The International Space Station retires soon. NASA won't run its future replacement.

Since its first modules launched at the end of 1998, the International Space Station has been orbiting 250 miles above Earth. But at the end of 2030, NASA plans to crash the ISS into the ocean after it is replaced with a new space station, a reminder that nothing within Earth's orbit can stay in space forever.

NASA is collaborating on developing a space station owned, built, and operated by a private company — either Axiom Space, Voyager Space, or Blue Origin. NASA is giving each company hundreds of millions of dollars in funding and sharing their expertise with them.

Eventually, they will select one company to officially partner with and have them replace the ISS. NASA says this will help them focus on deep space exploration, which they consider a much more difficult task.

But any company that is able to develop their own space station, get approval from the federal government and launch it into space will be able to pursue their own deep space missions – even without the approval of NASA.

Phil McCalister, director of the Commercial Space Division of NASA, told NPR's Morning Edition that NASA does not want to own in perpetuity everything in low-Earth orbit – which is up to 1,200 miles above Earth's surface.

"We want to turn those things over to other organizations that could potentially do it more cost-effectively, and then focus our research and activities on deep space exploration," said McCalister.

McCalister says the ISS could stay in space longer, but it's much more cost-effective for NASA to acquire a brand new station with new technology. NASA would then transition to purchasing services from commercial entities as opposed to the government building a next-generation commercial space station.

How space stations of the past inform the future

The ISS was designed in the 80s, so the technology when it was first built was very different from what is available today.

"I kind of see this as like an automobile. When we bought that automobile in 1999, it was state of the art. And it has been great. And it serves us well and continues to be safe. But it's getting older. It's getting harder to find spare parts. The maintenance for that is becoming a larger issue," McCalister said.

A new, private space station will have a lot of similarities and some differences from the current ISS.

Robyn Gatens, director of the International Space Station, says that despite it aging, not all the technology on the ISS is out of date.

"We've been evolving the technology on the International Space Station since it was first built. So some of these technologies will carry over to these private space stations," said Gatens. "We've upgraded the batteries, we've upgraded and added solar arrays that roll out and are flexible, we've been upgrading our life support systems."

Paulo Lozano is the director of the Space Propulsion Laboratory at MIT and an aerospace engineer. He said, "NASA has already changed the solar panels at least once and switched them from these very large arrays that produce relatively little power, to these smaller arrays that produce much more power. All the computer power at the beginning is nothing compared to what can be done today."

Gatens says the structure of the space station – which is the size of a football field – is what can't be upgraded and replaced. And something of that size is costly for NASA to maintain.

"The big structure, even though it's doing very well, has a finite lifetime. It won't last forever. It is affected by the environment that it's in. And every time we dock a vehicle and undock a vehicle, the thermal environment puts stresses and loads on that primary structure that will eventually make it wear out," said Gatens.

Gatens says we can expect a new space station to be designed a little more efficiently and right sized for the amount of research that NASA and its partners are going to want to do in low-Earth orbit.

What astronauts want in new stations

The structure of the ship is also extremely important to the people who work there.

The ISS carries scientists who perform research that can only be done in the weak gravity of space, like medical research. In space, cells age more quickly and conditions progress more rapidly, helping researchers understand the progression of things like heart disease or cancer more quickly.

Researchers on the ISS also work to understand what happens to the human body when it's exposed to microgravity. This research is aimed at helping develop ways to counteract the negative effects of being in space and let astronauts stay there longer – something essential to getting a human on Mars.

Gatens says a new space station will have updated research facilities.

"I'm looking forward to seeing very modern laboratory equipment on these space stations. We say the International Space Station has a lot of capability, but it's more like a test kitchen. I'm looking forward to seeing the future commercial space stations take these laboratory capabilities and really develop them into state-of-the-art space laboratories," said Gatens.

On top of having modern research facilities, new space stations will likely be designed to provide a cleaner environment for researchers.

"If you see pictures of the station, you'll think 'how can they work there?' It looks cluttered, it looks messy," Astronaut Peggy Whitson told NPR. She's spent more time in space than any other woman and is the first woman to command the ISS. Whitson is now Director of Human Spaceflight and an astronaut at Axiom Space, one of the companies funded by NASA to develop a space station.

Whitson said the reason there are cables all over the place is because the structure of the station wasn't designed for some of the systems it has now. She thinks having a method for making a station even more adaptable to new technology will be important in terms of user experience.

Whitson doesn't know what technology will be available five years from now. But she said Axiom Space will want to take advantage of whatever they can get their hands on, ideally without wires everywhere.

"I would like all that cabling and networking to be behind the panels so that it's easier for folks to move around in space," Whitson said. "Having and building in that adaptability is one of the most critical parts, I think, of building a station for low-Earth orbit."

Paulo Lozano says many of the electronic components on the ISS are bulky. But now that electronics are smaller, she expects the interior of future stations might be a bit different.

At the current ISS, there is one small inflatable module. That structure flies up, collapsed, and then expands as it gets filled with air once it's attached to the primary structure of the station — with it literally blowing up kind of like a balloon. Gatens says they are looking at multiple elements of a new space station being inflatable.

Whitson told NPR that on the space station Axiom Space is developing, they will have windows in the crew quarters and a huge cupola, what she describes as an astronaut's window to the world. On the ISS, they have a cupola you can pop your head and shoulders into and see 360-degree views of space and look down at the Earth.

On the proposed Axiom space station, Whitson said the cupola is so large that astronauts will be able to float their whole body in there and have it be an experience of basically almost flying in space.

Why commercialize low-Earth orbit?

NASA hopes that by handing responsibility of an ISS replacement over to private companies, it will allow the agency to develop technology more quickly and focus on their next goal of putting a station beyond low-Earth orbit for the first time. Current proposed low-Earth orbit stations include the Lunar Gateway, which is NASA's planned space station on the moon.

"What the space stations of today are doing is just paving the way for humans to actually explore deeper into space, which is going to be a significantly harder challenge to accomplish. The space stations of today are essential stepping stones towards that goal," said Lozano.

Gatens says one piece of technology that is being developed at Blue Origin is a big rotating space station that, when finished, would have artificial gravity.

For long trips in space, the lack of gravity is a main issue for the human body, causing bone-loss and other health issues. "If you could recreate that in space, that will be very beneficial," Gatens said.

Lozano says that a space station beyond low-Earth orbit would need new technology that is radically different from what's been used in the ISS. And both NASA and Lozano don't think it is possible to venture deeper into space, and eventually get a human on Mars, with U.S. government funding alone.

"I don't think we're very far away in terms of technology development. I think we're a little bit far away in terms of investment, because space technology is quite expensive and sometimes a single nation cannot really make it work by itself. So you need international cooperation." Lozano said.