Spacecraft Attitude Control Using Inertia Flywheels
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Solution Overview
Problem
Existing attitude control systems for spacecraft struggle to align the kinetic axis with a predetermined axis when the initial total angular momentum exceeds the absorption capacity of inertia flywheels, particularly in satellites transitioning from launch vehicles, as the initial momentum is often beyond the capacity of the flywheels.
Innovation Solution
A method involving a nonlinear control law for inertia flywheels to align the total angular momentum with a principal axis of inertia, where the internal angular momentum is controlled to maintain a constant sign expression Hact×J−1(Htot⊗J−1Htot), allowing alignment regardless of the flywheel's capacity, and a subsequent proportional-integral control law to ensure convergence and stabilize the axis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If inertia flywheels are used to absorb total angular momentum, then the spacecraft orientation can be modified, but the initial total angular momentum from launch separation is generally too great to be absorbed by the inertia flywheels
Solution Approach 1:
The patent applies preliminary action by aligning the total angular momentum vector with a principal axis of inertia of the spacecraft before using the inertia flywheels to absorb the angular momentum. This preliminary alignment step ensures that the subsequent absorption process can proceed within the flywheel capacity limits while still achieving the desired orientation modification.
Solution Approach 2:
The patent changes the parameter of angular momentum alignment by directing the total angular momentum along a principal axis of inertia rather than arbitrary orientation. This parameter change enables the system to work within the limited absorption capacity of the inertia flywheels while maintaining effectiveness in modifying spacecraft orientation.
2Quantity of substance
If chemical thrusters are used to reduce total angular momentum, then the angular momentum can be brought within absorption capacity, but future satellites will no longer be equipped with chemical thrusters
Solution Approach 1:
The patent performs the angular momentum reduction and alignment operation before the satellite needs to operate with only electrical thrusters. By completing the angular momentum management during the initial phase when chemical thrusters are available, the system prepares the spacecraft for subsequent operation with electrical thrusters alone, eliminating the need for chemical thrusters while maintaining angular momentum control capability.
3Quantity of substance
If inertia flywheels are dimensioned with high capacity to absorb large initial angular momentum, then the absorption capacity increases, but the device complexity and mass increase
Solution Approach 1:
The patent performs preliminary alignment of the angular momentum vector with a principal axis before using the inertia flywheels. This preliminary action allows the use of smaller, less complex flywheels because the alignment step pre-organizes the angular momentum in a way that minimizes the absorption capacity required from the flywheels themselves.
Solution Approach 2:
The patent changes the orientation parameter of the total angular momentum to align with a principal axis of inertia. This parameter change enables the system to achieve effective angular momentum absorption with reduced flywheel capacity requirements, thereby reducing device complexity and mass while maintaining functional effectiveness.
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 enables alignment of the kinetic axis with the principal axis of inertia, even when the initial total angular momentum exceeds the flywheel capacity, speeding up convergence and ensuring alignment without exceeding the flywheel's torque and momentum limits, thus overcoming the limitations of prior systems.
Implementation Method 1
a set of inertia flywheels adapted to form an internal angular momentum Hact of any axis in a craft reference frame
Implementation Method 2
the inertia flywheels are controlled so as to form an internal angular momentum Hact such that the following expression: Hact×J−1(Htot⊗J−1Htot)
Data Source
AI summary
A method of controlling the attitude of a spacecraft in spinning around itself with a non-zero total angular momentum HTOT. The spacecraft includes a set of inertia flywheels configured to form an internal angular momentum HACT. The axis of the total angular momentum HTOT is aligned with a principal axis of inertia of the spacecraft, in the course of which the inertia flywheels are controlled to form an internal angular momentum HACT. The following expression, in which J is the inertia matrix of the spacecraft:Hact×J−1(Htot⊗J−1Htot)is negative if the principal axis of inertia targeted is the axis of maximum inertia of the spacecraft and is positive if the principal axis inertia targeted is the axis of minimum inertia of the spacecraft.