As the distance a spaceship travels through space increases, so do the odds that it will collide with debris in its path – such as interstellar dust, micrometeorites, asteroids, dark matter, dark stars, etc.
If you are traveling at super high-speed, through uncharted territory, there is no way to know what is out there.
Even if it is charted territory, debris is always flying through – sometimes at incredibly high speeds. Especially when you near solar systems, or in denser areas.
It should be possible to say that after a certain distance the odds are 100% that a spaceship will experience a fatal collision.
As a result, only short range space travel is probably safe enough to be feasible unless some kind of shield technology is invented that can withstand the blasts that result from collisions with even tiny things at such high speeds.
My guess is that if advanced interstellar civilizations exist, they do not travel linearly through space because it is just too dangerous. They must have a way to "tunnel" – either by using or creating wormholes, or some other means of teleportation, or hyperdimensional travel.
In speaking about this, my friend Josh, suggested the following:
Yeah- and here's another aspect to that problem.
Assume you are using a near light speed drive to go from star to star.
Any detection system you are using (radar, etc) will only extend slightly in front of the ship- because it is only moving slightly faster than you are- and the faster you go, the less time you have to detect and deal with obstacles or objects.
If you are moving slowly- perhaps a generation ship or a "frozen cargo" scenario- you could use radar connected to an autopilot- but you still need something to protect you from micrometeorites and interstellar dust- maybe a big electrostatic shield extending far in front of the ship that will attract and deflect such objects (most meteroids are ferromagnetic, so they respond well to electromagnetic fields...)
You really need a rapid response detection system...