# Does speed in space really matter?

This is about validating the science from a science fiction novel.

My understanding is that speed is all relative. So while I am in a car on the freeway my speed relative to another passenger is zero, relative to a street sign is 75, relative to a car travelling the opposite direction is 150, and relative to some point off the planet it is much greater.

Now two cars traveling at the same speed and direction would have a relative speed of 0, but because of imperfect roads and wind resistance, the speed relative to earth would still impact the car's interactions. For example, walking between a board connecting the two cars would be much easier at 10 km/h than at 100 km/h. But the relative speed of the cars compared to a distant star has no measurable impact.

So how does this translate to two spaceships? Is a space ship traveling at 1000 km/h relative to a star in the solar system any more likely to strike debris at a faster speed, than one that is stationary relative to the star? Likewise, is it more difficult for two ships traveling at 1000 km/h relative to a star (both with the same heading, speed, etc.) to dock, than two ships stationary relative to that star?

It would seem like acceleration would be the only influence, unless solar winds have a bigger impact then I imagine. Without resistance, it would require just as much effort from the maneuvering thrusters to maintain a specific speed as it would be to hold still.

Theoretically, no mater how fast, or in what direction I am traveling, there is some point, at some distance, in space, to which I am stationary (relatively).

Your assertion that only relative speeds matter is absolutely correct. However, you might want to look at the velocity addition of special relativity for space ships or whatever else travelling at relativistic speeds. For speeds high above our everyday experience, two things which, relative to us, travel in opposite directions with a speed $v$ will not see the other as travelling with speed $2v$ in their stationary frames.