Ball Aerospace COSMOS is a free and readily available open source command and control system for operations and test that brings a set of functionality to the aerospace community that has previously only been available in proprietary and expensive COTS solutions. Open source software like COSMOS fills a very specific need for SmallSat/CubeSat missions where spending more money on a traditional ground system than the full cost of the satellite doesn’t fit within the budget. However, nothing is ever truly free and there are a lot of misconceptions around open source software in the Aerospace industry.  What are the actual costs of open source software? Is it safe to use open source software? Why would I open source my software? This presentation will answer those questions and more while highlighting the choices we made in open sourcing the Ball Aerospace COSMOS Command and Control System.  Additionally this presentation will discuss how adoption of COSMOS has gone in the two years since it was open sourced, and where it is going in the future.