Re: it's already doing 17.46 km/hour
@Barley registers Satellites have to keep incredibly precise time, down to the picosecond (which isn't macroscopic). Voyager 1 doesn't. As I said, time dilation takes place at any relative velocity but it takes a long time to build up to something meaningful. Even for GPS satellites it takes months to go a few picoseconds out of sync with Earth-based stations.