We're starting a brand-new chapter now — Chapter 18, the Global Navigation… — Page 307, Lesson 298

We're starting a brand-new chapter now — Chapter 18, the Global Navigation Satellite System, or GNSS. This is the system that lets an aircraft know exactly where it is anywhere on Earth, using satellites in space. Let me walk you through how the chapter is laid out first, because the structure itself tells you what's important. The chapter opens with an Introduction, then moves into Satellite Orbits — that's the geometry of how the satellites circle the Earth. After that comes the Position Reference System, which is the mathematical framework the whole thing hangs on. Then we get into the three big building blocks: The GPS Segments, which splits into The Space Segment, The Control Segment, and The User Segment. After that, the Principle of Operation — how it actually works. Then GPS Errors, System Accuracy, Integrity Monitoring, Differential GPS (that's DGPS), and finally Combined GPS and GLONASS Systems. The chapter closes with Questions and Answers. Now, before we dive into the technical detail, I want you to notice something important. The chapter is called GNSS — Global Navigation Satellite System — but the very first heading inside is "The GPS Segments." GPS stands for Global Positioning System, and it's the American system. GNSS is the umbrella term that covers GPS and other similar systems like GLONASS, which is the Russian one. So when we talk about GPS, we're talking about one specific implementation of the broader GNSS concept. The chapter will make that distinction clear when it gets to the combined systems section. Let me also flag the figures we'll be using. There's Figure 18.1, which is a diagram labelled "X2 Y2 Z" — that's going to relate to the position reference geometry. Then Figure 18.4 shows the GPS Satellite Constellation — that's the arrangement of satellites in orbit. And Figure 18.5 is about the C/A code and why using two frequencies matters. I'll bring those in when we reach the relevant sections. One thing I want to set straight right now, because it's a common trap: this is a professional pilot's course. When we say "satellite constellation," we don't mean a pretty picture of stars. We mean a specific, engineered arrangement of satellites positioned so that a receiver on the ground can always see enough of them to compute a position. The whole system is designed around that requirement. So here's the big picture before we get into the weeds. GNSS works because satellites broadcast signals, and the receiver in the aircraft measures how long those signals take to arrive. From that timing, it works out distance. From distance to several satellites, it works out position. But the devil is in the details — the orbits, the reference system, the segments, the errors, and the corrections. That's what this chapter is going to teach you, and that's what we're going to work through together. Let's start with the Introduction and Satellite Orbits, because everything else builds on that foundation.