The problem is when you work out the math on rocket that can sustain 1G for multiple days with any Earthly isp you realize the math just doesn't work. Even if you go nuts and plug in a number like 1 million seconds (our best chemical rockets are more like 450 seconds) for the isp it is still nowhere close to feasible using only the mass of our solar system.

As long as you are stuck flinging mass out of the back of your rocket to accelerate you don't get to go anywhere outside of our solar system.

Would it melt before then? Interstellar space is extremely thin, on the order of 1 atom per cubic centimeter (estimates vary). But, as we learned when Voyager finally left the solar system a few years ago, it is hot as hell. More than 54,000 degrees F according to National Geographic:

https://www.nationalgeographic.com/science/article/interstel...

The Voyagers didn't have today's ion engines. I don't know how much that gains us, though, as the main speed gain was by leeching momentum from planets' momenta, rather than from the hydrazine thrusters it carries

"Roundtrip Interstellar Travel Using Laser-Pushed Lightsails"

https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.10...