For a hundred years we expanded into the void using rocket engines that an Apollo Astronaut would have recognized. Our ships and stations spun to generate gravity. We spent weeks accelerating up to interplanetary speeds and using planetary slingshots to send us out to the edges of our star systems. Fuel bunkerage was what held us back. No ship could carry enough fuel to keep accelerating for weeks or months at a time. Science fiction dreamed of drives that could run forever on different scientific theories, but it was old-fashioned rockets and our very good friend Newton that took us to the stars.