Spacecraft Relative Positioning via Dual-Frequency Phase
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Solution Overview
Problem
Current spacecraft formation control systems face challenges in achieving precise relative positioning due to ambiguity in phase measurements and errors from multi-paths and calibration residuals, especially at high altitudes where GPS is unreliable and high-frequency signals require high power or directional antennas, limiting their use.
Innovation Solution
A control device equipped with emission/reception antennas and attitude sensors that use two spaced-apart RF frequencies to measure path length differences and rotation, allowing for precise estimation of signal directions and relative positions, and includes pseudo-random code modulation for distance measurement and synchronization, with processing to refine measurements and correct for multi-paths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If very high frequency signals (SHF or EHF) are used, then ambiguity removal is facilitated, but high emitted power or directional antennas are necessary, limiting the domain of use
Solution Approach 1:
The patent changes the frequency parameter from very high frequencies (SHF/EHF) to lower S-band frequencies (2.0-2.2 GHz). This parameter change resolves the contradiction by enabling the use of omni-directional antennas with low emitted power (below a watt) while still achieving precise relative position measurements through dual-frequency carrier phase measurements and ambiguity resolution techniques.
2Measurement precision
If very high frequency signals (SHF or EHF) are used, then ambiguity removal is facilitated, but directional antennas are necessary, limiting the domain of use
Solution Approach 1:
The patent changes the frequency parameter from very high frequencies to lower S-band frequencies, which enables the use of omni-directional antennas instead of directional antennas. This greatly expands the domain of use and adaptability, allowing measurements to be performed regardless of the orientation or position of the receiving spacecraft.
3Measurement precision
If phase measurements are used for centimetric precision, then measurement precision is improved, but ambiguity in phase measurements must be removed
Solution Approach 1:
The patent introduces an intermediary approach by using dual-frequency measurements. The combination of phase measurements from two different frequencies (f1 and f2) creates a virtual wavelength that is longer than the individual wavelengths, thereby reducing the ambiguity problem while maintaining centimetric precision through the carrier phase measurement technique.
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
Enables precise determination of spacecraft positions with centimeter-level accuracy, improving mission control and collision avoidance by resolving ambiguity and reducing measurement noise, while allowing for omni-directional antennas and lower power usage.
Implementation Method 1
each antenna of each assembly is charged with emitting and/or receiving first and second radiofrequency signals (RF), exhibiting first and second chosen frequencies
Implementation Method 2
The person skilled in the art knows how to customarily measure the phase with a precision equal to a fraction of the wavelength
Implementation Method 3
with ordering at least one chosen rotational turning of the spacecraft about the chosen axis, and with precisely estimating the direction of transmission of the signals emitted by the other spacecraft on the basis of the rotation measurement delivered by the attitude measurement means
Data Source
AI summary
A control device (D), for a spacecraft (S1) of a group of spacecraft moving in formation, comprises i) an assembly consisting of three antennas (A1-A3) installed on a face of the spacecraft (S1) and capable of emitting and/or receiving first and second RF signals exhibiting first and second frequencies spaced apart by a chosen frequency gap, ii) first measurement means (M1) charged with determining first and second differences in path length between antennas (A1-A3), corresponding to the first frequency and to the frequency gap, on the basis of the first and second signals received by the antennas and originating from another spacecraft, iii) second measurement means (M2) charged with delivering measurements of rotation undergone by the spacecraft (S1), and iv) processing means (MT) a) charged with coarsely estimating the direction of transmission of the signals received on the basis of first and second initial path length differences, b) with ordering the positioning of the spacecraft (S1) so that a chosen axis of a frame of reference tied to said spacecraft is aligned with respect to the coarse direction of transmission, c) with ordering the rotational turning of the spacecraft (S1) about the chosen axis, d) with precisely estimating the direction of transmission of the signals emitted by the other spacecraft (Si′) on the basis of the rotation measurement and of a measurement of variation of the first path length difference induced by this rotation.