Spacecraft Velocity Estimation via Magnetic Field Gradient
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Solution Overview
Problem
Current methods for determining a spacecraft's speed with respect to an inertial frame of reference suffer from increasing accuracy errors over time due to integration of acceleration measurements, making them less precise for long-duration flights.
Innovation Solution
A device comprising a network of magnetometers and a computer that estimates the velocity vector by solving equations relating the magnetic field produced by a celestial body, the spacecraft's position, and its rotational speed, allowing for precise speed estimation independent of flight time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the speed is obtained by integration of acceleration measurements over time, then the method is simple to implement, but the accuracy decreases linearly with time
Solution Approach 1:
The patent introduces magnetic field measurements as an intermediary reference frame (celestial body-fixed frame) to resolve the velocity estimation problem. By measuring the magnetic field vector in the spacecraft frame and using the known magnetic field model in the celestial body frame, the system creates a mediator relationship that allows solving for velocity without direct integration, thus maintaining accuracy while implementing a practical solution
Solution Approach 2:
The patent replaces the mechanical integration-based velocity estimation system with a magnetic field-based measurement system. Instead of relying on accelerometer integration which accumulates errors, the system uses magnetometers to measure magnetic field vectors and solves the velocity estimation through magnetic field relationships, substituting the mechanical integration approach with a field-based measurement approach
2Measurement precision
If a network of magnetometers is added to measure magnetic field vectors, then the speed estimation accuracy is maintained over time, but the device complexity increases
Solution Approach 1:
The patent makes the magnetic field measurements serve multiple functions: they provide the primary velocity estimation through the magnetic field vector relationships, and simultaneously enable determination of the spacecraft's orientation relative to the celestial body. This multi-functionality justifies the addition of magnetometers by extracting maximum utility from the same measurements
Solution Approach 2:
Instead of using velocity measurements to determine magnetic field characteristics, the patent inverts the approach by using known magnetic field models in the celestial body frame and measured magnetic field vectors in the spacecraft frame to solve for velocity. This inversion allows the system to achieve accurate velocity estimation without relying on integration
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 method provides a precise and time-independent estimation of the spacecraft's speed, reducing errors and maintaining accuracy over extended flight durations.
Implementation Method 1
capable of measuring, in a frame of reference linked to the spacecraft, a magnetic field vector produced by a star
Data Source
Figure 1~3
Figure 2
Figure 4~5
AI summary
The spacecraft (1) has an estimation device (5) whose gyrometer (9) measures an instantaneous rotational velocity vector of the spacecraft relative to an inertial reference frame, and spatially spaced magnetometers (15) measure a vector of magnetic field produced by a celestial body. A computer (20) estimates a velocity vector of the spacecraft by solving an equation relating the instantaneous velocity vector to a time derivative and a spatial gradient of the field vector, a spacecraft position vector, and a rotational velocity vector of a reference frame with respect to the inertial frame. The celestial body is the Earth, and the magnetic field is terrestrial magnetic field. The reference frame is related to the celestial body and is a geocentric-equatorial reference frame. Independent claims are also included for the following: (1) a method for estimating a velocity vector relative to an inertial reference frame of a spacecraft (2) a method for determining a corrected velocity vector of a spacecraft.