The crazy quest to send spaceships to an Earth-like planet at Alpha Centauri

Scientists recently announced they had found an Earth-like planet in the star system next door, and a bold project to send spaceships there is being backed by cosmologist Stephen Hawking, Facebook founder Mark Zuckerburg and billionaire tech mogul Yuri Milner.

But what will that really take? And how close are we?

Proxima b is the nearest Earth-like planet ever found, located just 4.22 light years from Earth. That's a 20-year journey for a spacecraft travelling at 20 per cent the speed of light, something scientists think can be achieved with light-propelled spacecraft.

The rocky planet slightly larger than Earth orbits Proxima Centauri, a red dwarf that's part of a triple-star system called Alpha Centauri, an international team of scientists announced in the journal Nature on Aug. 24.

That was just four months after Hawking and Milner announced Breakthrough Starshot, a $100-million US initiative that aims to send thousands of tiny light-propelled spacecraft to Alpha Centauri.

"Now, given the discovery of this planet, we may send the spacecraft to fly by and to measure the atmosphere, composition and also to check the physical composition of the planet to see whether there's life there," said Thiem Hoang, a postdoctoral researcher at the Canadian Institute of Theoretical Physics who is an informal member of the Breakthrough Starshot scientific collaboration.

He said scientists had expected to find exoplanets orbiting the stars of Alpha Centauri, but not this soon.

"It's very timely."

Nanocraft with lightsails

Breakthrough Starshot's vision is based on a NASA-funded paper written by Philip Lubin, a cosmologist at the University of California Santa Barbara. The paper has been submitted for peer review and publication to the Journal of the British Internplanetary Society.

Lubin proposes building and launching a fleet of "nanocraft" weighing a gram each, propelled to 20 per cent the speed of light by "lightsails" just a few hundred atoms thick and about a metre wide.

Similar reflective sails have been tested to capture the momentum from solar energy photons from the sun. The resulting small, continuous acceleration could theoretically allow such a spacecraft to reach extremely high speeds without any fuel.

Of course, Breakthrough Starshot couldn't rely on photons from the sun to power it, since it's planning on travelling far beyond the reach of the sun and out of the solar system.

Instead, Lubin proposes building a laser system to focus light on the sails and accelerate them to the target speed "within minutes."

Obviously, there are a lot of engineering challenges that need to be overcome before the project can launch. Many are listed on the website for Breakthrough Starshot, which is inviting scientists around the world to help solve them and hopes to offer grants and funding for that kind of work in the future.

Hoang recently collaborated with several other scientists, including Avi Loeb, a Harvard University astrophysicist who chairs the Breakthrough Starshot advisory committee, to tackle some of those challenges.

In particular, the researchers wanted to know how much damage the nanocraft would suffer by being hit by gas and dust particles en route to Alpha Centauri and whether they would even survive.

Hoang noted that an airplane can be seriously damaged by a collision with a bird at speeds of just a few hundred metres per second. The nanocrafts would be travelling at 60,000 kilometres per second.

Needle-shaped spacecraft

"The collision with even a small particle in the instellar medium can cause huge damage to the surface of a spacecraft," he said.

Hoang and his collaborators proposed that the damage could be minimized by making the spacecraft needle shaped — about five-centimetres long and three-millimetres in diameter — and protecting the nose of the spacecraft with several millimetres of graphite shielding. They have posted their findings and recommendations online and have submitted them for peer review and publication in the Astrophysical Journal.

Next, they plan to tackle the question of how to keep the nanocraft headed in the right direction.

Other Canadians who have been following the development of space travel technology say the challenges for Breakthrough Starshot remain quite daunting.

Kieran Carroll of Brampton, Ont., and Henry Spencer of Toronto were heavily involved in the Canadian Solar Sail project that aimed to race other solar sailing spacecraft to the moon a couple of decades ago. Due to lack of funding, the race never happened and the Canadian project was eventually cancelled.

But Carroll and Spencer remain interested in solar sailing technology, which was finally successfully tested in space by the Japanese space agency's Ikaros spacecraft, in 2010.

Biggest challenges

They think finding the right sail materials to be able to handle intense laser light instead of sunlight will be difficult, they told CBC News in separate interviews. But bigger challenges will be finding a way to make useful sensors small enough to fit on a spacecraft that weighs less than a gram, and figuring out how to communicate with a tiny spacecraft such a colossal distance away, they added.

If Proxima b really does exist, "it certainly would be a very interesting target," Spencer said. While Breakthrough Starshot is unlikely to yield results for the next decade or more, he added, "It's certainly worth throwing some money at to explore the technology."

As for Lubin, he thinks building the nanocraft themselves won't be a problem: "We basically know how to do that today."

Sending the data from the spacecraft back to Earth will be more challenging, he agrees. But the biggest challenge, he says, is building the laser to power them.

So far, only relatively tiny versions have been built. To power the spacecraft, we'd need something a million times more powerful and a million times bigger than anything that has been made so far.

"Once we master that technology, everything else will follow," he said.

But he added that a colleague recently illustrated the magnitude of the challenge by holding his fingers an inch apart and saying, "What you're proposing is this far away from impossible."

"I said, 'Yeah, that's a good way to put it,'" he recalled. "I personally will likely be dead by the time it launches."

Others, like Hoang, believe the challenges can be overcome sooner rather than later.

"I'm very optimistic about it," he said. "Given the discovery of the nearest exoplanet like Earth, it is very important for Earth to move our project, Starshot, ahead."