In inertial navigation, the term constellation refers to the network of satellites used for positioning, navigation, and timing (PNT) when an INS (Inertial Navigation System) is integrated with GNSS (Global Navigation Satellite System). A satellite constellation consists of multiple satellites working together to provide global coverage and accurate location data.
Major GNSS Constellations Used in INS/GNSS Integration
- Earth-Centered, Earth-Fixed (ECEF) Coordinates
• A Cartesian coordinate system with the origin at Earth’s center.
• Used for global navigation and satellite positioning.
• Coordinates are represented as (X, Y, Z) in meters.
- Geodetic Coordinates
• Uses latitude (φ), longitude (λ), and altitude (h) to represent a position on Earth.
• Commonly used in GPS/GNSS-assisted inertial navigation.
- Local Tangent Plane Coordinates
• Also called North-East-Down (NED) or East-North-Up (ENU) frame.
• Defines movement relative to the Earth’s surface at a specific location.
• Used in aerospace and military applications.
- Body Frame Coordinates
• The local coordinate system fixed to a moving object (e.g., aircraft, UAV, missile).
• Describes roll, pitch, and yaw relative to the vehicle itself.
- Inertial Frame Coordinates
• A non-rotating reference frame used to describe motion without external forces.
• Used in pure inertial navigation before GNSS updates.
Why Are Coordinates Important in INS?
• Precise Navigation – Allows INS to compute accurate position, heading, and velocity.
• Sensor Fusion with GNSS – GNSS data is typically in geodetic coordinates, while INS often works in ECEF or NED. Converting between them ensures seamless integration.
• Trajectory Correction – Helps in mapping, guidance, and control for aerospace, defense, and autonomous systems.
