A cryonic freezer unit, sometimes called a cryonic suspension chamber, cryotube or sleeper tube,
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. Pre-interstellar travel civilisations 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. Newer models were still used by the Earth Alliance, mostly to transport terminally ill patients to facilities better equipped to deal with their condition. The Psi Corps were known to use sleeper tubes to transport blips.
The longest known stay in a cryotube was the inhabitants of an otherwise deserted plnet, which in 2267 was over 1000 years and counting, for several billion people. 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.