[nine_k]

Sadly, not very feasible because of the hydrogen atoms floating around in the empty space, about 1 per cubic meter.

At speeds about 0.5C a collision with such an atom produces X-rays, and harder gamma rays at higher speeds. They are pretty hard to insulate against, and are actively harmful. For a spaceship of a considerable size, enough collisions would occur to be dangerous. The paper: https://www.scirp.org/journal/PaperInformation.aspx?paperID=...

[gigaparsec]

To make it even worse, that's based on an average density 1.8 atoms/c3. The real values would probably vary wildly, and you won't be able to "break" in advance in order to go through a high density area.

And then there's the problem of hitting an interstellar grain of sand at 0.5c.

[mr_toad]

I wonder what the odds of survival are compared to sailing around the world in a Galleon.