Sailing to the Stars

Can man-made craft ever hope to reach parts of the local Universe on the order of a few light-years away? The Sun’s next-door neighbor, Alpha Centauri, is all of 4.37 light years away. This figure tells us that, even if one could ride on a light beam, and travel through empty space at just under 300,000 km/sec, the journey would take nearly 4½ years.

Technologically, that sounds like a very tall order. – But sending something much lighter than an astronaut is not quite impossible, according to an idea hatched out by a team of prominent scientists. They hope to use laser beams to send miniature space probes on such a voyage in the near future. The technology they have in mind was recently outlined by the Russian billionaire Yuri Milner and the renowned theoretical physicist Stephen Hawking. Milner intends to invest 100 million dollars in the project, which he has dubbed “Breakthrough Starshot”. Hawking is chief scientist for the venture, and Facebook boss Mark Zuckerberg is on the Supervisory Board.

The basic idea is to send a fleet of tiny probes – each about the size of a postage stamp, mounted on an ultralight sail only a few atoms thick and accelerated by radiant pressure – to Alpha Centauri. Specifically, the scientists involved in the consortium intend to impel their craft through the expanses of outer space by directing an extremely powerful beam of laser light onto such a sail a meter or so across. The project’s initiators estimate that, with this approach, it would be possible to reach Alpha Centauri in 20 years. That calculation is based on the fact that a “space-raft” of this size could reach a maximum velocity equivalent to around one-fifth the speed of light (or 60,000 km/sec). But that is still 100 times faster than the maximum speeds attainable with conventional rocket technology. Despite its modest dimensions, each probe will carry its own energy supply, and be equipped with diverse sensors, cameras and a laser communications unit – which is why Milner and Hawking refer to their space-going vessels as “starchips”.

The physicists reckon that an array of lasers with a total power rating of 100 billion watts (equivalent to the total output of 100 nuclear power plants) will be required to “blow” such starchips to their destination. Such a drive system could be built on a high-altitude site in an extremely dry location, such as the Atacama Desert in Chile.

The project’s protagonists are confident that they can develop the required nanosails (weighing only a few grams) within the next 15 years or so. These would then be tested in our own celestial backyard. Probes with these specifications could reach Pluto in a mere 3 days! In the first stage of such a mission, the satellites would be hoisted into orbit on board a conventional rocket. On their release, the sails unfold and are irradiated by the focused output of the laser array for 2 minutes – enough to accelerate them to their maximum speed. During this time the sails are exposed to forces equal to 60,000 the force of gravity. And by the time the lasers are switched off, the probes are well on their way into the wild star-studded yonder.