It seems like the stuff of science-fiction or the absurd plot of a particularly unbelievable film – a social media mogul, a Russian billionaire and one of the world's most acclaimed scientists team up to send a tiny, wafer-thin spaceship 25 trillion miles through the vastness of space to discover if aliens exist.

But that's exactly what Professor Stephen Hawking, Russian billionaire Yuri Milner and Facebook's Mark Zuckerberg hope to do. The unlikely trio are heading up the Breakthrough Starshot project, which aims to fire the lightest spacecraft ever flown to the solar system Alpha Centauri, our closest neighbour.

The voyage would take tens of thousands of years using current technology, but it is hoped the project will be able to do it in just 20 using a spaceship weighing one gram, a massive group of lasers and tens of billions of dollars.

If successful, the spacecraft will be able to send back images of Alpha Centauri, shining a light on the solar system's existing planets and, potentially, signs of life.

Launching the initial $100 million phase of the Starshot mission, Hawking said: "There are no greater heights to aspire to than the stars. What makes human beings unique? There are many theories. Some say it is language or tools, others say it is logical reasoning. They obviously haven't met many humans.

"I believe what makes us unique is transcending our limits. Gravity pins us to the ground, but I just flew to America. I lost my voice but I can still speak. 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 and light sails and the lightest spacecraft ever built we can launch a mission to Alpha Centauri within a generation."

The team behind the mission claim that much of the technology already exists, but there are a number of challenges including developing the extremely lightweight equipment needed for the spacecraft and the production of a 100 gigawatt laser.

It is estimated it will take 20 years to develop the necessary technology, 20 years to get to Alpha Centauri and four years for the data collected to make it back to Earth.

Funding is also an issue – Milner is fronting $100m (£71m) towards the initial phase of the project, but costs are estimated to run to between $5 and $10 billion. "There is a technology just over the horizon which can get us to the speed we need," says Milner. "Actually we already use some of the basic principles. Leave the fuel behind. It was not possible before, but it is possible in the near future.

"If this comes to fruition it will tell us as much about ourselves as about Alpha Centauri. For the first time in human history we can do more than just gaze at the stars. We can actually reach them."

If successful, it is hoped the Starshot project will not only determine whether or not there is life in Alpha Centauri, but if there is a planet suitable for human life.

Hawking added: "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."


One of the biggest challenges to the project is building the laser, or light beamer. It is hoped that a huge array of relatively modest lasers will be able to sync up and focus into one powerful, 100 gigawatt beam, that will propel the tiny spacecraft towards Alpha Centauri. The laser will reflect off thin, lightweight sails attached to the spacecraft to get it to the target speed of 20 per cent of the speed of light, or 100 million miles per hour, within minutes.

It will also rely on deformable mirrors, known as adaptive optics, to compensate for the distorting effects the atmosphere can have on laser beams. The exact site for the laser array has not been specified, but it will be ground-based at a place on Earth which has high altitude and dry conditions. It will stretch across a kilometre at a site which must be capable of generating and storing a few gigawatt hours of energy for each launch. The same light beamer will also be used to receive data such as images from the spacecraft four years after it gathers it.


The Starshot spacecraft, or nanocraft, will consist of two parts – a wafer-size chip and a super-thin sail. The Breakthrough Starshot project hopes to eventually launch thousands of the smartphone-sized craft into space aboard a mothership, before releasing them. Once released, the sails will be opened and the laser will propel the craft towards Alpha Centauri. Each craft would weigh one gram and be loaded with cameras, thrusters, a power supply and navigation and communication equipment. They will effectively be fully functional, but tiny, space probes.

Once they reach Alpha Centauri they will take one day's worth of images and data to be transmitted back to Earth as they pass by the system. The craft will not be tracked beyond that. While some of the technology does not yet exist, the project claims that "Moore's Law" – which observes that transistors in a circuit roughly double every two years – means it will soon become available.

Alpha Centauri

Alpha Centauri is the nearest star system to earth but is still 4.37 light years away, meaning that getting there with current technology would take 30,000 years. It is currently unknown whether or not Alpha Centauri has planets, but astronomers estimate that there is a reasonable chance of an Earth-like planet existing in its habitable zones. It has several advantages as a first target, including its relative closeness to Earth, its system of sun-like stars and the fact it may be up to three million years older than the sun, giving more time for life to emerge on any potential habitable planet. It also contains a third star, known as red dwarf Proxima Centauri, the closest star to Earth, which might also host a planet. Within the next two decades, ground and space telescopes will be able to tell if the system has planets, and if so their size, mass, atmosphere and any possible signs of life. If it is discovered that an Earth-like planet does exist, the spacecraft will be aimed within one Astronomical Unit (93 million miles) of it in a bid to capture an image showing its surface make up such as continents and oceans.


While it is hoped Breakthrough Starshot will be able to determine whether or not Alpha Centauri contains other life forms, Hawking claims the probability of finding other intelligent alien life is low. However, the project could determine if there are other habitable planets suitable for humans – a discovery which the professor believes is important "if we are to survive as a species". Ultimately, Breakthrough Starshot want to make history, scope out the prospects for life in other solar systems, and pave the way for humanity to expand beyond the constraints of our own solar system. But the technology used in the project will also be able to be used for other purposes such as detecting Earth-crossing asteroids at large distances. The light beamer will also be able to be used as a kilometre-scale telescope for space observations, while it will also make a considerable contribution to solar system exploration.