Worked example: Calculate the round-trip latency of a GEO satellite phone call. Step 1: GEO altitude = 35,786 km. Signal path: ground → satellite → ground = 2 × 35,786 = 71,572 km. Step 2: Time = distance / speed of light = 71,572 km / 300,000 km/s ≈ 0.239 s one way for the space segment. Step 3: A conversation needs the reply too, and processing adds margin: total delay ≈ 0.5–0.6 s. Step 4: Compare LEO at 550 km: path = 1,100 km, time ≈ 0.0037 s — about 65 times faster. Conclusion: that half-second pause on satellite calls is pure physics — light-speed travel to GEO and back — which is why LEO constellations are built for interactive internet.