A cryonic freezer unit, sometimes called a cryonic suspension chamber, cryotube or sleeper tube, is a device for putting life-forms into cryonic suspension, a state of metabolic hibernation over an extended period.[1]
Although in theory a cryochamber can indefinably preserve a living being, there is always a risk that a mechanical failure can be fatal to the sleeper. Under ideal conditions, it is best that there is always someone attending a cryotube to ensure the safety of the person inside, or failing that a redundant automated system that will trigger the revival process of there is a problem.[2][1][3]
Pre-interstellar travel civilizations have been known to use cryotubes to suspend crews over long duration flights, where at relativistic speeds it can take decades or even centuries to reach even a nearby star system. Earth Sleeper Ships were so equipped, though with the acquisition of hyperspace capability following first contact with the Centauri, the units quickly became obsolete. A few units were retained and later put on display at the Air and Space Museum.[2] Newer models were still used by the Earth Alliance, mostly to transport terminally ill patients to facilities better equipped to deal with their condition.[1] The Psi Corps were known to use sleeper tubes to transport blips.[4]
The longest known stay in a cryotube was the inhabitants of an otherwise deserted planet, which in 2267 was over 1000 years and counting, for several billion people.[3] Other long duration freezes include Anla'Shok Marcus Cole and Mariah Cirrus. Cole was frozen in 2261 following a total metabolic shut-down and successfully revived almost 300 years later in 2560; while Cirrus was frozen for a deep space exploration mission in the 2240s and revived over a century later in 2259.[5]