On: Relativistic Spaceship

[senectus1]

what about for the period of time that you're travelling sideways with a largely unshielded broadside facing not exactly empty space?

[eru → senectus1]

You wouldn't literally turn around.

You'd probably move your rocket engine over to the other side (or have both a front and back engine in the first place).

Most of the mass of your spaceship will be fuel (like 90%+). You can use that as shielding.