Definition
Satellites placed in orbit approximately 22,236 miles above the equator, where their orbital period matches the Earth's rotation. As a result, each satellite remains over the same point on the Earth's surface at all times. In the WAAS system, geosynchronous satellites broadcast GPS correction and integrity data to aircraft receivers within their coverage footprint.
Plain English
Satellites that hover over the same spot on Earth because they orbit at the same speed Earth spins. WAAS uses them to send GPS correction signals down to aircraft.
Context Anchor
Seen in WAAS and GPS navigation discussions, especially when explaining how WAAS correction information reaches the aircraft.
Derivation
From Greek 'geo' meaning Earth, plus 'synchronous' from Greek 'syn' (together) and 'chronos' (time) -- literally 'in time with the Earth.' The satellite's orbit is timed to match Earth's rotation, so it appears to stand still in the sky.
Why Pilots Care
These satellites provide the continuous, wide-area correction signals that allow WAAS to improve GPS accuracy and integrity for instrument approaches.
Analogy
Think of it like a radio tower placed very high above Earth that appears to stay in one spot, so many aircraft across a large area can receive the same WAAS information.
Grounding Statement
Imagine a satellite parked in the sky above one point on the equator -- not moving across the sky like the moon, but holding still because it's circling Earth at exactly Earth's spin rate.
Intuition Check
GEO synchronous does not mean the satellite is sitting still in space. It means the satellite is moving in a way that matches Earth’s rotation, so it appears nearly fixed from the ground.
Example Sentence 1
WAAS uses geosynchronous satellites to broadcast correction data that improves GPS accuracy for instrument approaches.
Example Sentence 2
WAAS relies on GEO synchronous satellites positioned to cover the continental United States with reliable augmentation signals.