Many organizations can no longer afford to develop mission-specific software in-house. Commercial satellite software that can be used for multiple missions is playing a growing, cost-saving role in enabling not only successful but economical space activities. Commercial off-the-shelf (COTS) software that is stable, accurate, and well-supported is key in all phases of a satellite's life—from pre-launch analyses to ground support through to graveyarding The paper shows the benefit of using COTS software in the big international projects, related to construction of reusable, generic software "building blocks" based on legacy software. In theory, new missions could then select among these building blocks to build systems in an object-oriented manner