Geostationary Slot Coordination Simulator

GEO Slot Traffic

Starting operators 8

ITU coordination arc 2.0°

Ring status

Satellites in ring

Tightest gap

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Worst-case C/I

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Pairs interfering

How it works

The Outer Space Treaty (1967) never defines a mechanism for allocating the geostationary belt or managing traffic on it — that job fell to the ITU's Radio Regulations, a first-come-first-served coordination process built around one number: angular separation on the ring.

GEO radius:      42,164 km  (period = 1 sidereal day)
Off-axis gain:   G(θ) ≈ 29 − 25·log₁₀(θ)  dBi   [ITU-R S.580 envelope, 1°≤θ≤7°]
Carrier/Interf.: C/I(θ) ≈ G_main − G(θ)
Coordination trigger: C/I below ~26 dB → operators must formally coordinate

θ is the angular gap between two satellites as seen from a ground antenna. A dish that is sharply focused on the wanted satellite still picks up some signal from any neighbor within a few degrees — how much is set by the antenna's off-axis sidelobe pattern.
Below the coordination arc (2° is the traditional C-band figure; some Ku-band and NGSO-adjacent filings now squeeze closer), the interfering signal's carrier-to-interference ratio drops below the threshold operators need for a clean downlink — the pair turns red and a beam is drawn between them.
File a coordinated slot respects the current arc and drops the new satellite into the widest open gap. Squeeze in a paper satellite ignores it — mimicking an operator that files a "paper" slot to claim spectrum rights before it has a real payload, the practice the OST's silence on space traffic left no clear brake on.
The ring itself rotates with Earth beneath it (once per sidereal day, ~23h56m) — a true geostationary satellite never moves relative to the ground station it serves, which is exactly what makes its longitude slot a scarce, fought-over resource in the first place.

Coordinated satellite Interfering pair (C/I below threshold)

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