Cryogenic Sleep

Space travel is slow and boring. It takes three days to deliver humans to the moon. Six months to Mars. Years to get anywhere beyond Mars. Based on current technology, it would take 18,000 years to reach the nearest star, Alpha Centauri.

Stars are interesting. So are planets. Finding other travelers out in the void? Also interesting. Slow and steady progress in interplanetary or interstellar space for years on end? Not so much. Best to just skip over it completely. Enter the trope of cryogenic sleep or suspended animation, saving science fiction writers and readers from the boring bits of space voyages since the genre’s inception.

With cryogenic sleep, the crew is suspended in an ageless slumber while their computers or trusty robots handle the day-to-day operations of the ship. Months or years pass, the crew wakes somewhere new and interesting, and conflict abounds!

Well, I had a similar storytelling problem. I wanted to get Aspire’s crew to the edge of the solar system without breaking physics or inventing a radically new type of propulsion. That meant going the long way around—seven years out to Neptune’s orbit. Naturally, I wanted to skip over the transit time, so I incorporated a cryosleep module into the ship’s design.

Imagine my surprise when I started researching, only to discover that cryogenic sleep is actually scientifically plausible. What? What?!

Bears, and many other mammals, hibernate through the winter in a state called torpor. Biological processes lower their body temperatures, slow their metabolisms, and help them ride out the cold in a deep sleep. And it turns out humans might have the same genetic pathways necessary to induce a similar torpor state. Once again, what?!

This Vice article provides a nice summary of the medical uses of ‘cryosleep’ and where current research is headed with respect to space travel. It boils down to this: if the bears can do it, so can we, we just need to figure out how to induce and regulate it with modern technology. Even if we figure out the medical/genetic tricks of inducing a torpor state, there are a few other biological realities that cryosleep technology would have to contend with. 

• Food! Even in a low metabolic state, humans still need some sort of sustenance. There’s a reason why the grizzlies of Katmai National Park bulk up every fall. Bears sleep off fat reserves, while humans might require intravenous nutrition. And then there’s the opposite side of this equation—what goes in must come out.
• Muscles waste away during inactivity. Bears seem to have solved this problem with some clever gene expression and amino acid production tricks during torpor. Maybe the same could one day work for humans. If not, we might use neuromuscular electrical stimulation to keep our bodies ship-shape while we slumber.
• The ‘grooming’ problem. I couldn’t find any information on this one, but it makes decent sense that, even in a low metabolic state, hair and nails still grow, skin still sheds. It’s likely that humans would emerge from cryosleep looking shaggy and in desperate need of an exfoliating scrub.

The representation of cryosleep in media ranges from squeaky clean to downright disgusting. In Interstellar, the crew is submerged in liquid and comes out years later looking exactly the same, as if they hadn’t aged. In Project Hail Mary, Ryland Grace is thawed and must contend with all the messy human considerations of hibernation, including dealing with a ‘butt tube.’ And finally, in the movie Pandorum, multiple characters stumble from their cryogenic pods and scrape the dead skin off their bodies.

That last one will probably haunt me forever. No thanks, no matter how accurate it might be.

When faced with writing a few cryosleep scenes of my own, I plotted a course somewhere between Interstellar and Project Hail Mary. I love the imagery of bursting from a pool of liquid and gasping in air for the first time in years. The mechanics of the technology can be fun to a point, like climbing out of a pod in a tangle of electrodes and hoses (I skipped over the butt tubes). And of course, if a character is confused about what’s going on, the extra shock of touching their face to find an unexpected beard is great fun. 

So there we go, cryogenic sleep isn’t so sci-fi after all. Maybe one day soon, humans will transit the solar system without having to endure the tedium of interplanetary space.