Our ambitions for space exploration have taken men to the Moon, rovers to Mars, and spacecraft to the outer reaches of the solar system. But could men or spacecraft ever reach Alpha Centauri, the closest star system to our planet?
Alpha Centauri is approximately 4.4 Light years (about 40 trillion kilometers) from Earth and is home to three separate stars. The nearest star, Proxima Centauri, is also home to an exoplanet that scientists believe may have the conditions necessary for life.
But reaching this star system would be no small feat. NASA estimates that using a space shuttle like NASA’s now retired 38-meter-long DiscoveryIt would take almost 150,000 years to reach Alpha Centauri.
If humans could travel at the speed of light, they could reach Alpha Centauri in four years. However, the laws of physics dictate that only light, massless particles called photons can reach that cosmic speed limit. So while humans will likely never reach Alpha Centauri, it is possible that spacecraft designed to travel at a much smaller fraction of the speed of light could reach those stars in a human lifetime. To even hope to get a spacecraft to reach that maximum speed, scientists would need a craft much smaller than Discovery.
Marshall Eubanks, CEO of startup Space Initiatives Inc and a member of NASA’s Innovative Advanced Concepts program, is exploring ways to visit Proxima Centauri remotely using swarms of picometer-sized spacecraft (a picometer is one billionth of a meter).
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Artist's rendering of a blue planet with circular shapes on the left
It is possible that a tiny spacecraft could reach Alpha Centauri in a human lifetime. (Image credit: Courtesy of Space Initiatives Inc.)
“We are in the midst of a revolution in spaceflight and space exploration, with extremely small systems,” Eubanks told Live Science in an email. “While a small individual spacecraft will not be as capable as a larger spacecraft, like the Voyagers, their development times are much shorter; they are relatively inexpensive.”
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Smaller spacecraft also require less energy to propel them, which could be a key advantage in increasing their speed.
Eubanks isn’t alone in pursuing this type of research. Breakthrough Initiatives has begun its Starshot Project in 2016 to combine nano-sized spacecraft with light sails, and in 2017NASA has begun funding its own project to launch a mission to Alpha Centauri by 2069100 years after Apollo 11.
Although small spacecraft are easier to accelerate than larger probes, traditional fuel sources are not powerful or abundant enough to propel these craft to near the speed of light. Philippe LubinA physics professor at the University of California, Santa Barbara, whose ideas about interstellar travel inspired the Starshot team, told Live Science that these craft will likely rely on light instead.
Artist's rendering of a planet with white shapes on the right
A spacecraft flying over the Alpha Centauri star system could see if the planet orbiting Proxima Centauri shows signs of extraterrestrial life. (Image credit: Courtesy of Space Initiatives Inc.)
Solar energy
To go fast in space, it’s best to be small and have low mass. One of the main advantages of light propulsion is that it’s massless, Lubin said. Traditional rocket fuel, on the other hand, creates propulsion by converting heavy fuel into energy by burning it. Using a solar sail, powered by sunlight, or a photonic sail, powered by laser light, gives you all the power without any of the weight.
Lubin said that you can think of this as throwing a ball at a piece of paper. When a ball hits the paper, it applies a force that causes the paper to recoil or push back. Similarly, the the impulse carried by light is transferred to the spacecraft, causing it to recoil and accelerate.
“The system is actually a giant flashlight – it’s a giant laser array [on Earth]”, Lubin said. If spaceships are sailboats, then laser light is the wind in their sails.
The technology to create and test such craft, including communications equipment small enough to fit inside them, is still being developed. But there is no physical reason to believe such a spacecraft could not perform a flyby mission of Alpha Centauri, Lubin said.
This mission could behave very similarly to the Voyager 1 and 2 probes and transmit high-resolution images of the star system back to Earth, some of which could contain our first glimpse of the potentially habitable planet Proxima Centauri.
While Lubin stressed that a trip to Alpha Centauri would be a long-term endeavor, Eubanks said he was confident that big breakthroughs could come this century.
“I think we’ll reach the Alpha Centauri system, with small probes launched in the 2040s, and so into the 2060s,” Eubanks said. “Much larger probes should be possible by the end of the century, but without unexpected breakthroughs in propulsion physics, I think crewed missions will be a task for the next century.”
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