Original Question (answered in 2026 C.E.): Will interstellar travel ever be possible?
The deck is stacked against us. It may one day become physically possible, but we would probably not have the political will to make it happen.
Consider the following points:
- Because we will never achieve anywhere near light-speed in terms of travel, humanity would have to be willing to do a 100,000 year-long space mission for most worthwhile interstellar human travel to work, but so far, humanity has only had nothing greater than about a 50-year-long space mission (the Voyager mission)
- The target interstellar system should be a yellow-white dwarf star (like our Sun) or an orange dwarf star that isn’t known for too many harsh flares, because almost nothing else will work well with us in context of our normal green photosynthesis environment and radiation tolerance; and this limits the total star systems anywhere realistically close to us that are attractive
- The political will to continue sending resources out into space to help the interstellar space-station must remain high enough for about 100,000 years despite the fact that countries never last anywhere close to that long in years of time and despite the fact that politicians won’t get a lot to point to as successes to their constituents except for the space program as a jobs program for people on Earth
- Radiation shielding for the space station must be adequate for interstellar space as well as for dealing with the radiation profile of the target star that the space station is supposed to orbit around
- The people and robots in the space-station must be able to repair the space-station
- The design of the space-station would be ring-shaped with spokes (like a bicycle wheel) or micro-planet-shaped in order to overcome the micro-gravity problem of weightlessness in space, and these are both expensive designs to construct in outer-space itself
- Humanity presumably has to figure out how to keep the space-station heated on the inside for tens of thousands of years while the space-station is too far away from stars to get a reliable amount of heat energy from them; presumably, lots of nuclear power plant electricity would be the solution
- Duplication of essential functions (from water filtration to heating to oxygen management systems) will be preferred in order to ensure the mission’s success
Interstellar space travel is a money-pit, and people will clamor for millennia about how much money civilization is burning away to keep alive a hope of traveling to a distant star.
So, what are the prospective star system candidates that we might want to try to reach? Well, remember that they would likely be solar systems with stable yellow-white stars and orange dwarf stars within a realistic range of travel (even in this astronomical marathon of travel scenario). We have less than 15 candidates, with some being iffy.
Prospective stable orange dwarf and yellow-white star candidates (with distance away from the Sun in parentheses at the end):
- Toliman (i.e., Alpha Centauri B): borderline okay orange dwarf star with an occasional flare and elevated X-ray production (4 light years away)
- Rigil Kentaurus (i.e., Alpha Centauri A): yellow-white star in a binary star system with Toliman (4 light years away)
- Epsilon Eridani (i.e., Ran): orange dwarf star that might have strong stellar winds (10.5 light years away)
- Procyon A (i.e., Alpha Canis Minoris): technically a white F5 star but probably close enough to also work, though it is part of a binary star system (11.5 light years away)
- Epsilon Indi: orange dwarf star with a binary system of brown dwarf stars orbiting it at a far-out distance (11.9 light years away)
- Tau Ceti: yellow-white star with a dust or debris field but no other orbiting star (11.9 light years away, about the 20th nearest known star system to the Sun)
- 40 Eridani: triple star system with an orange dwarf star (16.3 light years away)
- 70 Ophiuchi A: an orange dwarf star in a binary orange dwarf star system (16.7 light years away)
- Sigma Draconis: orange dwarf star (18.8 light years away)
- Eta Cassiopeiae A: yellow-white star in a binary star system with a weak orange dwarf star with an orbit at a substantial distance away of 35 to 105 astronomical units (19.4 light years away)
- 36 Ophiuchi C: orange dwarf star in a triple star system (19.5 light years away)
- HR 7703 A (i.e., Gliese 783): orange dwarf star in a binary star system that is somewhat approaching the Sun (19.6 light years away but eventually expected to get to 7 light years away)
- 82 G. Eridani: yellow-white star similar to our Sun but apparently with large planets orbiting close to the star (19.7 light years away)
- Delta Pavonis: yellow-white star that is traveling towards the Sun and is at risk of turning into a red giant star but is otherwise one of the closest stars to the Sun in attributes (20 light years away)
Does anyone seriously think we are going to even try to do anything over 20 light years away? The more time it takes to reach the destination, the more money it’s going to cost to keep the mission going, and that is all going to be in a parabolic fashion with financial costs the further distance that the space-station has to go.
Gliese 570 is also an orange dwarf star within 20 light years of the Sun but has at least one red dwarf star in its local star system.
Addendum:
Someone named Daniel responded to my above post, saying:
To say that we can never achieve anything close to light speed is fallacious. We have the technology now. But we do not have the funding or global resources.
Speeds close to light speed could be achieved with a high powered laser and a solar sail. Warping spacetime is known to be a viable theory consistent with general relativity and no scientific finds have contradicted it yet.
Neither radiation protection or artificial gravity are as big a challenge as you make them out to be.
We don’t have any technology to warp spacetime in any special way like the science fiction concept of a warp drive, and I suspect that that is not possible. We can use planets, moons, our Sun, and maybe a small blackhole (if we find one in a good location) to help slingshot a spaceship along, but again, we’re not going to get close to light-speed.
Solar sails are an interesting concept. Maybe we could cut down the years some through that method, but we won’t be getting close to light-speed with them in any spacecraft large enough to send people or the ingredients for a new ecosystem for humans in them. The inverse square law would also apply in terms of how much thrust the spacecraft would get for acceleration away from our star. That will limit the total speed of the spacecraft.
As I type this, the Wikipedia article on solar sails suggests a much lower speed than light-speed for solar sails.
For Saturn, the minimum trip time is 3.3 years, with an arrival speed of nearly 19 km/s…
It has been proposed that an inflated sail, made of beryllium, that starts at 0.05 AU from the Sun would gain an initial acceleration of 36.4 m/s2, and reach a speed of 0.00264c (about 950 km/s) in less than a day. Such proximity to the Sun could prove to be impractical in the near term due to the structural degradation of beryllium at high temperatures, diffusion of hydrogen at high temperatures as well as an electrostatic gradient, generated by the ionization of beryllium from the solar wind, posing a burst risk.
Google Gemini AI says 950 km/s is about five times faster than what we have achieved in space probe travel (such as with the Parker Solar Probe), but is “approximately 0.317% of the speed of light.” So, multiply the light years of distance by 315 for the time it would take for a space probe-sized object. An Alpha Centauri journey then still takes over 1,260 years to complete on a one-way trip, and a journey to 82 G. Eridani would take 6,300 years; but if Wikipedia is right, even that fast of travel from solar sails might not be possible. I have my doubts.
Then there’s also the likelihood that Earth would still need to send the space-faring humans more resources over time as they try to make a home on a planet in the target stellar system. That adds to the total amount of years needed for the mission as a whole.
One of the main points in my answer is on financial cost. Adequate radiation protection and artificial gravity for an interstellar mission aren’t going to come cheap here, and some radiation shielding may also need repairs over time, which is part of the total price tag.