With audacity, we have sent rovers to Mars, humans to the moon, and spacecraft to the furthest regions of the solar system. The closest star system to Earth is Alpha Centauri; is it reachable by spacecraft or by people?
Alpha Centauri is about 4.4 light-years from Earth. That’s roughly 25 trillion miles or 40 trillion kilometers. There are three different stars in this stellar system. The closest star, Proxima Centauri, even has an exoplanet that scientists believe could have the conditions necessary for life.
However, reaching this star system is no small feat. NASA estimates that, using a space shuttle like NASA’s now-retired 122-foot-long Discovery, it would take close to 150,000 years to reach Alpha Centauri.
We could reach Alpha Centauri in four years if we could travel at the speed of light like humans do. But according to the laws of physics, only photons—massless light particles—are permitted to travel at this cosmic speed limit. Therefore, even though it is unlikely that humans would ever reach Alpha Centauri, spacecraft built to travel at a far slower speed than light may be able to do it within a human lifetime. Scientists will want something far smaller than Discovery in order to have any chance of accelerating a spaceship to its maximum speed.
Tiny Spacecraft: A Big Leap
Scientists are investigating the possibility of sending hordes of tiny spacecraft to visit Proxima Centauri. These spacecraft are incredibly small, measured in picometers (one-trillionth of a meter).
Tiny spacecraft have several advantages. While an individual small spacecraft will not be as capable as a larger one, such as the Voyagers, their development times are much shorter, and they are relatively inexpensive. They also need less energy to go forward, which may be a major factor in their ability to accelerate.
This research is not isolated. Initiatives like Breakthrough Starshot, started in 2016, aim to combine nanometer-sized spacecraft with light sails. In 2017, NASA began funding its project to launch a mission to Alpha Centauri by 2069, 100 years after Apollo 11.
Light-Powered Propulsion
Small spacecraft can accelerate more easily than larger probes, but they cannot reach near-light speed on their own thanks to the limited power and abundance of conventional fuel sources. Rather, these vessels are probably going to be powered by light.
The masslessness of light-powered propulsion is one of its main advantages. Conventional rocket fuel burns heavy fuel to produce energy, which powers propulsion. All the power without any weight is provided by using either a solar sail, which is driven by the light of the sun, or a photonic sail, which is driven by laser light.
Consider it similar to hurling a ball towards a sheet of paper. A ball will exert force on paper when it hits it, pushing it away or causing it to recoil. Similarly, the momentum carried by light is transferred to the spacecraft, causing it to recoil and accelerate.
This propulsion system is like a gigantic flashlight—a giant laser array on Earth. The laser light is the wind in their sails if the spacecraft are sailboats.
Communications equipment small enough to fit on these tiny spacecraft is one example of the technology being developed to build and test them. However, there’s no scientific reason to think that a spaceship of that kind couldn’t carry out an Alpha Centauri flyby. This mission might return high-resolution photographs of the star system to Earth and behave similarly to the Voyager 1 and 2 probes. Some of these images might contain our first look at Proxima Centauri’s potentially habitable planet.
Alpha Centauri: The Long Road Ahead
While a journey to Alpha Centauri is a long-term endeavor, significant advances could come this century. Small probes could launch in the 2040s and arrive in the 2060s. Significantly larger probes might be possible by the end of the century.
Reaching Alpha Centauri with crewed missions will likely be a task for the next century unless there are unexpected breakthroughs in propulsion physics. For now, the focus is on these tiny, light-powered spacecraft that could one day unlock the mysteries of our closest neighboring star system.
