Interstellar Expansion WITHOUT Faster Than Light Travel

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.

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.

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.

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

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

What we need is lots of spice

Another issue, especially with the 6000-year trip: The first generation or so will have attachments to Earth and the motivation and training to keep things going. A few generations into it and it'll be, "What's Earth?", "The heck with future generations, what about my needs?", and "Dad, I don't want to be an engineer, I'm an artist." Chaos Theory and Murphy's Law are undefeated.

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!

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

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.

6,300 year travel is a comically long mission timeline. Though I think this could be a fun and thrilling sitcom.

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.

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

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.

Remember Spacetime, a common mistake @3:51 : cryogenics is not the technology that froze Hans Solo. That's cryonics. Cryogenics is the study of production and usage of really cold non-biological material, like liquid H2 and O2 rocket fuels and cooling the magnets in the LHC.

6000 years living on worms and yams. Where do I sign up!

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 😂

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.

One way to explore these ideas is to study what can be discovered of Pacific islanders. Small groups set out on long journeys into the unknown, found islands and established some richly independent cultures.