How to Fly to Alpha Centauri

Talking about building an interstellar space ship makes you sound like a sci-fi fan who’s lost touch with the real world. Unless you’re Mae Jemison, a former astronaut — the first African-American woman in space. Then you might legitimately wonder, “How in the hell do you get to another star system?”

Jemison actually needs to answer that question; she’s the head of 100 Year Starship, an organization the home page of which boldly commands, “Let’s make human interstellar travel capabilities a reality within the next hundred years.”

“That time frame is reasonable, why?” she asks rhetorically. “If you said ten years — ‘Nah, we know that’s not long enough.’ If you said 500 years, people would say, ‘I can kick back for another two to three hundred years because I don’t have to worry about it.’ One hundred years is close enough.”

The problem: space is big, and our current rocket technology isn’t cutting it. “If you’re travelling with technology we can already conceive, like say the Voyager spacecraft, it’s going to take about 80,000 years to travel a distance to our nearest neighboring star,” says Marc Millis, the head of the Tau Zero Foundation. “And it is going 0.00006 times the speed of light.” Nuclear-powered spacecraft might go much faster, and have their proponents, but are politically and environmentally dangerous: no one wants to risk a nuclear meltdown during liftoff. 

The heads of yet another interstellar organization, Starship Century, think they are on the right track. James Benford is president of a company that does microwave research; his identical twin brother Gregory is an astrophysicist at the University of California, Irvine. The Benfords make a strong case for a technology right out of a science fiction novel. The technology is the beam sail, and the book is Rocheworld, written by Robert Forward in 1982. “[It’s] a very solid scientific concept for a starship,” James says.

A beam sail is like a regular sail — “envision it as a giant umbrella, maybe 100 meters across,” says Gregory — pushed with microwave beams, instead of wind, to extremely high speeds. Beam sails are still in the experimental phase, and far more tests will be necessary on Earth and in space before we know if they can propel an object across the galaxy. Even Jemison admits that the hundred-year estimate is kind of a tease — it’s more about figuring out the physics than building the Enterprise.

But Gregory Benford likes to remind us of how greatly we underestimate the pace of change. “Thomas Jefferson said in 1812 that it will take 1,000 years for the republic to reach the Pacific. He never envisioned that 57 years later, a train would run all the way to San Francisco.”