 percent the speed of light.


In a fascinating new paper, amateur astronomer Alberto Caballero suggests a combination of near-future technologies could carry people to the Alpha Centauri system, home to the nearest potentially habitable exoplanet, at about 22 percent the speed of light.

But is Caballero cooking with gas, or is this all hot air? There’s a lot to unpack here.

In his paper, which he posted to the non-peer-reviewed, preprint service arXiv, Caballero proposes the concept and design of a new spacecraft he dubs Solar One, which would integrate a larger version of NASA’s Sunjammer light sail, the U.S. Navy’s compact fusion reactor, and several DE-STAR laser systems. Here’s the concept art:

solar one concept art

MARCO PURICH

With a mile-long light sail, Caballero says, Solar One could reach “an average of 22 [percent] the speed of light, arriving to the closest potentially habitable exoplanet in less than 19 years with the help of a Bussard scoop.”

A refresher: Solar sailing, a term first coined by science fiction writer Arthur C. Clarke in his 1964 short story “Sunjammer,” is a method of powering small spacecraft without the use of an expensive propellant. Instead, the spacecraft has a large, mirror-like sail, which harnesses the power of the sun.

NASA retired its Sunjammer light sail in 2014, after a few years of work and a tiny-scale demonstration, but before a planned test flight of a much larger sail at a much higher altitude. But NASA, Bill Nye’s space-travel foundation, and many others players continue to invest in light sails of different kinds.

The U.S. Navy’s compact fusion reactor (CFR), meanwhile, is a developing piece of nuclear technology that smashes atoms together to produce plentiful energy … hypothetically. (Here’s the wild patent.) So far, no fusion reactor has made more energy than it consumes, but virtually all plans for far spaceflight involve some kind of nuclear reactor for propulsion.

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Parts of the patent for the U.S. Navy’s compact fusion reactor.GETTY/ USPTO

And DE-STAR is, in its creators’ own words, “a modular phased array of kilowatt class lasers powered by photovoltaics.”

bussard interstellar ramjet

An artist’s concept of the Bussard Interstellar Ramjet, which uses interstellar hydrogen scooped up from its environment as the spacecraft passes by to provide propellant mass.NASA/PUBLIC DOMAIN

Finally, the Bussard scoop Caballero mentions is more far out than even the rest of these untested ideas.

This is like a spacecraft’s version of a whale’s baleen, skimming all of the protons from a chunk of space and somehow turning that into a nuclear rocket. As that cached NASA page puts it, “There are a variety of limitations to this concept, such as how many protons can be scooped up, the drag created from scooping them—not to mention getting these protons to engage in nuclear fusion for a rocket.”


Caballero posits that the CFR will gather up a terawatt of energy, which would fuel the DE-STAR array. The lasers would scan ahead to dissolve obstacles, behind to increase propulsion, and finally, ahead again to slow the craft as it nears the final destination among the exoplanets. The massive Sunjammer, meanwhile, will more passively propel the craft.

What’s maybe most interesting about Caballero’s idea is that, since he’s an outsider scientist, it’s made from all public information. Even his calculations are powered by, he says, “an online calculator provided by […] a company specialized in lasers.”

So, could the Solar One really fly? That’s hard to say, because even near-future technology is still far away from where we sit in 2020.

Sneaking the Bussard scoop in there feels like a fakeout, because that idea is far further into the future than the others—firmly in the area of pure ideas at this point, without even a tiny amount of proof of concept. But imagining these spacecrafts is arguably just as important today, when scientists, and funders, are making decisions that could influence where humanity can go in the next 100 or even 500 years.

And in that sense, Solar One is a great exercise in what could be possible.