Hi all! I've been doing spacecraft system engineering since grad school and got to keep doing it after school at Care Weather. I tried several approaches for keeping hundreds of napkin math equations and connected simulations up-to-date, but none of them were both reliable and easy to use. To solve that, I made Oneil, a design specification language with clean syntax for specifying and evaluating math describing a complex system. Oneil has been really helpful as we design one satellite iteration after another for ground testing and spaceflight.I'm really interested in hearing feedback and whether anyone finds this useful. If you know of other tools that do the same things, please let me know as well, since I haven't been able to find any.