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How long to travel to Alpha Centauri?

The distances between stars are vast, which is why star travel is so far. Read here about conventional propulsion and warp drives, plus about Breakthrough Starshot’s new idea to send nanostarships to Alpha Centauri.

Photo via BreakthroughInitiatives.org.

Artist’s concept via Breakthrough Starshot.

Outer space is big. Really, really, really big. And that’s why NASA has no plans at present to send a spacecraft to any of the several thousand known planets beyond our solar system. Meanwhile, with respect to star travel, NASA isn’t the only game in town anymore. In April 2016, Russian high-tech billionaire Yuri Milner announced a new and ambitious initiative called Breakthrough Starshot, which intends to pour $100 million into proof-of-concept studies for an entirely new technology for star travel, aimed at unmanned space flight at 20% of light speed, with the goal of reaching the Alpha Centauri system – and, presumably, its newly discovered planet Proxima b – within 20 years. Is it possible? No one knows yet, but Alpha Centauri is an obvious target. It’s the nearest star system to our sun at 4.3 light-years away. That’s about 25 trillion miles (40 trillion km) away from Earth – nearly 300,000 times the distance from the Earth to the sun. Follow the links below to learn more about why star travel is so formidable, and about how we might accomplish it.

Why won’t a conventional rocket work?

Warp drive?

Breakthrough Starshot

These 4 conventional spacecraft are headed out of the solar system. A 5th spacecraft, New Horizons, will also eventually leave the solar system. But conventional spacecraft move slowly in contrast to the vast distances between stars. It’ll be tens of thousands of years before one of these craft encounters a star. Image via Wikimedia Commons.

Why won’t a conventional rocket work? Consider the Space Shuttles, which traveled only a few hundred kilometers above Earth’s surface, into Earth orbit. If Earth were the size of a sand grain, this distance would be about the width of a hair in contrast to a 6-mile (10-km) distance to Alpha Centauri.

The Space Shuttles weren’t starships, but we have built starships. Five craft from Earth are currently on their way out of the solar system, headed into interstellar space. They are the two Pioneer spacecraft, the two Voyager spacecraft, and the New Horizons spacecraft. All are moving extremely slowly relative to the speed needed to travel among the stars.

So … consider the two Voyagers – Voyager 1 and Voyager 2 – launched in 1977. Neither Voyagers is aimed toward Alpha Centauri, but if one of them were – assuming it maintained its current rate of speed – it would requires take tens of thousands of years to this next-nearest star. Eventually, the Voyagers will pass other stars. In about 40,000 years, Voyager 1 will drift within 1.6 light-years (9.3 trillion miles) of AC+79 3888, a star in the constellation of Camelopardalis. In some 296,000 years, Voyager 2 will pass 4.3 light-years from Sirius, the brightest star in the sky. Hmm, 4.3 light-years. That’s the distance between us and Alpha Centauri.

What about the New Horizons spacecraft, the first spacecraft ever to visit Pluto and its moons. NASA’s New Horizons spacecraft travels at 36,373 miles per hour (58,536 km/h). Launched from Earth in mid-January, 2006, it reached Pluto in mid-July, 2015 … nine-and-a-half years later. If New Horizons were aimed toward the Alpha Centauri system, which it isn’t, it would take this spacecraft about 78,000 years to get there.

So conventional rockets won’t work because they are too slow.

Credit: Mark Rademaker/Mike Okuda/Harold White/NASA.

What a spaceship with warp drive might look like. Credit: Mark Rademaker/Mike Okuda/Harold White/NASA.

Illustration via the Anderson Institute.

Illustration via the Anderson Institute.

Warp drive? What if we could travel faster than light? Countless sci-fi books and movies are built around the concept, which brings with its challenges to physicists’ understanding of how space and time actually work. Still, a few years ago, Dr. Harold “Sonny” White – who leads NASA’s Advanced Propulsion Team at Johnson Space Center – claimed to have made a discovery which made plausible the idea of faster-than-light travel, via a concept known as the Alcubierre warp drive.

This concept is based on ideas put forward by Mexican physicist Miguel Alcubierre in 1994. He suggested that faster-than-light travel might be achieved by distorting spacetime, as shown in the illustration above.

Harold “Sonny” White has been working to investigate these ideas further. They are highly speculative, but possibly valid, and involve a solution of the Einstein field equations, specifically how space, time and energy interact. In June of 2014, White unveiled images of what a faster-than-light ship might look like. Artist Mark Rademaker based these designs on White’s theoretical ideas. He said creating them took more than 1,600 hours, and they are very cool. See the 2014 faster-than-light spacecraft designs on this Flickr page.

The video below presents Harold White’s talk at the SpaceVision 2013 Space Conference in November, 2013 in Phoenix. He talks about the concepts and progress in warp-drive development over recent decades.

Is it faster-than-light travel possible, via the Alcubierre warp drive? As with conventional propulsion systems, the problem is energy. In this case, it’s the type of energy the warp drive would need. Daily Kos reported:

In order to form the warp field/bubble, a region of space-time with negative energy density (i.e. repulsing space-time) is necessary. Scientific models predict exotic matter with a negative energy may exist, but it has never been observed. All forms of matter and light have a positive energy density, and create an attractive gravitational field.

So faster-than-light travel via the Alcubierre warp drive is highly speculative, to say the least.

With current technologies, it’s not possible.

However, if it could be accomplished, it would reduce the travel time to Alpha Centauri from thousands of years to just days.

Want technical details on the Alcubierre warp drive? Read this 2014 article at Daily Kos.

Or try this January 2017 article on the Alcubierre warp drive, at Phys.org

NASA has a whole area on its website about faster-than-light travel, in which it basically says … it’s not currently possible.

The Alpha Centauri system. It’s at least a double system, maybe a triple system, but we see it with the eye as just one star. In this image – via MSX/IPAC/NASA – you can almost make out the double nature of Alpha Centauri. At 4.3 light-years away, this star system is the closest to Earth.

Breakthrough Starshot. In April, 2016, Yuri Milner’s organization Breakthrough Initiatives announced a $100 million investment in proof-of concept studies for an all-new way to get to the stars.

Well, not all new., exactly. The Breakthrough Starshot project relies on technologies that are being tested now, and also on some new technologies that have been around only a few years. But it does put these technologies together in a way that’s entirely new, and extremely visionary.

The Breakthrough Starshot team has some heavy hitters, including physicist Stephen Hawking and Facebook’s Mark Zuckerberg. It proposes to use the $100 million to learn whether it’s possible to use a 100-gigawatt light beam and light sails to propel some 1,000 ultra-lightweight nanocraft to 20% of light speed. If it’s shown to be possible, such a mission could (hypothetically) reach Alpha Centauri within about 20 years of its launch.

There are a lot of appealing things about this project. For example, the use of lightsails is currently in the process of being tested by another organization, the Planetary Society, with a publicly funded project called LightSail.

But the most appealing thing is that the Breakthrough Starshot project is truly innovative, yet still grounded in current, cutting-edge science and technology. Just realize that all existing spacecraft are huge and clunky in contrast to the gram-scale nanostarships – dubbed StarChips – being proposed by Breakthrough Starshot. Can tiny, light ships – on sails pushed by a light beam – fly 1,000 times faster than the fastest spacecraft built up to now? That’s what Breakthrough Starshot is exploring with its ongoing proof-of-concept studies.

Starshot envisions launching a mothership carrying the 1,000 tiny spacecraft to a high-altitude orbit. Each craft is a gram-scale wafer, carrying cameras, photon thrusters, power supply, navigation and communication equipment, and “constituting a fully functional space probe,” the Starshot team has said.

Mission controllers would deploy the nanocraft – send them on their way – one by one. A ground-based laser array called a light beamer would be used to focus light on the sails of the ships, to accelerate individual craft to the target speed “within minutes.”

The plan is to stick four cameras (two-megapixels each) on the nanocraft, allowing for some elementary imaging. The data would be transmitted back to Earth using a retractable meter-long antenna, or perhaps even using the lightsail to facilitate laser-based communications that could focus a signal back towards Earth.

The original idea was to send the spacecraft flying through the Alpha Centauri system without slowing down. After all, how can they slow down? It turns out someone has already figured out a possible way. In early 2017 two scientists announced the results of their study of a possible braking method, using the radiation and gravity of the Alpha Centauri stars themselves. We don’t know yet if such a thing can work, but it’s heartening to see scientists getting involved in this idea!

Clearly, the Breakthrough Starshot project is one that’s worth watching.

On April 20 and 21, 2017, Breakthrough Initiatives held the second of what it says will be an annual conference – called Breakthrough Discuss – aimed at bringing together leading astronomers, engineers, astrobiologists and astrophysicists. This year, they held the conference at Stanford University and focused it on discoveries of potentially habitable planets in nearby star systems, including Alpha Centauri. Videos related to discussions at the conference are archived on Breakthrough’s Facebook page, if you’re interested.

Illustration via FutureHumanEvolution.com

Illustration via FutureHumanEvolution.com

Bottom line: At 4.3 light-years away, the Alpha Centauri system is the nearest star system to our Earth and sun, but getting there would be extremely difficult.

Breakthrough Starshot aims for Alpha Centauri

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Deborah Byrd

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