STS-88 (Unity Docking)

STS-88 turned two separately launched pieces of hardware into the beginning of an actual space station. Two weeks after the Russian-built Zarya module reached orbit, Space Shuttle Endeavour launched carrying Unity, the first American-built ISS component, along with a crew tasked with physically joining the two together for the first time.

Commanded by Robert Cabana, the six-person crew included Russian cosmonaut Sergei Krikalev, whose presence symbolized the genuinely international character of the new station from its very first assembly flight. Endeavour rendezvoused with Zarya in orbit, and the crew used the Shuttle's robotic arm to grapple the Russian module and carefully mate it to Unity, already secured in the payload bay, connecting an American module to a Russian one in orbit for the first time.

The mission required three spacewalks to complete the necessary electrical and mechanical connections between the two modules, work that established the physical and technical foundation the rest of the station would be built upon over the following decade. Astronauts also entered the joined modules for the first time, becoming the first humans to set foot inside what would eventually become the International Space Station.

Endeavour undocked and returned to Kennedy Space Center on December 15, leaving behind a two-module station, uncrewed but fully assembled and functional, awaiting the additional pieces and eventually the permanent crew that would arrive over the following two years. STS-88 proved that the ambitious, multi-year construction plan behind the ISS could actually work in practice, one careful assembly flight at a time.

STS-88 proved that the International Space Station's ambitious construction plan could work in practice, successfully joining hardware built on opposite sides of the world into a single functioning structure in orbit.

The mission established assembly and spacewalk procedures that NASA and its international partners repeated and refined across dozens of subsequent Shuttle flights over the following decade, eventually building a station larger than a football field.

Sergei Krikalev's presence aboard this first assembly flight, and his later role as part of Expedition 1's first resident crew, made him a defining figure connecting the earliest days of the ISS to its permanent, continuously crewed future.