A light sail designed using artificial intelligence is about 1000 times thinner than a human hair and weighs as much as a grain of sand 鈥� and it could help us create a spacecraft capable of reaching another star sooner than we thought.
The Breakthrough Starshot mission to travel to Alpha Centauri 鈥� the closest star to our solar system 鈥� was announced in 2016 and invited researchers to design a spaceship powered by light.
The mission would involve a fleet of tiny probes tethered to light sails that could be propelled by powerful laser beams fired from Earth until reaching about a fifth of the speed of light to traverse the 4.4 light years to Alpha Centauri. These sails would need to be some 10 square metres each, weigh less than a gram and be extremely reflective for a wide range of light frequencies, but no material like this currently exists.
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Now, at Delft University of Technology in the Netherlands and his colleagues have developed such a light sail from a silicon nitride wafer, using an artificial intelligence algorithm to devise a pattern of billions of holes in it.
The prototype is about 36 square centimetres in area, about the size of a human palm, weighs a few micrograms and is just 200 nanometres thick. 鈥淭his thing looks like a big bubble, that鈥檚 how thin it is,鈥� says Norte. 鈥淚t鈥檚 probably thinner than a normal bubble, actually, but it鈥檚 a bubble that鈥檚 covered in nanoscale holes.鈥�
The prototype is much smaller than the full-sized sail required for the mission, but Norte and his colleagues wanted to build it so that they could test its reflective properties and show that their new production process works.
They used an AI algorithm to find a pattern of bean-shaped holes designed to leave a surface that is as reflective as possible for the least weight. The holes are large enough that Norte and his team could use a different production process than the one relied on with previous designs, which punched out the holes one-by-one.
This faster process, called flood lithography, uses a kind of stencil and light to create all the holes in one go. 鈥淣ow, instead of it taking you 15 years to [produce] one sail, we鈥檝e gotten this down to about a day,鈥� says Norte. It is also cheaper, with an estimated cost of around 鈧�3000 ($2764) for a full 10-metre sail.
It is based on the way wafers are manufactured and etched with circuits in the manufacture of semiconductors for computer chips. While the lithography process is scalable enough to make a full-size sail, commercial semiconductor facilities are currently only equipped to make 400-millimetre chips, says Norte, so a custom facility would need to be built.
Having a cheap and fast production technique is crucial for the success of a mission like Breakthrough Starshot, says at the University of Liverpool, UK, but there are still lots of engineering challenges, such as how many of these light sails will be controlled together at the same time. Even if this technology isn鈥檛 used to travel to Alpha Centauri, around which a roughly Earth-sized planet orbits in the habitable zone, it might be useful for other spacecraft or projects like harvesting solar power from space, she says.
arXiv
