LEO satellites low orbit, step by step Height, period, ground track, footprint, AOS and LOS, elevation and azimuth, TLEs: with Kepler, understand how low satellites go round, and how to catch them. All of Discovery
Pick a level 1 Low orbit Height, period, speed: find the 100-minute orbit. ☆☆☆ 2 The ground track It moves each orbit, and climbs as far as the inclination. ☆☆☆ 3 Footprint and pass What the satellite sees, AOS, TCA, LOS: why ten minutes. ☆☆☆ 4 Elevation and azimuth A good pass, a rotor or a hand, and point the antenna. ☆☆☆ 5 The two-line elements Inclination, eccentricity, mean motion, checksum. ☆☆☆ 6 Final quiz Ten questions to go over it all. ☆☆☆ The tutorial needs JavaScript.
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The tutorial's formulas Period : T = 2π √(a³/μ), with a = 6,371 km + the height and μ = 398,600.4418 km³/s².Speed on a circular orbit: v = √(μ/a). At 400 km: 7.67 km/s, 92.4 minutes.Track shift : 360° × T / 86,164 s (the sidereal day) westwards each orbit, about 23° for the ISS.Footprint above an elevation ε: a circle of angular radius acos(R cos ε / a) − ε.TLE : period (min) = 1,440 / mean motion; semi-major axis a = (μ / n²)^(1/3), n in radians a second.The model Circular orbits, a spherical Earth held still during a pass, a fixed orbital plane: enough to understand and to be right within a few per cent. Tracking software (SatMe, for one) goes further with the SGP4 model and recent TLEs.
The sources The tutorial's figures and advice rest on these references:
ESA, « Types of orbits » — low orbit: below 2,000 km, about 90 minutes, about 7.8 km/sNASA, « Space Station Facts and Figures » — the ISS: 16 orbits in 24 hours, about one every 90 minutesAMSAT, « Keplerian Two Line Element Set Format » — the TLE's columns, the 2004 ISS example, the modulo 10 checksumAMSAT, « Working Satellites » (W2JV, WD9EWK) — pick passes above 30° to start with, hand-held antennaAMSAT, Satellite Gen 255 — the longest passes when the satellite goes nearly overhead, the shortest near the horizon