Comment It's been up far longer than intended. (Score 1) 18
Zvezda was originally built in the mid 1980s by the USSR to be the core of Mir-2 then mothballed until it was repurposed and modified for the ISS. I can't find a good source for the design service life of Mir-2 was, but Space.com says Mir had an intended lifespan of 5 years and Astronautix says Mir-2 also had an intended service life of 5 years.
Mir was in orbit for 15 years, three times its design life and by the mid 1990s the cooling and Elektron oxygen generating systems were starting to break down . Next month Zvezda will have been in orbit for 25 years, probably five times its design life.
I find it amazing that it is still functioning as well as it is, but ???