What changed that made this cost-effective?<p>1) The companies pursuing this, SpaceX, Blue Orgin, etc., can&#x27;t be the first to think of it. If the first stage accounts for 75% of the cost of a launch, as one article I read says, I&#x27;m sure many have considered, going back to the first launches decades ago, how to reuse it.<p>2) The technology to land rockets vertically has existed for a long time, going back to the lunar lander at least.