A renewed era of space exploration is upon us, and many exciting missions will be headed to space in the coming years. These include crewed missions to the Moon and the creation of permanent bases there. Beyond the Earth-Moon system, there are multiple proposals for crewed missions to Mars and beyond. This presents significant challenges since a one-way transit to Mars can take six to nine months. Even with new propulsion technologies like nuclear rockets, it could still take more than three months to get to Mars.
In addition to the physical and mental stresses imposed on the astronauts by the duration and long-term exposure to microgravity and radiation, there are also the logistical challenges these types of missions will impose (i.e., massive spacecraft, lots of supplies, and significant expense). Looking for alternatives, the European Space Agency (ESA) is investigating hibernation technology that would allow their astronauts to sleep for much of the voyage and arrive at Mars ready to explore.
This researcher was the subject of a recent study led by Alexander Choukér, a professor of Medicine at the Hospital of the Ludwig-Maximilians-University (LMU), and Thu Jennifer Ngo-Anh – a payload coordinator with the ESA’s Directorate of Human and Robotic Exploration Programs. The paper that describes their findings was recently published in the journal Neuroscience & Biobehavioral Reviews.
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As they indicated in their study, the main challenges when planning for a mission to Mars involve optimizing the overall mass of the spacecraft and maintaining the crew’s physical and mental health. In terms of supplies alone, this means bringing enough food, water, and other necessities (like medicine) to last at least two years. As Ngo-Anh said in a recent ESA press release:
“We are talking about 30 kg [66 lbs] per astronaut per day, and on top of that we need to consider radiation as well as mental and physiological challenges. Where there is life, there is stress. The strategy would minimize boredom, loneliness, and aggression levels linked to the confinement in a spacecraft.”
This strategy involves inducing a state of torpor in the astronauts, similar to what mammals experience during hibernation. This consists of reducing the metabolic rate of an organism until they enter a period of “suspended animation,” which allows them to preserve energy. In the context of spaceflight, reducing the metabolic rate of a crew en route to Mars by 25% would dramatically reduce the necessary supplies and the size of the habitat involved.
Hibernation & Torpor
The practice of putting people into a state of suspended animation has been carried out in hospitals since the 1980s. By inducing hypothermia in patients reducing their heart rate and metabolism, doctors can perform complex and time-consuming surgeries with a greater chance of success. However, this process is not an active energy reduction method and doesn’t include most of the advantages of torpor.
In nature, animals hibernate to survive through winter when temperatures drop for months and food and water become scarce. During this time, they will reduce their heart rate, breathing, and other vital functions to a fraction of their normal rate, and their body temperature will drop close to that of their surroundings (aka. ambient temperature).
While many species rely on hibernation to survive long periods of scarcity (like tardigrades, frogs, and various species of reptiles), bears are perhaps the best known. They also appear to be the best role model for human hibernation in space since they have a comparable body mass to humans, reduce their body temperature by only a few degrees, and acquire extra body fat before entering this state.
But as medical research has shown, humans also lose more muscle mass and bone density and are at greater risk of heart failure than their ursine kin. As Prof. Choukér explained:
“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.”
The crucial factor appears to be lower testosterone levels in humans since estrogens 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,” Prof. Choukér added.
To accommodate deep-space hibernation technology, engineers could build soft-shell pods with fine-tuned settings aboard future generations of spacecraft. This would consist of a quiet environment with low lighting, high levels of humidity, and low temperatures of less than ten degrees Celsius (50 °F). The astronauts would wear clothing to prevent overheating and wearable sensors to measure their posture, temperature, and heart rate.
Water containers would surround every capsule to provide radiation protection as the astronauts remain in a state of torpor. Meanwhile, artificial intelligence will maintain the ship and wake the crew if an anomaly or emergency. As Alexander explained:
“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. Besides monitoring power consumption and autonomous operations, the computers onboard will maintain optimal performance of the spacecraft until the crew could be woken up.”
These efforts mirror similar studies conducted by NASA, which entered into a partnership with Atlanta-based aerospace company SpaceWorks to investigate the long-term potential of hibernation technology. The initial 24-month study concluded in 2016, with NASA announcing its intent to keep supporting the company’s research. These and other studies on hibernation for deep-space missions could also lead to new applications for patient care on Earth.
As the 21st century unfolds, we could see interplanetary missions that resemble the well-established sci-fi trope – crews awaking from their “cryo chambers” to deal with mission-related problems. Here at home, induced torpor could become a common medical procedure for people with a terminal illness or severe injuries, giving doctors the time they need to come up with treatments.
The applications might even extend to interstellar travel! Given the distances involved and the limits of our propulsion technology, a crewed interstellar mission could take centuries or millennia to reach even the nearest stars! Assuming future generations want to undertake these voyages and don’t have some fancy new propulsion system (or a huge budget), hibernation technology may be the way they’ll get it done!
Further Reading: ESA, Neuroscience & Biobehavioral Reviews