These stations have re-entered the atmosphere and disintegrated.
The Soviet Union ran two programs simultaneously in the 1970s, both of which were called Salyut publicly. The Long Duration Orbital Station (DOS) program was intended for scientific research into spaceflight. The Almaz program was a secret military program that tested space reconnaissance. <span class="wikitable" style="background:#fdd; width:3em; padding:.5ex"> <sup></sup> </span> = Never crewed
These stations are prototypes; they only exist as testing platforms and were never intended to be crewed. OPS 0855 was part of a cancelled Manned Orbiting Laboratory project by the United States, while the Genesis stations were launched privately. The Genesis stations were "retired" when their avionics systems stopped working after two and a half years, yet they remained in orbit as derelict spacecraft as their orbits gradually degraded over the next 18 years. Both Genesis stations re-entered the atmosphere and were destroyed two months apart in mid-2025.
As of , two stations are orbiting Earth with life support system in place and fully operational.
These space stations have been announced by their host entity and are currently in planning, development or production. The launch date listed here may change as more information becomes available.
Most of these stations were canceled due to financial difficulties, or merged into other projects.