GPS (Global Positioning System)US Space Force· US· first launch 1978· 7 active in catalogUS satellite navigation constellation. ~31 active sats in MEO at ~20,200 km.Satellites in this constellationGPS BIIRM-1 (PRN 17)GPS BIIRM-2 (PRN 31)GPS BIIRM-3 (PRN 12)GPS BIIRM-4 (PRN 15)GPS BIIRM-5 (PRN 29)GPS BIIRM-6 (PRN 07)GPS BIIRM-8 (PRN 05)