A Federation colony ship launched in 2274 for Septimus Minor, which went off course through a guidance failure and landed its passengers on Tau Cygni V.
The SS Artemis is a colony transport whose story is told in the episode The Ensigns of Command. It left for Septimus Minor in 2274, but its guidance system failed and it was never heard from again.
The ship in fact reached Tau Cygni V, a world bathed in hyperonic radiation and ceded by treaty to the Sheliak. Many colonists died before the survivors adapted, and over ninety years they built a community of more than fifteen thousand.
In 2366 the Sheliak find the settlement and demand its removal. Data, the only officer who can withstand the radiation, is sent down to persuade the descendants of the Artemis colonists to leave the home their ancestors won at such cost.