Space is a near perfect vacuum so there's very little particulate matter to interact with. Even at very high velocity at sublight speeds it would take an enormous amount of volume to accumulate enough matter. The basic interstellar medium has a overall density of no more than a few thousand to a few million particles per square centimeter. A cubic centimeter of hydrogen on Earth has 42 million billion times more atoms.

Space is a near perfect vacuum so there's very little particulate matter to interact with. Even at very high velocity at sublight speeds it would take an enormous amount of volume to accumulate enough matter. The basic interstellar medium has a overall density of no more than a few thousand to a few million particles per square centimeter. A cubic centimeter of hydrogen on Earth has 42 million billion times more atoms. the only source of drag would come from interstellar mediums of a very high density like a Nebula, gas cloud, particulate stream, solar wind and energetic wave.

Star Trek uses deflectors to push away the interstellar matter travelling at faster than light speeds and sublight speeds. In essense much like a cowcatcher on a train or a snow plow. Even microscoping particles, running into them at a fraction of the speed of light. The device also aids in ships navigation by relaying particle affilation to determine particle density and composition.