SpaceX has plans to send two private citizens around the Moon, CEO Elon Musk announced today.

It will be a private mission with two paying customers, not NASA astronauts, who approached the company. The passengers are "very serious" about the trip and have already paid a "significant deposit," according to Musk. The trip around the Moon would take approximately one week: it would skim the surface of the Moon, go further out into deep space, and loop back to Earth — reaching a distance of approximately 300,000 to 400,000 miles.

The two private customers have already paid a "significant deposit"

The plan is to do the mission in the fourth quarter of 2018 on the Crew Dragon spacecraft with the Falcon Heavy rocket, which is due to perform its maiden launch this summer. Of course, Musk is well-known for his unrealistic deadlines — in 2011, he promised to put people in space in just three years. Meanwhile, the Falcon Heavy’s launch was originally slated for 2013 or 2014, but has been repeatedly pushed back until this year.

The two people going on the trip, who weren’t named, already know each other. They will begin initial training for the trip later this year. Musk declined to comment on the exact cost of the trip, but said it was "comparable" or a little more than the cost of a crewed mission to the International Space Station. For context, one ticket on the Russian Soyuz rocket costs NASA around $80 million.

Musk believes these private missions could be a "significant driver of revenue" for the company and expects to have at least one or two a year, possibly making up 10 to 20 percent of SpaceX revenue.

A "significant driver of revenue"

A permit from the United Nations will not be necessary, according to Musk, though the trip will need to be licensed by the Federal Aviation Administration.

This announcement comes as NASA is thinking about a similar mission. The agency has considered putting astronauts on the first flight of its next big rocket, the Space Launch System (SLS). The plan was for NASA to fly the SLS for the first time, uncrewed, in the fall of next year. But a memo sent to NASA employees earlier this month showed that the agency was considering making the first flight of the SLS a crewed mission instead. That flight would take a crew around the Moon, echoing SpaceX's Moon mission plans.

"It’s a particularly opportune moment to announce this as a new administration comes in and grapples with their plans for NASA," Phil Larson, a former space advisor to President Obama and a former SpaceX representative, tells The Verge. "We’ve all seen the reports of the NASA team looking at opportunities with the Moon, and the announcement by NASA that they’re studying moving [Exploration Mission 2] up with Orion and SLS goes to show the new team is looking at new ways to do things in space. I don’t know if they’re looking for this kind of partnership or not but presents a new opportunity for them that a private company will do something like this."

Musk has made it clear that NASA would have priority in any lunar orbit mission. "If NASA decides to have a mission of this nature be a NASA mission, then of course NASA would take priority," he says.

"the success rate is quite high."

SpaceX has already been developing the Crew Dragon to carry people for NASA, as part of the agency's Commercial Crew Program. It's an initiative that tasks two private companies — SpaceX and Boeing — with developing vehicles that can carry people to and from the International Space Station. NASA applauded SpaceX for "reaching higher" in a statement the agency published online. "We will work closely with SpaceX to ensure it safely meets the contractual obligations to return the launch of astronauts to U.S. soil and continue to successfully deliver supplies to the International Space Station."

The company expects to fly an uncrewed Crew Dragon on the top of a Falcon 9 to the ISS by the end of this year. Then the goal is to fly another mission six months later with a NASA crew. Six months after that, if those missions go as planned, is when the two people would fly around the Moon. These paying customers "are entering this with their eyes open, knowing that there is some risk here," says Musk. "We’re doing everything we can to minimize that risk but it’s not zero."

The Crew Dragon, which hasn’t yet flown, will operate autonomously for most of the flight. If there is an emergency, the passengers will probably need to step in, but "the success rate is quite high," says Musk. There will be changes to the Dragon’s communication system, mostly to allow deep space communication.

Spaceflight is inherently dangerous, and there are no government regulations in place specifically to keep people safe during commercial space travel. In 2004, Congress passed the Commercial Space Launch Amendments Act, which created a "learning period" without regulations for the private sector. Though it was set to expire in 2012, it has been extended through 2023. Up until now, though, the vast majority of commercial spacecraft have been uncrewed. The FAA is concerned about the spacecraft that will carry people, like this one, and the agency has expressed interest in regulating commercial spaceflight in the future.

the target of 2018 should perhaps be taken with a grain of salt

However, the Moon mission’s target date of 2018 should perhaps be taken with a grain of salt. SpaceX may be aiming to fly people on the Crew Dragon for the first time next year, but a recent report from the Government Accountability Office suggested that the company’s vehicles may not be certified until 2019. Musk has tweeted that, despite the report, SpaceX will be ready.

And SpaceX has never been a company to meet its initial deadlines. The company originally promised to begin ferrying astronauts to the ISS by 2017 for the Commercial Crew Program. That date is clearly no longer on the table. Also, in 2011, Musk told The Wall Street Journal that his best-case scenario was to put people on Mars by 2021 (his worst-case scenario was between 2026 and 2031). Last year, he said he was planning to put people on Mars as early as 2024.

However, Musk is confident that people will fly on the Crew Dragon in 2018. "Next year is going to be the big year for carrying people," says Musk. "This should be a really exciting mission that hopefully gets the world really excited about sending people into deep space again."

Update 7:10PM ET, 2/27: Updated to include a statement from NASA.

Correction: A previous version of this article stated the flight is supposed to take place in the second quarter of 2018. It is slated to occur in the fourth quarter, and the article has been updated.