Why selling off the International Space Station would be a tricky mission for the U.S.

The International Space Station is considered a shining example of the uniting power of science.Since the late1980s,countries that were once at war with each other have worked together to further scientific research applied both on Earth and in space.

But in its proposed 2019 budget released last month, theUnited States,thebiggest financial backer ofthe ISS,indicated it will stopfunding the station in 2025,and instead look at transitioning theorbiting laboratory to commercial enterprises.

The headlines that followed seemed to suggest the U.S. plansto sell the station and moonwalk away. But experts say it's not quite that simple.

For starters, the U.S. doesn't have the authority to go ahead and privatize the entire space station.The U.S. could essentially rent out its share of the station, says Ram Jakhu, who teaches international space law at McGillUniversity in Montreal.

"The U.S. may use its part for private purposes so the whole idea of saying privatizing [the station] is wrong."

There's already significant commercial involvement in the ISS.Boeing, for example,runs technological components in the U.S. module. The European Space Agency (ESA)has an agreement with Airbus to allow the companyto install a platform where companies could buy space to conduct experiments or install instruments of their own.

The U.S. can't simply sell itsshare because Russia, Japan, Europe and Canada are all its partners. In order for the U.S. to do so, all the partners would have to agree to terms under the International Space Station Intergovernmental Agreement, often referred to as the IGA.

The same goes if the U.S. wanted to sell its share to another country.

It wouldn't be easy, Jakhu says.

"There are legal constraints, which are much more serious. Then, of course, there arethe financial constraints."

Money, money, money

If a single company was looking to take over the station, it would need verydeep pockets. The U.S., which foots most of the bill, contributes up to $4 billion a year.

David Parker, director ofESA'shuman and robotic exploration program, says theISSnewsin the Trump administration's budgetwas very carefully worded. It says NASA would no longer directly fund the space station after 2025; not that it's planning to stop participating in the space station altogether.

"It's more of an indication of a process to transition to commercializing the space station," he says. "And that's not the same as saying it's commercial."

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The U.S.could continue to fund research on theISS, but paya company or companies to conduct the experiments, he says.

"How that's going to workexactly is an open point at the moment."

He says all the space agencies are thinking about what comes after the ISS.

The U.S., Canada, Japan andESAplan to build the Deep Space Gateway, a much smaller space station that will orbit near the moon.

"The partners, all space agencies, will need a platform in low-Earth orbit after the ISS reaches its end of life," says Gilles Leclerc, director general of space exploration with the Canadian Space Agency.

ESA's Parker sees this as a transition from a "monolithic project the ISS to a more diverse set of projects in low-Earthorbit and in deep space."

And that, he believes is a step in the right direction.

After more than 50 years of space stations and space access limited to governments, a new type of space age what many are referring to as "new space" is in full swing.

So, come 2025,NASA will likely still be involved in a space station in low-Earth orbit. It's also likely there will be some partnership with commercial companies, just as NASA has contracted Boeing andSpaceXto build the next launch vehicles to head to theISS.

"I don't see what's happening today is unexpected," Jakhu says.

"There is a democratization of space going on that you could never imagine 10 years ago."