Interstellar Expansion WITHOUT Faster Than Light Travel

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.

What we need is lots of spice

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

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

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.

Hey Space Timers! If you enjoy thinking about the realities of human space travel, then check out the documentary Space: The Longest Goodbye. And if you head over, let them know (politely) that Space Time sent you! https://www.youtube.com/watch?v=MT-pV48XBI4&t=0s&ab_channel=PBS UPDATE: Currently the YT Link is only accessible in the US. We're working to see if we can get full international access.

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

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.

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.

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.