(covers information from several alternate timelines)
In an alternate timeline in 2375, the starship USS Voyager crashed on a class L planet in the Takara sector, after attempting to use quantum slipstream drive to return to the Alpha Quadrant, due to a phase variance in the slipstream which caused Voyager to be thrown into normal space. The crew attempted an emergency landing on the planet, but the ship was too heavily damaged, and all hands were killed on impact, except for Commander Chakotay and Ensign Kim, who were piloting the Delta Flyer ahead of Voyager.
Fifteen years later, in an attempt to alter history, Chakotay and Kim stole a salvaged Borg temporal transmitter and tracked down Voyager on the planet, salvaging The Doctor's program and mobile emitter and Seven of Nine's corpse. Using The Doctor's expertise to dissect and analyze Seven's interplexing beacon to determine its unique frequency, they used the temporal transmitter to send a new set of phase corrections to Seven. These phase corrections caused the slipstream to disperse and return Voyager safely to normal space before the crash. This alteration to the timeline constituted a temporal inversion, the effects of which had to be repaired by Captain Braxton, a Starfleet officer from the 29th century. (VOY: "Timeless", "Relativity")