Elon Musk’s SpaceX plans to land an unmanned spacecraft on Mars as soon as 2018 with the help of NASA, an extraordinary collaboration between the public and private sectors in an effort to eventually get humans to the Red Planet.

SpaceX made the announcement on Twitter Wednesday, laying out an ambitious timeline for an incredibly difficult mission that only governments have dared try. Landing a spacecraft or a robot that can then operate successfully on the Martian surface is so difficult that the U.S. is the only country to have done it, and many attempts over the years have failed.

The partnership between SpaceX and NASA, which has the goal of sending humans to Mars in the 2030s, is yet another example of the significant shift in the role NASA is playing in space exploration. While it continues to pursue its own deep space missions, the agency has also spent years, and billions of dollars, helping to support a robust commercial space industry, which it is increasingly partnering with to develop the technologies to explore the cosmos.

In a statement, NASA said it is providing “technical support” for SpaceX’s mission, without financial support. In exchange, SpaceX would provide “valuable entry, descent and landing data to NASA for our journey to Mars, while providing support to American industry.”

Musk, the billionaire entrepreneur who also runs the electric car maker Tesla, founded SpaceX more than 10 years ago with the goal of colonizing Mars.

Getting to Mars, however, is exceedingly difficult. On average, it’s 140 million miles from Earth, though the planets come to within about 35 million miles every 26 months. But even under the best circumstances it takes months to get there. And the terrain of deep space is tremendously harsh. Skeptics think that despite its grand aspirations, NASA is nowhere close to getting humans there. And of the 43 robotic missions to Mars, including flybys, attempted by four different countries, only 18 have been total successes.

In 1971, the Soviet Union became the first country to successfully land a spacecraft on Mars when its Mars 3 lander transmitted for several seconds before going quiet.

Musk's announcement Wednesday, then, “is a pretty bold statement from a guy known for bold statements,” said Lori Garver, the former deputy NASA administrator.

The collaboration “is more similar to what you might have with a government-to-government agreement,” she said. “So it is breaking new ground, and I think it’s a good sign that NASA is even a partner. It shows there are people at NASA who are as excited about this as a lot of us are.”

Once a spunky startup, SpaceX, based in Hawthorne, Calif., has become a major force in the burgeoning space industry, with more than 4,000 employees, a backlog of orders to launch commercial satellites and multi-billion dollar contracts with NASA to fly cargo and eventually astronauts to the International Space Station on its Falcon 9 rocket.

In its first launch to resupply the International Space Station since its rocket exploded last year, Elon Musk’s SpaceX landed its unmanned rocket on a floating 'drone barge' in the Atlantic Ocean. The landing, the first ever of a rocket’s first stage at sea, is seen as a breakthrough for commercial spaceflight. (Jorge Ribas/The Washington Post)

Recently it pulled off feats once thought impossible—the vertical landings of its Falcon 9 rocket’s first stage, one on a helicopter-like pad at Cape Canaveral and another on a ship in the ocean. The accomplishments of recovering and reusing rockets that were normally discarded after each flight could help lower the cost of spaceflight. And the successes have reignited interest in space, which has seemed dormant since the retirement of the space shuttle in 2011.

SpaceX is currently developing a new Dragon spacecraft that would be able to fly humans—and not just cargo—to the space station. It’s also working on a more powerful rocket, the Falcon Heavy, which SpaceX says would become the world’s most powerful rocket with thrust at liftoff equivalent to 18 747 jetliners.

On twitter, Musk said that the Dragon "is designed to be able to land anywhere in the solar system." But he said he wouldn't recommend using it for missions beyond the moon because the inside is tight -- about the size of a SUV. "Wouldn't be fun for longer journeys," he wrote.

On its website, SpaceX says that the Falcon Heavy rocket "was designed from the outset to carry humans into space and restores the possibility of flying missions with crew to the moon or Mars."

The rocket is slated to launch for the first time later this year from the Kennedy Space Center in Florida. SpaceX is leasing the historic launch pad 39A, which launched many of the Apollo and space shuttle missions.

John Logsdon, a noted space historian and a professor emeritus at George Washington University, said that SpaceX "likes to do bravado things."

He noted that the company has yet to launch its Falcon Heavy, and it has yet to land its Dragon using its own engine thrust, a key component in landing in the Martian atmosphere.

SpaceX pushes "the limits of feasibility," he said. "To think that you can get this all together in two years since two of the key steps have not been demonstrated." But he praised the company's engineering prowess and said it was smart to partner with NASA.

"NASA has more expertise in getting to and landing on Mars than any other organization in the world," he said. "So if a U.S. company wants to try it on a no-exchange-of-funds basis, why not?"

In a blog post, NASA Deputy Administrator Dava Newman said that collaboration with industry and international partners is key to getting to Mars, and that the agency is reaching out to “partners in boardrooms, classrooms, laboratories, space agencies and even garages across our country and the world.”

While the Cold War competition between the U.S. and Soviet Union propelled NASA to the moon in the 1960s, there is a different tone today, she said.

“In the international space community, gone are the days of the ‘space race’ when the dominant theme was that of various nations racing against each other,” she wrote. “Instead, we’re increasingly running together.”

For Musk, Mars has long been something of an obsession. Before he founded SpaceX, he was curious to know when NASA planned to send humans there, so he checked the agency’s website, he said at a conference a few years ago.

“Because, of course, there had to be a schedule,” he said at the time. “And I couldn't find it. I thought the problem was me. Because, of course, it must be here somewhere on this website, but just well hidden. And it turned out it wasn't on the website at all. Which was shocking.”

In an effort to drum up support for NASA and galvanize the public, he decided to buy a rocket and send a greenhouse to Mars, which would be the furthest life had traveled and the first living thing on Mars. But buying a rocket proved to be too difficult and expensive, and Musk decided he’d build them on his own. Musk, the co-founder of PayPal, invested $100 million of his own money into SpaceX.

Later this year, he is expected to lay out how SpaceX plans to fly humans to Mars. He has said he wants to colonize Mars so that humanity has a back-up plan in case anything should happen to Earth, such as an asteroid hitting it.

At a recent conference he said he wants to go to Mars for “the defensive reason of protecting the future of humanity, ensuring that the light of consciousness is not extinguished should some calamity befall Earth.”

But what drives him most is what has drove generations of explorers before him, what NASA long stood for, which was, simply, “that this would be an incredible adventure.”