Sep 30 2016

Barriers to Colonizing Space

theexpanse_galleryWe are in an interesting time in human history with regard to humans in space. We have space programs. We have been to the moon, and we have a continuous presence in low-earth orbit. But we haven’t colonized space or any other world. We are thinking about it, and some people are even planning it, but no clear program yet.

What this means is that we are probably in the period of maximal speculation. We have a lot of information about space and space travel, and some experience, but we do not yet have any experience with actual colonization.

As is often the case, much of the speculation takes the form of science fiction. The Martian was an excellent novel and book that tried to seriously explore the issue of surviving on Mars (with some concessions made for narrative purposes).

The best speculation I have seen is in the recent TV series The Expanse. This takes place a couple of hundred years in the future, when humans have colonized our solar system. There is no magic high-tech to make the problems they would encounter go away. There is no artificial gravity, transporter, warp drive, force fields, or anything similar. They get by with extrapolations of existing physics and technology.

What are the major barriers we would encounter? One is radiation. The earth protects us in a shield comprised of the earth’s magnetic field and a thick atmosphere. There is no other place in the solar system with such protection on the surface of a world.

Radiation is not an insurmountable problem – it just requires adequate shielding. This is not a problem on a base or large station. It is an issue with a space ship because shielding is likely to be heavy, and more weight means more fuel. There are possible solutions there as well, such as storing a ships water supply in the outer hull to provide extra shielding and using strong magnetic fields. For long journeys you can also dock with larger ships that act as a highly shielded ferry and only need to be accelerated up to speed once.

Food, water, and oxygen is another problem. The earth has an ecosystem and, at least theoretically, sustainable resources. We would have to recreate a smaller version of that on any colony. We would need adequate starting materials, and a carefully balanced system to recycle all waste. No new technology is needed for this, just enough energy and careful planning and monitoring. Essentially a colony would be a human closed terrarium.

Perhaps the thorniest problem of space colonization is gravity. In fact the inspiration for this post was a recent question I received from SGU listener, Chris:

Something I’ve always had my own hypotheses about, but never heard addressed, yet seems like the elephant in the room in any discussion about space colonization, is the problem on gravity. I would assume that on a planet like Mars that has .37G, there is no way a human being can properly develop from an embryo to adulthood in that kind of gravity. I would imagine there would be ALL kinds of malformities and biological complications resulting from building a body in non-Earth gravity. I would think pregnancies would miscarry, and if not, everyone would be die somewhere in early childhood. I know we are amazingly adaptive, but variations in gravity are not something that Earth biology has ever encountered or had to be prepared for.

I think Chris is essentially correct, depending on the amount of gravity we are talking about. In the case of gravity space ships would actually be easier to fix than colonies on planets or moons. You can make artificial gravity in a ship by spinning it. Think of the space station in 2001: A Space Odyssey.

Spinning can also be used for colonies inside hollowed out asteroids or small moons. In the series The Expanse, they made a colony inside the dwarf planet Ceres. Ceres was then “spun up” in order to provide about 0.3 g. This was enough for the show so that people could walk around without any special effects. However, people who were born and lived in Ceres had weak bones and could not tolerate the gravity of earth.

Spinning is probably not an option for colonies on the surface of Mars (surface gravity 0.38 g) or the Moon (0.1654 g).

What do we know about human biology in low or even micro gravity? Not much, but what we do know is very concerning.

First, adults in microgravity experience a host of health problems. Fluid shifts occur which can adversely affect the eyes. Vestibular function is impaired. Bones and muscles weaken over time, a process that can be reduced but not eliminated by a strenuous exercise program. Research done on the International Space Station (ISS) is giving us a pretty clear picture of the health effects of life in microgravity.

But what about embryonic development? The concern is that in order for cells in an embryo to divide properly, and then separate out to form the different layers that will become different parts of the developing embryo, a gravitational gradient is needed.

During space flight there have been experiments with flies, amphibians, and reptiles. They show that fertilization and development can occur, but success rate and lifespans are reduced.

Perhaps the best evidence we have in mammals was a Japanese study in 2009. The study was actually done on earth and used spinning chambers to cancel out the net direction of earth’s gravity. They found that fertilization was not a problem, but development was hampered and live births were significantly reduced in mice.

Later research in embryonic stem cells finds that heart development is affected through dysregulation of genes in simulated microgravity. Microgravity also affects cell-cell interactions.


Colonizing space is not going to be easy, but all of the known problems are likely to have plausible solutions. Gravity might be the most difficult problem to solve, however. Living in low gravity has dramatic affects on the body that can only be partially mitigated.

The prospect of a self-sustaining colony is even more challenging because there seems to be a negative effect of microgravity on embryonic development. The exact extent and long term effects of these development changes is unknown. Also, they may not be present in low (Moon or Mars) gravity, but at present we have no data.

A lot more research will need to be done, and we probably won’t know the full effects until after we actually establish colonies on the Moon and Mars. We also will need to see the extent to which humans can adapt to these non-earth environments. We actually may eventually see the development (or deliberate creation) of human subspecies adapted to different space environments.

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