• Visit our partners: Our Partners:
  • Visit our partners: Our Partners:

Breakthrough Starshot: Sending Probes at a Fifth of the Speed of Light

Written by Morris M.


It’s a project that will push human engineering to its limits. A space mission that will cost unimaginable sums and utilize new tech at the absolute cutting edge.

Launched in 2016 with a dramatic speech by Stephen Hawking, Breakthrough Starshot is an attempt to do for deep space exploration what the Apollo project did for Moon landings. With the backing of billionaire investor Yuri Milner, the program envisages creating a fleet of tiny craft equipped with lightsails: sails designed to catch pulses from powerful laser beams that will – hopefully – propel them to a fifth of the speed of light. 

At such speeds, a craft could cover the distance from the Sun to Pluto in a little over a day. Yet it’s not the outer solar system that these computer chip-sized probes are intended to visit. 

Rather, their mission is to become humanity’s first interstellar objects. 

Across 20 years, the probes will fly to our nearest star system: Alpha Centauri. There, they will set about exploring up-close our interstellar neighbor. 

At least, that’s the plan. To get to this stage, though, the team will have to overcome gigantic engineering challenges. Engineering challenges that truly make this a Mega Project.

Touching from a Distance

4.367 light years away lies our closest solar neighbor. 

Alpha Centauri is a system composed of three stars: two Sun-like objects known as Alpha Centauri A and B, and – closer to Earth – a smaller red dwarf called Proxima Centauri. 

Of course, ‘closer’ here is relative. At 4.2 light years distant – equivalent to 40 trillion km – Proxima Centauri is still so unbelievably far from Earth that it makes the Kuiper Belt look like a weird stranger with zero sense of personal space. 

While light can travel between us and Proxima Centauri in the course of a single presidential term, even our fastest spacecraft would take tens of thousands of years to cover the same distance. 

Voyager 1, for example, is moving at 17km per second (or over 38,000mph). Even so, we would have to have launched it scores of millennia before the invention of agriculture to have it reach our stellar neighbor in time for 2024.

And Voyager isn’t even the fastest manmade object! The Parker Solar Probe set a new record in late 2021, clocking in a staggering 532,000 km/h. Yet this is still a mere 0.0005% of the speed of light. 

In other words, accelerating a regular, rocket-powered probe to the sorts of speeds required to reach our closest star is effectively impossible. 

By the time it arrived, humankind would either be so advanced the probe would’ve been forgotten… or so long dead the data beamed back would only ever be seen by Earth’s new insect overlords. 

For those of us who love the idea of one day reaching Alpha Centauri and making contact with Trisolaris, such limitations are what scientists like to call “a major bummer”. One that can’t be solved by just building more-powerful rockets.

Since rockets run on chemical fuel, the energy they create is inherently wasteful. Way less than one percent of a rocket’s total mass can be converted into energy,  

Hence why Captain Picard never crossed star systems sat atop a massive version of Apollo 11. To go the vast distances of space, you need to get creative. 

Luckily, creativity is what humans excel at. 

Over the decades, scientists have proposed multiple different methods of powering an interstellar craft: from nuclear reactions, to collisions between matter and antimatter.

But this is really just the slightly more-acceptable version of proposing a craft powered by wizards. The technology is so beyond modern humans that it’s effectively magic. 

If we’re to visit another star within our lifetimes, we’ll need to harness more practical tech. Something that may not exist now, but at least could theoretically be achieved within a couple of decades. 

Something like a lightsail.


Golden Wind   

Interestingly for something that sounds so cutting edge, the concept of a lightsail goes way back. 

An ultra-thin piece of material attached to a probe, a lightsail uses the pressure exerted by radiation – in the form of light – impacting on its surface to propel the craft up to high speeds. 

But while this sounds like something we could’ve only dreamed up in the last ten years, the idea dates to at least the 1920s, when Soviet scientists Konstantin Tsiolkovsky and Friedrich Sander appear to have sat down and collectively decided “let’s blow some comrades’ minds!”.

And that’s just one possible start-point. Back in 1610, Johannes Kepler and Galileo Galilei exchanged letters talking about “sails built for heavenly winds” that might allow humans to explore space. 

Still, serious research mostly took place in the 20th Century. After Tsiolkovsky and Sander’s paper, the next to work on the proposal was another member of the Communist Bloc: the Hungarian György Marx. 

Marx’s contribution is especially interesting, because he was the first to articulate what would become a central tenet of Breakthrough Starshot’s vision: using high-energy lasers to accelerate a craft beyond what sunlight could achieve. 

But it was a guy working not in Eastern Europe but the free West who would soon push the idea to its limit.

Robert Forward was a fascinating dude. A physicist and sci-fi novelist, he’s also one of the only scientists whose name will bring up links to He-Man if you Google it, thanks to his son’s role as one of the show’s writers.

More-importantly for this post, though, Forward was fascinated by lightsails. 

Not only did he use the concept in his Rocheworld book series, he also published papers on the technology’s feasibility and – in 1985 – made detailed plans for a lightsail probe he called Starwisp. 

Powered by directed microwave radiation that would accelerate it to one tenth the speed of light, Starwisp was a fundamentally insane idea. One so outside the bounds of what 1980s folk thought possible that you might as well file it alongside equally unlikely things like “gay marriage” or a Donald Trump presidency.

Importantly, though, Starwisp didn’t defy the laws of physics. And it inspired others. Others, like Geoffrey Landis, who both expanded the idea and kept it in the public consciousness. 

Nor was he the only one. 

As the 21st Century dawned, some seriously clever people were starting to think seriously about how to create working lightsails. 

As early as 2005, there were attempts to launch a functional one into orbit. But it would take one spacefaring nation to prove the technology once and for all. 

Launched in 2010, Akatsuki was Japan’s first successful Venus orbiter – a landmark probe for the Japan Aerospace Exploration Agency. 

It was also a major test of the lightsail idea. While Akatsuki itself was a conventional probe, it carried onboard an additional craft named IKAROS.

Once in space, IKAROS detached from its parent. There, in June of 2010, it slowly unfurled a 14m (or 46ft) wide, ultra-thin sail.

And we mean ultra-thin. IKAROS’s lightsail was so thin – at 7.5 micrometers – that a human hair would look chunky in comparison. 

Yet it worked. By July, the radiation pressure from the Sun had acted on the lightsail to accelerate the probe. Nowhere near to a quarter of the speed of light, but enough to demonstrate that the technology worked. 

The successful deployment of a lightsail put the concept firmly back on scientists’ radar. Just six years later, in 2016, Stephen Hawking traveled to the US to unveil a plan to effectively reboot Forward’s Starwisp proposal. 

Now known as Breakthrough Starshot – and backed by investor Yuri Milner – it envisaged using directed lasers to propel probes equipped with a lightsail to 20% the speed of light. 

As Hawking put it:

“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, thanks to my voice synthesizer. How do we transcend these limits?

With our minds and our machines.”

And, just like that, interstellar travel left the realm of science fiction… 

…and began its long, painful journey towards becoming reality. 


The Starshot

OK, so that’s the set-up. The part that details how we got to where we are. 

But this is MegaProjects, and things wouldn’t be complete without us rolling up our sleeves and digging into how this will all work. How will we get a series of mini probes from Earth to far away Alpha Centauri? 

The basic plan is deceptively simple. 

First, tiny probes will be created that can take photos, capture information, and transmit the data back to Earth. 

Weighing hopefully just a single gram (or 0.03 ounces), they will look like little more than computer chips. Hence their name: StarChip. 

Secondly, they will be attached to ultra-thin lightsails and deployed to space, where the third step comes in. 

This is the crazy part. The part that involves using a huge array of powerful lasers to fire concentrated beams at each lightsail in turn – using radiation pressure to quickly accelerate them to speeds no other human craft could dream of. 

From there, the StarChips would streak across the heavens. A long line of probes launched one after the other – at the rate of one a week – heading to our stellar neighbor at one fifth of lightspeed. 

Finally, after twenty years, they would arrive in the Alpha Centauri system, where they would beam back their discoveries to Earth. 4.367 years later, we’d get our first, up-close look at another solar system. 

As the saying goes, though, “easier said than done”. And Starshot’s deceptively simple plan in reality hides a kaleidoscope of incredibly un-simple challenges and highly-creative answers.

One such challenge is the laser array itself. 

In a perfect world, the laser array would be based in space, to avoid any dispersion from our planet’s atmosphere.

Sadly, this is a world of social media and disappointing Thor sequels: it’s far from perfect. 

That means Starshot will have to base its array on our planet, which makes collimation – or the process of focusing the beam on a single area – that much harder. 

In fact, it may be too hard with current tech. Researchers are assuming a minimum improvement in laser technology by a factor of ten over the coming years to make propulsion possible.

Another area where the team are basically waiting for things to get better is with condensing the entire probe down to a maximum of 4 grams. 

To reach the intense speeds required to make the journey worthwhile, the StarChip craft have to be extremely small. 

Right now, though, reducing their size to that degree means reducing what they can do. Afterall, the goal isn’t just to send something to another star, but to send something that can transmit data back.

Luckily, this is one area where technology will almost certainly catch up with humanity’s dreams. 

Thanks to Moore’s Law, it gets easier to build smaller, more-powerful gadgets all the time. Just imagine being able to send the phone you’re watching this on back to yourself 20 years ago. Minds would be blown

Already, we can build simple cameras that weigh a gram. By the time the laser tech issue is sorted, the hope is that one-gram cameras of 20 megapixels might be possible; with other lightweight instruments equally capable of being grafted on. 

In 2019, a test craft was even sent up that weighed little more than a box of paperclips, yet was able to take 4,000 images of Earth from 30 km up.

So, StarChip itself is really more of a waiting game. But that still leaves perhaps the biggest challenge: the lightsail. 

While Japan demonstrated over a decade ago that functional lightsails can be built, there’s a major difference between IKAROS and StarChip: the light they use. 

IKAROS was propelled by the sun. StarChip, by contrast, will be blasted with pulses of 100 gigawatts of concentrated laser light, generating 10 pascals of force. 

That means the probe’s lightsail must firstly be strong enough that it doesn’t tear, and secondly reflective enough that it doesn’t melt. In fact, it has to be so reflective that a mere 1 out of every 100,000 photos is absorbed by the material. 

That’s a tall order. However, it’s also a challenge scientists are making real headway on. 

A 2022 study in Nano Letters, for example, demonstrated how having a sail that “billows” like a sea ship sail could reduce the risk of tearing. 

Meanwhile, a separate study from the same year recommended tackling the melting problem by using (quote):

“2H-phase molybdenum disulfide, crystalline silicon nitride, and nanoscale patterning.”

This will hopefully allow efficient harvesting of the laser’s energy, thereby reducing the time the delicate lightsail will need to be exposed to powerful pulses. 

Sadly, these aren’t the only issues currently facing the Starshot project. 

There may be others that are far more intractable.

“I Think It’s Gonna be a Long, Long Time…”

Right now, Voyager 1 is the most-distant manmade object – some 156 times farther from us than the Earth is from the Sun.

While that’s impressively far – about four times farther than Pluto’s average distance from our star – it’s a mere fraction of the distance to Proxima Centauri. 

Even so, Voyager’s signal has become incredibly dim. So dim, that a basic watch battery is about 20 billion times as powerful. 

That’s not a problem for communicating with Voyager. We know exactly where it is, and the probe directs its signals to us very precisely. 

But it does show a problem with interstellar communications: the further probes go from Earth, the dimmer their signals get. By the time you get a craft transmitting from another star system, the array you’d need to build to capture such a signal becomes an engineering migraine. 

Hence Starshot putting so much energy into figuring out new methods of communication. 

One solution is to include an incredibly tight laser beam onboard StarChip. A 2020 paper argued that a 30m telescope on Earth could pick up a signal sent at 1.02 micrometers and received at 1.25. 

Still, directing a precision laser beam from another star system comes with its own set of problems. Which may be why scientists are currently turning toward the pipeline solution. 

From the moment it was announced, the idea behind Starshot was to send not just one craft, but dozens. Even hundreds. A great swarm of probes, stretching out across the void. 

Since they would be launched one after the other – possibly in three waves – you’d have a scenario where some probes would reach Proxima Centauri while others were still a lightyear away; and yet others were much closer to Earth. 

And that raises an intriguing possibility. Rather than transmit directly back to us, the forward probes could instead transmit to the ones following them, who could transmit to the ones following them, and so-on, until the data at last reached NASA. 

In effect, the probes would become the pipeline, drastically reducing the risk of data loss.

Of course, the problem then is what happens once the last craft has been sent and has nothing to relay data back to. But it’s an innovative solution to a vexing problem.

Unfortunately, it’s not the only difficult problem that still needs to be solved.

There’s also the issue of collisions. 

Despite its reputation as, y’know, empty space, space itself is full of dust and gasses and little particles whizzing around.

For a craft as small as StarChip, this normally wouldn’t be a problem. In its entire four-year journey, the chances of it colliding with any particle over a micron in size is close to zero. The only impacts it should expect are with particles so small they’d make a micron-sized speck look like a boulder. 

The trouble is, StarChip will encounter these extremely tiny particles while moving at extremely fast speeds. 

And, as anyone who has ever been hit by a bullet can tell you, tiny things going very fast can do a whole lotta damage. 

Given the density of space, its likely at least one 0.5-micron particle will impact StarChip on its voyage.

When it does, it will impart 7.2 Joules of energy. That’s not a huge amount, but it’s just the start of the collisions we might expect. 

Astrophysicist Ethan Siegel calculated that each StarChip should encounter something in the order of 10 million particles with a diameter of 0.01 microns. Although they would each only impart 36 micro-Joules of energy per impact, those impacts would soon add up. 

By the time StarChip reached Alpha Centauri, it should’ve had around 800 Joules of energy deposited on every single square centimeter of its surface. 

For such a tiny craft, that’s the equivalent of you or I getting hit with a freight train. Siegel was highly skeptical that any StarChip could survive such consistent impacts. And, so far, Starshot doesn’t seem to have any concrete solutions to this problem. 

But then, that’s a big part of the Starshot game plan. Pretty much none of this can be realized in the here and now. It all relies on investing in new technologies today, with the dream of payoff five, ten, even twenty years down the line. 

And the good news is that – even if visiting Alpha Centauri winds up being impossible within our lifetimes – there are still plenty of other uses for StarChip. 

Not least exploring our own solar system. 

The Road to Nowhere

The 2020s are an exciting decade for NASA missions. There’s the upcoming Europa Clipper that will travel to Jupiter’s moon; the Dragonfly mission to Titan that will launch in 2027; plus the VERITAS and DAVINCI probes to Venus. 

Each of these is a big deal. A mission costing anywhere from hundreds of millions to billions of dollars, and each will likely last years.

But what if there was another way of exploring our solar system? What if – instead of all that time and investment – NASA could simply build and launch a probe in a single month, for less than $1,000?

Well, that’s the future some are envisioning. And it could all come about thanks to the advances of Starshot

While the focus of Starshot is getting to Alpha Centauri, the StarChip probes wouldn’t only function on an interstellar voyage. NASA could just as easily deploy them in our local environment.


Now, this wouldn’t be great for super in-depth exploration requiring specialized instruments. But as a method of quickly getting to all the interesting objects in our solar system and at least doing a bare bones study? It’d be second to none.

The best part is that we wouldn’t even have to be able to accelerate the probes to a quarter of the speed of light to make them useful. Using far-weaker lasers, its thought we could easily accelerate a lightsail to four times the speed of Voyager 1

And that alone would make it all worthwhile.

Imagine: a world where sending a probe to Pluto doesn’t take nine years – like New Horizons – but a mere two. A world where flight times to Jupiter are cut to a handful of months; and probes can reach Mars in a couple of weeks. 

Now combine this with a world where basic, miniaturized probes are so cheap to produce that we don’t have to send them one at a time, years apart, but can dispatch them in swarms. Hundreds of probes zipping out to every corner of our solar system, on an unparalleled mapping spree.

Well, this is exactly the sort of world we might soon live in.

Even if Starshot never makes it to Alpha Centauri. Even if lightsails fail to accelerate a probe more than 0.0005% of the speed of light; this bright future of intense solar system exploration could still come about from investing in these technologies. 

And that’s just a ‘consolation prize’ scenario. 

In the best case, we could – in the next two to five decades – be launching the first wave of miniature probes towards another star. A crossing of the void on a par with the great viking sea voyages to North America. 

Who knows what we’ll find when we get there? Who knows if it’ll actually happen in our lifetimes? 

But it’s worth our taking seriously now, because it has the ability to change everything. To open up a whole new frontier for humankind. 

Starshot might be a mere theoretical curiosity right now. But it has the power to transform our understanding of the entire universe.



Astronomy, a voyage to the stars within our lifetimes: https://astronomy.com/magazine/news/2021/06/breakthrough-starshot-a-voyage-to-the-stars-within-our-lifetimes 

CNet, overview: https://www.cnet.com/science/this-cosmic-sail-could-blast-spacecraft-to-new-star-systems-at-hyper-speeds/ 

Astronomy, 2022 update on lightsail progress: https://astronomy.com/news/2022/03/developing-light-sail-technology-billows-into-the-future 

Receiving messages from Starchip: https://phys.org/news/2020-05-interstellar-probes-starshot.html 

BigThink, reasons to be skeptical: https://bigthink.com/starts-with-a-bang/breakthrough-starshot-survive/ 

Universe Today, further uses for lightsails: https://www.universetoday.com/154668/laser-powered-sails-would-be-great-for-exploring-the-solar-system-too/#more-154668 

Related Articles


Please enter your comment!
Please enter your name here

Stay Connected


Random Article


Evacuation of Industry: That Time the Soviet Union Moved 1,500 Factories

Introduction The second world war was the bloodiest and most destructive war in human history. It saw armies, navies, and air forces pitted against each...

Latest Articles