Imagine: falling asleep and waking up in the neighborhood of another planet. We were all made familiar with the notion of crysleep through Sci-Fi classics, such as 2001: A Space Odyssey, Alien and more recently Interstellar.
Manned missions to distant planets would only be possible if crew could be put into a low-metabolic, deep-sleep state of torpor, otherwise known as a short-term hibernation. If bears can do it, why shouldn’t we? It is not unknown to happen naturally in humans in cases of hypothermia. A form of therapeutic hypothermia has been a recommended method for increasing chances of survival of wounded soldiers since antiquity.
Many mammalian spices are able to put themselves into state of hibernation during prolonged periods of time when food is scarce and life conditions too hard to survive. Scientists have been researching this possibility in humans for years, not only for long-term space voyages, but for more down-to-earth problems, like extending the life of patients with critical trauma, until they could receive the necessary treatment.
Such a solution has been present in theory since the 1960s. Robert Etinger, a physics teacher from Michigan, in his book The Prospect of Immortality, had proposed freezing people who could not otherwise be saved by existing medical treatments till such a technology is available. Since mid-2000s in most major hospitals around the USA there are protocols for inducing a therapeutic hypothermia in certain medical situations, like cardiac arrest, stroke, and traumatic brain or cord spinal cord injury.
DARPA is currently funding couple of research projects which are exploring the possibility of putting people into a state of suspended animation. Cryonic suspension for a specific duration of time would contribute to minimizing mission consumables and amenities, reducing the size of a spaceship and easing the stress the crew would be experiencing during the prolonged flight.
The longest period of time a human has been put into the state of targeted temperature management (therapeutic hypothermia) is 10 days, but most often this time is limited to one week. Problems which may arise from longer periods of suspended animation involve muscle atrophy, bone demineralization, thromboembolism, and other.
Some of those problems could be mitigated by creating torpor habitats equipped with various sensors which would monitor the condition of every individual, electromagnetically stimulate their bodies to avoid muscle atrophy and thrombosis, and manage intravenous feeding known as Total Parenteral Nutrition. Some designs even envision faster-spinning habitats which would induce artificial gravity, thus helping reduce muscle degeneration and bone loss.
Most of the studies propose that one member of the crew should always be awake in order to monitor crucial health parameters of those in stasis and control the ship to avoid possible mishaps with a rogue AI, as seen in 2001: A Space Odyssey.
It is interesting that those who have undergone therapeutic hibernation reported sensations of infinite tranquility and altered state of mind which experiences time in a subtly distorted fashion.
Advances in therapeutic hypothermia are proving us that keeping a person in a state of torpor, without serious side effects, is possible for limited periods of time. The next challenge scientists need to tackle is how to prevent tissue damage from longer periods of low blood flow, caused by low blood temperature.
Although the technology of inducing, say, a 30-day cryosleep in humans is still far-fetched, it would be so beneficial for many areas of future human activity, some of which we are yet not aware of, and is certainly worthy of scientific effort.