In the not-too-far future, Mars hosts a few mining complexes that extract, refine and send materials back to our planetary system, as well as some scientific research bases. Commutes between them and Earth are sparse and mainly reserved for the ore, with even sparser travels dedicated to rotating people in and out, so those complexes are of course equipped to be able to survive in autarchy for extended periods of time if need be — facilities, gear and qualified personnel.

When suddenly

Oh no, something funny happens to people on Earth. Due to the nature and unfolding of the event, travels between Earth and Mars have not been resumed in time for the colonists to be brought back before such an operation became impossible, so now they're stuck on their barren rock indefinitely, with no contact with anyone.

Well, fuck it. They've got mines, mining gear, refineries, automated and remote-controlled instruments and vehicles capable of assembling stuff and repairing each other, advanced machinery supported by A.I. software designed to synthesize materials ranging from anti-radiation shielding to medical products, all the brains (organic or artificial) needed to operate and engineer; they'll just build their own ship and get back to their homeworld on it.

The catch

For story reasons, I need this enterprise to be a multi-generational one stretching as long as a few centuries. Tee-hee.


There isn't really a shortage of factors I can leverage to push back the project's finish line:

  • The sheer size of it. Even with a relative abundance of raw resources and tools that are advanced for their original mission, the sustained engineering and building efforts alone make for a formidable challenge, I don't think I really need to expand on that. Especially since the assembly will be made in orbit, to stay in line with the "realistic-looking" approach I would like to take.

  • The resources allocation balance between the project and basic survival. Dedicating them to the ship means dedicating less to other daily essential tasks. This includes material resources as well as the personnel themselves. And survival will always take priority over the ship, should resources become scarce for whatever reason.

  • Building the ship might involve, at some point, stripping and repurposing parts from the colony among the ones most difficult (if possible at all) to manufacture — I'm mainly thinking about microchips for instance, but it could also be extreme late-game cases like using the generator(s) to power the ship. If it comes to that, then they start trading the operational status and the productivity of the colony for progress on the project.

  • So much could go wrong with the population. I should probably do the math to determine how many people there are, but regardless of what the figures are, the nature of the project (and the conditions under which it's being undertaken) forces the colonists to not grow over time, or to a minimal extent. That means everyone is an actively valuable individual, and any untimely death by accident, disease, homicide or suicide is a potential blow to the project. Also if, God forbid, they fall below the minimum viable population number, there isn't even the hope for an eventual recovery.

  • The previous point can be extended to gear/buildings. Having repair machines that can also take care of each other is one thing, but losing a complex, specialized facility to something as stupid as a fire is another.

  • How do you find time for the ship when you've got kids to care for, raise, and teach to? As I was writing the point about the population, I realized the colonists will also have to do that eventually — and do it well. They really can't afford to neglect that part, as ending up with a next generation that is not up to the task of carrying on their work makes the whole thing utterly pointless. So this is a major strain on both resources and the time they've got on their hands.

Those are the main things that come to my mind, I'm sure there are others. So my question is: several hundreds of years to complete the ship, in the realm of reasonable suspension of disbelief or way overkill?

Additional note: for the sake of framing, I should specify that whatever happened on Earth affected the population, not the environment, which the colonists know. Earth is still perfectly inhabitable and infinitely more preferable than Mars as a home, so they do have a strong incentive to go back there, as opposed to just declaring that Humans are now a Martian species and roll with it.

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    $\begingroup$ Seems like you could write an arbitrary number of setbacks into the construction of the ship. This seems like a story question not a worldbuilding one. Please remember that we're not a brainstorming site asking us to generate ideas for you is not permitted on this site. $\endgroup$
    – sphennings
    Apr 22, 2023 at 2:48
  • $\begingroup$ For future reference, please be aware that the help center states that offering your own answers and asking for more is prohibited (a reason to close the question). The only time it's permissible to offer "answers" is when you're explaining why they're insufficient. In that case, they become restrictions and conditions that help us understand how to get you better answers. $\endgroup$
    – JBH
    Apr 22, 2023 at 3:40
  • $\begingroup$ @JBH Ah, I the implication of my question was that I doubted my "answers" were sufficient for the timescale that interests me, my apologies if it wasn't clear! $\endgroup$
    – Kubler
    Apr 22, 2023 at 10:11
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    $\begingroup$ There's another question which might be of interest: Spaceships without computers?. If they go down the "we sure need a computer" route first, then finally settle for a ship without, think of the time wasted... $\endgroup$ Apr 22, 2023 at 15:31
  • $\begingroup$ @AngryMuppet Good suggestion, thanks! $\endgroup$
    – Kubler
    Apr 22, 2023 at 15:49

4 Answers 4


They don't know how...

Granted, it wasn't much of a test, but on a whim I tried to find the construction schematics and fabrication details for the Space Shuttle (any one of them) on the Internet.

I failed.

We tend to think that the all-knowing, all-powerful Internet has everything on it. In reality, it has only a smattering of human knowledge. It may be true that things are accessible if you know how and have the right credentials... but the fact of the matter is, I can't find the information I need to build a space shuttle.

Neither can your Mars inhabitants. In fact, they can't find anything other than cutaway drawings of anything that would be remotely useful. They can't even find specs to build old stuff. Which isn't unreasonable. Why haul the entirety of human knowledge to Mars when chunks of it can be made available upon request? That minimizes the infrastructure required to house, maintain, and make all that data available.

If you think about it, it's really unlikely that there's one spot on Earth that's publicly accessible and hosts all of the knowledge available via the Internet. It wasn't actually designed that way. I'd be surprised if even Google had all the eggs in one basket... even accounting for redundancy. Distributed resources are always more useful than a single resource.

So, the reality is that there will be a LOT of experimentation, innovation, and investigation just to get the knowledge needed to push a ship from the surface of Mars to anywhere else. And when you start thinking it through, the amount of information that's needed to do that even today... is breathtaking. And we've already worked it all out.

They haven't.

So I can easily see multiple generations just on this alone.


By definition you need to work weaknesses into your system that rationalize the goal you're seeking. That's really not hard. Your AI is focused on specific solutions to expected problems. Why worry about programming an AI-controlled medical center to do full research and analysis on any previously unencountered pathogen when the odds of that happening in a controlled environment like Mars makes the whole idea cost prohibitive? Just ship it back to Earth where the military can classify it quick anyway. And why build an AI to control your mining operations that also knows how to figure out rocket engines?

Your people will be reconfiguring what they have something awful to do the one thing humanity is reasonably good at that usually takes a whomping long time anyway: inventing something out of nothing.

And in the mean time they're also trying to figure out how to make due without the regular Earth supply runs. No city on Earth today is wholly independent. Neither's Mars. Now you have a multi-generational race against time. I like it!

  • $\begingroup$ Lots of stuff I'd missed here! Many thanks for this great answer. $\endgroup$
    – Kubler
    Apr 22, 2023 at 10:05

There's some options here:

1: There's no Rocket construction, Test and Launch facilities on the surface of Mars

So, you said that people regularly rotated in and out before something happened, but if we presume that there is a ferry type spacecraft that takes the bulk of Cargo/Personnel from Mars to Earth and that it stays in orbit (getting into Orbit takes a lot of fuel and energy) and it uses smaller vessels to ferry from Orbit to the Surface, you could make a reasonable case that it never made sense to have a Rocket Facility on the surface of Mars.

Finding a suitable location (Flat, Away from the populace - safe from meteor strikes etc.) could easily take a few years.

Then you've got to terraform the launch site - in earth on a regular construction project, this could take several months to over a year - but we will double/triple the time taken cause Mars and no atmosphere and the additional challenges of working not on earth.

Finally once the site is prepped you need to actually build the facilities - think of how long it must have taken to build Cape Canaveral from scratch - and again, double/triple the time taken cause atmosphere. So just to build the area to start this project, we've got a 20-30 year project.

Rocket motor Testing!

So - anyone right now could jump online and learn exactly how a rudimentary, open-bolt, fixed firing pin Sub-Machine gun works. Big Spring, Big chunky bolt, Barrel, trigger/sear and Magazine. Easy. Right? Well, although the mechanics are relatively simple, there are a lot of Gotchas that without doing a lot of trial and error and starting from a position of Zero gunsmithing experience takes time - And that is an object with 3 moving parts (Bolt, Trigger and the Magazine) - Something like a Rocket Motor - which although in it's most basic form is 'simpler', when we are talking about a motor that is capable of inter-planetary travel - is much more complex - we will need years of testing. And we can only safely do that testing after we've built the facilities. Call it 20-30 years. Consider this - there are nations on earth right now that know what an ICBM is - have seen American and Russian Missiles and know the basic theory of how they work (Even Werhner von Braun would understand how a modern rocket works...) - yet are spending years upon years to produce something that reliably works and does that they want it to. So already, we've got 60 or so years worth of time spent.

More Testing

So, we've got our Rocket, we've got our facilities - let's jump in and go, right?

Would you be willing to do this? Hell it took the Apollo missions 10 years almost to get from first tests to landing on the moon. But Mars is much further, despite achieving this in the 60s, we haven't put a man on Mars yet - so that's another 60 years of faffing around testing, overcoming technical challenges etc.

So we are up to around 110 years.

Catastrophic Failure and set-back

Nothing sets a project back like a high-profile catastrophic failure. Think Apollo 1, Apollo 13, the Columbia Disaster etc. etc.

You can easily waste a decade or two on a major safety event that was high-profile and calls into question the competence and leadership of the team - something where even a lay-person would be like 'How did they miss that?' - The O-Ring on Columbia is a perfect example of this.

And this leads nicely to the best way to make a project go into development hell that lasts for a long time:

Politicking and Corporate in-fighting

The challenges and the physical construction and time spent can give you ~ 100-150 years of believable reasons for the delay. Building everything from scratch, having to develop the practical skills of rocketry, the inherent challenges of large-scale projects in a hostile environment. But nothing will slow a project down more than a bunch of self-righteous Middle Managers, Bean Counters and Political whores (e.g. people who play office politics and have their own little agendas and suck up to the boss - not ladies of the night)

Throw some of that in at key junction points and you could probably stretch it out to over 200 or so years.


I'd politics and microchips.

1 - As soon as the shit hits the fan on Earth (caused by politics, right?), you'd also have factions on your colony. Not necessarily the same as on Earth, but those for assigning all resources to get back as soon as possible, those who don't want to go back, and those more prudent in between. Build some infighting, sabotage and colony splits and it can last a LONG time before they manage to build anything difficult.

2 - Microchips are one of the most difficult thing to build right now. There's only 2 (3?) factories on earth for the most advanced ones and they cost tens of billions and decades to build. There's no way they can replicate them, unless they want to use Apollo-era guidance systems for their return trajectory. So the longer they stay, the fewer microchips they'll have and the more 'native' they'll become (cf 'politics' above).

Compared to the above, building a rocket engine to leave Mars' gravity well sounds almost trivial if you have some quality metals.


Century or less

Your colony is self-sufficient, they have facilities to produce stuff they need. It needs to be, as you cannot have a large scale colony off-world because lifting stuff ot of Earth's orbit is way too expensive for the colony to be dependant on trade with Earth. And if for some reason your colony need some thing from Earth to survive, then your colonist will die out shortly (and thus no story will happen).

As for the problems other answers provided: they seem to forget that we put a man on the Moon just years after launching the first satelite. And we lacked much of the knowledge we have today. Often the hardest thing is to figure out that something is actually possible, and your colonist will KNOW it is possible to build interplanetary spaceships. So even if they had to go trough space program from scratch it wouldn't take THAT long. As for microchips... Even a few decades ago almost every important country build its own microchips. Sure, your colonist wouldn't have knowhow to build cutting-edge ones right from the start, but they can develop that tech, same as with everything else. Just look what we achieved in the last century on Earth!

Honestly, the biggest issue in that spaceship building project is the population size. You need a certain number of people to even attempt such big projects. But the number of people on your colony cannot be super small, as otherwise they would have inbreeding issue and you would again have a problem of them never finishing the spaceship (and probably dying out).


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