Just in case you were under any illusions about the age of the International Space Station, Monday marked the 25th anniversary of the launch of the Zarya module. This Russian-built power and propulsion module formed the cornerstone of the space station, and the first residents arrived two years later.

In other words, some hardware on the space station has now been in the harsh environment of outer space for a quarter of a century. Questions about how long it can last are, increasingly, more than theoretical.

NASA has been grappling with how to move on from the International Space Station for some time. There is a general sense that, given that we've had humans living in low-Earth orbit for more than two decades, it would be good to keep that streak going.

The plan that NASA has settled on is continuing to fly the International Space Station—if it is possible given the aging nature of the hardware and at-times tenuous relationship with Russia—through 2030. After that NASA would like to see one or more private companies begin operating facilities in low-Earth orbit. The agency would then lease time on those commercially operated stations, sharing them with astronauts from other nations, as well as space tourists.

The problem is that it now appears entirely possible that no private facilities will yet be flying in orbit by 2030, leading to the dreaded "g" word—in NASA parlance, a gap in capabilities.

To gap or not to gap

After the final Apollo crewed flight in 1975, the US space agency had no capability to fly astronauts into space until the advent of the Space Shuttle in 1981. This six-year gap in human spaceflight was painful for the space agency. It repeated the process in 2011, when the Space Shuttle retired and NASA had to wait nearly nine years for a replacement, in the form of SpaceX's Crew Dragon.

Both of these gaps were caused by a combination of poor planning, inadequate funding, and over-optimistic schedules. Fortunately, it is difficult to imagine NASA facing a gap in human spaceflight capability any time soon. Not only does the agency have the Dragon spacecraft, but also, Boeing's Starliner vehicle should soon start flying. NASA also has its own Orion deep space vehicle. Looking further down the line, SpaceX has the larger Starship spacecraft coming, Sierra Space intends to eventually add crew to Dream Chaser, and Blue Origin is also planning a crewed spacecraft. As El Guapo says in Three Amigos!, NASA will soon have a plethora of crew vehicles.

The larger problem now is where they will go.

NASA has been planning for a transition to "commercial LEO destinations," known as CLDs, for about half a decade. It has development contracts with Axiom Space, Blue Origin, and Voyager Space for three different concepts and is working with other companies, including SpaceX and Vast Space, on different plans. The agency expects to award large "services" contracts to one or more companies in 2026 to support the development of private stations.

The real question is whether these options will be ready four years later. Space stations are hard. It took NASA and half a dozen other space agencies around the world a decade to plan, build, and launch the first elements of the International Space Station. These companies are expected to do this faster and with far less money.

Maybe a gap is OK

On Monday, during a meeting of the NASA Advisory Council’s Human Exploration and Operations Committee, a NASA official said he does not want to see a gap in low-Earth orbit. But Phil McAlister, director of the Commercial Spaceflight Division at NASA Headquarters that oversees the CLD program, said he could accept one if the result is a long-term solution.

"That would be bad, and I don't want a gap," McAlister said. "But if the CLDs are not ready, we might have one. Personally, I don't think that would be the end of the world. It would not be unrecoverable, especially if it's relatively short-term. It might impact some research somewhat, but we could leverage Crew Dragon and Starliner to lessen the impact of a gap."

McAlister said the two spacecraft could be provisioned to allow a two-person crew to remain in space for up to 10 days to complete necessary research.

One reason a gap may be inevitable is funding. McAlister noted the likelihood of federal budget cuts in coming cycles as the US government reins in spending. "With all the budget challenges we have ahead, you know, something has got to give," he said.

The US Congress was already somewhat reluctant to fully fund commercial space stations, and it seems not unreasonable that less funding for commercial space stations will slow their development.

Although McAlister did not address it Monday, some commercial space station companies have also raised concerns about the specter of an extension for the International Space Station. If NASA or Congress were to push for an extension of the aging facility beyond 2030, that would likely impair their ability to raise private capital for commercial replacements.