Definition
A satellite placed in a circular orbit about 22,236 miles above the equator that travels at the same rotational speed as the Earth, so it appears to remain over a fixed point on the ground. In the WAAS network, GEO satellites broadcast correction and integrity messages to GPS receivers, improving position accuracy and providing the integrity assurance required for instrument approaches.
Plain English
A satellite that sits in one spot in the sky from the ground's point of view, because it circles the Earth at exactly the same speed the Earth spins. WAAS uses these satellites to send GPS-correction signals down to aircraft receivers.
Context Anchor
Seen in WAAS discussions when explaining how improved satellite navigation information gets from the WAAS ground system to the aircraft.
Derivation
From Greek geo- meaning 'earth' and 'stationary' meaning 'not moving.' The satellite isn't actually motionless — it's orbiting at high speed — but because it matches Earth's rotation, it stays parked over the same spot from our point of view.
Why Pilots Care
Fixed position allows continuous broadcast of WAAS corrections over wide areas without the aircraft needing to acquire different satellites as they move.
Analogy
A home satellite TV dish can point in one direction because the satellite appears to stay in the same part of the sky. A GEO works on the same basic idea for WAAS signals.
Grounding Statement
Picture a satellite hovering over the equator that always looks like it's in the same place in the sky — that's a GEO satellite, and it's the antenna that beams WAAS data to your aircraft.
Intuition Check
Geostationary does not mean the satellite is motionless. It means the satellite moves around Earth at the same rate Earth turns, so it appears to stay in one place in the sky.
Example Sentence 1
The GPS receiver picks up correction data from a WAAS GEO satellite to refine its position fix.
Example Sentence 2
Because the GEO satellite remains over the same longitude, the WAAS network can deliver consistent integrity data across the entire service volume.