Space, Physics, and Math

Not just a dream

Space hibernation could make long-haul space travel cheaper and safer

December 14, 2016
Long a staple of science fiction, space hibernation could become a reality as early as our first mission to Mars. [Image credit: John Bradford/NASA | CC0 1.0]

For decades, space hibernation has been a featured solution for long-term space travel in science fiction. And now, as visiting and even colonizing Mars looks increasingly realistic, scientists are getting close to testing the real-life feasibility of space hibernation.

But humans aren’t bears or bats. We have not evolved to hibernate. There are challenges and real risks involved in inducing a hibernation-like state in astronauts. One of them will be on the big screen in December, when the movie “Passengers” hits theaters. In the movie, two space travelers played by Chris Pratt and Jennifer Lawrence wake up 90 years too early on an interstellar journey.

How realistic are these sci-fi movies, though? Here’s everything you need to know about the science – not fiction – of induced space hibernation:

What is space hibernation, anyway?

Space hibernation, explains Mayo Clinic anesthesiologist Matthew Kumar, is an induced state of deep sleep similar to animal hibernation. An astronaut’s body temperature would be very low – probably about 86-90 degrees Fahrenheit (30-32 degrees Celsius). That doesn’t sound much lower than the body’s resting temperature of 37 degrees Celsius, but for every one degree drop, the body’s metabolic rate drops by seven to eight percent. So at a low body temperature, an astronaut’s metabolic rate — the rate at which her body consumes calories — would be much lower than normal, too.

One way to induce this state would be to deliver a spray of cool mist into the astronaut’s nasal cavity, directly underneath the base of her skull. As the mist evaporates, it would rapidly cool down that area to near 36 degrees Fahrenheit (2 degrees Celsius). As blood circulates through the region, it would chill the rest of the body. European researchers are testing such nasal cooling system in clinical studies.

This induced state isn’t the same thing as animal hibernation, since animals can stay cold and stop eating for months, suppressing their metabolic rate up to 80 percent. Humans could almost certainly never do that. But hibernation is also a handy term for the kind of forced sleep astronauts could enter on space voyages, so we’ll use it here.

Why is hibernation a good strategy for long-haul space travel?

An astronaut whose metabolic rate has been decreased would need a lot less food, water and oxygen, and would produce less waste. These changes would significantly cut the weight of spacecraft payload, which is crucial for an interplanetary mission. Heavy spacecraft can be astronomically expensive. No estimate for a Mars mission is available yet, but successful launches in the past suggest that every extra pound of payload would add over $40,000 to the cost of the mission, according to Guy Webster, a spokesman at NASA’s Jet Propulsion Laboratory in California.

Another advantage to hibernation would be a reduced risk of boredom or mental illness. “As you get away from Earth [to Mars], you won’t be able to look at Earth and take pictures,” says former NASA astronaut Leroy Chiao, as he did on the International Space Station. “So going on a trip to Mars would be a very different environment.”

Hibernation, he says, makes sense “to conserve resources to make a smaller vehicle and to alleviate boredom.”

Alleviating boredom also means minimizing the need for psychological stimulation. Even for a 12-hour flight from Minneapolis to London, Kumar says, the airline has to “show you a movie so that you won’t get bored and start picking a fight with your neighbor.” Just like sleeping on a transcontinental flight, hibernating in long-term space travel would definitely have psychological benefits.

Any other reasons?

Yes! There’s another very important reason: In a hibernation-like state, astronauts may become more resistant to space radiation.

“Basically, if you are an astronaut, you can be in space for about a year, and then you contract so much radiation that it becomes damaging to your DNA,” says Rob Henning, an expert in animal hibernation at the University of Groningen in the Netherlands. The one-year limit is for current low Earth orbit space missions like the International Space Station. Astronauts receive less radiation in this region, and are therefore safer, than in deep space.

Beyond the low Earth orbit, astronauts would lose the protection of the Earth’s magnetic field to block cosmic rays. Travelers to Mars would get much more space radiation overall, including more dangerous charged particle radiation.

Why might hibernation help protect against radiation?

Research shows hibernating animals live longer than non-hibernating ones when exposed to radiation like X-rays. Researchers aren’t certain why, but the leading theory is that chilling a body slows down cell division, giving the body’s natural cellular repair mechanisms more time to fix any radiation-induced damage, according to Marco Durante, a physicist at the Trento Institute for Fundamental Physics and Applications in Italy.

If this is correct for humans, too, it could be a huge breakthrough for long-haul space travel. Not only would astronauts be safer, but their spacecraft might not need the thick shielding that would add so much weight and cost to the voyage, Durante explains.

“So [if] the hibernating state increases your resistance to radiation, this is really what we want,” says Durante.

Sounds great, but can scientists actually induce long-term hibernation in a human?

Not yet, but they’re close. In recent years, emergency physicians have been successful in helping critical patients survive strokes or heart attacks by chilling them to 90-93 degrees Fahrenheit (32-34 degrees Celsius) for one to three days. This therapeutic hypothermia minimizes brain damage by drastically slowing down metabolism and inflammation.

With interplanetary spaceflight in mind, researchers are trying to safely induce a hibernation-like state in humans for a much longer period. NASA estimates that a one-way trip to Mars will take six to eight months, depending on the relative positions of the two planets.

Kumar says the goal is to maintain the hypothermic state as long as possible, ideally to “go to sleep and wake up there once you reach the other land.” That would require overcoming some fundamental challenges posed by human physiology, though. As humans are not evolved to hibernate, “we don’t have the internal physiological mechanisms to be in hibernation for any protracted period of time,” explains Kumar. “So we have to compensate some of those changes that happen inside the body, hopefully with some interventions and medications.”

One example would be to provide nutrition for a hibernating astronaut so she doesn’t starve. Kumar plans to study whether it would be better to deliver nutrients via the digestive tract or the vein.

Other physiological risks of long-term hibernation include bone and muscle loss. “When you are [under zero gravity] in space travels, you don’t have weight on your bones and then you lose calcium. It’s like getting osteoporosis,” says Craig Heller, a Stanford biologist who studies hibernation in bears. “And similarly if you don’t use muscles, the muscles atrophy.” He suggests that studying bears may give us clues about how to overcome these problems. “A bear doesn’t lose its muscle mass and it doesn’t lose calcium in its bone. So it would be good to understand how these processes are protected in the bears.”

So if it turns out that astronauts can’t sleep all the way to Mars, is there an alternative?

Yes. If long hibernation proves to be medically impossible, an alternative would be much shorter periods. Since we already know from therapeutic hypothermia cases that humans respond well to short periods of induced hibernation, one possibility might be for astronauts to “sleep” for three days a time, warm up for a day and go back down for another three days, explains Kelly Drew, a hibernation biologist at the University of Alaska Fairbanks.

“That is what hamsters do,” says Drew. “That might be something that people can do.” Heller agrees that this kind of approach could succeed.

How soon until we find out whether this will work?

There are still many medical challenges to overcome, Kumar acknowledges, including how to remove waste from a hibernating astronaut and how to find the right level of “sleep” that’s neither so deep, protective reflexes are lost nor so shallow, participants are easily woken.

He and others hope to work out all these challenges by doing animal experiments first, including inducing hibernation in pigs, which normally do not hibernate and share similar thermoregulation systems with humans.

Kumar is a consultant to SpaceWorks Enterprises Inc., an Atlanta-based aerospace company that just got a $500,000 grant from the NASA Innovative Advanced Concepts program. SpaceWorks hopes to build a habitat that would allow astronauts to enter a hibernation-like state during long-term space travel.

Although there is still a lot to be done, the habitat “can be available on the first human mission to Mars in 15 to 20 years,” says John Bradford, the president and chief operating officer of SpaceWorks.

Researchers at the European Space Agency are also working on the problem. “There is no convincing evidence that humans could not use hibernation mechanisms,” ESA scientist Leopold Summerer wrote in an email. His team is studying how animals enter hibernation and maintain vital functions the entire time.

Excited about the future, Kumar believes he will be recruiting for human trials of hibernation technology in three to five years. “Maybe you could volunteer!”

About the Author

Cici Zhang

Cici Zhang grew up in China and studied neuroscience at Swarthmore College and (for her M.S.) Washington University. While she came to America for endless possibilities, she’s still surprised her blogging could start a journey towards being a science journalist in NYC. Combining meeting people, traveling and her love for science and words, this career seems like a dream in reality. Cici enjoys Instagram, movies and beautiful things that satisfy her curiosity.

You can follow Cici on Twitter here.



"JJ" says:

Repectfully, it may not be appreciated by the NASA fellow, nor apparently by either the hibernation and hypothermia biologists that unless core temperature reaches lower than ~ 28 °C, which corresponds to a brain temperature of ~ 29°C, loss of consciousness will not automatucally manifest. This critical threshold must be exceeded for animation to be suspended in various type/sized mammals, including, obligate hibernators (e.g., ground-squirrels), facultative hibernators (e.g., bears) and non-hibernators, specifically, humans. Indeed, in humans treated with therapeutic hypothermia, both awakedness and consciousness can be readily sustained to this threshold but the plug-and-play system is so severely compromised as to reduce humans to incoherent, confused, forgetfull and babbling idiots. The degree of cooling proposed by this artificial biomimetic approach, some 4-6 °C off threshold is no small measure and will, strictly, not work. Chronically druging astronauts to knock them out is obviously neither practical nor safe, least not without some seriously major untoward downstrean effects.

Hate to be a cold blanket putting a damper on this approach but the reality is that nothing shy of the real deal thing might work. But no surprises here, we’ve known of this since at least the 50s. The situation is not, however, altogether list and hopeless as the torpor phenotype in humans has been known to exist since the 30s, from desert adapted Australian aborigines; this was subsequently confirmed by both both Scholander in the late 50s and again by Hammel in the early 60s.

"JJ" says:

PS: Also, sustained parenteral feeding is practically not feasible beyond about a week, as the Swiss have observed (cf. Heidegger & Pichard)

"JJ" says:

PPS: … and drowsiness is most severe and persists from a day to several following active rewarming and/or following prolonged hypothermia; the more rapid the rewarming the greater the drowsiness (cf. Bloch, 1967). Of course, this presents major problems in itself.

"JJ" says:

In regards radiation protection it only works in hypoxia and LET rays not particules. Though I’ve seen a hypoxia effect protection factor of 6 under special conditions, if radiolysis of water occurs O2 will simply locally form , which is what happens in particle radiation. To offset you dope with H2. The healing features of hiberbation are mjinimal in anything but LET gamma and x. Survivability should only be considered, which reduces the DRF. It may stop bystander effect but this han’t been quantified.

What hibernation can realy do is allow for much thicker shieldjng because living spave needs to be only very small (14 tons if 1 m thick H20; LH2 might reduce that to 50 g/cn^2). But the best is riding the solar wind maximum which in this state requires no forecasting and takes on all commers; half the solar minimum GCR.

"JJ" says:

In regards radiation, hibernation is well cited to significantly confer greater protection and tolerance but only for x-rays and low level gamma rays, not (off-Earth-like) charged and high energy particulate GCR. The only thing hibernation might offer in this respect is an order-of-magnitude reduction in living space so that we can afford the thicker passive shielding needed.

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