How to get to Alpha Centauri

Sail away
Light sails might be another way to go — giant, thin, lightweight reflective sails that rely on the slight push provided by light beams. "The point is to not carry the energy you need for propulsion with you, but to get it transmitted to you," explained Jordin Kare, a Seattle-based technical consultant on advanced space systems.

Instead of relying just on the enormous amount of light given off by the sun, light sails to Alpha Centauri could also ride laser beams that earthlings would fire carefully at those ships to give an extra boost, especially when sails were too far away to catch much light from our sun.

The idea with a laser sail is that the sky is the limit in regards to speed. You just keep accelerating, albeit gradually.

The problem with interstellar travel with laser sails is that a lot of light needs to be used for a long time to get fast enough to get to Alpha Centauri within a human lifetime. This means very powerful and extraordinarily large lasers are needed in order to focus on sails that get farther and farther away, Kare explained.

An idea similar to light sails that Landis helped come up with involved firing a particle beam at a spaceship that would ride that energy. "The problem with laser beams is that they disperse over distance, so we thought about particle beams," Landis explained. The beam would have to have a neutral electrical charge so as not to disperse itself over time. "It would be a feasible idea," he said.

Bombs away!
Another idea for space travel would involve riding explosions through space. Such "pulsed propulsion" would hurl bombs behind a ship, which is shielded with a giant plate. The explosions would push against the plate, propelling the ship. Project Orion suggested using nuclear bombs, while other proposals have since proposed smaller explosives.

Hbar Technologies LLC / Elizabeth Lagana An artist's conception shows an antimatter-driven sail designed for a deep-space mission to the Kuiper Belt.

"Nuclear pulsed propulsion works best for really big systems. If you want to send a colony of 1,000 people to space, an Orion-type ship is definitely the way to do it," Kare said. "If you want to send a one-ton probe, I would say a laser system is the way to go."

A variant on both the laser sail and pulsed propulsion idea that Kare came up with was the "sail beam." Essentially, a laser would propel lots of miniature sails like bullets at a distant ship. The impact of these sails would propel the spacecraft.

"The idea is to get a craft up to about a tenth of the speed of light that way," Kare said. "It could get you to Alpha Centauri in 60 to 70 years."

So far no one has created technology that is widely agreed upon as capable of caring for or preserving humans across the lifetimes it might take to get to Alpha Centauri. It might easily take more than one lifetime to reach the star system — one antimatter engine design would take 200 years to send humans there. If that proves so, mission designers might have to take sex and family into account so offspring of the original crew would be around at the end of the trip, unless someone successfully invents a technique for placing people in suspended animation.

Then again, warp drives and similar far-out ideas might one day zip us faster than light to Alpha Centauri and beyond. "We don't know all the physics there is to know yet, and something we don't know yet might give us tremendous capabilities," Landis said.

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