How Close Are We to Interstellar Travel?

Humanity has long dreamed of one day reaching the stars, but how close are we to interstellar travel becoming a reality?

It’s no secret that interstellar travel is incredibly complicated given the unimaginably vast distances involved, but does that mean that we’re forever confined to the realms of our tiny corner of the universe? No, at least not in theory. In fact, the Voyager 1 probe has already ventured beyond the borders of the solar system, reaching interstellar space in August 2012. Nonetheless, even travelling fast enough to reach Jupiter two years after its launch in 1977, it would still take some 80,000 years to reach the nearest star beyond the Sun, if it were on a direct course.

Setting Our Sights on Alpha Centauri

NASA

An artist’s impression of the sky as seen from planet Proxima b during the day time. In the background are the two Sun-like stars Alpha Centauri A and B.

It only makes sense that our first interstellar destination will probably be Alpha Centauri, seeing that it’s the closest star to our own. Our nearest neighbour is a mere 4.37 light years away. It’s home to three stars in total, including two sun-like stars and a small, dim red dwarf that appears to be gravitationally bound to the two larger ones. One planet has been discovered in the system as well. Proxima Centauri b is a rocky Earth-sized world that orbits the red dwarf component of the trinary system. There are likely to be more planets too, including ones orbiting its sun-like members.

According to SETI astronomer Jeff Coughlin, we already have the technology to send a probe to Proxima b within a the next few decades, but getting there within a human lifetime is quite another matter. While our technology is significantly further ahead than it was in the late seventies, we are still completely reliant on chemical rockets, which are woefully impractical for interstellar travel due to their inherent limitations such as lack of fuel efficiency. Even combined with gravity assists from giant planets like Jupiter, the journey time still runs into tens of millennia.

Sailing with Laser Light

Futurilla, from public domain images

The well-funded Breakthrough Starshot could see a laser-powered lightsail nanocraft making mankind’s first foray into solar systems beyond our own.

Breakthrough Starshot is a $100-million programme announced in April 2016 to make interstellar travel to our nearest neighbour a reality by cutting down the journey time to about 20 years. This requires coming up with a space probe design concept that’s able to achieve an eye-watering 37,282 miles per second (60,000 km/s). Researchers are currently looking into the viability of sending a fleet of around a thousand tiny spacecraft the size of sugar cubes, powered by Earth-based lasers arranged in a square kilometre array.

Although the concept is better developed than most others, the challenges facing its adoption are still enormous. To name just a few, scientists still need to find a way to pack everything, including a plutonium-based nuclear battery to power the on-board instruments, into just a few grams. However, the spacecraft would also be equipped with metre-square solar sails, which will use the radiation pressure provided by the lasers as a means of propulsion. According to the Tau Zero Foundation, an organization seeking to promote further research into interstellar travel, we’re still decades, or even centuries, from making boosted light sails a reality, however.

Pushing Existing Technology to the Limit

NASA

Nuclear pulse propulsion was first conceptualized in the 60s as a way to send spacecraft throughout the solar system and beyond at immense speeds.

While liquid-fuel rockets and gravity assists will never provide a practical way to get us to the stars, nuclear propulsion is another possibility. However, unlike light sails, nuclear energy is something we’re already very familiar with. For example, Project Orion was initiated way back in 1958 that came up with a spacecraft design that used atomic bombs detonated behind the spacecraft, allowing it to reach speeds of up to 6,200 miles per second (10,000 km/s). Nonetheless, even at this enormous speed, reaching Alpha Centauri would still take 133 years.

Project Orion remains one of the few remotely viable ways to send a probe to the nearest stars, even though the project was closed in 1963 by the Partial Nuclear Test Ban Treaty. The treaty, which prohibits all test detonations of nuclear devices in outer space, was eventually signed by 123 nations, thus sealing the fate of nuclear pulse propulsion to reach the stars. Nonetheless, further research has been conducted since, leading the scientific community to consider it an applicable technology rather than just a theory.

Stepping Beyond the Limits of Accrued Physics

AllenMcC

A warp bubble involves expanding space behind a craft and contracting space in front of it, thus allowing it to achieve apparent faster-than-light travel.

The limits of physics as we currently understand them disallow us from breaking the universal speed limit of light. However, if we ever want to make interstellar travel truly viable and, indeed, if we ever want to go far beyond the dozen or so other stars that lie within 11 light years of Earth, we’re going to have to find a way to effectively travel faster than light. However, we simply don’t even know if it’s even possible to find a way around the speed limit of light.

Although there is currently no known viable way to overcome the universal speed limit, the warp drive concept has long been at the forefront of faster-than-light (FTL) research. With this concept, spacetime is warped in such a way that greatly reduces the effective distance between two points while the spacecraft remains stationary within its own frame of reference. This would also eliminate the problem of time dilation, whereby time runs faster the closer one gets to the speed of light, while back on Earth, the passage of time stays the same.

While NASA is generally more concerned with goals less lofty than interstellar travel, the US space agency continues to invest money into relevant research. In 2012, a team working at the Johnson Space Center started conducting experiments to detect the warping of spacetime on a microscopic level using a setup called the White–Juday warp-field interferometer. Although the experiments have yet to achieve anything ground-breaking, it does show that there is serious research into the concepts behind the warp drive. Unfortunately, however, we’re a long way off from the realms of routine FTL travel or, indeed, any kind of manned interstellar exploration.

Taking It Slowly

Donald Davis, NASA

Going to the stars the slow way would require a fully self-sustaining artificial biosphere complete with gravity simulated by centrifugal force, as depicted in this artist’s impression of an O’Neill cylinder colony.

If we can’t ever break the light barrier, manned interstellar travel will be forever fraught with enormous challenges. The concept of a slow manned mission to the stars lasting centuries or more is a popular one in science fiction. If, indeed, we ever needed to leave Earth and settle on a suitable, albeit so-far undiscovered, planet in our stellar neighbourhood, the slow method would likely be the only viable option. However, speed isn’t the only challenge of interstellar travel. I’ll be looking at some of the many other challenges in a future article.

One approach that’s long been a staple of science fiction, is to put people in suspended animation so they use fewer resources and live long enough to complete the journey. While it’s likely theoretically possible, there is still no known viable technique to achieve so-called cryo-sleep or human hibernation. Another option considers building an interstellar ark on which people live for generations, whereby only the descendants of the original crew who started the journey would make it to the destination. Similarly, however, such a concept, while theoretically possible, is far from feasible with today’s technology.

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Humanity’s voyage to the stars has, in a way, already begun, but we still have an enormously long way to go before real interstellar travel becomes a viable reality. Manned travel is many times more complicated again, but does that mean our dreams for exploring the wider universe are forever dashed? Do you think we’ll ever be able to explore worlds around other stars in person? Let me know in the comments below.

Further Reading