Key PointsStarlink subscribers reached 13.6 million at the end of September, showing explosive growth.Despite subscriber growth, Starlink's ARPU has been (mostly) on the decline.If Starlink and Space Exploration Technologies can innovate and give subscribers a reason to pay more and reverse the larger ARPU trend, it could be a huge tailwind for the bottom line.Motley Fool Issues Rare "Total Conviction" Buy Alert › Space Exploration Technologies …