In science fiction, when people need to travel immense distances through outer space and don’t have a wormhole nearby, they bed down for a very long nap. For this, the heroes of films like "Aliens," "Avatar," "Interstellar," and "Passengers," have put themselves into suspended animation.
It would be convenient if real astronauts could hop in a sleep pod and wake up years later without aging a day. The bad news is we’re nowhere near this reality.
But scientists and engineers are collaborating with NASA and other space agencies to develop suspended animation projects for missions to Mars and beyond. Instead of being frozen in time, though, astronauts could be knocked out for weeks or months in a state called torpor that resembles hibernation.
If these projects are successful, ships could be more compact and more sparsely equipped, making them less expensive to propel through space. Astronauts could also spare their physical and mental health. And torpor could help us here on Earth, too.
On a voyage to deep space, humans will be more demanding cargo than a rover or satellite. For one, we must eat. We also need room to move around and tend to chafe at sharing cramped quarters for long periods. And our bodies will be bombarded with cosmic rays and face numerous health issues caused by low gravity, including loss of bone density and muscle mass.
Putting astronauts into a hibernation-like state could help with some of these problems.
“The core characteristic of hibernation is that you suddenly stop consuming energy,” says Matteo Cerri, a physiologist at the University of Bologna in Italy. “If you’re not consuming any fuel you’re going to cool down.”
During hibernation, an animal’s metabolism grinds to a near standstill. The heart beats more slowly and body temperature drops. The hormones and composition of the blood are altered. Breathing, cell replication, and brain activity slow. “It’s like a movie that progressively slows down," Cerri says. "Every frame gets slower and slower."
But humans can’t hibernate. “We’re just trying to make them appear to hibernate, or creating the benefits…of hibernation,” says John Bradford, president and COO of SpaceWorks Enterprises, an Atlanta-based aerospace engineering firm working with the NASA Innovative Advance Concepts (NIAC) Program.
If the crew could spend most of the flight in torpor, they would need less food and could occupy a smaller living space. Shipping anything into space is incredibly expensive because of added fuel costs for each extra pound, so a smaller spaceship would be a huge advantage.
It might also be more pleasant for the astronauts.
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“If you’re in a small tin can with the same other three people for nine months and you can’t really move about the cabin…it may actually be that sleeping for 14 days is the preferred way to go,” says Jason Derleth, program executive of NIAC.
Torpor could also have health benefits. While hibernating, animals don’t suffer muscle atrophy or bone degeneration from lack of use, although it’s not clear why. And there’s evidence that animals are less vulnerable to radiation during hibernation. So torpor might give astronauts added protection during spaceflight. On the other hand, a lowered metabolism means the body may not repair itself as quickly, so radiation damage might be more profound, Derleth says.
Having the crew stay in one place would make it easier to shield that portion of the ship from radiation since it would be incredibly expensive and impractical to shield a whole spacecraft.
The European Space Agency is working with Cerri and his colleagues to study suspended animation. They have already used drugs to shut off a brain area that controls metabolism in non-hibernating rats, sending the rodents into torpor.
Meanwhile, SpaceWorks has a team of engineers, former astronauts, physicians, and hibernation researchers that are pondering how to send astronauts into torpor safely and how a spacecraft could be designed to accommodate them.
SpaceWorks’ ideas build on a procedure used in emergency rooms called therapeutic hypothermia, in which the body is cooled to prevent brain damage after crises like cardiac arrest. But this has been done for days, not weeks or months. And it’s unclear whether it causes side effects because the people who receive this treatment are already ill.
To enter torpor, astronauts would only need to drop their internal body temperature about 9 degrees Fahrenheit. It’s possible this temperature drop could be done by cooling the surrounding air, Bradford says. Astronauts would be given a sedative to relax and prevent shivering as they slip into torpor.
A spacecraft could also have special pods to chill each crewmember. Or it could be equipped to cool the entire habitat or just a chilly area where crew in torpor are separated from other astronauts.
While in torpor, astronauts will need life support systems to monitor their vitals and take care of them. “We’re not like bears," Bradford says. “Unfortunately we don’t get to stock up and put on 300 pounds and then wake up nice and fit.” Food could perhaps be delivered intravenously.
Astronauts can enter torpor in shifts so someone is always alert. Initially, SpaceWorks aims to place people in torpor for two weeks. Later, they may work up to months, which would help with future colonization efforts. “If you want to send hundreds of people to Mars, you don’t want to have everybody waking up every two weeks,” Bradford says.
Awakening from torpor will not be instantaneous. Astronauts must be roused slowly so different body parts can adjust at the right rates. As the body warms, every organ will be clamoring for energy, but the brain must first provide for itself, the heart, and other vital areas. Otherwise, those areas could be deprived of blood flow, possibly leading to a heart attack or stroke.
To combat radiation, the crew could be surrounded by their food bags while they sleep to help block them from exposure. But that protection would diminish as their contents are imbibed. “Does that mean that you put the person’s waste back in those bags?” Derleth asks.
Researchers will also have to investigate potential side effects of torpor, like an erratic heartbeat, infections, or blood clots. And we don’t know yet how torpor will affect cognition and memory, or what it will feel like for a healthy person.
“Below a certain degree of temperature…there is probably no consciousness anymore,” Cerri says. “But in the beginning, it could be quite odd, maybe even unpleasant.”
One thing torpor can’t do is stop astronauts from aging. Hibernating animals do tend to live longer compared with other species similar in size, so it’s possible that torpor would slow human aging a little, but not enough to send people on 100-year jaunts through space.
For that, we would need to freeze astronauts, replacing their blood with an antifreeze to prevent their cells from bursting. Since we don’t know how to resurrect people from this chilly oblivion, cryonics isn’t yet a practical option for deep space travel. “Even if you were defrosting the body with no damage to the tissues, the body will still be dead when you warm it up,” Cerri says.
Torpor is a much better bet. And it wouldn’t only be useful for space exploration. Soldiers wounded on the battlefield could be put into torpor until help can arrive. Or it could keep donor organs viable longer.
Cerri is now investigating whether torpor or hypothermia can protect healthy cells from radiation damage. If so, people could be put into torpor for cancer treatment. Doctors could then use a more intense dose of radiation to blast tumors because the surrounding tissue would be less vulnerable.
Bradford thinks technologies to use torpor could be ready by the early 2030s, when people are setting off on the first missions to Mars. NASA is not currently planning to use torpor for any future journeys, but if torpor proves its mettle, it could enable more ambitious voyages, Derleth says. “It does open up the possibility for 100 years from now traveling out to asteroids or even deeper in space.”