GSO vs NGSO: How ITU Satellite Coordination Changes

Geostationary and non-geostationary satellites don't just fly differently — they're coordinated under meaningfully different rules at the ITU. Confusing the two frameworks is an easy way to screen for the wrong kind of conflict.

Same treaty, two different regimes

A geostationary (GSO) satellite holds a fixed orbital slot on the equatorial arc, so coordination has historically focused on frequency and orbital-position overlap with other GSO networks nearby on that same arc. A non-geostationary (NGSO) system — a constellation of satellites moving relative to the ground — doesn't occupy a single slot at all, which is exactly why the ITU built a separate protection mechanism for how NGSO systems interact with the GSO arc.

The key asymmetry: protection isn't mutual

Under Radio Regulations No. 22.2, NGSO fixed-satellite and broadcasting-satellite systems must not cause unacceptable interference to GSO networks, and cannot claim protection from them. This isn't a peer coordination relationship — it's a one-directional protection obligation. In practice, that obligation is enforced through Equivalent Power Flux Density (EPFD) limits under Article 22, which cap how much aggregate signal an NGSO constellation is allowed to direct toward the GSO arc, regardless of how many satellites are involved.

What this means for screening, in practice

If you operate	What you're mainly checking for
A GSO network	Frequency overlap with other GSO filings at nearby orbital positions, plus confirming any NGSO systems sharing your band stay within their EPFD limits toward your slot.
An NGSO system	Frequency overlap with other filings as usual, plus demonstrating EPFD compliance against the GSO arc — a separate technical showing that ordinary frequency-overlap screening doesn't cover on its own.

A pure frequency-overlap check — the kind covered in our interference screening guide — is still the right first pass for both cases. It just isn't the whole picture once an NGSO system is involved: EPFD compliance is a distinct technical requirement, evaluated with dedicated validation software rather than a simple overlap check.