Is Hawking's Interstellar 'Starshot' Possible?

When viewed on a cosmic scale, humanity lives on a tiny grain of sand floating in an unimaginably-deep ocean. Huge expanses of space separate even the closest stars, ensuring that, should any sufficiently intelligent life form want to spread across the galaxy, it would take a momentous effort to launch across the interstellar seas.

As we look toward the stars, hoping that we may visit them some day, many would argue that interstellar travel is impossible. After all, the nearest-known star system is over 4 light-years away.

Let's think about that for a moment: It takes light 8 minutes and 20 seconds to travel from the sun's surface to our planet's atmosphere. So when you look up at the sun, that solar heat you feel on your face traveled 90 million miles through interplanetary space and arrived on your skin less than 9 minutes later.

But it would take light to travel from our sun to Alpha Centauri, the nearest star system beyond our solar system, nearly four and a half years to cover the 26 trillion miles of interstellar space. Now we have an idea of scale; if we send a spacecraft to Alpha Centauri, using the propulsion methods currently available to us, it would take us nearly 80,000 years to complete the trip. It's little wonder we see ourselves quarantined by a cosmic void.

As we can see, interstellar travel isn't something to be taken lightly; the challenge is historic and it will take a global effort to make it possible. And a growing body of scientists are realizing that, actually, it may well be possible.

So when the "Breakthrough Starshot" announcement was made on Tuesday, on the day of the 55th anniversary of Yuri Gagarin's heroic launch into space, the world suddenly became aware there is a group of engineers, scientists, futurists and entrepreneurs that see a future where humanity will make that momentous step into the deep unknown, sending a possible fleet of tiny robotic explorers to that "impossible" destination: Alpha Centauri. What's more, British theoretical physics heavyweight Stephen Hawking is leading the effort while Russian billionaire investor Yuri Milner is putting up $100 million to seed the project. Big names like Mark Zuckerberg are on the board of directors and former director of NASA's AMES Research Center Pete Worden will lead the project.

This certainly isn't the first project to consider interstellar travel. Hopping from star to star has been the fodder for science fiction storylines for decades, but the first notable plan came from the British Interplanetary Society in the 1970s, culminating in "Project Daedalus" - a monstrous unmanned interstellar vehicle as big as the Empire State Building. Most of Daedalus' bulk came from the sheer amount of fuel that would be required to accelerate the vehicle and slow it down once it reached its destination. When exploring interstellar space, Daedalus sent a powerful message: Go big or don't even think about going.

In this case, the starship would be propelled by a chain of nuclear explosions via a method conceived in the Cold War known as nuclear pulse propulsion. This concept assumed a lot, chiefly that there would be disruptive technologies and huge advances in materials research in the future that would allow such a vehicle to be constructed.

Currently, an international group of scientists and engineers have picked up where Daedalus left off, re-imagining this original effort as part of the non-profit group Icarus Interstellar, which began as Project Icarus (the "son of Daedalus"). Icarus now has several projects all with the same aim in mind: to propel humanity to the stars and find solutions to technological and socioeconomic barriers along the way.

There's been few seriously funded efforts to further develop interstellar technologies, but that changed in 2011 when the US research agency DARPA and NASA provided $500,000 to seed the "100 Year Starship Project" that is headed by ex-NASA astronaut Mae Jemison. But the interstellar community has never seen such a huge financial interest that Breakthrough Starshot brings, a fact that has excited members of the interstellar research community.

"It's awesome to see," Andreas Tziolas, co-founder and President of Icarus Interstellar, told Discovery News.

Key to Icarus Interstellar's goals is to build a grassroots effort to enthuse the world for interstellar exploration. Like countless historic examples, humanity shines when pushing the envelope and having such lofty goals can create breakthrough, or "disruptive," technologies.

Well-known examples include the space race, when political ideals drove the US and Soviet Union into orbit and then to the moon landing in 1969. The technologies developed to gain the ultimate military "high ground" matured to give us space technologies we take for granted today.

Often, new technologies developed along the way to a bigger goal have applications that may initially not appear to have purpose, but their unforeseen application to achieve that goal could transform our planet, from developing clean power sources to finding ways to slow and perhaps reverse the impact of climate change.

Usually research into new technologies are born to fix a problem, and Tziolas was able to identify serious challenges the Starshot project will encounter almost immediately.

The key idea behind Starshot is to develop tiny spacecraft that will use laser propulsion to accelerate them to around 20 percent the speed of light. Key to Starshot's ultimate goal is to reach Alpha Centauri within a generation. These spacecraft, dubbed "nanocraft", will need to travel 1,000 times faster than the fastest spacecraft built by humankind. NASA's New Horizons spacecraft, which flew past Pluto in 2015, is blasting through the outer solar system at a rate of 740,000 miles per day. The Voyager 1 spacecraft is even faster, covering nearly a million miles per day. Though fast, both New Horizons and Voyager 1, if pointed at Alpha Centauri, wouldn't reach their destination for tens of thousands of years Interestingly, Voyager 1 is already an interstellar probe that has left the magnetic bubble of our sun's heliosphere and is currently the only spacecraft stepping into the interstellar shores. But considering the nuclear-powered spacecraft was launched in 1977 and has taken nearly 4 decades just to reach interstellar space, we need to go faster. Much much faster.

And the Starshot team realizes this and opted to miniaturize the whole effort with the view to construct a fleet of tiny spacecraft weighing no more than a gram each. Of course, packing all the instrumentation required to operate and steer such a mind-blowingly small spacecraft into such a restrictive mass may seem like a fool's errand, but this entire research effort will be a paradigm shift from most other interstellar concepts. These will be tiny robots, equipped with cameras, sensors and navigation equipment, all attached to a thin and lightweight sail that will use the force of a powerful ground-based laser to shoot it out of the solar system toward Alpha Centauri.

But, as Tziolas points out, though laser technology is advancing quickly, it's hard to envisage what material these nanocraft will be constructed from. Even if their laser sails reflected the majority of the laser energy that hits them, there's going to be a huge heating problem. To be frank, the nanocraft would be incinerated by the hypothetical 100 gigawatt propulsion laser if the heat isn't efficiently radiated. But to radiate heat, the nanocraft would need radiators, which will add to the nanocraft mass.

"In the absence of a coolant, you have to radiate (the heat) back out into space, and the only way to really do that is with microwaves and the only way to really do that is to increase the surface area," said Tziolas. "So you'll need radiators that are designed to radiate the heat, which adds weight ... the radiators would likely be metal sheets."

Could this be one of those challenges where new technologies are spawned? Ultra-lightweight, high temperature, highly radiative materials may be developed that could have a huge number of spin-off uses in space and industry. Who knows.

Assuming these nanocraft can be launched and sent beyond the solar system, they will need to be extremely durable and bundled with failsafes. But 20 years is a long time in space and though the interstellar medium pretty empty by solar system standards, should these craft hit anything, even the tiniest grain of dust along its 20 year path could impact any component like a hypervelocity bullet smashing into a bone china teacup. Let's not forget that these things will be traveling at 20 percent the speed of light - that's over 130 million miles per hour. Although they are small, will they also need shielding? Probably, but this will once again increase their weight, ultimately slowing them down.

According to the current plan, mission failure will be mitigated by sending a huge number of nanocraft on the mission. Though many nanocraft may die on their journey, perhaps a few might make it to their destination.

Then there's the nuts and bolts of communication. It's one thing to send tiny spacecraft to another star, but what's the point if we can't see the pictures? These nanocraft need transmitters to send data home, but how powerful will these transmitters need to be?

"By my thinking, the big problem is communications," said Robert Freeland, Icarus Deputy Project Leader. "A few members of the Project Icarus team spent several months last year designing a communications system for the Icarus vessel. Admittedly, the data rates for Icarus are orders of magnitude higher than those of this project, because Icarus is designed to fully decelerate into the Alpha Centauri system and set up shop for long-term, detailed observations."

Freeland's work focuses around the Firefly Starship concept that would use nuclear fusion as propulsion. You can read more about this fascinating project in a previous Discovery News article.

Freeland points out that the Starshot nanocraft are designed to simply fly past Alpha Centauri, not enter orbit, a key advantage to keeping them small and lightweight. During the flyby, they will need to take a rapid series of observations and then beam back the data some time after. But attenuation (loss of signal quality) over the vast interstellar distance could become a problem with a low power transmitter packed into such a tiny vehicle.

"If that's the case, then it argues for bigger probes, with bigger power supplies," he added. "Give me a kilogram of payload, and the problem becomes a bit more tractable. But boosting a payload 1000x bigger would require some combination of a bigger beamer, bigger sail, longer boost time, or lower top speed."

Then the challenges seem to quickly multiply.

What about navigation? Sure, the nanocraft may have tiny cameras that can act as starfinders, orienting them the correct way, but how will we know when they reach Alpha Centauri? If snapping photos of a hypothetical planet orbiting a star is the goal, how will these probes know where (and when) to look? Always keep in mind that it will take over 4 years for the nanocraft to beam back the data and we'll need to send "encounter" commands 4 years before the probes reach Alpha Centari! Perhaps, before launch, we'll have space telescopes that have already pinpointed exoplanets in the Alpha Centauri system and these nanoprobes will have some kind of artificial intelligence to help them work out their orbits on arrival.

What about the practicalities of having a powerful laser, on Earth, blasting through the atmosphere? Might it be a hazard to nature, air traffic and (possibly) space traffic? Perhaps we'd need to rethink the plan to have this laser on Earth, perhaps we need to find a way of basing it in space. How about the moon?

Challenges and apparent impossibilities abound but at least it's a start. For the first time there seems to be a global interest in reaching for the stars and it's starting to be matched by significant quantities of money that will be used to make huge advances in basic interstellar science. Starshot's eventual mission may not even resemble the plan it's starting out with, but interstellar science needs this kind of investment to at least test the theory and work the problems encountered.

"We've got to start somewhere ... the interest in interstellar exploration, that's what we've been fighting for," said Tziolas. "It's one of the missions of Icarus Interstellar to make interstellar research commonplace and to raise awareness."

It's groups like Icarus Interstellar, 100 Year Star Ship and now Breakthrough Starshot that will identify the challenges and come up with solutions, along the way finding new technologies that could transform our way of life. Like the surge in commercial space interests in the US, supporting cargo deliveries to the International Space Station and launching satellites into orbit, perhaps we're seeing a burgeoning industry in advanced propulsion technologies that could attract business and inspire kids to embark on an education in the fields of science and technology.

But there's a few very basic reasons why humanity should be motivated to sail the interstellar seas. Stephen Hawking is an outspoken advocate of pushing our species to the stars, in case our planet fails in the future. "Earth is a wonderful place, but it might not last forever," he said in the Starshot news release. "Sooner or later, we must look to the stars. Breakthrough Starshot is a very exciting first step on that journey."

Though a failing Earth is certainly a motivator, I'd argue that, as a species, we are hardwired to explore the frontiers of our world and our intellect. Pushing into space, exploring new worlds in our solar system and pushing to the stars melds the best qualities of our species, a profound journey that could help us understand our place in the cosmos.