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In my space western setting, I went nuts with the time scale, so now I have a faction living entirely in space stations (with planets used for transit and agriculture, but that's irrelevant for now), which is about 5000 years old.

How can people keep their space station preventing from falling apart for such a long time?

Or if it's unfeasible, what would be the fastest way of replacing them? Using the planets for temporary habitats, while sounds good, is mostly against the point of the faction: they refuse living on planets.

On the other hand, I can loose on this principle, but before doing so, I'd wait for suggestions here.

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    $\begingroup$ Build well, repair when necessary, have a planet handy to replace consumable that leak away. Otherwise, why would a space station fall apart? There are quite a number of Earth buildings still in use 1000+ years after they were built, despite being exposed to Earth's weather. Some examples: gizmodo.com/… $\endgroup$ – jamesqf May 21 '17 at 3:56
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    $\begingroup$ The answer seems to simple to me that I'm afraid I've missed something: just keep repairing it... like we do with real-life buildings/machinery. Or actually easier since there is no "up/down" (it would be hard to repair a weak fundament of a skyscraper) and you can replace modules by just attaching a replacement somewhere else and then dismantle the broken one, in extreme cases. So, what is the actual question? ;) $\endgroup$ – AnoE May 21 '17 at 21:25
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    $\begingroup$ One idea I've seen in numerous SciFi books for mothballing a station - with the expectation it will work again when needed - is to open the doors and let the vacuum in; and if that got your pedant gland screaming, yes, I mean letting the air out. :-) But do that and most or all of the problems with any kind of corrosion or chemical based degradation are gone. $\endgroup$ – Grimm The Opiner May 22 '17 at 12:01
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    $\begingroup$ using planets for temporary habitats - would they really need to do this? I expect that the station will be distributed and redundant. One large compartment isn't as safe as multiple smaller compartments connected but isolated via airlock - with failsafe backups (unused compartments) that can be put into operation in case one of them fails. And once you have extras, you can always "park" the old/damaged ones in a repair dock and have them refurbished (perhaps using materials from the planet you're orbiting). $\endgroup$ – ArjunShankar May 22 '17 at 12:39
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    $\begingroup$ @AnoE : Just keep repairing doesn't work in the long term. Stress accumulates over time and sooner or later interior deterioration goes undetected and there is a catastrophic failure cascade (a domino effect); usually due to some extreme but routine stressor. That isn't just possible, but over a long enough time, likely to happen. (some of my statistical work on parts reliability is still in use by the FAA). The way to make it unlikely is to start over, with young steel that hasn't been subjected to any usage stress (except for initial testing). $\endgroup$ – Amadeus May 22 '17 at 15:18
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The space station needs multiply redundant systems for all its systems. Fortunately, it is in space where the deterioration of machinery is minimized. Space probes and satellites routinely exceed their estimated working lives (except those that malfunctioned early in their careers).

Space station personnel will receive expert training in space station from birth especially if this is their heritage. Folks who are born and die on space stations need to be extra well versed and educated in all aspects of space station maintenance.

Your space station should be equipped with an army of repair and maintenance robots. There should be diagnostic sensors in every suitable location to detect the slightest system or structural failure. Every system and component needs to checked and rechecked for good running. This will be part of your space station's design. Easy access to all systems for checking, inspecting and, when needed, repairing.

Space station longevity begins with good systems and structural design. Make sure yours is designed for millennia. Do not you cut too many cost corners. The life of your space station and the lives of those living on it don't come cheap. You don't want them going cheaply either.

Make sure reliable supply routes are handy. For those occasions, when all your normal systems and procedures for maintaining, repairing and sustaining your space station fail. This could be the usual space piracy, interstellar wars, space whale rustlers or a rogue black hole.

Keep handy a goody supply of raw materials that can be converted into manufactured components. Have access to an external energy source by using large solar power collectors or nuclear based power generators (this can be fusion all the way up to antimatter). The power is needed to make and process components.

Recycle, recycle, and, don't forget, to recycle. To ensure long term survival, the golden rule is waste not. Defunct components are raw material. Use them again and again. Even if this means reducing to their constituent elements. Remember that's why your power generators are there.

Maintain friendly relationships with your neighbours. They are an excellent source for replacement parts and raw materials. Considering most of your raw materials will be extracted from asteroids, moons, and, sometimes, even planets. Territorial claims over who can access and use the material in those astronomical bodies may be in place. If you trespass on their asteroids and remove matter without permission you get a missile up your probic vent.

Be nice and respectful. It's a good idea to look after the neighbourhood. Even if they own the local system's asteroids, they might be grateful and let you extract minerals for shipping to their habitats, so in return you could be allowed to take some for yourself.

Good design, good work, well trained space station personnel and robots, good relationships with neighbours and suppliers, and leave nothing to chance. Take care for it, and it will take care for you.

Five millennia, hah! This baby's good for at least fifteen.

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    $\begingroup$ +1 for minimised deterioration in space, although for some materials the opposite might be true. $\endgroup$ – Pere May 21 '17 at 16:15
  • $\begingroup$ @Pere No-one would expect it to true for all materials. Degradation of materials due to radiation will be a problem, but if the space station builders minimize materials which will deteriorate in space that would be a positive factor. $\endgroup$ – a4android May 22 '17 at 5:27
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You have solar power, I presume you have reasonably intelligent robots, the solution is to take a clue from biology: Constantly, whether it is needed or not, replace every molecule of the space station with newly fabricated parts, smelt down the old parts, bring in new steel or whatever from asteroids. Make so no part of your station is ever more than 20 years old, and that goes for the robots too. All it takes is a constant investment of energy, which you should have in abundance from the sun. Make sure you are replacing those solar cells or furnaces while you are at it.

I say from biology, because our own bodies do the same thing; the only reason we grow old is we did not evolve a perfect replacement system or way to identify what needs to be replaced, so our telomeres get short and cells stop functioning properly. For a machine you don't have to emulate that, just emulate the idea: constantly retire the parts and replace with new parts. The atoms of iron, carbon and other metals never age; extreme heat will rejuvenate them, and you can recast them into steel just as good as new.

Added due to comments:

  • I did not address high energy particles; those are atomic size and I assume can't cause any kind of strucural failure (unless in a beam intended for an attack); and if they did alter some steel, we can have sensors tell us where. On aircraft for example, we can run a tiny electric current through a part at one end and detect the shape of the signal at the other; if there is any change in the shape the composition has changed: cracks, rust, deformation, getting wet, etc. Similar to a motion detector: For a motion detector every position produces a different echo pattern, but it doesn't have to know what the pattern means: Just that if the pattern changes, something has moved.

  • I also did not address attack, or asteroid strike: At some point anything can be overwhelmed by sufficient force. I was only addressing deterioration.

  • A little more added to discuss outgassing: I presume we can liberate the gases from asteroids, moon, or other materials. Beyond any structural issues I presume this station is also self-sufficient, or it cannot maintain itself.

Simple polished aluminum in a parabolic arc (or partial dish) can focus enough sunlight to melt, or indeed vaporize, anything. The parabola can be piecewise; meaning an arrangement of flat panels with centers on a parabola, but easily replaced should they be damaged by micrometeorites or debris.

Any heat source is energy; we can use to convert to mechanical energy (Stirling engines, closed-cycle-steam engines) which we can convert to electricity. Remember the electro-splitting of water into H and O: That does not only apply to water; we can liberate gases from other compounds as well. We can melt rocks, turn them into vapor, and using distillation techniques (closely monitored heat so some compounds vaporize while others remain liquid) and centrifugal separation (of liquefied rock, spun hard to separate elements by atomic weight then cooled to retain that separation) we can obtain very pure elements; and remix them to our desire. We can obtain any gases we need to replenish the air and fuels on the station. Solar does it all; and in many ways it is easier in micro-gravity space without any atmosphere. Most benefits of gravity we want we can get with centrifugal force, and control to a fine degree.

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    $\begingroup$ "stole" my answer by few seconds... $\endgroup$ – L.Dutch - Reinstate Monica♦ May 21 '17 at 3:55
  • $\begingroup$ Good idea, but wouldn’t there still be some loss of gasses (assuming the station is pressurized)? What would high energy particles do to the station? Would they knock off significant amounts of material or cause radioactive decay over such a long time? $\endgroup$ – Michael May 21 '17 at 9:20
  • $\begingroup$ @Michael your issues are addressed by adding material in block quote. $\endgroup$ – Amadeus May 21 '17 at 12:57
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    $\begingroup$ Metals are damaged by high-energy radiation, even in vacuum (though the effects are much less than metal in contact with something to react with, such as water or steam.) So even structural parts will eventually need to be repaired. However the timescale for that is probably thousands of years, for anything thick. Thin metal membranes/shells will have problems much earlier. There's a fair bit of tech lit in the nuclear power industry and space/satellite design. $\endgroup$ – Catalyst May 21 '17 at 13:02
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    $\begingroup$ @Catalyst Good to know. My thought is that 100% replacement is built in from the start; it takes the robots X years to build the station, and the moment they are done, they immediately start replacing the first thing they built with brand new material, whether it needs it or not. There may be "repairs" in unusual circumstances, but not usually. Think of modern electronics: Nobody repairs a transistor or capacitor or resistor or chip; they just replace it with a new one. The station would be specifically designed to allow such continual replacement every X years without disrupting operations. $\endgroup$ – Amadeus May 21 '17 at 14:49
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Minimize moving parts.
Make nondurable parts modular and easy to replace

Moving is what wears things out. Your Methuselah stations must have the minimum necessary moving parts. A favorite way to make artificial satellites is to hollow out some natural structure. An asteroid full of tunnels should be good for 5000+ years.

If something has to move, have it move as seldom as possible. Move one thing many times rather than a lot of things occasionally, and plan to replace the one moving thing regularly.

If something must move a lot, expect it to wear out and have it be easily replaceable. I like the idea of things being modular and easily replaceable because that offers narrative possibility: modules could be recognizable by age and characterized by features of that age, coexisting with newer and older modules. Sort of like walking through an old city with an awareness of architecture: you see how the past integrates with the present. Occasionally you recognize something really old which has persisted to the present. I read an account of the observatory on Haleakala which said that as you walked through the workrooms, you could find computers from every era, each still at its station performing some task which it did so satisfactorily that it did not need to be replaced.

Items could also be made regenerable, if that is a word. For example, an airlock with seals somehow made of ice, which replenishes itself from an immense reservoir as small amounts sublimate off into space. Or at certain wear-prone places (hangar bay?) the nickel-iron of the asteroid could periodically be melted and recast in place to accommodate wear and gradual shape change.

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Over the course of five millennia, every part of the station will fail. Every integrated circuit, every hull panel, every airlock will fail.

To bypass this problem, your people will need to be able to replace every single part, including their manufacturing equipment. So not only are they going to need a lot of manufacturing capability, they need multiple sets of manufacturing hardware, in separate sections so that damage to one section doesn't completely cripple them.

In addition, everything will need to be decentralized so that no failing or damaged component will cause an emergency. Decentralized life support, decentralized power, decentralized storage. And every part of the life support and power grids is going to talk to every other part, so that way damaged parts don't cause cascading failures. If one module reports depressurization, the adjacent modules will need to cut off air to prevent the entire station from getting depressurized. (Hopefully after everyone is out.)

Now that you have that setup, you can now lose any module or device to damage, age, or because you're replacing it. With this system, you construct new modules and systems as the old ones start failing. As long as you have a trickle of raw materials to replace losses, you're golden.

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    $\begingroup$ Is it even humanly possible to make such a complicated yet utterly safe space station to design? I really wonder what technical capabilities should such a system imply. $\endgroup$ – Katamori May 21 '17 at 4:09
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    $\begingroup$ Well, things probably wouldn't be completely decentralized. However, the ISS right now has three computers that majority vote on situations to prevent failure of any one computer (whether malfunction or damage) from causing problems. So distributed control? While it isn't solved it's hardly some arcane problem. Power is similar in scope (hard, but once you crunch the numbers you're fine) Life support would be substainally more complex and require a lot of experimentation to get right but it's still plausible. Also, another point - if you have multiple stations you don't need multiple... $\endgroup$ – ltmauve May 21 '17 at 4:13
  • $\begingroup$ ... manufacturing hubs per station as the stations would have an agreement to trade parts for those. $\endgroup$ – ltmauve May 21 '17 at 4:16
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    $\begingroup$ @Katamori : Yes it is possible; Think of the station like a residential neighborhood. Mine has several hundred houses, each self-contained, each connected to water, gas, electric and sewer grids, and three com grids: Telephone, TV, and Internet. Each has its own environmental controls, computers, and equipment for chilling, freezing, storing and cooking food. If any house is damaged, it can be repaired or replaced with little disruption to the rest of the complex. There is plenty of space for all living functions, for thousands of people. Adapt the same idea to a space station. $\endgroup$ – Amadeus May 21 '17 at 10:23
  • $\begingroup$ @Amadeus: Your neighborhood is unable to replace even the simplest electrical things - try to create a light bulb (and I'm not even talking about LED lamps). $\endgroup$ – Martin Schröder May 22 '17 at 23:02
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Most of the answers are about the need for redundancy and maintenance, which are probably a good way to go, but there is another option I think should be mentioned, which could function with little maintenance or repair.

The basic idea is to construct a self regulating biological ecosystem within a very over engineered hull.

In general engineering there is the concept of a safety factor; for a given design parameter, such as thickness of material, calculate if it will break under the expected load, if it is close to breaking you increase the thickness by the safety factor to account for errors and unforeseen situations. In general the higher the safety factor the more robust the design.

As an example for your space station: hull thickness, measure meteorite impact rates (micro and otherwise), solar wind ablation, radiation embrittlement or other parameters likely to lead to hull failure and make the hull thicker until it doesn't fail for your 5,000 year desired lifetime. You are likely to need a very thick hull to do this, I'm thinking around a km at a minimum to account for some large meteor impacts. This would be difficult and expensive, but not impossible, and your extra thick hull would add passive radiation shielding as a plus.

Some key points in addition to an extra thick hull:

  • Use a biological ecosystems to regulate the air and provide food and water, and recycling of wastes, this is going to take up a lot of space requiring a big internal volume.

  • Use large solar reflectors and very thick windows to allow for passive solar heating and energy input for your ecosystem.

  • Possibly use spin to provide artificial gravity.

  • Minimize moving parts or computerized systems as far as possible, and when necessary use redundant systems that are modular for easy maintenance and replacement. The likely problem areas will be airlocks or docking systems for ships.

The ecosystem may require balancing if you are moving large amounts of materials on and off the station, i.e. if each ship that docks fills up on water, eventually your habitat ecosystem turns into a desert not producing enough oxygen to keep the station alive. You would need to keep a strict mass balance on incoming and departing ships or more likely provide periodic resupply of critical elements.

What I have in mind is similar to the O'Neil cylinders or Kim Stanley Robinsons Terrariums. Effectively you are making an artificial planet, specifically designed to be solar powered and require minimal maintenance and function for a very long time.

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Start with rocky asteroid material mashed together until it forms a sphere about the size of our Earth. Put it into rotation around a Sol sized star for long lasting energy source, give it a molten core, and an atmosphere filled with a nice biologically conducive array of gasses. Make sure the distance from the star is in that star's Goldielocks zone. Give it a quick little spin for some nice weather effects.

Sure, it's going to seem like a planet to everyone else, but these guys will know it's actually their self-renewing, self-maintaining, redundant energy systems, millennially lasting space station. How will they know this? Well, because THEY made it.

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