New projects for an ultra-fast solar sail capable of reaching Proxima Centauri in a couple of decades were proposed by American and Russian engineers from the University of Pennsylvania and the University of California at Los Angeles, working as part of the Breakthrough Starshot initiative, announced on April 12, 2016 by astrophysicist Stephen Hawking and Russian entrepreneur Yuri Milner . These innovations are mainly aimed at finding ways to achieve a balance of strength and low mass vehicles, which is necessary for interstellar travel. Two related articles have been published in Nano Letters.

“The idea of ​​a light sail has been in the air for some time now, but we are just now figuring out how to make these designs withstand such a journey,” explains Igor Bargatin, a mechanical engineer at the University of Pennsylvania.

Just as air particles hit a sail made of fabric, radiation waves exchange momentum with whatever objects they hit. But unlike air molecules, photons, or light quanta, do not have a rest mass, so the acceleration imparted by each such photon will be very small. For example, the light reflected from the body of a tanning person is equivalent in its effect to the weight of about one thousandth of a gram. To increase this pressure and make an object in space accelerate, it is necessary either to make a very large sail, or to increase the intensity of the light beam - for example, by directing powerful lasers at the sail.

However, as the apparatus accelerates, the wavelength of the radiation incident on it will slowly shift towards the red end of the spectrum, which imposes additional restrictions on the types of materials that should not absorb too much infrared radiation and overheat.

Engineers are now suggesting either making a sail with two layers of molybdenum disulphide and silicon nitride compounds to minimize light absorption, or redesigning the sail to make it more stable by flexing like a large parachute. The researchers also tried to vary the acceleration time to find the right balance of mechanical and thermal loads during the entire journey. Breakthrough Starshot will need to make the craft light enough that it can reach about 20% of the speed of light and travel 4.2 light years to Proxima Centauri in just a couple of decades.

It is important to note that this technology cannot be used to transport passengers, but will provide a closer look at another planetary system within the life of the current generation of earthlings.

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