Spacecraft Attitude Control via Axis Alignment
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Solution Overview
Problem
Spacecrafts experience significant disturbance torques during safing mode due to aerodynamic and gravity gradient torques, which require frequent use of momentum control actuators, increasing fuel and power consumption and mass.
Innovation Solution
A control system that aligns the principal axis of the spacecraft with the orbit normal vector and rotates it by half a rotation per orbit, reducing both gravity gradient and aerodynamic torques using internal and external actuators, while minimizing the need for momentum control actuators and requiring only partial ephemeris knowledge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If momentum control actuators are used frequently to counteract disturbance torques during safing mode, then attitude control stability is improved, but fuel consumption and power consumption increase
Solution Approach 1:
The spacecraft is oriented with its principal axis aligned to the orbit normal vector before entering safing mode, and this orientation is maintained throughout the safing period. This preliminary positioning minimizes the disturbance torques that would otherwise require active compensation, thereby reducing fuel and power consumption while maintaining attitude stability
Solution Approach 2:
The patent converts the harmful effect of disturbance torques into a beneficial passive stabilization effect by aligning the spacecraft's principal axis with the orbit normal vector. This orientation causes the gravity gradient torque and aerodynamic torque to naturally balance or cancel each other, transforming what would be destabilizing forces into a self-stabilizing configuration that reduces the need for active momentum control actuator usage
2Reliability
If momentum control actuators are used frequently to counteract disturbance torques, then attitude control stability is improved, but spacecraft mass increases
Solution Approach 1:
The spacecraft is oriented with its principal axis aligned to the orbit normal vector before entering safing mode, and this orientation is maintained throughout the safing period. This preliminary positioning minimizes the disturbance torques that would otherwise require active compensation, thereby reducing fuel and power consumption
Solution Approach 2:
The patent converts the harmful effect of disturbance torques into a beneficial passive stabilization effect by aligning the spacecraft's principal axis with the orbit normal vector. This orientation causes the gravity gradient torque and aerodynamic torque to naturally balance or cancel each other, transforming what would be destabilizing forces into a self-stabilizing configuration
3Measurement precision
If accurate ephemeris knowledge and magnetic field models are used for magnetic torque rod control, then attitude control precision is improved, but device complexity increases
Solution Approach 1:
The patent extracts and eliminates the dependency on complex external data systems (GPS, detailed ephemeris knowledge, magnetic field models) by using a simpler geometric relationship based approach. The control strategy relies only on the spacecraft's orbital parameters and the alignment of its principal axis with the orbit normal vector, removing the need for these additional complex subsystems
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 significantly reduces disturbance torques, decreases fuel and power consumption, and allows for smaller momentum control actuators, thereby reducing the spacecraft's mass and operational costs.
Implementation Method 1
Gravity gradient torque is created when a difference in gravity exists between some parts of a spacecraft. The difference in gravity may be created when some components or portions of the spacecraft are located closer to a celestial body when compared to some other portions of the spacecraft.
Implementation Method 2
Aerodynamic torque is created as a spacecraft orbits around a celestial body having an atmosphere. For example, aerodynamic torque is created as a spacecraft moves through the Earth's atmosphere.
Data Source
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AI summary
A control system (22) for reducing disturbance torque of a spacecraft (20) is disclosed. The spacecraft (20) revolves around a celestial body (36) surrounded by an atmosphere. The control system (22) includes processors (1032) in electronic communication with one or more actuators (28) and a memory (1034). The memory (1034) stores data into a database (1044) and program code that, when executed by the one or more processors (1032), causes the control system (22) to instruct the spacecraft (20) to enter a safing mode. In response to entering the safing mode, the control system (22) instructs the one or more actuators (28) to align a principal axis (A-A) of the spacecraft (20) with a vector (60) that is normal to the orbit (38) around the celestial body (36). The control system (22) also instructs the actuators (28) to rotate the spacecraft (20) about the principal axis (A-A), where a rotational orientation of the spacecraft (20) relative to the celestial body (36) is shifted by about one-half a rotation about the principal axis (A-A).