What prevents to create a sail for flight to Alpha Centauri

Participants in the Breakthrough Starshot project have prepared a list of problems that they will have to solve in order to create a solar sail of suitable sizes for flying to Alfa Centauri for 20 years.

“The first results of our analysis were unexpectedly optimistic – the materials already existing today, in combination with new production methods and measuring their properties, in principle allow creating a prototype of a sail suitable for dispatching an interstellar ship,” write Harry Atwater and his colleagues from the California Institute of Technology in Pasadena (USA).

In April 2016, the late British cosmologist Stephen Hawking and Russian billionaire Yuri Milner told about their next “space” initiative within the Breakthrough Initiatives series of projects – Breakthrough Starshot. In his framework, the businessman allocated $ 100 million to create a spacecraft based on the idea set forth by California physicists under the guidance of Philip Lubin (Philip Lubin) two years ago.

Its essence is to send to the distant planets not classical spaceships, but extremely light and flat structures of reflective material that will be accelerated to near-light speeds using a powerful orbital laser.

Such an interstellar “sailboat”, according to the calculations of American physicists, will be able to reach Alpha Centauri in 20 years, and will fly between Mars and the Earth in just three days without payload, and for a month with a load of 10 tons.

The main problem in both cases will be the braking of the probe – while the team that devised it has no idea how to make the laser sailer safe. Similar problems will arise, as other physicists later suggested, when it is dispersed – the sail will either be burned by a laser, or it collapses when colliding with dust particles.

Etwater and his colleagues at the institute who are directly involved in the Breakthrough Starshot first studied in detail how this sail behaves when interacting with the laser and the interstellar medium and formulated a set of minimum requirements for its manufacture.

As scientists found out, despite the almost “impossible” set of characteristics – an area of ​​10 square meters, weight in grams and a reflectivity of 99.999999% – the main problem in making a sail is not the selection of material, but a number of other things. It turned out that there are already a number of materials on the Earth, including films from molybdenum disulfide, amorphous silicon and a number of other semiconductors that have similar properties.

If this film is sufficiently thin, then, paradoxically, collisions with helium and hydrogen atoms present in the interstellar medium will almost not affect the life of the sail. Most of the atoms will pass through it without causing harm, and collisions with dust particles, as calculations of physicists show, will damage no more than 10% of the total area of ​​the sail.

The problem, in turn, lies in the fact that today there are no technologies that would allow growing very homogeneous and thin films of these substances of the right size. Scientists will have to find a way to glue relatively small fragments of these films, with a diameter of 10-20 cm, and this operation should be carried out in fact with atomic precision.

On the other hand, Etwater and his colleagues are sure that similar methods of “gluing” pieces of sails can be developed quickly enough, relying on those technologies that are used today in the IT industry for soldering individual elements of microcircuits. Their creation will allow Breakthrough Starshot to solve one of the main problems and start creating a laser installation capable of dispersing this sail to the required speed.

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