A phenomenon in which all matter aboard a ship is duplicated while its antimatter is not, leaving two Voyagers sharing one failing engine in the episode Deadlock.
A spatial scission is a split in space that copies every particle of matter passing through it. Antimatter is not copied, so the two resulting ships occupy the same point, slightly out of phase, and draw on a single supply of fuel.
In the Voyager episode Deadlock in 2372, the ship enters a plasma drift to avoid Vidiian vessels and is divided in this way. One Voyager fires proton bursts to stop the drain on its antimatter, unaware that each burst is tearing the other apart. Aboard the damaged ship Harry Kim is lost through a hull breach and Samantha Wildman's newborn daughter dies.
The two Janeways make contact across a rift, but attempts to merge the ships fail. When the Vidiians board the intact Voyager to harvest organs, its Janeway destroys the ship, first sending her Harry Kim and the baby Naomi across to take the places of those lost.