Well voyager depended on a solar system alignment that only happens every 175 years(?) so it'd be a while before we get that same advantage again. The longer it takes the further of a head start voyager gets?
A flyby of both Jupiter and Saturn can be done every two decades or so (the synodic period is 19.6 years)
New Horizons (which has the distinguishing feature of being the fastest human-made object ever launched from earth https://www.scientificamerican.com/blog/life-unbounded/the-f... ) is traveling at 12.6 km/s.
The key part there is that it got multiple gravity assists as part of the Grand Tour https://en.wikipedia.org/wiki/Grand_Tour_program . You can see the heliocentric velocity https://space.stackexchange.com/questions/10346/why-did-voya... https://www.americanscientist.org/article/the-voyagers-odyss...
The conjunction for the Grand Tour is once every 175 years. While you might be able to get a Jupiter and Saturn assist sooner, it is something that would take the right alignment and a mission to study the outer planets (rather than getting captured by Jupiter or Saturn for study of those planets and their moons).
While I would love to see a FOCAL mission https://en.wikipedia.org/wiki/FOCAL_(spacecraft) which would have reason for such a path, I doubt any such telescope would launched... this century.
IE either what speed Voyager 1 launched at excluding the gravity assists, or what speed New Horizons would have reached if it were launched 175 years after Voyager 1 (to take advantage of the same gravity assists)?
Another part in this is the "the probes are slowing down over time" - and you can see that with the Voyager 1 data that while the velocity after assist is higher than before, its not a line at slope 0 but rather a curve that is slowly going down.
This is further complicated because New Horizons had a launch mass of 478 kg and voyager was a twice as massive at 815 kg.
They also had different mission profiles (Could Voyager 2 taken a redirect from Neptune to Pluto? That trajectory change would have required a perigee inside the radius of Neptune...)
Voyager was done with a Titan III-Centaur rocket (that had a misfire) https://en.wikipedia.org/wiki/Titan_IIIE
> Voyager 1's launch almost failed because Titan's second stage shut down too early, leaving 1,200 pounds (540 kg) of propellant unburned. To compensate, the Centaur's on-board computers ordered a burn that was far longer than planned. At cutoff, the Centaur was only 3.4 seconds from propellant exhaustion. If the same failure had occurred during Voyager 2's launch a few weeks earlier, the Centaur would have run out of propellant before the probe reached the correct trajectory. Jupiter was in a more favorable position vis-à-vis Earth during the launch of Voyager 1 than during the launch of Voyager 2.
Note also in there that a few weeks difference between Voyager 1 and Voyager 2 had different delta V profiles (which is why Voyager 1 is faster)
New Horizons was done with an Atlas https://en.wikipedia.org/wiki/Atlas_V
... and I don't have enough KSP background to do the orbital mechanics for this.
That alignment will happen many more times in the history of humanity. That is to say, I don't know if a spacecraft to overtake Voyager will be launched on the next alignment or one 10,000 years from now, but it doesn't seem unlikely to happen.
Once we leave the solar system in a self sufficient way I can’t see any event which would cause a species level extinction
And we would have to establish the reason for the colony … I’m not talking about a research base, but a place where people would settle, do useful ecomonic activity, raise families and live out most of their lives … I cannot 5hink of a reason why people would want to do 5hat anywhere but Earth.
Interstellar travel is a physics problem, not an engineering one. Even make believe nuclear propulsion is still aggressively limited by the rocket equation and still wont get you anywhere in a meaningful time frame.
There will never be an interstellar empire. It will never make sense to do trade between two planets that are otherwise capable of producing things, because the energy cost of doing anything in space absolutely dwarfs any possible industrial process. It doesn't matter how low quality your local iron ore is, importing ore from a different planet will never be a better option because transportation costs are effectively infinite.
Human trade is almost entirely based on the fun quirk that sea based transportation is ludicrously efficient, such that you can ship a single pound of product all over the globe and it can still be cheap. The physics of space are essentially the opposite of the physics of sea travel, in that it is dramatically harder and more energetically expensive than almost anything else you can do, and the energy regime it operates in will dwarf any other consideration.
If there was a magical way to turn joules directly into a change in kinetic energy, as in a machine that could magically extract every joule of "energy" from matter in an E=mc^2 way and directly reduce an object's kinetic energy by that much, taking a 100 kilogram human up to half the speed of light and eventually slowing them down again would take 31 kilograms of matter to "burn", and you have to accelerate all that matter too. That matter would require another like 10kg of matter to "burn" and then you have to accelerate that matter too and so on and so on.
And we do not come even remotely close to any mechanism, real or theoretical, that could convert mass to a change in kinetic energy. Even if you had like a magic antimatter machine that could come very close to turning a gram of matter into it's entire "energy" content, ways of turning thermal or electrical energy into thrust have their own inefficiencies, difficulties, and do not even come close to mapping to "Each joule of energy equals a joule of kinetic energy change".
And even with our magic spacecraft machine that cheats physics, that's still an 8 year round trip to Alpha Centauri and back, with something like a 50%-65% payload fraction.
The scale of things in space combined with the nature of that space makes interstellar anything nonsensical. Even interstellar travel of just information is fairly mediocre. SciFi will never exist in our world, and at this point should probably just be called "Fantasy with more plastic"
Its not "interstellar speeds" but I'm pretty sure we could get probes further out than Voyager 1 faster if we put the money behind it.