There are no protons during the vast dark space between
the sun’s. Keep in mind we are only 9 light minutes away from the sun so we on earth get stuff discharged by our sun. The next nearest star is 4.25 light YEARS away. You must get your mind focused on the distances.
As for maintaining a vector, there are no forces on a bridging the gap between solar systems, so once aligned, it's a straight line. If you can harness cosmic rays, you can adjust if for some reason you needed to. And you only have to get close enough to catch rays from the next star to navigate through that solar system.