Spinning Projectile Inertial Navigation Using Upfinding and Physics Models
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Solution Overview
Problem
Spinning projectiles face challenges in navigation due to unbounded angular rate measurement errors from inertial sensors, which accumulate quickly and affect the accuracy of position and velocity estimates, leading to inaccurate trajectory followings.
Innovation Solution
A model-based inertial navigation system that utilizes a strapdown navigation processor, a propagator-estimator filter, and a spinning projectile physics model to bound errors by incorporating measurements from inertial sensors and an upfinding navigation aid, which generates angular attitude measurements to correct navigation solutions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If inertial sensors are used to measure angular rates in a spinning projectile, then navigation data can be obtained, but unbounded measurement errors accumulate quickly due to high rotation rates and gyro scale factor errors
Solution Approach 1:
The patent implements feedback by using a propagator-estimator filter that continuously processes inertial sensor measurements and updates the navigation solution. The filter uses the predicted state from the physics model and compares it with actual sensor measurements, generating corrections that are fed back to bound the accumulating errors in angular rate and attitude measurements.
Solution Approach 2:
The patent introduces an intermediary physics-based propagator model that acts as a mediator between raw inertial measurements and the navigation solution. This propagator uses known projectile dynamics and forces to predict state transitions, providing a reference framework that constrains the unbounded error growth from gyroscope measurements.
2Measurement precision
If gyroscope measurements are used to track projectile attitude, then navigation accuracy can be maintained, but windup affect causes errors to accumulate without bound in the spinning axis direction
Solution Approach 1:
The patent applies parameter changes by transforming the measurement framework from body-fixed gyroscope readings to Earth-referenced attitude estimates. The propagator-estimator filter changes the reference frame parameters and uses upfinding navigation aid measurements to determine the projectile's orientation relative to the Earth, thereby eliminating the windup effect that plagues traditional spinning-axis gyro measurements.
3Productivity
If inertial measurements are integrated into navigation filters, then position and velocity can be tracked, but large gyro scale factor errors manifest as errors in all navigation parameters
Solution Approach 1:
The patent implements universality by creating a multi-functional propagator-estimator filter that simultaneously processes multiple types of measurements (inertial sensors, upfinding navigation aid), predicts multiple state variables (position, velocity, attitude), and generates corrections for all navigation parameters in a unified framework. This universal approach ensures that errors in one parameter do not propagate unboundedly to all other parameters.
Data Source
AI summary
Model based inertial navigation for a spinning projectile is provided. In one embodiment, a navigation system comprises: a strapdown navigation processor; a propagator-estimator filter, the processor inputs inertial sensor data and navigation corrections from the filter to generate a navigation solution comprising projectile velocity and attitude estimates; an upfinding navigation aid that generates an angular attitude measurement indicative of a roll angle; and a physics model performing calculations utilizing dynamics equations for a rigid body, the model inputs 1) projectile state estimates from the navigation solution and 2) platform inputs indicative of forces acting on a projectile platform, and outputs a set of three orthogonal predicted translational acceleration measurements based on the inputs; the filter comprises a measurement equation associated with the physics model and the upfinding navigation aid and calculates the navigation corrections as a function of the navigation solution, the predicted translational acceleration measurements, and attitude measurement.