Projectile Up-Finding Using Magnetometer and Polarized RF Link
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Solution Overview
Problem
Conventional guidance control systems for projectiles face challenges in accurately determining the up direction during ballistic flight, especially for spinning projectiles, as accelerometers and IMUs are unreliable and impractical, leading to contamination of elevation and azimuth commands.
Innovation Solution
A guidance control system incorporating a magnetometer and a polarized RF or EO communications link, using the magnetometer to determine the up direction within ±20 to 40 degrees and the polarized link to determine orientation relative to a horizontal or vertical reference with high accuracy, reducing uncertainty in up-finding and improving guidance control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If accelerometers or IMUs are used for up-finding in ballistic flight, then up direction can be determined, but the measurement precision deteriorates due to projectile spinning and free-fall conditions
Solution Approach 1:
The patent replaces mechanical accelerometers and IMUs with a magnetic field-based magnetometer system. The magnetometer measures the Earth's magnetic field vector to determine the up direction, eliminating the unreliability of mechanical sensors in spinning ballistic flight conditions. This substitution of measurement principle resolves the contradiction by using a non-mechanical field-based approach that is not affected by projectile rotation or free-fall states.
Solution Approach 2:
The patent changes the measurement parameter from acceleration (which is unreliable during spinning and free-fall) to magnetic field vector components. By measuring the magnetic field in multiple axes and computing the up direction from these magnetic parameters rather than acceleration parameters, the system achieves reliable up-finding despite projectile motion conditions that render accelerometers ineffective.
2Measurement precision
If magnetometer alone is used for up-finding, then device complexity is reduced, but measurement precision is insufficient (±20 to 40 degrees accuracy)
Solution Approach 1:
The patent merges the magnetometer with a polarized communication link receiver system. The same antenna structure serves dual purposes: receiving polarized communication signals and measuring the magnetic field for up-finding. This consolidation achieves high precision up-direction determination (within 2-3 degrees) without significantly increasing device complexity, as the magnetometer shares hardware resources with the communication system.
3Loss of information
If conventional up-finding methods are used, then device complexity is low, but loss of information occurs in elevation and azimuth commands (33% contamination)
Solution Approach 1:
The patent implements feedback by continuously measuring the magnetic field vector and computing the up direction to correct guidance commands. The system uses the magnetometer data to determine the actual up direction and feeds this information back to correct elevation and azimuth commands, reducing information loss and command contamination from 33% to 3-4%. This feedback loop ensures accurate guidance despite uncertainties in the projectile's flight state.
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 accurately determines the up direction to within 2 to 3%, reducing contamination of elevation and azimuth commands from 33% to 3 to 4%, enhancing the precision of projectile guidance and trajectory control.
Implementation Method 1
the magnetometer is used for determining up to within +/−20 to 40 degrees
Implementation Method 2
a polarized EO communications link is used to determine orientation relative to a horizontal or vertical polarized reference, for example, to within 2 to 3%
Implementation Method 3
a polarized RF communications link is used to determine orientation relative to a horizontal or vertical polarized reference, for example, to within 2 to 3%
Data Source
AI summary
A system for finding up in a projectile flight relative to earth. The system having a transmitter which transmits polarized reference signals to a guidance sub-system on the projectile. The guidance sub-system includes a magnetometer and polarized and non-polarized receivers. Measurements from the magnetometer are used to determine a general up direction. The polarized and non-polarized receivers are arranged such that, during rotation of the projectile, reference signals received by the polarized receiver modulate whereas reference signals received by the non-polarized receivers are unaffected. A ratio of the strengths of the signals received by the polarized and non-polarized receivers determines alignment of a vertical axis. From the general up direction and alignment of the vertical axis, a precise up direction of the projectile in flight relative to the earth can be determined.