I am not using the hard-science tag for now because I do not want to restrict your imagination. However, I will add it if I get mostly speculative answers with no support in actual science. Please provide links supporting your ideas. Please, don't be shy, I love reading.
Please ask for clarifications before you write your answer if you need more details. My worldbuilding project is rather detailed already; if your answer is based on wrong assumptions it would not be as helpful.
The space station is a permanent habitat for the last human survivors in the known universe. If this station fails the humanity will cease to exist forever. The survivors are working on a terraforming project to build a more comfortable and lower maintenance habitat, but it will take centuries if not millennia before they can establish bases on the ground. Please, do not challenge this premise.
My initial design includes these ideas (this can be challenged and improved):
- the basic structure is a wheel about 10km in diameter;
- artificial gravity is created by centrifugal force, the maximum g (at the rim) is 1.2;
- the wheel is separated into self-sufficient compartments that can be fully sealed in case of a hull breach or any other malfunction threatening life-support systems;
- the station is run by the AI, which is possibly sentient and sapient (this is a topic for a heated debate in my world) and prioritises humanity's survival to the point of obsession; the AI is still young, however, and does not have necessary expertise and experience to handle all tasks related to the station, but they are learning fast;
- humans can override the AI's decisions on everything that does not relate to the immediate safety of the station and a human;
- life-support systems are partially organic: water filtration and air oxygenation, for example, are done using algae with the help of vertical farms and small gardens placed strategically around the station;
- the station has thrusters for orbital corrections, but no big fancy engines to travel around the star system;
- the station is also equipped with solar panels and sails.
- this is a virtually post-scarcity society, there are plenty of resources around (asteroid belt, nearby moons, etc.) that can be mined and delivered to the station's building site; time is the only restriction, resource-wise;
- post-scarcity does not apply to organic materials — only those that can survive a 2-century-long journey are present;
- the technological level is slightly higher than ours:
- please assume that any technology showing promise today is available;
- advanced robotics and almost full automatisation;
- no FTL or magic-like matter manipulation;
- cloning technologies exist in theory, but without artificial wombs or some similar technology cloning humans (or animals) is not possible;
- the survivors have access to all knowledge and information gathered by humanity by the date of departure from Earth.
- people are the most valuable resource, there are very few of them and, ideally, they all need to survive and procreate successfully.
I am mostly interested in these aspects of the space station design (these are not separate questions, they are parts of the overall design):
- radiation shielding;
- structural integrity;
- feasibility of several small eco-systems vs one large eco-system (I am not creating complete biomes, my eco-systems are closer to aquaria: a limited number of species with constant maintenance and fertilisers, but the bigger the aquarium the more stable it is);
- safety and redundancy features.
What would be the best or optimal design for a space station given all the constraints listed above?
Answers to the clarification requests
- Why can't they find a planet or a moon or something bit o plant roots on?
They want to be close to their terraforming project. The station is envisioned as a permanent satellite for their future home. It is not possible to land on their chosen moon since it will undergo heavy bombardment as part of the terraforming project.
The moon orbits a gas giant just slightly beyond the Goldilock zone of an M-class star. The moon itself is bare and has no atmosphere. The gas giant's composition is to be determined in greater detail, but it does have some water. Please do not challenge this. It works.
- Young AI? How does that work? It's like copying a book, nothing is messing unless you decide not to copy that page.
AI is not a book. It is a set of self-learning algorithms, various programming libraries, and databanks. The AI needs to learn things to gain expertise and experience. The space station is new, many things are different from what is observed on Earth, so the AI needs time to collect data about the new environment to optimise the performance. The AI is smart, but not a god.
- How many people are on that station?
About two hundred on the arrival day. The station must support up to 10000 people in the future.
- How do they handle food or water? Without a steady supply of them their farming and water will ground to a halt. Are they "farming" an asteroid?
Yes, they are mining asteroids, nearby moons, and their friendly gas giant. Inorganic materials are not of any concern. They just need to be delivered to the construction site.
- Do you want the rotation wheel-like space-station to precess? Or not?
Whatever works best for a station orbiting moon orbiting a gas giant. There are other moons as well. The gas giant does not have rings. The colonists are planning on building a giant magnetic shield to create an artificial magnetosphere for their future home. But the station is their #1 priority. The ship feels way too overcrowded :)
- One point of clarification though - is there a question whether the AI is sentient or whether it is sapient?
It is debatable. The AI passes Turing and similar tests. However, the status of the AI as sentient or sapient being is irrelevant. This is only a subject of philosophical debates among humans. If you are interested, the AI does not have anything resembling Asimov's 3 laws.
- What's the AI's threat profile? Is it mostly worried about astronomical phenomena that could be dangerous, or about the dumb humans breaking things inside it, or about an external threat (one presumes there's a reason this is the last enclave of humans...) coming after them?
The main dangers are natural astronomical phenomena and human errors. There are no foreseeable external threats. Big scary aliens with even bigger and scarier guns/lasers/biological weapons do not exist in my universe.
Please assume that humanity's self-destruction crusade has finally ended in total and indisputable victory. My people are the last remnants who want to avoid past mistakes.