Sleeper ship

A sleeper ship is a hypothetical type of manned spaceship in which most or all of the crew spends the journey in some form of hibernation or suspended animation. The only known technology that allows for long-term suspended animation of humans is the freezing of early-stage human embryos through embryo cryopreservation, which is behind the concept of embryo space colonization.

The most common role of sleeper ships in fiction is for interstellar or intergalactic travel, usually at sub-light speed. Travel times for such journeys could reach into the hundreds or thousands of years making some form of life extension, such as suspended animation, necessary for the original crew to live to see their destination. Suspended animation is also required on ships which cannot be used as generation ships.

Freezing the astronauts would probably involve whole body vitrification and would, most likely, be frozen at 145 Kelvin to reduce the risk of fracturing.

Suspended animation can also be useful to reduce the consumption of life support system resources by crew members who are not needed during the trip, or by an author as a plot device, and for this reason sleeper ships sometimes also make an appearance in the context of purely interplanetary travel.