C.E. Evans wrote:
Voyager-6 was equipped with an early impulse engine not too unlike those used on the DY-100 ships of that time. It was able to quickly overtake all five of the five previous Voyager probes prior to its disappearance.
I like that idea.
Also, I always figured that in the ST universe there is a black hole lurking somewhere near the Solar System, as indicated by the "black star" encountered in Tomorrow Is Yesterday.