Note to Science Fiction Authors: If your world building is completely imaginary you don’t need to read this. However if you want your fictitious world to be at least plausible you’ll want to keep the science plausible and you might want to read further; particularly if you are writing a space opera and need to describe a plausible spacecraft or space colony. 😉
After writing my September 30th blog post, Liquid Water (… er … Brine) Discovered on Mars and a Future Martian Colony, it occurred to me that it might be informative and even fun if I were to post about some of the things that will need to be considered when we eventually do create a human extraterrestrial civilization. Understanding these things is also important if you are writing fiction and want to keep your story and world plausible. Considering all of the requirements of a space faring civilization would be a huge multidisciplinary undertaking so I don’t propose to tackle it all in a single blog post or even in many blog posts. Instead, from time to time, I will choose a specific topic relating to how we will one day live beyond Earth and discuss them here. I’ll stick to topics that I find interesting or to answer questions I receive from you.
In the Sept 30th post I mentioned that the 0.38 G Martian surface gravity could be a significant issue if we ever intend to establish more than simple temporarily crewed research outposts on Mars. As I mentioned in that post, we evolved in a one G environment from long before we were even human so all of our bodily systems are designed to work in one gravity. We already know that a free fall environment, such as on board the International Space Station (ISS), weakens the human body in a myriad of ways and that the more time we spend in free fall the more our bodies’ systems become compromised. Astronauts have to engage in a rigorous exercise regime to minimize these effects and if they spend more than a few days or weeks in free fall the resulting health issues require months to recover from and some of those effects may not be entirely reversible. To my knowledge, there has been no research into the effects of low gravity environments on the human body at all.
As I mentioned in the Sept 30th post, if we are going to create a space-faring civilization then we are going to want to be able to ‘live, work, and play in space’ (to borrow the old L5 Society slogan) and as part of living we are going to need to procreate and raise healthy children in that environment. Obviously a free fall environment is not the place we want to raise children because we don’t know if they can grow properly without gravitational stresses on their skeletal, cardiovascular, and other bodily systems. Even if they could grow to live healthy lives in free fall they probably would never be able to visit a planetary surface without significant complications and possibly even death. So on a permanent basis, what is the minimum (and maximum) gravitational environment we need to inhabit to perform all of our life functions including child rearing and remain healthy? No one knows yet. The 0.38 G environment of Mars might be adequate, but I question that. What about the 0.17 G environment of the lunar surface? Discovering the lower limits of our gravitational tolerance for permanent residence in space will be a major area of research (and ethical debate) in the coming decades.
When most people think about a future human space faring civilization they think in terms of humans living on other planetary surfaces. While this will probably happen once we’ve attained the ability to travel between stars and have found other truly Earth-like planets, I suggest that this will not be the rule within the Solar System other than in temporarily crewed research outposts*. The only terrestrial planet that has approximately the same gravitational environment as Earth is Venus (0.90 G) but the searing surface temperatures and sulfuric acid clouds present other major obstacles**. All indications are that there is no solid surface on the gas giant planets. All the various moons, asteroids, and comets have low gravity environments.
A favorite science fiction fix for this issue is something like Star Trek’s ‘gravity plating’. I don’t know of any theory in physics that even hints at such a technology being possible. So if we are considering permanent residence beyond Earth, but within the Solar System, that leaves us with the necessity of spinning our habitats, spacecraft, and space colonies to keep our inhabitants healthy and allow them to raise healthy children.
While rotation does not provide true gravity, it does provide us with the necessary acceleration environment required to remain healthy and raise healthy children. The only side effect I have come across, is that rotating environments induce Coriolis forces that affect the inner ear resulting in dizziness and motion sickness. These effects are greatly reduced with lower rotation rates and increased rotational radius. Early studies suggested an upper limit of one rpm would be required to effectively mitigate this side effect. If we are restricted to a maximum of one rpm then the rotation radius must be almost a kilometre to achieve a one G acceleration within the colony. However, recent work by Al Globus and Theodore Hall (2015) suggest higher rotation rates might be acceptable. If this turns out to be true, it would greatly reduce the size and mass of a spacecraft or space colony. With higher rotation rates the rotational radius could be significantly reduced. (If you are designing a spacecraft for your space opera you can easily calculate the rotational radius required using the equation I provide below***.)
Although at first rotating space colonies would probably be smallish, there is no reason why they couldn’t eventually become very large habitats. The necessary resources to build large space structures exist within the various asteroids, comets, and small moons. Hence, I think we’ll eventually see space habitats that will be very large. Some could even become population centres in their own right.
So what do you think? Please feel free to leave a comment or ask a question.
–Ron Evans (October 2015)
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*I am assuming we won’t be using genetic manipulation to create new bodies that can remain healthy in low gravity or even free fall environments. If this happens then my discussion here is moot. 😉
** We could construct colonies that float in the Venusian atmosphere at an altitude where the temperature and pressure are not too great. These colonies would need to be coated by a substance (glass or other ceramic?) that can resist corrosion from the sulfuric acid clouds. We could also construct floating colonies in gas giant atmospheres but the fact that gas giant atmospheres are composed primarily of hydrogen (and some helium and other ‘impurities’) would require our ‘balloon’ to be ‘hard shelled’ and filled with a relative vacuum or we wouldn’t get a lot of buoyancy. This is probably not an insurmountable issue and except for Jupiter (~2.5 G) the gravitational environments of the other gas giants would be comparable to Earth’s, so maybe. The issues here are more the depth of the gravity wells and the availability of the resources required for life. These are topics for another time.
*** [Warning the following contains MATH!] 😉
Good luck.
Science Anywhere 