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A group of astrophysicists think they have a way to get a probe across interstellar space to Alpha Centauri, using lasers. The team, which includes Stephen Hawking, plans to deploy a swarm of tiny probes via rocket into orbit, where each will unfurl a thin sail. A powerful laser will push the sails until each probe is speeding on its way at about .20 light speed.

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The plan was announced with great fanfare, but it’s not actually a new idea. Similar technology was first proposed nearly 30 years ago. The idea of using beam propulsion was originally conceived in the 1980s as a way to power observation craft. A 1987 Canadian prototype plane was made of balsa wood and weighed less than 5 kg. Once launched, a microwave transmitter beamed power to the plane. While never put into effect, the system was intended to keep a craft aloft at an altitude of 20 km for several months at a time at a fraction of the expense of a satellite.

Engineers studying the project at the time estimated that microwaves could be used to accelerate a small (4 g) probe to roughly 1/5 the speed of light, basically exactly the same plan. At the time, technology did not exist to pack sufficient instrumentation into a package that small. Subsequent advances in micro-circuitry now mean that even a tiny probe will actually be able to record meaningful data and send it back to Earth.

Speaking of data, assuming that the probes actually reach Alpha Centauri, what will they find there? Located in the Centaur Constellation, visible only from the Southern hemisphere, Alpha Centauri has the virtue of being our Sun’s closest stellar neighbor. Multiple measurements have determined that Alpha Centauri is 41.32 trillion km away, or 4.37 light years— i.e. it takes light, the fastest known force in the universe, 4.37 years to get from Alpha Centauri to Earth.

Alpha Centauri is a binary system, with two stars, Alpha Centauri A and B, circling one another. Alpha Centauri A is similar in luminosity to our sun and slightly larger; Alpha Centauri B is about a third the sun’s brightness and slightly smaller. Both of these are orbited by the much smaller, dimmer dwarf star Proxima Centauri, which at only 4.22 light years is technically the closest star to Earth. There may be a planet orbiting Alpha Centauri B, but the discovery is not confirmed.

If it works, the plan will take about 20 years to put into effect and each probe will still take 20 years to reach Alpha Centauri. It will take an additional 4.37 years for any information to return (a paltry 4.22 years if the probes buzz Proxima Centauri first). A long time, for sure. But they might actually get there.


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American Scientist, Vol. 76, No. 2 (March-April 1988), pp. 130-132
Sigma Xi, The Scientific Research Society
American Scientist, Vol. 42, No. 4 (OCTOBER 1954), pp. 572-588
Sigma Xi, The Scientific Research Society