For example, impulse engines can not accelerate a ship to anywhere near the speed of light. But they can accelerate it to enough of a fraction of C that things like time dilation become problematic. No breaking of physics but surprise surprise now your crew is 3 minutes younger than they should be, relative to Earth. Add that up over time and you’d potentially have to start swapping out crew members so that they don’t end up younger than their children when they retire. The Star Trek Voyager Technical Manual lists “full impulse” as 1/4C, or nearly 75,000 kilometers per second, which is probably why you hardly ever see it in use unless it’s a life or death situation.
For example, impulse engines can not accelerate a ship to anywhere near the speed of light. But they can accelerate it to enough of a fraction of C that things like time dilation become problematic. No breaking of physics but surprise surprise now your crew is 3 minutes younger than they should be, relative to Earth. Add that up over time and you’d potentially have to start swapping out crew members so that they don’t end up younger than their children when they retire. The Star Trek Voyager Technical Manual lists “full impulse” as 1/4C, or nearly 75,000 kilometers per second, which is probably why you hardly ever see it in use unless it’s a life or death situation.