GPS Roll Rate Measurement Using Carrier Phase Differences
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Solution Overview
Problem
Existing methods for measuring the roll rate and roll angle of spinning platforms, such as projectiles and spacecraft, are costly and inefficient, especially for high-speed applications, as they require expensive inertial rate indicators and are susceptible to interference, while traditional GPS-based methods struggle with accurate attitude determination at high rotation rates.
Innovation Solution
A GPS signal-based system using multiple antennas disposed circumferentially on the platform's spin axis, processing carrier phase differences to determine roll rate and angle, with optional inertial data integration through a Kalman filter for improved accuracy, allowing for cost-effective roll angle and rate measurement at high rotation rates without the need for expensive inertial instruments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional inertial rate indicators (MEMS gyroscopes) are used to measure roll rate and angle, then measurement accuracy is improved, but cost and device complexity increase significantly
Solution Approach 1:
The patent replaces mechanical inertial sensors (MEMS gyroscopes) with a GPS-based electronic measurement system. By using multiple GPS antennas and processing carrier phase differences, the system achieves roll rate and angle measurement without mechanical moving parts, thereby reducing cost and eliminating calibration requirements while maintaining measurement capability
Solution Approach 2:
The patent introduces GPS carrier phase signals as an intermediary measurement medium. Instead of directly measuring roll motion with inertial sensors, the system uses GPS satellite signals received by multiple antennas, processes the phase differences of these signals, and derives roll rate and angle information indirectly, achieving the measurement goal through a different physical pathway
2Measurement precision
If magnetometers are used to measure roll rate and angle, then measurement capability is provided, but susceptibility to interference from local magnetic fields increases
Solution Approach 1:
The patent substitutes magnetometer-based magnetic field measurement with GPS-based radio wave phase measurement. By using electromagnetic waves at GPS frequencies (L-band) instead of measuring static magnetic fields, the system avoids interference from local magnetic sources such as on-board actuators and electronic components
Solution Approach 2:
The patent employs standard GPS receiver hardware and antennas that are commercially available and relatively inexpensive, replacing expensive and sensitive inertial measurement units. The system uses off-the-shelf GPS components rather than specialized scientific instruments, reducing overall system cost and complexity
3Measurement precision
If long baselines between GPS antennas are used for attitude determination, then roll measurement accuracy is improved, but device complexity and space requirements increase
Solution Approach 1:
The patent changes the measurement parameter from absolute carrier phase to carrier phase difference between multiple antennas. This parameter transformation allows the system to extract roll information from small baseline configurations, as the phase difference directly relates to the antenna separation vector and platform attitude, eliminating the need for long baselines
Solution Approach 2:
The patent transitions from single-antenna or two-antenna configurations to a multi-antenna array disposed circumferentially about the spin axis. This spatial arrangement in three dimensions creates multiple baseline vectors that provide redundant measurements and enable roll determination without requiring any single baseline to be particularly long
4Device complexity
If GPS-based roll measurement is used for high spin rate platforms, then cost is reduced, but measurement accuracy deteriorates due to high dynamics
Solution Approach 1:
The patent exploits the periodic nature of the GPS signal carrier phase and the periodic modulation that occurs as the platform rotates. By analyzing the time-varying characteristics of the carrier phase at the spin frequency and its harmonics, the system can extract roll rate and angle information even at high spin rates where the rotation period is comparable to or shorter than the GPS signal integration time
Solution Approach 2:
The patent implements a feedback mechanism where the measured carrier phase differences are processed to determine roll angle and rate, which are then used to correct and refine the measurements. The system continuously updates the roll state estimate based on the observed phase differences, maintaining accuracy despite the high dynamics and rapid changes in platform orientation
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
This approach provides accurate and cost-effective measurements of roll rate and angle for spinning platforms at high rotation rates, maintaining satellite visibility at all roll angles and integrating with inertial data for enhanced performance, reducing the reliance on expensive navigation sources.
Implementation Method 1
The difference in carrier phase between the signals received from the same satellite on two discrete antennas, which are typically (but not necessarily always) mounted on the platform circumferentially about its spin axis and pointed in different directions, is related to the difference in path lengths from the satellite to those two antennas; that path length difference is related to the attitude of the platform
Data Source
AI summary
A system and method for determining the roll rate and roll angle of a spinning platform, using the measured phase differences between the GPS satellite signals received on two or more antennas. The measured phase differences and the navigation solution from a GPS receiver are processed in a Kalman filter to obtain the desired information. Data from non-GPS measurement sources is optionally provided to update the navigation solution. Although of wide applicability, the invention is uniquely suited to the measurement of roll rates and roll angles of fast spinning platforms with small baselines, in which the antennas are separated from each other by distances that are a fraction of the GPS signal wavelength.