NASA plans to allow private citizens to fly to the International Space Station and wants to open the orbiting laboratory to more commercial interests, including filming advertisements, the agency announced Friday.

While NASA touted the plan as a way to help fund its ambitious plan to return astronauts to the moon by 2024 while trying to build a sustainable economy in space, it’s unclear how much the agency stands to make under the new policy. Private contractors would keep an estimated $50 million per seat that citizens are expected to pay for the flights.

NASA’s announcement is a significant change for the agency, which has had a long-standing prohibition against allowing tourists on the station. Russia, however, has allowed several private astronauts on the station.

Under the NASA plan, as many as two private citizens per year could fly to the station and stay for up to 30 days with the first mission coming as early as next year.

Jeff DeWit, NASA’s chief financial officer, estimated the cost per trip would be about $50 million a seat. But the cost and arrangements would be left to SpaceX and Boeing, the two companies NASA has hired to fly crews to the station. They would keep that money and also have to make sure that private astronauts “meet NASA’s medical standards and the training and certification procedures” for crew members.

While on board the station, NASA would charge people for food, storage and communication, a cost that would come to about $35,000 a night.

“But it won’t come with any Hilton or Marriott points,” DeWit said.

In addition, NASA would charge companies as much as $18,000 per kilogram for a round trip to and from the station. It also would charge for astronauts’ time: $17,500 an hour.

Still, that is not likely to make a dent in the massive costs required to get people to the surface of the moon.

“This is smart policy move by NASA in that it engages a broader range of industry and increases visibility for space and the space station,” said Carissa Christensen, the CEO of Bryce Space and technology, a consulting firm. “That said the revenues generated from tourism and filming are likely to yield more good public relations than financial returns.”

Gwynne Shotwell, president and COO of SpaceX, said in a statement that the company “was founded with the goal of helping humanity become a spacefaring civilization. We are looking forward to working with NASA and other commercial partners as we open up low Earth orbit to an exciting new chapter of human exploration.”

Space Adventures, a Virginia company that has helped several private citizens get to the station on Russian rockets, has a contract with Boeing to help sell seats aboard its spacecraft. A spokesman said the company has not yet determined a price.

Right now, commercial activity on the station is largely limited to science experiments.

But under the new policy, NASA would allow businesses to pursue profits by allowing them a range of pursuits, including marketing and advertising.

“We have no idea what kinds of creativity and literally out of the world ideas can come from private industry,” Bill Gerstenmaier, NASA’s head of human exploration, said during a news conference.

The goal is to help the agency generate additional revenue to help offset some of the costs of a moon mission, while also helping American industry open up new markets.

“It’s hard to project what’s going to come back,” DeWit said.

“What we’re hearing is a lot of excitement in the commercial sector for this. But it’s hard to get accurate projections until six or 12 months from now, when we see what actually comes back in and who partners with us.”

Gerstenmaier acknowledged that the policy changes were a risky bet that may not produce results immediately.

“Economic market development takes a long time, transitions take a long time,” he said. “This is the very beginning.”

The announcement comes as the agency is trying to return humans to the moon by 2024, a mission that officials said would require significant additional funding.

NASA has already amended its budget request for next year to ask for an additional $1.6 billion, and has said that it would need significantly more money in the years to come to have any chance at pulling off such an ambitious plan.

There is a long history of businesses going to space to market their products. In 1999, Pizza Hut paid to paint its logo on a Russian rocket. In the mid-1990s, an Israeli milk company filmed a commercial on the space station Mir, and a pair of Russian cosmonauts even appeared on QVC to sell a pen able to write in a weightless environment.

NASA Administrator Jim Bridenstine has said he wanted to raise the profile of the agency’s astronauts by allowing them to appear in commercials and on cereal boxes. But that was met by pushback from critics who said it would violate government ethics regulations that prohibit government officials, even astronauts, from using public office for private gain.

In the proposal unveiled Friday, NASA astronauts’ participation in such activity would be limited to commercial activities “with ties to microgravity, NASA’s mission or sustaining a low-Earth-orbit economy.” They would be prohibited from appearing in advertisements, for example, and NASA said it would continue its policy of not endorsing any particular brand.

Traditionally, NASA has steadfastly stayed away from that — even going so far as to call the M&Ms astronauts gobble in space “candy-coated chocolates” out of fear of appearing to favor one brand of candy.

Private astronauts, however, would be free to conduct a wider range of commercial activity as long as it meets a list of requirements, such as not endangering the crew and ensuring it doesn’t reflect unfavorably on NASA.

NASA’s new directive would also allow a private module to be attached to the station to be used for commercial activities.

“NASA is entering an era of finical exploration where we need to discover what the different commercial activities are that could sustain a presence in low-Earth orbit,” said Mike Gold, the vice president of civil space for Maxar Technologies who also served on a NASA advisory committee.

Richard Garriott, an entrepreneur whose father was a NASA astronaut, traveled to the space station as a private astronaut in 2008 on a Russian rocket. At the time, NASA was so opposed to his trip that it tried to prohibit him from entering the U.S. segment of the space station. “I was basically banned,” he said in a recent interview.

Ultimately, though, it was up to the commander of the space station to make that call and so he was allowed after all.