Space Station Relay Link Coverage

Orbit & Relay Setup

Time speed 6 min/s

Orbital inclination 51.6°

Ground-station elevation mask 10°

Active TDRS Relays

Link Status

Current link

—

Next event in

—

Mission elapsed

0 min

Coverage over last orbit

0.0%

How it works

A low-Earth-orbit station cannot see a fixed ground antenna most of the time — Earth's curvature gets in the way. Real stations relay through geostationary satellites (TDRS-class) instead, which sit high enough (≈35,786 km) to see almost half the planet at once.

Line-of-sight test (station ↔ relay), segment P1→P2, Earth center O, radius Rₑ:
  d = P2 - P1,  f = P1 - O
  a = d·d,  b = 2(f·d),  c = f·f - Rₑ²
  Δ = b² - 4ac
  blocked  ⇔  Δ ≥ 0  and  a root t of at²+bt+c=0 lies in (0,1)

Ground elevation angle (station ↔ fixed antenna):
  ẑ = normalize(antenna position)        (local zenith)
  el = asin( ẑ · normalize(P_station - P_antenna) )
  visible  ⇔  el ≥ elevation mask

Time speed — simulated minutes per real second; the station's real orbital period here is ≈92.7 min.
Inclination — tilts the orbital plane; the ISS itself flies at 51.6°. Earth keeps rotating underneath, so the ground track drifts west each pass.
Elevation mask — the minimum angle above the horizon a direct ground antenna needs before atmosphere and terrain make the link unusable.
TDRS-East / TDRS-West — toggle each relay off to see the "zone of exclusion" grow: gaps where no relay and no ground antenna has a clear line of sight, so the link drops.

Coverage % is measured over the trailing one orbital period — exactly what a mission planner reads off a real TDRS scheduling chart.

Station (LEO) TDRS relay (GEO) Ground antenna Active link

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