Interstellar Expansion WITHOUT Faster Than Light Travel

In the far future we may have advanced propulsion technologies like matter-antimatter engines and compact fusion drives that allow humans to travel to other stars on timescales shorter than their own lives. But what if those technologies never materialize? Are we imprisoned by the vastness of space—doomed to remain in the solar system of our origin? Perhaps not. A possible path to a contemporary cosmic dream may just be to build a ship which can support human life for several generations; a so-called generation ship.

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[savionhathorn]

I wonder if the generations who live and die on the ship would feel a little similar to the phrase at the start. Too late to see earth, too early to see the destination.

[billyfugate]

One of my favorite things to think about is a generation ship arriving at their new world only to be absolutely baffled by finding an even more advanced human civilization because FTL was figured out during the generation ships journey

[kapsi]

What I never see in discussions of long time space travel, is how to keep machines going for hundreds, thousands or more years. Everything eventually breaks down from usage, and you'd have to keep many spares, or manufacture needed components on the ship, which also seems hard to do. Here in current reality, it's a miracle that Voyager 1 still works (barely) after 50 years, and that's a super simple machine, compared to a generational ship to Alpha Centauri.

[Maladjester]

"We'll have to have a society based on teamwork, harmony, and mutual respect." Well, there goes that idea.

[aerohard]

Imagine arriving after the 6300 year journey and finding out humans just warp jumped to Proxima a couple decades after your generation ship was launched.

[FlorianGampe-zc]

Going towards Proxima Centauri to escape from the tri-solarians seems like a bad idea...

[TehJumpingJawa]

Given how accurate Humanity's prior estimates have been for future space endeavors, I'm confident that 30 year countdown would be just long enough for us to realize we'd need another 70.

[eirrenia]

Realistically, I think our best first step would be building space colonies/stations. Once we have those working reliably we can start thinking about generation ships.

[markcentral]

The existential threat scenario is the only one where this analysis makes sense. If this wasn't the case, you'd expect in the 6400 years it takes the slower ship to arrive, humans will devise a much faster form of propulsion -- and so the second or third ship they send will overtake the first one and get there first. Imagine the feeling of being on spaceship one, arriving at the destination, and discover there's been an existing human colony there which arrived 5000 years earlier 😂

[reconnaissance]

Imagine you're on route, have been for like 35 years into your generation, and then some futuristic ship with lightspeed picks you up and gets you the rest of the way.

[gewinnste]

One issue Matt didn't mention is the _energy problem_ : In fact, if all the recycling necessary would be improved to at least 99.9(9?)%, then energy would be the only limiting resource.

It's difficult to gauge whether a fission reactor would be suitable (lifetime of the reactor etc.) - But regarding the required fissile fuel, let's estimate the needed mass:

Upscaled from the ISS, 500-1000 crew members would need very roughly 10 MW, but upscaled from a Virginia Class nuclear submarine, 500-1000 crew members would need ~115-230 MW. Most of the energy in a nuclear sub goes into propulsion, but then again, maybe almost as much (or even more?), fraction-wise per crew member, would be needed to keep homeostasis (growing food etc.) in a generation ship.

So let's semi-optimistically say 100 MW for 500-1000 people. That would amount to very roughly 500-1000 tons of ~30% enriched uranium (nuclear subs use >20% enriched uranium, >50% would maybe be too dangerous (?)) for 6000 years for 500-1000 people:

1 kg pure U235 --> 24, 000, 000 kW/h = 86, 400, 000 MJ (~86 TJ) --> 864, 000 seconds at 100 MW = 10 days --> 36.5 kg/year --> ~220 tons 100% U235 for 6000 years --> 730 tons 30% U235 for 6000 years. If that could be stored as one giant cube (which it won't), it would be a cube of edge-length ~3.4 meters, so very manageable.

In reality the space for storing the equivalent in uranium rods would be a lot larger, but it's certainly not a deal-breaker (neither volume- nor mass-wise). An unknown factor is the life-time of the reactor though - that could in fact be a deal breaker. 6000 years is ~ 100-250x a regular nuclear reactor lifetime!

Then, since fusion is always 30 years away ;-) it might not be an option, but even if, there's the reactor-lifetime problem again.

What about solar panels?

They only work efficienctly (energy per surface area) close to a star and the vast majority of the trip will be very, very far from either star (Sun and target star), so photovoltaics are under no circumstances feasible: Even at Earth-orbit distance from the sun, 100 MW would require the surface are of a ~700x700 meter square of 15% efficient solar panels and that area quadruples for every doubling of the distance to the sun. I.e. at Neptune that square would need to have an edge-length of 21 km and somewhere in the Kuyper belt of ~100 km edge-length. And that's just 0.05% of the trip to the nearest star!

So it looks like we'd need a very, very long-lived fission or fusion reactor or one that can be "refurbished" with onboard resources hundreds of times;
Or something like an Epstein drive, but that would bring about the problem of micro-asteroids or just dust grains doing a lot of damage on impact.

[SmartMaterial]

I predict future colonists will be groups of cells in a petri dish.

[stevesmith]

One of the concepts missed is "not putting all eggs in one basket". If the only constraints are time and technology, and not costs, resources and volunteers, then we're going to have to launch a number of these colonizing ships, just to increase the odds that one succeeds.

Multiple ships with communication between the ships may help out with some of the human, psychological challenges too.

[erics]

There's an ethical side to this discussion that I think is just as important to explore as the feasibility of being able to pull all of it off. The first generation will, presumably, be volunteers, and that is fine. But every subsequent generation has been forced into what is likely going to be a dismal existence without any say in the matter. At some point there will be no surviving first-generation passengers and the ship will be filled with people who only know of living on a planet through second hand sources. It will be important for the success of the mission to try to understand how these people might react to being in that situation. I suspect there will be a lot of resentment, which will not bode will for the successful completion of the mission.

[JonCofer]

Generations of humanity born on a spaceship, learning about earth from VR and getting life advice from a growing AI therapist is the most SciFi thing I’ve ever heard. I love it

[noiJadisCailleach]

Children of Time by Adrian Tchaikovsky.
Multi-generational ship? Check.
Traveling to another world? Check.
Disasters happening en route? Check.
Humongous sized ship? Check.
Psychological stability issues due to environmental conditions? Check.
Ship has AI? Check.

If the things in the vid somewhat intrigues you, I highly recommend that book!

[DobromirManchev]

Thinking about a 6000 years journey is absurd. Imagine how much humanity has changed on Earth in the last 6k years. The countless discoveries, wars, diseases, struggles and things... it's mindboggling. There's absolutely no way that you can get a tiny set of people, stick them on an isolated hunk of metal for 6k years and expect it to work. Tbh, they'll probably not even last 20 years.

[thebourgeoispunk]

When you stop to think about it, Earth is a pretty great spaceship except for that last part of figuring out how we’re all supposed to live together. that’s the hardest to figure out.

[crewrangergaming]

"We are the middle child of human history" this is well put.

[iNeo]

One aspect of the challenge missing here is the repair and maintenance of the ship. Most machines we have today last less than a human lifetime. Cars and computers don't work much more than 20 years, so a much more complex ship will need a self sufficient way to recycle not only water and air, but also every single one of its electronic and mechanical components. Let's say a computer on board needs a motherboard. The ship will need a machine that can melt down this mother board after and build a new one. That machine will need to be able to rebuild itself too. It will be the spaceship equivalent to eating your own arm in order to regrow the other. Such a ship can't just pull over next to an asteroid and mine new resources.