written by Daniel Pütz

Imagine you’d wake up from a deep long slumber and the first thing you’d see would be something like this

http://www.enjoyspace.com/uploads/news/decembre2009/avatar/pandora-avatar.jpg

Maybe you recognize the picture, it is Pandora from the movie Avatar. The point here is that Jake, the protagonist, travels to Pandora while sleeping, or more scientifically spoken, hibernating. But how realistic is this scenario of humans travelling to distant planets while sleeping through the inconvenient trip time? Will it be the basis for future serious concepts regarding interstellar space travel or will it remain a vision of Sci-Fi stories?

First let’s clarify why hibernation is such an interesting method to transport humans for very long distances. The most important advantage of hibernation would be a tremendously smaller habitat. Compared to a human who is awake and wants to walk around, move, talk and so on a sleeping human is much easier to satisfy and needs very little space in comparison. This means that you can save a lot of weight on your starship making it easier to propel the ship to high speeds. The second most important advantage is that a hibernating human wouldn’t need much resources. He wouldn’t breath, eat and drink as much as human normally would do. This means that you don’t have to bring along so much food, oxygen etc and that you can downsize the life-support system, which again reduces the weight of the starship. Also a sleeping human wouldn’t be able to get angry and argue with his teammates. If you imagine you would be confined with some others on relatively little space for many years you probably can imagine that this is also a serious issue of interstellar travel.

Actually the basic idea of shortening the perceived time of a long journey by sleeping through part or even all of it is quite common actually. For example the sleeper cabin on trains also utilizes this concept to make the trip more comfortable. Of course the time span we are talking about is on a whole different level. Normally a human sleeps for six to twelve hours a day, sleeping for much longer than a whole day would be pretty strange already, but sleeping for several years seems kind of impossible at first. So why do we even consider that it might be possible?

As a starting point you have the examples of other hibernating mammals like bears, which sleep up to six month during winter. But as you are aware we aren’t bears, however there are some reports indicating that even humans could hibernate. The most prominent and amazing report was that of a japanese business man who survived for 24 days without food or water in cold weather, by falling into a state similar to hibernation.

So let us take a closer look how this hibernation works. For mammals like squirrels, who naturally hibernate, it is simply a method of preserving resources during harsh times like winter. They are able to enter this state by using a certain molecule called adenosine. Humans actually also produce this molecule, but there is something else which is required for hibernation. In humans adenosine only causes us to fall asleep over night. Squirrels however are able to start hibernating because they have certain adenosine receptors in their brain, which non hibernating mammals, like we humans, lack.

If you want to cause a similar effect in mammals without these receptors you have two different choices which are currently being researched:

(Suspended animation means the slowing of life process without killing the subject through artificial means, which makes it quite similar to hibernation. In fact the main difference is that it is caused artificially.)

With this method you first drain part or even all the blood of the subject and replace it with a low temperature solution, keeping the subject alive but cooling the whole organism. This causes the metabolism to slow down or even stop completely.

Basically you let the subject breath a atmosphere which contains slight doses of Hydrogen Sulfur (H2S), a gas that it is toxic and in higher doses is lethal. The H2S molecule binds to the same place as oxygen normally would thus reducing the organism capability to take in oxygen. The body then has an undersupply of oxygen and slows down the metabolism to counteract this danger.

Both of these methods sound quite crude if you describe them this simple and you probably ask yourself whether or not they actually work. What has science achieved so far?

For the temperature induced approach scientist were able to put dogs and pigs into a state of suspended animation. The first tests were made with dogs and after three hours of being clinically dead, which means that their metabolism had completely stopped, they were brought back to life. The problem is that some of the dogs suffered such severe brain damage that they were called “zombie dogs”. A similar result was achieved with pigs reaching a 90% success rate of reanimation. So out of 10 human 9 would reach their target alive and without brain damage.

 The chemical method was successfully tested on mice and possibly even without the risk of brain damage. But up to now that cannot be said for sure. The bigger issue however is that experiments on larger mammals like sheep and pigs have failed so far.

After this excurse into hibernation let’s come back to our space traveling Jake. Now if you’d be an engineer thinking about whether or not you could use hibernation technology on a space ship within the next 100 years what would your answer be?

You need to regard that at the moment hibernation hasn’t even been proven to be possible for humans especially for the duration that would be required if you are flying to another star. And we are talking about a huge difference here. From 3-48 hours, which scientist have achieved so far, to 50 years and more is a quite high jump.

But let’s dismiss this issue for the moment and simply assume that it would work on humans. If we do this another problem arises. For interstellar space flight you would need the hibernation process to lengthen the life of the hibernating human. Otherwise the trip time would be limited to at most 50 years. Why 50 years you ask? If you consider sending a 20 year old crew on a flight that would last 50 years they would be 70 years old, which is fairly old to start exploring a unknown planet. But such a short trip time would raise the difficulty of finding a propulsion system that is able to provide enough impulse to accelerate your star ship to the required speed. And if you consider such a short trip time you should also ask yourself if it wouldn’t be better to send the humans without taking the risks of hibernation. Because if you can achieve such a short travel time you wouldn’t require a large crew with a lot of reproduction power like a worldship would need, which would also keep the spacecraft quite small. Of course a hibernation ship with the same crew size would still be smaller, but also carries the greater risks of someone sustaining brain damage or something going wrong on the trip. For example if the hibernation chambers cease functioning you wouldn’t have a large enough habitat for the whole crew which would mean that you’d have to sacrifice most of the crew in order to keep at least a few people alive.

 This means an increased lifespan is mandatory for the hibernation concept to be feasible. Up to now scientists managed to increase the lifespan of a roundworm by 70% using Hydrogen Sulfur, so it isn’t completely out of question, but still it is even less certain than the question if hibernation would work at all. The other problems that would arise with a hibernation ship, like dealing with human waste, degenerating musculature etc. aren’t even considered here, because they would be fairly easy to solve in comparison.

Of course the possibility that hibernation will work at some point in the future can’t be ruled out, but right now we just don’t know it and thus, from the feasibility point of view you      would consider using a more “sophisticated” technology. Meaning a technology that at least          has been proven to work at all.