In an unprecedented boost for interstellar travel, the Silicon Valley philanthropist Yuri Milner and the world’s most famous cosmologist Stephen Hawking have announced $100m (£70m) for research into a 20-year voyage to the nearest stars, at one fifth of the speed of light.

Breakthrough Starshot – the third Breakthrough initiative in the past four years – will test the knowhow and technologies necessary to send a featherweight robot spacecraft to the Alpha Centauri star system, at a distance of 4.37 light years: that is, 40,000,000,000,000 kilometres or 25 trillion miles.

A 100 billion-watt laser-powered light beam would accelerate a “nanocraft” – something weighing little more than a sheet of paper and driven by a sail not much bigger than a child’s kite, fashioned from fabric only a few hundred atoms in thickness – to the three nearest stars at 60,000km a second.

Milner, a Russian-born billionaire investor who began as a physicist, was one of the founders of the Breakthrough prizes, the biggest in science, announced in 2012 and awarded for fundamental research in physics, life sciences and mathematics. Last year, he and Professor Stephen Hawking of the Centre for Theoretical Cosmology at Cambridge announced another $100m Breakthrough Listen initiative to step up the search for extraterrestrial life beyond the solar system. The project has just released its first data from stars within 16 light years of Earth. The entrepreneur describes science as his “hobby.”

Today’s announcement comes on the 55th anniversary of the first orbit of the planet by the Russian cosmonaut Yuri Gagarin. Milner, who was born in Moscow in 1961, was named after the cosmonaut.

Facebook Twitter Pinterest Yuri Milner and Stephen Hawking: reaching for the stars. Photograph: Stuart C. Wilson/Getty Images for Breakthrough In

“The human story is one of great leaps,” he said. “Today we are preparing for the next great leap – to the stars.” And Professor Hawking said: “Earth is a wonderful place, but it might not last forever. Sooner or later we must look to the stars. Breakthrough Starshot is a very exciting first step on that journey.”

Near-lightspeed flight by a spacecraft would have been unthinkable 15 years ago. The gamble is that it could be possible within 15 years, with accelerating advances in microelectronics, nanotechnology and laser engineering. The research programme will be led by Pete Worden, until last year the head of the Nasa Ames research centre. Milner, Hawking and the Facebook founder Mark Zuckerberg, already a partner in the fundamental science initiative, comprise the board, which will advised by a committee of distinguished engineers and scientists. This committee has already identified 20 formidable challenges to be overcome before any possible takeoff for the stars.

The project’s begetters argue that they have Moore’s Law working for them: the memory and processing power available on a computer chip doubles every 18 months or so. New advances in nanoscience mean that fabrics with unique properties can be made to order. And advances in laser technology mean that huge power can be generated at relatively low costs.

At the heart of the project will be the starchip and lightsail. The great hurdle in all space missions is the cost of launch and the weight of fuel. The headlong miniaturisation of microelectronics means that it might be possible to pack the entire control system, the sensors, camera, navigation equipment, photon thrusters, transmitter and power supply onto a tiny silicon wafer, and mount it on an ultra-thin sail weighing only grams, that would respond to the pressure of light.

“We hope to have good answers to the key challenges in about 10 years. At that time we hope to have assembled a coalition of high net-worth individuals to fund the full-scale project and begin work on what will likely be a 10 year or more construction effort,” Worden told the Guardian. “The key challenge is that the final interstellar system is affordable – by that we mean its final cost is comparable to other large scientific endeavours such as the Cern accelerator.”

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He added: “We would welcome participation by governments, national and international organisations and space agencies. Indeed, we have already discussed our plans with several space agencies around the world.”



Researchers worked out more than 50 years ago that sunlight could power a space mission, and by 1989 had calculated that solar radiation alone could slowly accelerate a spaceship with vast lightweight sails – and no fuel to carry – to 100kms a second: faster than any spacecraft so far. Even at that matchless speed a journey to the nearest star would take thousands of years.

But falling costs and increasing processing power mean that spacecraft could become ever smaller and lighter: they could be launched by the thousand from a mothership and then driven by the proposed Light Beamer, a billion-watt laser array, mounted somewhere high and dry such as the Atacama desert in Chile.

This could multiply the radiation pressure, and accelerate the space sailors to a significant fraction of light speed. This would reduce such a journey to the timescale of one human generation: some of the scientists caught up in the beginning of the project could expect to see results within a working lifetime.

“We take inspiration from Vostok, Voyager and the other great missions,” said Worden. “It’s time to open the era of interstellar flight but we need to keep our feet on the ground to achieve this.”

The research funded by the Breakthrough Starshot initiative will be entirely in the public domain. Nobody pretends that any of it will be easy. Avi Loeb, of the Harvard-Smithsonian Centre for Astrophysics, who heads the advisory board, said that to power the spacecraft, researchers have to work out how to link lasers into one massive array. Since the range of focus of a big laser on a small target would be no more than a million kilometers, the fragile spacecraft must reach terminal speed in just two minutes, and survive an acceleration of 60,000 times the force of gravity.



The night sky. Photograph: Babek Tafreshi/SSPL via Getty Images

He believes that starship could record images and data as it nears the red dwarf Proxima Centauri, the nearest to Earth. The big challenge would be to transmit the information across a distance of more than four light years to a receiving station on a planet already far away and long ago. The laser array – the Light Beamer – would double as a telescope system to receive the signal back from the receding nanocraft.

“Just imagine reversing the direction of time,” he said. “Instead of an electromagnetic wave coming out of the system, it can receive a wave.”

Speaking at the project’s launch on Tuesday, Hawking said transcending our limits was what made humans unique. “Gravity pins us to the ground but I just flew to America. I lost my voice but I can still speak thanks to my voice synthesiser. How do we transcend these limits? With our minds and our machines.

“The limit that confronts us now is the great void between us and the stars. But now we can transcend it, with light beams, light sails, and the lightest spacecraft ever built we can launch a mission to Alpha Centauri within a generation. Today we commit to this next great leap into the cosmos, because we are human and our nature is to fly.”

Freeman Dyson, the American physicist and writer, said that in the quest to find life elsewhere, humans should focus not just on planets, but on asteroids, comets and even the dust clouds that hang in interstellar space. “All kinds of small places are much better for life, and the huge advantage is that it’s easier to get off one object and move to another,” he said. “You can hop into space, fly over to your neighbour’s, have a cup of tea, and come back again, which is hard to do when you are on a planet.”