Ask Lemmy

Greg Egan's Diaspora sets out how humanity could explore the galaxy and even the multiverse, which if you can't be bothered reading consists of:

1. Upload conciousness into computers, leave physical bodies.
2. Miniaturise computers until we have spaceships in the grams/nano grams
3. As we're no longer connected to time we can build massive solar system sized technologies, built by nanotech, that sure could take hundreds of years to build but in our virtual realms we could easily sleep.
4. Use Lasers to propel our nanogram spaceships to 90% light speed. Even then for the astronauts, time is almost nothing (time goes slower the faster you go). A trip across the galaxy would feel like mere weeks to you. We could explore the universe as immortals.
5. At this point we should have a pretty good understanding of dark matter/energy and how to move between universes (the multiverse, depending if you accept it as a base for explaining non locality)
6. Which would allow us become eternal.

In the here and now the only way to travel to another system with our current tech is via nuclear pulse engines.

Basically you build a large spaceship. Stick it on massive shock absorbers which are in turn connected to a metre plus thick steel plate.

Cut small hole in the middle. Have a door that opens closes.

Eject 1kt explosive device out door. Repeat 500x till you get to orbit.

Basically you could get a spaceship up to very high speed with nuclear pulse engines to turn a multi hundred year journey into less then 100 years.

That said the biggest problem with interstellar journeys is that our material science and manufacturing tolerances are pretty shit. Essentially all of the air will leak out through the metal skin of the spaceship.

I still think carving put an asteroid, sticking engine on it (see nuclear pulse engines) , covering it in ice and water will solve the problems radiation shielding, losing critical gases and provide ample fuel and water for a very long journey.