On August 12, 2018, NASA launched it's Parker Solar Probe on a course to put it in a decaying orbit around the sun. The probe weighed barely 3,000 pounds, if that much. It was launched on our biggest rocket at the time, the Delta Heavy, which is made to launch up to 50,000 pounds into orbit. The Delta Heavy was fully fueled, too. It gave that little satellite a huge speed. So why such a big rocket for such a small satellite? Here's another little bit to further the mystery: the Delta Heavy wasn't enough. The Parker solar probe had to get a gravity assist from Venus, come almost all the way back to Earth's orbit, then with all the speed it picked up from it's pass by Venus, head for the sun. If it weighed so little, why was all that speed necessary?