Hibernating astronauts could be the best way to save mission costs, reduce
the size of spacecraft by a third and keep crew healthy on their way to
Mars. An ESA-led investigation suggests that human hibernation goes beyond
the realm of science-fiction and may become a game-changing technique for
space travel.
When packing for a return flight to the red planet, space engineers account
for around two years' worth of food and water for the crew.
"We are talking about 30 kg per astronaut per day, and on top of that we
need to consider radiation as well as mental and physiological challenges,"
explains Jennifer Ngo-Anh, ESA research and payload coordinator of Human and
Robotic Exploration and one of the authors of the paper that links biology
to engineering.
Torpor during hibernation is an induced state that reduces the metabolic
rate of an organism. This 'suspended animation' is a common mechanism in
animals who wish to preserve energy.
Reducing the metabolic rate of a crew en route to Mars down to 25% of the
normal state would dramatically cut down the amount of supplies and habitat
size, making long-duration exploration more feasible.
"Where there is life, there is stress" reminds Jennifer. "The strategy would
minimize boredom, loneliness and aggression levels linked to the confinement
in a spacecraft," she adds.
Mimicking therapeutic torpor, the idea of putting human into a state of
hibernation, has been around in hospitals since the 1980s—doctors can induce
hypothermia to reduce metabolism during long and complex surgeries. However,
it is not an active reduction of energy. Studies on hibernation to visit
other planets could offer new potential applications for patient care on
Earth.
Don't wake the bear
Animals hibernate to survive periods of cold and food or water scarcity,
reducing their heart rate, breathing and other vital functions to a fraction
of their normal life, while body temperature lowers close to ambient
temperature. Tardigrades, frogs and reptiles are very good at it.
Bears seem to be the best role model for human hibernation in space. They
have similar body mass to us and reduce their body temperature only by a few
degrees—a limit considered safe for humans. Like bears, astronauts should
acquire extra body fat before falling into a slumber.
During hibernation, brown and black bears retreat into their dens and
experience six months of fasting and immobilization. If a person spends six
months in bed, there is a major loss of muscle, bone strength and more risk
of heart failure.
"However, research shows that bears exit their den healthily in spring with
only marginal loss of muscle mass. It only takes them about 20 days to be
back to normal. This teaches us that hibernation prevents disuse atrophy of
muscle and bone, and protects against tissue damage," explains Alexander
Choukér, professor of Medicine at the Ludwig Maximilians University in
Munich, Germany.
Lower testosterone levels seem to aid long hibernation in mammals, estrogens
in humans strongly regulate energy metabolism.
"The very specific and different balance of hormones in females or males and
their role in regulating metabolism suggest that women could be preferred
candidates," adds Alexander.
Enjoy your pod
Scientists suggest engineers build soft-shell pods with fine-tuned settings
for sweet hibernation: a quiet environment with low lights, low
temperature—less than 10 °C—and high humidity.
The astronauts would move very little, but would not be restrained, and wear
clothing that avoids overheating. Wearable sensors would measure their
posture, temperature and heart rate.
Every capsule should be surrounded by water containers that act as shield
against radiation. "Hibernation will actually help protect people from the
harmful effects of radiation during deep space travel. Away from Earth's
magnetic field, damage caused by high-energy particles can result in cell
death, radiation sickness or cancer," says Alexander.
With the crew at rest for long periods, artificial intelligence will come
into play during anomalies and emergencies.
"Besides monitoring power consumption and autonomous operations, the
computers onboard will maintain optimal performance of the spacecraft until
the crew could be woken up," explains Alexander.
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Space & Astrophysics