When it was discovered in August 2016, Proxima b – the closest planet to Earth to date – was a source of wonder. Now, it’s shrouded in skepticism. It turns out that this mass orbiting around the red dwarf Proxima Centauri – “only” 4.25 light years away from us – is actually “inhospitable,” “uninhabitable” and “hostile.” A wave of disenchantment seems to have swept over the scientific press.

Lodged at the heart of the Alpha Centauri system, which includes three stars, Proxima b is a bit of a misnomer: on a human scale, it’s located really far away, almost 40 billion kilometers from us. That’s 2,000 times farther than we’ve ever traveled from Earth. And yet, it’s given new hope to the possibility of one day living beyond our planet. To space enthusiasts, there is no doubt: today more than ever, interstellar travel is possible as a long-term endeavor. And if Proxima b proves to be uninhabitable, we will find another planet and work to undertake the longest and most ambitious crossing ever achieved by humanity: hundreds of years spent aboard a ship, in which generations of astronauts will embark on a new conquest of space.

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Artistic rendering of Proxima Centauri b

But there’s still a long road before we can even send an exploratory sensor. Such a feat would already be an enormous leap, if not for humanity, for astronomy at least, and would allow us to discover, for the first time, what is hidden in the confines of our galaxy. To then take refuge there in case of cataclysm here, well, that’s even further down the road. But that distance hasn’t stopped some physicists from thinking about the ship that would brave the perils of the universe, its systems and its galaxies.

From Daedalus to Icarus

In 1973, in the midst of the race for the skies, the British Interplanetary Society launched a five-year project to design an unmanned spaceship that would be able to perform an interstellar flight. For the first time, such a mission looked like a possibility in the near future. Quickly, the Daedalus Project – named after the character in Greek mythology known for his ingenuity – was tasked with the following ambitious challenges: reach dizzying speeds, maintain a sufficient amount of fuel, and not explode mid-flight due to space debris.

Building off the progress made in the field of nuclear fusion, the team finally chose a nuclear-powered rocket that would fly at a speed of more than 10,000 kilometers per second. An autopilot system would guide the brave passengers who agreed to board the craft. In 1978, the project’s final report stated that it was feasible for this 190-meter-long automatic vessel to fly to Barnard’s star in about 40 years. But then, Daedalus was abandoned. That doesn’t make the dream any less real: today, it continues to inspire future generations.

The same organization that gave birth to Daedalus decided to give it a son in 2009. They called it the Icarus Project. The scientists Kelvin Long and Richard Obousy were entrusted a team of about 20 scientists. For the last 10 years, they’ve worked on the second millennium version of the vehicle. Michel Lamontagne is one of the project’s researchers. He works on the thermal aspects of the vehicle – meaning, its cooling system. “I was contacted in 2013 to draw the vehicles for a design competition,” he says. “When I read the proposals, I noticed several shortcomings in the cooling system’s design, which is my professional specialty, and little by little I agreed to work on correcting them.”

Icarus is an updated version of Daedalus. “We preserved everything we could,” says Lamontagne, notably “the loading capacity of the vehicle, which remains at 150 tons.” For the propulsion – the main technical challenge – several alternatives have been retained, two of which are based on nuclear fusion. Two other possible modes of propulsion involve so-called ICF fusion and the Z-Pinch. “We rejected a single solution in favor of a variety of concepts, since no one fusion technology has a clear advantage over others, and because there are more than 20 possible ways to achieve nuclear fusion.” To date, neither of the two methods are functional, but they remain promising, according to scientists. “The power levels required are very high and the thermal losses are significant. Efficiency in reality is, at the moment, still far from efficiency in theory.”

When it comes to flying, the Icarus Project has had to drop some of Daedalus’ ambition. “We’ve reduced the top speed, which results in a longer mission time: 100 years as opposed to the 40 years we originally imagined.” A hundred years! A whole century during which brave volunteers would be born, live and die aboard the vessel?

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Whiffs of 2001: A Space Odyssey

Hibernation?

This is the question on everyone’s mind. What would life aboard a spaceship on a century-long journey be like? How would passengers be able to feed themselves, how would they drink, how many could they be? An interstellar flight poses a multitude of questions about passengers’ living conditions. A study by anthropologist John Moore from the University of Florida, for example, estimates that an initial team of 160 people would be needed to ensure a viable population for 200 years.

Not to disappoint science fiction fans, but research indicates that it may still be a while before humans get on board. “The Icarus project is in favor of a robotic probe,” explains Michel Lamontagne. “However, we are thinking of the possibility of having a crew in hibernation, like in many works of fiction, from 2001: A Space Odyssey to Avatar and Passengers.” Without the ability to hibernate, Lamontagne explains, “a trip to another star could last several centuries, because you’d need a large vessel to accommodate a  large population, of the order of 40,000 individuals, to ensure the social and genetic diversity required for the survival of an isolated society.”

Lamontagne hopes the final report of the Icarus Project will be finalized in 2018. It will propose two options for the vessel: Firefly, which operates via Z-Pinch; and Espérance, named after the ship that sailed around the world between 1824 and 1826. The latter would rely on ICF fusion. Firefly is “long, with large radiators that shine bright orange when propelled. A long cylinder contains the liquid deuterium that serves as fuel.” For its part, Espérance looks more like a pizza cutter.

But we’ll all have to be patient. “Icarus Interstellar has set a 100-year objective for the development of the robotic exploration probe. If hibernation technologies are developed in the next century, it is conceivable that manned ships will be able to take off shortly thereafter,” says Michel Lamontagne. Another interstellar project – which does not plan on welcoming calves, cows and pigs for human nourishment – presents real prospects in the short term.

Breakthrough Starshot

Did Youri Milner fall in love with space because he was born in 1961, the year Youri Gargarine became the first man to enter space? That’s what Milner thinks, at least. One thing is certain, and that’s that this Russian billionaire has wild ambitions. Last November, he announced that he wanted to compete with NASA in searching for traces of extraterrestrials on Enceladus, one of Saturn’s satellites. But that’s not even the craziest project the entrepreneur’s undertaken. In 2016, he injected some $100 million into Breakthrough Starshot. He was in good company. The late Stephen Hawking, one of the great believers in the existence of extraterrestrial life, also supported the project, along with Mark Zuckerberg and a few dozen other specialists, like Pete Worden, the former director of a NASA research center, and Freeman Dyson, the famous physicist and mathematician. In short, Starshot has a solid base of support.

There are no humans aboard this tiny spaceship. All it contains is a tiny probe, pushed along by a solar sail. It’s an undeniably innovative project. Instead of a massive vessel, like Icarus proposes, we’re only dealing with a swarm of StarChips: small electronic chips the size of a coin, each equipped with a solar sail four meters wide, so light that they should reach nearly a fifth of the speed of light, powered by a laser beam. The trip is predicted to last two decades only, traveling at a speed of 60,000 kilometers per second. The first electronic chip fleet should be sent in just 20 years. The advantages of this technology are considerable: the use of light for propulsion eliminates the need for fuel, and accordingly, fuel storage, all of which would weigh the vehicle down and delay its trajectory. Additionally, the most miniaturized design of the probe would make it 3,500 times faster than a traditional rocket.

In the early stages of the project, its goal remained rather undefined. As journalist Ann Finkbeiner reports in a 2017 article, Freeman Dyson himself would have said the project was “stupid,” but that the ship was “interesting.” Then a few months later, Proxima b was discovered. The extrasolar exoplanet, of a mass comparable to that of Earth, seemed to present characteristics compatible with the existence of liquid water on its surface. And it was only 4.25 light years away from us. Starshot suddenly made more sense.

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Starshot’s plans

However, Milner’s baby remains a huge challenge in terms of engineering. “The Starshot project is exciting,” admits Michel Lamontagne, “and the solar sail is credible, but it requires a lot of infrastructure for large-scale vehicles.” If the project can secure financing – in total, it needs about 8 billion euros – it would still run into several difficulties. It must be tiny, able to contain very advanced technologies, extremely resistant to the force of the beam that will hit it, and it must be able to predict and avoid any debris it may encounter on its way. Moreover, “the observation time will be a few hours after 20 years of travel. The amount of information collected may be small compared to the effort deployed, but it is certainly the most accessible technology in the short term”.