Projectile Attitude Determination via GPS and Magnetometer Fusion
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Solution Overview
Problem
Existing systems for determining the attitude of a projectile in flight are sensitive to roll rate and prone to errors due to coning motion and noise, especially during day/night operations and maneuvers, which affects accurate target interception.
Innovation Solution
A system comprising at least one GPS antenna, a signal receiving unit, magnetometers, and a processing unit that uses the TRIAD method to determine the projectile's attitude by combining earth-referenced velocity and magnetic field vectors, providing a high bandwidth measurement of roll attitude and insensitivity to roll rate and maneuvers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If GPS signal sensing combined with satellite location information is used to determine roll attitude, then a measurement of roll attitude can be obtained, but the measurement is sensitive to roll rate and cannot be made when roll rate approaches zero
Solution Approach 1:
The patent introduces magnetometers as an intermediary sensing mechanism that measures the Earth's magnetic field vector. This magnetic field measurement serves as a mediator that can determine roll attitude without being sensitive to roll rate, thereby resolving the contradiction between obtaining roll attitude measurement and maintaining reliability at low roll rates.
Solution Approach 2:
The patent combines GPS velocity vector measurements with magnetometer magnetic field vector measurements to determine projectile attitude. This merging of multiple sensing approaches creates a composite measurement system that overcomes the limitations of individual sensors, particularly the roll rate sensitivity of GPS-only methods.
2Measurement precision
If gyroscope is used to sense rate of change of pitch attitude, then direct measurement of roll attitude can be obtained, but the measurement is corrupted by coning motion and gyroscopic precession
Solution Approach 1:
The patent replaces the mechanical gyroscope-based measurement system with a field-based measurement system using magnetometers and GPS. This substitution eliminates the mechanical coning motion and gyroscopic precession that corrupt gyroscope measurements, while still providing roll attitude determination through the magnetic field vector measurements.
3Measurement precision
If gyroscope measurement is used for attitude determination, then pitch and yaw rates can be measured, but bias and noise in the measurement affect accuracy
Solution Approach 1:
The patent uses the Earth's magnetic field vector as an intermediary reference that is independent of projectile motion. By measuring the magnetic field vector with magnetometers, the system obtains attitude information that is not affected by the bias and noise inherent in gyroscope measurements, particularly during maneuvers.
Solution Approach 2:
The patent changes the measurement parameters from rate-based measurements (which accumulate bias and noise) to field-based measurements. By measuring the magnetic field vector directly rather than integrating rate measurements, the system achieves more reliable attitude determination during dynamic maneuvers.
4Measurement precision
If conventional attitude determination methods are used, then attitude information can be obtained, but the system is sensitive to day/night operation variations
Solution Approach 1:
The patent creates a universal attitude determination system that functions independently of lighting conditions. By using magnetometers to measure the Earth's magnetic field vector and GPS to determine velocity vector, the system achieves day/night operation adaptability while maintaining measurement precision through the TRIAD method.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system effectively determines the projectile's attitude with reduced sensitivity to roll rate and coning, enabling accurate target interception by providing reliable roll, pitch, and yaw attitude measurements, even under varying operational conditions.
Implementation Method 1
a plurality of magnetometers mounted onto the projectile and configured to ascertain the projectile referenced earth's magnetic field vector
Implementation Method 2
a GPS receiver mounted on the projectile and determining a velocity vector of the projectile in an earth reference frame
Data Source
AI summary
Disclosed is a system for determination of attitude for a projectile in flight. The system includes at least one antenna mounted on the projectile. Each antenna is configured to receive Global Positioning System (GPS) signals. Further, the system includes a signal receiving unit communicably coupled to the each antenna to receive the GPS signals and to ascertain the earth referenced velocity vector. The system also includes a plurality of magnetometers for ascertaining a projectile referenced earth's magnetic field vector. Moreover, the system includes a processing unit. The processing unit is configured to utilize a known projectile referenced velocity vector and a stored prediction of the earth referenced earth's magnetic field vector along with the measured earth referenced velocity vector and the measured projectile referenced earth's magnetic field vector to determine the attitude of the projectile. Further disclosed is a method for determination of attitude for a projectile in flight.