Researchers improve the photonic sails that will visit Proxima Centauri

We remember that in 2016, to celebrate the 55^and anniversary of the flight Yuri Gagarin on April 12, 1961, the Russian billionaire Yuri Milner had announced – with the support of stephen hawking – that he was launching an interstellar probe project: the project Breakthrough Starshot. It was a question of starting the study of a photonic nanoveil propelled by laser beams intended for stars closest to Sunin the Alpha Centauri system.

We know that this star system is triple and that there exists exoplanets around Proxima Centaurii.e. Alpha Centauri C also called α Centauri C. The probe reaching a notable fraction of the speed of light would still have time to take close pictures of these exoplanets and then send them back to Earth. Reaching the Alpha Centauri system would only take about 20 years using a photonic sail towing a probe weighing a few grams at most and propelled by laser beams sent from Earth. The principle is therefore analogous to that already experienced in the solar sail, propelled by the rays of the Sun. It would take nearly 80,000 years for a probe initially powered by conventional rocket engines to cross the chasm of about 4 light years separating the triple system of Alpha Centauri from Solar system.

A photonic sail that should neither tear nor melt

Studies regarding the probe and the sail that would carry it to the stars have continued and two papers have recently been published proposing to modify somewhat the initial concept of the photonic sail envisaged. She has to bear the radiation pressure laser beams and these must produce, in the future, to ensure the success of the interstellar mission a flux ofenergy millions of times more intense than that of the Sun and which has already been used for experiments like that of the Ikaros solar sail (Interplanetary Kite-craft Accelerated by Radiation Of the Sun). This Japanese Jaxa mission, the equivalent of NASA orESAwas launched in 2010 and it was very successful.

However, the photonic veil which must withstand the pressure of laser photons for 20 years is about three meters in size and a thousand times thinner than a sheet of paper.

The researchers, authors of two articles published in Nano Letters, explain in the first that it is necessary that the photonic sail constructed from an ultrathin sheet ofaluminum oxide and disulphide of molybdenum swells under the breath of light, taking the form of a parachute, rather than remaining flat as assumed by most previous research. The structure should be curved so that it is almost as deep as it is wide to support without tearing a pressure capable of producing an acceleration thousands of times greater than that of the gravity earthly.

In one second itemthe same researchers dealt with the problem of resistance to the heating produced by a laser beam at least a million times more powerful than the Sun. Even a small fraction of the energy dissipated in the sail, if it absorbs it, could cause it to heat up to the point of melting.

To avoid this, the sail will in fact have to adopt a grid-like structure with regularly spaced holes in relation to the wave length laser photons.

It remains to manufacture this sail and test it with lasers to check if the calculations and reasoning of the researchers are correct.

Interstellar exploration comes to fruition with this very promising material

Paris Observatory article published on 08/23/2020

In the same way as the wind inflates the sails of the boat, a photonic sail is propelled by the pressure exerted by light. Traveling outside the Solar System, which would be no more than a suburb of our dear Planet, will soon no longer be science fiction but a reality. How? ‘Or’ What ? Perhaps thanks to aerographite which seems endowed with adequate properties to make this dream come true. From the ISS, such solar sail would make it possible to reach Mars in 60 days of travel and escape from the Solar System…

airbrusha type of carbon synthesized for the first time in 2012, is a new material made of carbon nanotubes intertwined. It is among the lightest known materials, with a density of only 180 grams per cubic meter, a density approximately 7 times lower thanair that we breathe (1225 g/m³). Its other remarkable property is its “darkness”, that is to say its ability to absorb light almost perfectly: less than one incident photon out of 1,000 is reflected.

On the way to Alpha Centauri

These two properties make it an ideal material for the design of photonic sails: its great lightness and its ability to absorb photon energy allow it to accelerate very efficiently when illuminated. by the light. This light can be that of a laser, as in the Breakthrough Starshot concept, or simply sunlight as in this study.

The astronomers calculated that a spherical shell 1 meter in diameter and 0.5 mm thick, dropped from the International Space Station ISS, could reach the planet Mars in just 60 days of travel and Pluto in just over 4 years, with no other propulsion than the light of the Sun.

Due to its very low density, a spherical sail 5 meters in radius and 0.1 mm thick could even carry a payload of 55 grams at sufficient speed to escape from the Solar System.

Such a probe would be an excellent precursor for a interstellar mission to our close neighbour, Alpha Centauri, and the telluric planet located in the habitable zone of the weakest of its three component stars, Proxima Centauri b.