Streaking white dots

I was sunbathing in the mid-afternoon on the back deck of my family's home looking straight up into the blue sky. Suddenly I saw 3 or 4 white dots, in a straight line, streak across the sky from west to east. The streaking white dots appeared to be at very high altitude and moving incredibly fast. Within in one to two seconds they had crossed the sky. My first impression were that they were high flying jets. It was hard to comprehend...to cross the sky that high that fast. Then within 30 seconds, the event repeated. White dots streaking across the sky in a straight line, west to east. I continued to see white dots streak across the sky, in the same line of path, every 30 seconds or so. Now I thougt they must be satellites, but how could they circumnavigate the globe that fast to re-appear within 30 seconds? Just wondering what I saw?
Date is approximate.  Source is anonymous.  Satellites do not circumnavigate the Earth in 30 seconds.  PD