Government agencies need to explain and promote the value of their efforts to taxpayers. They’re in a constant fight for government tax dollars as surely as corporations are in competition for consumer dollars. An all-star social media user within the U.S. government is NASA. Let’s take a look at how they use social to their best advantage and contrast their efforts with two of their closest counterparts: the European Space Agency (ESA) and Elon Musk’s Space Exploration Technologies Corporation, better known as SpaceX.