From TLEs to Real-Time Satellite Tracking: Building an Orbital Backend with Spring Boot and Orekit

I've worked on projects where getting the right data was the bottleneck. You can't build features without data, and sometimes the data just doesn't exist or is locked behind paid APIs. Satellite tracking is different — the orbital data is publicly available. That shouldn't be a story, but it is. Most developers never think about it because they assume someone else has already built the tracking layer. They call an external API and move on. I didn't want to move on. I wanted to understand: how do two lines of numbers become a real-time position on Earth? And could I build that myself, with no aerospace background? I looked at existing satellite tracking tools, but most were black boxes — they called an external API and rendered the result on a map. I couldn't see how it worked. That bugged me. I wanted to build it myself and find out. That question led me into orbital mechanics, TLE propagation, and Orekit — a Java library used by the European Space Agency. Orekit is powerful,