How to Grow a Treehouse in Space

Post by AJ Rise:

Biology’s reputation as a “soft” science is ill-deserved. It’s a field of many wonders still unknown to mankind, and endless possibility. I think it likely that many of the technological advancements in the near future will be rooted in the deep study of living systems. Millions of years of evolution have gifted us a nearly endless supply of machines which can be artfully manipulated to our advantage.

One morning I woke up thinking about a somewhat obscure application of genetic engineering: bioships. Living, breathing creatures of space, majestically populating the heavens. They have appeared a handful of times in science fiction, and represent a neat concept. Rather than building the spaceships of the future out of metal, wires, and fuel, what if instead they were grown from carbon, hydrogen, nitrogen, and phosphorous, like everything that walks and breathes on earth? What if they had DNA, cells, and proteins just like us?

Of course, the appearances of bioships in sci-fi are all fairly abstract, which begs the question of their actual composition. If they were to exist, how? And what earthbound life would living spacecraft resemble?

After some reflection, I believe the answer is trees.

Let’s begin by breaking down the essential functions of a manned spacecraft: power (for heat, controls, communications, etc), controlled propulsion, living space, and life support. Every spacecraft will have a means of achieving each of these things, and a bioship will need to as well.

So far as I can fathom, the best way to run a bioship is the same process that gives us all energy: the age-old, happy marriage of cellular respiration and photosynthesis.

Consider a ship with a photosynthetic exterior, shaped like a cylindrical pipe with a hole in the middle for the crew and their amenities. This interior would have hardened cellulose walls – essentially tree bark, rather than forcing astronauts to live and breathe in the stomach of some space-faring squid.  I like to think of the structure as a tree that’s been turned inside-out.

On board the ship are a crew of astronauts to breathe in oxygen and eat food (glucose), producing carbon dioxide and water, which are then transferred back to the ship to carry out photosynthesis. The exterior then behaves like a plant on earth, converting sunlight, carbon dioxide, and water into oxygen and glucose. This process provides the astronauts with a breathable atmosphere, and their metabolism becomes part of the ship’s power source.

It gets better: the glucose products of photosynthesis are used on for things like growing and defense and producing seeds and such, but a spaceship needs to do none of these things. Therefore, the extra sugar can be diverted to another use: propulsion. There are microbes on earth which ferment glucose into ethanol and carbon dioxide. This is commonly known as making alcohol. However, ethanol is also a powerful liquid fuel, used in the Redstone rocket which launched the first United States satellite. After the leftovers from the  plant’s metabolism were collected, all it would take is some yeast and liquid oxidizer to generate thrust. Excess carbon dioxide can be either re-absorbed by the space tree to make more glucose and oxygen or stored and eventually expelled for additional propellant. The amount of glucose actually produced by the ship would ultimately be equivalent to the amount of food consumed by the crew. Therefore, a pre-stocked astronaut food supply and sunlight could be a futuristic fuel used to propel a spaceship. (Just imagine a stranded astronaut holding a cardboard sign: will eat for rocket fuel). Like any other rocket, a chemical reaction yields the rapid expulsion of gasses through a nozzle, generating thrust. This particular reaction is just much slower and more complex, and all living creatures depend on it.

To clarify, the technology required to genetically engineer an entirely new, single organism capable of surviving in space remains far-fetched. Trees aren’t usually geared towards surviving in space. Generally, exposing something to a vacuum is a good way to kill it. It would be difficult to regulate temperature and electric power without a heavy reliance on inorganic components as well. Measures would need to be taken to combat radiation as well. We also do not have the necessary command over genetic engineering to create a completely new organism, so drastically different from the ones we see on earth.

That is not, however, to say that we cannot utilize components of this. Keeping specific foliage on board a spacecraft could still prove advantageous. It is certainly more possible to engineer a plant to make excess glucose readily available, perhaps in the form of a specific fruit-like carrier. This glucose can then be fermented to produce small amounts of fuel, perfect for deep-space precision maneuvers. Such a plant would also help maintain a breathable environment aboard the spaceship.

This is where I believe biological engineering can leave its mark on space travel. It may not always be the most efficient solution, but when designing spacecraft, the available work of millions of years of natural selection should be considered as possible tools.