Is human hibernation possible? Going to sleep for long duration spaceflight
A potentially Earth-like planet has been discovered orbiting a star located right next door to the sun. The newly discovered planet, known as Proxima b, orbits the star Proxima Centauri, the closest star to the sun. Proxima Centauri is about 4.22 light-years — or 25 trillion miles (40 trillion kilometers) — from Earth.
Current and near future technology could see us reach speeds of 10-20 percent the speed of light (about 134.12 million mph, or 215.85 million km/h). At that rate, the a ship could reach Proxima Centauri in 20 to 25 years.
That is a long time for a crew be kept mentally and physically healthy and would require an incredible amount of supplies. Even a relatively short mission to Mars of around 3 years would require around 42 tons of consumables to keep the crew healthy.
Some day soon, astronauts packed into rocketing tin cans bound for other planets may be protected from radiation and space sickness by having their metabolisms depressed to a fraction of their typical rate. They’ll hibernate like bears as they hurtle through space for months at a time.
The idea, long promoted by science fiction writers, of being able to induce a state of hibernation, is taken seriously by scientists and has prompted a closer look at how some animals hibernate. Scientists call this phenomenon “torpor-induced hibernation". Once considered outlandish, torpor induction is under serious study for long-duration spaceflight.
In many locations on Earth the availability of food varies with the seasons, typically in winter food is scarce. For some species the food shortage is life threatening in which case there are two choices, migration or hibernation.
Larger animals and birds with diets critically affected by winter shortages tend to migrate to warmer climes but that isn't an option for smaller animals such as rodents and most insects. Their solution to combat food shortage is to hibernate. There are exceptions to this rule, bears are very large animals but they don't migrate, they hibernate, and a tiny North American bird, the Common Poorwill also hibernates.
Though the Arctic ground squirrel hibernates for two-thirds of the year, it experiences only minor bone and muscle loss.
During hibernation the rate of metabolism is substantially depressed for months and the body temperature is lowered. A particularly dramatic example of this is the Arctic ground squirrel. Adult females hibernate from early August to late April and their core body temperature drops from 37 degrees Celsius to minus 2.9 degrees. Their heart rate drops to just one beat per minute.
No scientist understands exactly what triggers its hibernation, although a particular brain and muscle receptor—the A1 adenosine receptor—appears to make the squirrel grow cold and sleepy, only to emerge with minimal bone and muscle loss eight months later.
If low body temperature is included in the definition of hibernation then bears strictly speaking don't hibernate, their core body temperature drops by only about 5 degrees to 32 degrees. During this period of several months, bears have the ability to recycle proteins which prevent their muscles breaking down; they can also recycle urine avoiding the requirement to urinate.
Hibernation is different from sleep, the physiological changes such as metabolism and temperature depression are more profound in hibernation. In an interview on Radio New Zealand, Auckland University researcher, Tony Hickey, pointed out that in hibernation the shut-down extends to mitochondria, the cellular power stations of the body. Hibernating animals have short periods where they must wake up, presumably to reconstitute their neurons and stop their synapses degenerating.
Another state of decreased physiological activity is referred to as torpor which is a less severe form of hibernation related to the time spent in a state of low body temperature. Water shortage has been shown to drive lemurs to a state of torpor.
Today, physicians use moderate hypothermia (roughly 89 degrees) as a staple of care for some newborns in medical distress, such as those born premature or suffering from fetal oxygen deprivation (hypoxia). The babies are treated with cooling caps for 72 hours, which lower their metabolism just enough to reduce tissue oxygen requirements and allow the brain and other vital organs to recover.
Under a research grant with NASA's NIAC program in the Space Technology Mission Directorate (STMD), SpaceWorks is currently maturing technologies to enable human stasis via mild hypothermia. This technology would be used for the transit phases of human exploration missions and significantly reduces system mass and habitat volume requirements.
The proposed medical treatment relies on using techniques similar to the ones surgeons perfected to induce hypothermia. For example, cooling nitrogen gas could be fed to astronauts via nasal cannula, lowering brain and body temperatures to between 89 and 96 degrees—close enough to normal to maintain torpor without overcooling the heart or increasing the risk of other complications. Cooling tends to decrease the body’s ability to clot, Tisherman says. He has also noted that patients who are cooled to mild levels of hypothermia—93 degrees—for 48 hours or more have more infections than uncooled people.
Significant decrease in mission consumables due to inactive crew and reduced metabolic rates
NASA Innovative Advanced Concepts (NIAC) has awarded two innovation grants since 2013, supporting one company’s detailed plans for torpor-enabled Mars transfer habitats. The project leader, SpaceWorks Enterprises.
In 2013 NIAC awarded SpaceWorks a Phase 1 grant of $100,000 to develop a rough torpor-enabled architecture for exploration-class missions—those with four to eight crew members heading to Mars or its moons.
In the SpaceWorks habitat, robotic arms in the module would be programmed to carry out routine chores, manipulate astronaut limbs, and check body sensors, urine evacuation lines, and chemical feeds. Robots would administer electrical stimuli to astronauts’ muscles to maintain tone, along with sedation to prevent a natural shivering response. The astronauts would also receive total parenteral nutrition, in which all nutrients—electrolytes, dextrose, lipids, vitamins, etc.—are administered via liquid through a catheter inserted in the chest or the thigh. SpaceWorks outfitted TPN supplies in the experimental module to last 180 days; should the habitat be required for a prolonged Martian stay, the module would have another 500 days’ worth of nutrition. In all, the SpaceWorks Mars Transfer Habitat reduced total habitat mass, including consumables, to 19.9 tons (low-Earth-orbit weight). By comparison, NASA’s TransHab habitat, with consumables specified in the agency’s Mars Design Reference Architecture 5.0, weighs 41.9 tons. That’s a 52 percent decrease in mass. Compared with the NASA model, SpaceWorks was able to shrink total habitat consumables by 70 percent.
The astronauts wouldn't need to move around, so you could keep them nice and snug in little pods for the journey. And they wouldn't get into fights with each other, after six to nine months of nothing but day after day of spaceflight.
We know that weightlessness has a negative effect on the body, like loss of bone mass and atrophy of muscles. Normally astronauts exercise for hours every day to counteract the negative effects of the reduced gravity. But SpaceWorks suggests a more effective strategy might be to just put the astronauts into a rotating module and let artificial gravity combined with electrical muscle stimulation do the work of maintaining their conditioning.
The crew probably wouldn't all sleep for the entire journey. Instead, they'd sleep in shifts for a few weeks. Taking turns to wake up, check on the status of the spacecraft and crew before returning to their cryosleep caskets.
Bradford’s team moved further. Designing three interconnected habitat modules for a 100-passenger “settlement class” Mars mission—colonists, in other words—the team produced a spacecraft and habitat that departed completely from anything in NASA’s plans. The SpaceWorks settlement-class craft includes two compact, rotating habitat modules, each accommodating 48 passengers in torpor. Rotation at varying speeds would produce artificial gravity to mitigate astronauts’ bone loss.
Yet there are still several hurdles to overcome. Hibernation isn’t simply a matter of turning the knob on your metabolism; it involves a host of other related adaptions. Foremost among these is waste management. Animals that hibernate are able to essentially halt their urination and defecation during hibernation, Drew says, sometimes through a process of re-absorption to preserve nutrients. Unfortunately, humans can’t do this, though there are proposals such as using rectal catheters.
And even if we figure out the poo problem, there are other challenges. Body temperatures below 37 degree Fahrenheit tend to disrupt the human digestive tract and may cause pain. Cold temperatures can also suppress the immune system, making people more vulnerable to infections. It may turn out that humans simply weren’t meant for hibernation.
NASA funded stage 1 of the SpaceWorks proposal, and in July, 2016 NASA moved forward with Phase 2 of the project, which will further investigate this technique for Mars missions, and how it could be used even farther out in the solar system.
If scientists can make it possible for humans to hibernate during spaceflight, it will certainly be a great achievement. The problem is that hibernation is a very complex physiological and biochemical trick acquired by certain species over millions of years of evolution. The nearest planet so far discovered with a reasonable probability of supporting human life is 12 light years from Earth.
Using conventional spacecraft, it would take over 200,000 years to get there. In the absence of finding a way to hibernate astronauts, the only way to travel to planets beyond our solar system will be to find a way to travel much faster, closer say to the speed of light (300,000 kilometres per second) – that would reduce the travel time to just over 12 years but attaining such speeds would need a huge technological leap.
Can we go further, putting people to sleep for decades and maybe even the centuries it would take to travel between the stars?
Right now, the answer is no. We don't have any technology at our disposal that could do this. We know that microbial life can be frozen for hundreds of years. Right now there are parts of Siberia unfreezing after centuries of permafrost, awakening ancient microbes, viruses, plants and even animals. But nothing on the scale of human beings.
When humans freeze, ice crystals form in our cells, rupturing them permanently. There is one line of research that offers some hope: cryogenics. This process replaces the fluids of the human body with an antifreeze agent which doesn't form the same destructive crystals.
Scientists have successfully frozen and then unfrozen 50-milliliters (almost a quarter cup) of tissue without any damage.
In the next few years, we'll probably see this technology expanded to preserving organs for transplant, and eventually entire bodies, and maybe even humans. Then this science fiction idea might actually turn into reality. We'll finally be able to sleep our way between the stars.