Object observed in the sky I don’t believe was man made.

While driving I observed a very brief very white flash or strobe from the sky. This caused me to look skyward which I did. After looking up into a clear blue cloudless sky I saw nothing for 8 - 10 seconds. I then observed an object that I would estimate to the size of a commercial airliner drifting to the east at an elevation of 15,000 - 20,000 ft. Battleship gray in color. After observing this object for maybe 5 - 8 seconds it disappeared. I continued to look in the sky and saw nothing. Another strobe or flash occurred in the sky but I saw nothing in the sky. I produced a drawing of the object but it looked much more advanced than I could create in a drawing. I checked with local law enforcement, see if they had any reports of something unusual in the sky. They had none. Also checked with the Vero Beach Air Traffic Control Tower, see if they have anything on radar during that time frame. They would not tell me anything.
I am a good witness. I was a Fire Rescue Lieutenant for almost 33 years with no need to fabricate anything.