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.