Galactic Colonization

Galactic empires are common plot elements in science fiction writing. But as I showed in another post titled “Faster Than Light Travel,” the likelihood is that it will never be possible to maintain an empire stretching across the galaxy. The laws of physics, as we presently understand them, simply won’t support it.

But would it be at all feasible to colonize the galaxy? Yes, and in fact it’s almost inevitable– assuming our species and our culture can survive long enough. Let’s assume for the moment that it is possible to build a spacecraft that can accelerate to 1,000,000 miles per hour. That may sound extremely fast, but it’s only about 0.15% of the speed of light. Even so, it’s roughly three times faster than the fastest man made spacecraft ever built– the Parker Solar Probe. One light year is about 5.87×1012 miles. At 1,000,000 miles per hour it would take about 6700 years to travel ten light years. That may seem like an extremely long time– and it certainly is as compared to the history of human civilization. But as compared to the 225 million years that it takes the Earth to make one complete orbit around the center of the galaxy, it’s hardly anything at all.

The Earth’s orbit around the galactic center is roughly 170,000 light years in circumference. At the rate of 1,000,000 miles per hour it would take roughly 114 million years to traverse the Earth’s orbit. That’s only about half the time it would take the Earth itself to travel the same distance.

But there are plenty of complications in this broad overview. Spacecraft carrying humans to distant planets for the purposes of colonization must accelerate and decelerate. And it may be necessary to refuel, which might require slowing down to orbit a planet. All of that will take additional travel time.

We would also need to consider how to design a spacecraft to support human life for an extended period. There are only three major possibilities. First, the spacecraft could be designed to contain all the comforts of home. There would be gardens for growing food, recycling plants to reprocess waste, living quarters for each person on board, and air and water sufficient to support every living thing aboard the spacecraft.

This option is the most difficult and most costly to implement, and it is the one most prone to catastrophic failure. Any leak in the air system, however minute, could result in a complete loss of atmosphere by the end of a 6700 year voyage. Any failure of the agricultural systems would mean starvation for the entire crew. And normal wear on the complex systems involved could mean that crucial equipment fails long before the spacecraft arrives at its required destination. One can provide spare parts, or the raw materials necessary to fabricate any part on the spacecraft– but all of that would add weight, and additional weight adds a requirement for additional fuel, and additional cost.

An important fact to bear in mind about this option is that a 6700 year voyage means that there will be hundreds of generations of people who live and die aboard the spacecraft. There will be no room aboard for cemeteries, so the bodies of those who die will have to be recycled back into the agricultural systems.

The second option is to put the members of the crew into some form of suspended animation. Ideally we should like the crew to be maintained in a state that requires no air, no water, and no nourishment to maintain their bodies for a 6700 year period of time. And of course we would want to revive each passenger after the voyage with no significant loss of physical or mental capabilities. No one has ever found a way to do that. Assuming that it becomes possible in some as-of-yet unforeseen future, this option would require far fewer supplies and complex systems than the first.

But it is not without its own risks. When the spacecraft finally reaches its destination, a site must be chosen for landing and disembarkation. The personnel could be awoken as the spacecraft approaches the selected target planet, thereby permitting the decision to be made by humans. But there remains the possibility that the chosen destination planet is not a good option for colonization, and the spacecraft must travel on to another planet or perhaps another star system. That would require putting those crew members who have been awoken back into suspended animation, and that may involve its own unpleasant side effects. Alternatively, the spacecraft could be designed to survey the planet, check for required living conditions, and select an optimal spot for landing– without human intervention. That would clearly require a highly sophisticated system of software– one which can run for thousands of years without a hitch.

The third option is less of a realistic option than it is a dream. The spacecraft would not be transporting humans, but rather only human gametes. Once the ship arrives at its destination the male and female gametes would be allowed to fertilize and grow.

This last method would appear to require the least resources of the three. It would afford fewer opportunities for catastrophic failure, and it would require less fuel. But it would also require a method for raising and educating the infants that would result. And who will do that?

There is only one possible answer to that question– robots. An army of robots would have to attend to the infants as they are born. That would require feeding, bathing, playing, teaching– not the sorts of activities one ordinarily associates with robots. The robots would have to behave very much like humans– though it isn’t necessarily the case that they would have to look like humans. And of course the robots would have to provide all of the background information necessary to help the children adapt to their new environment.

Once a spacecraft designed for this third option arrives at its destination, the children will have to grow up in an environment that supports all aspects of human life. There will need to be systems for agriculture, waste processing, air filtration, water reclamation– everything that is required to support human society. But that environment would have to be developed and maintained without human intervention, until such time as the children have matured to the point at which they can take over all aspects of operation. That interim environment would therefore have to be built and maintained by the robots.

In some respects this last option is the most complex. It would require a level of robotic sophistication far beyond anything that has thus far been developed. But over the course of the next several centuries, it just might be possible.

This highlights another important aspect of galactic colonization– the search for viable planets. Before embarking on a 6700 year mission it would be best to get a fair idea of which destination planets are likely to be most habitable. We would want to know that the planet has an atmosphere with plenty of oxygen, that it’s surface temperature falls within an acceptable range, that it has liquid water on its surface, that it gets plenty of light from its star, that it isn’t already occupied by a hostile species… All of these conditions are very difficult to assess from a distance of several light years. That means it is highly possible to travel for thousands of years only to find that the chosen planet is unsuitable.

It will therefore be necessary to send advance unmanned probes first. These probes should be small, but would be outfitted with a full array of sensors. They should be set off on their travel to the stars at a significant percentage of the speed of light. At 50% of the speed of light a probe could reach a star 10 light years distant in 20 years and could return its findings to Earth in 30 years. A 50% speed of light velocity might attainable via a slingshot route around a nearby star. Such a route would undoubtedly result in g forces too extreme for human passengers, but should do no harm to unmanned probe.

Ideally we would want each probe to land on a planet, take physical samples, and assess the planet’s suitability to human habitation. In a system with multiple potential planets we would want these probes to visit as many planets as possible. That means each probe will need to be independently maneuverable, which means more fuel, and therefore more weight, and therefore more complexity, and greater cost.

Another major problem with colonization concerns the problem of adapting the environment of the chosen planet to human life. We can carry with us a storehouse of knowledge as to how to smelt ores, build power plants, pump water, grow food, build houses. But what if the planet’s atmosphere has too little (or too much!) oxygen? Or too little carbon dioxide? What if the surface is too cold for growing crops? What if water is only available deep underground? What if there is a bacterium that is airborne and fatal to human life? What if there is an intelligent life form that is hostile to our intervention? The potential problems of living on a completely alien world are innumerable.

This suggests that the best option is a multi-phase process. First, exploratory probes evaluate each potentially habitable planet. To those which qualify, a team of robots is sent to establish a human habitation, with all the systems necessary for the operation of a human colony. Once habitations have been built, then humans can be placed on transports to carry them to the colonies.

There will be plenty of time to assess and address these problems. It may be that we will have to be extremely choosy in evaluating planets for habitation. We shouldn’t expect that suitable planets will always be available along our preferred routes through the galaxy.

Interstellar travel is certain to be much harder than science fiction writers have thus far described it to be. It will take time– quite a long time, I suspect– to develop a process for galactic colonization. The opportunity is undoubtedly immense. Billions of stars and planets, each with its own geology, biology, wonder, and possibility. But there is really no guarantee that any planet within a reasonable distance would be suitable to our habitation. There will undoubtedly be a great deal to learn.

Copyright (c) 2022, David S. Moore. All rights reserved.

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