Global coverage with geosynchronous communication satellites How many geosynchronous communication satellites are typically required to provide near-global coverage of all inhabited regions of Earth (excluding high polar latitudes)?

Introduction / Context:
Geostationary satellites at approximately 35,786 km altitude provide wide Earth coverage from the equatorial plane. A classic communications engineering result is that only a small constellation is needed for near-global service (excluding extreme polar regions, which are poorly viewed from GEO).

Given Data / Assumptions:

• Satellites are positioned near longitudes about 120° apart.
• Coverage excludes high-latitude polar areas where elevation angles are very low.
• Goal is continuous coverage of inhabited regions.

Concept / Approach:

The visible Earth disk from GEO spans roughly one-third of the globe per satellite, depending on minimum elevation constraints. With three satellites spaced about 120° in longitude, overlapping coverage footprints can encompass essentially all inhabited areas.

Step-by-Step Solution:

Verification / Alternative check:

Many global operators deploy triads of GEO satellites to support TV, telephony, and data services worldwide, adding more spacecraft for capacity rather than fundamental coverage.

Why Other Options Are Wrong:

Two satellites leave major gaps; five or ten exceed the minimum needed for coverage (though may be used for redundancy/capacity).

Common Pitfalls:

Assuming perfect polar coverage is possible from GEO; polar regions typically require other orbits (e.g., Molniya, polar LEOs).

Final Answer:

3