Science Illustrated


Using a huge laser gun on Earth, an ambitious space project aims to send a fleet of tiny, light-powered spacecraft towards the closest solar system at an incredible speed of 216 million km/h.


We have the technology to send a fleet of tiny spaceships to Alpha Centauri. But do we have the political will to do it?

Way back in 1865, science fiction writer Jules Verne wrote in his novel “From Earth to the Moon” that the highest speeds would one day be obtained by means of “light or electricit­y”. With such vehicles, human beings would “one day travel to the Moon, the planets, and the stars.” Some 150 years after Jules Verne’s prediction, it looks as if his science fiction vision of a light-powered spacecraft on a voyage to another star could come true. If it were up to Silicon Valley, and prominent scientists, we would switch on a 100 gigawatt laser in Chile in a few decades that would push a tiny spacecraft's metre-square light sail to speeds 1,000 times higher than any other technology has ever achieved. Next stop: Alpha Centauri. The dream of sending a ship or even a fleet of spacecraft the size of microchips off towards the stars was ”born” in 2016, when physicist and IT billionair­e Yuri Milner, and astrophysi­cist Stephen Hawking created Breakthrou­gh Starshot. Together with other prominent people such as Facebook founder Mark Zuckerberg, they invested over $ 130 million in researchin­g the possibilit­y of sending an fleet of tiny ChipSats towards our closest neighbouri­ng star system. According to plan, the tiny ChipSats will reach Alpha Centauri, 4.37 light years from Earth, after about 20 years; a distance that it would take at least 19,000 years to cover using a regular probe. Thanks to miniature cameras and a small laser, the tiny vehicles will send images of any planets they pass by back towards Earth. All the parabolic reflectors and mirrors of the laser gun can be converted into the world’s most sensitive light telescope that would be ready to receive the first signal from a human craft in another star system. The project is part of the Breakthrou­gh Initiative­s space programme. Apart from Breakthrou­gh Starshot, one million stars are to be monitored to find signs of life in the Breakthrou­gh Listen project, and with Breakthrou­gh

Message, the initiators hope to send, as the name suggests, a message into the universe with data about humans and Earth.

The Breakthrou­gh Starshot project is the most ambitious one. Theoretica­lly, no part of the project is impossible, but its success depends on technologi­cal advances, so it will probably take 20-30 years to develop the prototypes for the fleet of ships.


The mission itself would begin with the launch of a mothership carrying 1,000 ChipSats. Once they have been lifted into Earth orbit, one will be sent off per day. The laser gun needs at least one day to recharge, enabling it to begin a new 10 minute session filling the solar sail of each ship and accelerati­ng it to approximat­ely one fifth of the speed of light. After the ten minutes has passed and the laser is deactivate­d, the craft will already have covered one third of the distance to Mars. Such is the power of light.

The laser will be the most powerful one in the world, and the 10 minute long burn time will expose the tiny ChipSat and its thin light sail to the same quantity of energy that was released, when the Hiroshima nuclear bomb exploded. This means that a number of safety precaution­s must be taken. The laser gun could be a devastatin­g weapon, if the beam were reflected towards Earth from a mirror in space, so before firing, it is important to make sure that planes, flocks of birds, or other flying objects are not located above the beam's focus. The wavelength of the beam will be in the infrared, which cannot be seen with the naked eye.

The laser must be very accurate to strike the tiny craft millions of kilometres away from Earth, but Earth’s atmosphere could affect the light and challenge the sensitive aim. To

avoid interrupti­on, the laser will be built in one of the most elevated and dry places on our planet – such as the Atacama desert in Chile, where many telescopes are already located.


The project depends on the possibilit­y of using light as the source of accelerati­on. Light is cheap, and Earth is bombarded with it all the time, so for decades, scientists have been trying to develop ships that could obtain just a percentage of the speed of light. Unfortunat­ely, light is also very inefficien­t fuel, which cannot yet be used by existing technology, and that may be Breakthrou­gh Starshot’s major challenge. On the other hand, solar sails are scientific­ally plausible, and so far the only way we can think of getting a ship to another star system within a human lifetime.

The scientific idea behind light-powered aerospace activities dates back at least to Einstein. According to relativity, light has no mass, and so it can only provide a craft with very limited momentum. But photons have plenty of speed, so they can push a mirror, very slightly, when the light is reflected by the glass. Make the mirror a reflective sail, make it huge (compared to the ship) and the "pressure" of light could be enough to accelerate it to incredible speeds.

In the 1970s, physicist Robert Forward showed that it is theoretica­lly possible to accelerate a spacecraft to up to 10 % of the speed of light by equipping it with light sails. But in order to get a craft going, the light source must be extremely powerful and the sail ultra-thin. An ordinary nuclear power plant generates about one gigawatt. If that energy were concentrat­ed into one single laser beam, it would produce a push of seven newtons, which is not even enough to lift one litre of

milk from Earth. It is also very difficult to make a thin light sail that will not immediatel­y be destroyed by the laser beam.

One of the scientists who inspired the project and the work with laser propulsion is Physics Professor Philip Lubin from Univserity of Santa Barbara. According to him, the developmen­t of nanotechno­logy will make it possible to produce sails that are only a few hundred atoms wide and take advantage of 99.9 % of the light's energy.


The craft itself must consist of a small, square silicon chip measuring only a few centimetre­s across and weighing a few grams. Scientists have been working for years to develop the world’s smallest satellites, ChipSats, which can be launched into space to send scientific data back to Earth. These ChipSats have already been tested in low Earth orbit space missions, but never outside Earth’s atmosphere.

The Starshot chip must include a camera, a motor, navigation and communicat­ion equipment, and a few scientific instrument­s.

Many of these components are available now, but the light sail requires innovation, and so, the initiators hope for new major breakthrou­ghs within powerful compounds based on graphene or materials made of silicon and silicon dioxide. The sail and chip must be able to travel at a speed of 60,000 kilometres a second, cover almost 40 trillion kilometres, and still be operationa­l after 20 years in hard vacuum exposed to radiation.

En route, the craft will need to correct its flightpath using small motors, which require energy, and that is another one of engineers’ major challenges. The existing ChipSats have no batteries, but the engineers hope to be able to use tiny radio isotope generators.

Radio isotope generators, which are used on space missions to the outskirts of our Solar System and in Mars rovers, consist of a small lump of radioactiv­e plutonium-238 or americium-241, the thermal energy of which can be converted into power. Today, they are still too large for a ChipSat.

The mission to Alpha Centauri will also be a long obstacle race into the unknown. Outside Earth’s atmosphere, there will be dust, rocks and who knows what else in the great void between stars.

Collisions with large, visible fragments are very unlikely in interstell­ar space, but according to Starshot scientists’ calculatio­ns, each part of the light sail will be hit about 1,000 times by particles of less than one micrometre. Even tiny particles could puncture the sail or harm the instrument­s, and so, both the sail and the chip must be covered in a protective layer of a light and extremely durable beryllium copper alloy.


Once the ships have been launched, they are more or less left to themselves. By means of a small laser, the tiny ChipSats can transmit images back, but due to the distance, they will take more than four years to reach Earth. The large laser gun can be made to reverse, functionin­g as the world’s most sensitive l i ght telescope. No existing telescopes are able to capture a signal from a ChipSat, as the light would

simply drown in the background radiation.

The craft will come as close to Alpha Centauri as the distance between Earth and the Sun and have a unique opportunit­y to photograph any planets that might be there.

We do know the star system consists of three stars, Alpha Centauri A, Alpha Centauri B, and a small red dwarf: Proxima Centauri. Recently, the European Southern Observator­y spotted an exoplanet orbiting Proxima Centauri. The planet’s distance to its star means that it may include liquid water.

And that could mean life.


The total cost of Breakthrou­gh Starshot will easily exceed $13 billion, which is comparable to the price of other huge scientific projects such as CERN, the ISS,, and a mission to the Moon, which have all contribute­d new knowledge to many scientific fields.

Although the paramount aim of the project is now Alpha Centauri, the laser gun and the tiny spacecraft could also explore the Solar System. The ships can reach Mars in one hour and Pluto in one day, and after a week, the tiny, solar-powered craft could even catch up with the Voyager and Pioneer probes that have reached the outskirts of the Solar System after 40 years.

In 10-20 years, when space agencies are ready to send people to Mars, the ChipSats could be sent ahead to transmit data back from the planet within a few hours. The laser system could also be used as an extremely powerful telescope to detect asteroids dangerousl­y close to Earth.

In short, Breakthrou­gh Starshot could revolution­ise research and allow us to visit places in the universe for the first time that used to be pure science fiction.

 ??  ?? New Horizons left Earth in 2006, reaching Pluto nine years later in July 2015.
New Horizons left Earth in 2006, reaching Pluto nine years later in July 2015.
 ?? CLAUS LUNAU & HENNING DALHOFF ?? The Breakthrou­gh Starshot project aims to send a fleet of tiny ChipSats off towards the closest star at a speed of one fifth of that of light. Starshot travel time: 20 YEARS 19,000 YRS Normal travel time:
CLAUS LUNAU & HENNING DALHOFF The Breakthrou­gh Starshot project aims to send a fleet of tiny ChipSats off towards the closest star at a speed of one fifth of that of light. Starshot travel time: 20 YEARS 19,000 YRS Normal travel time:
 ??  ?? Physicist Yuri Milner holds the tiny "ship" in his hand.
Physicist Yuri Milner holds the tiny "ship" in his hand.
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