Attitude refers to a spacecraft’s orientation in space. To be effective and precise in its operations, its attitude must be both stabilized and controlled to precisely point its high-gain antenna, conduct experiments aboard, and perform propulsion maneuvers.
Given that attitude cannot be directly measured, its estimation must be calculated through sensor readings. Attitude determination systems use statistics to combine prior attitude estimates with current measurements in order to estimate its current state.
Spacecraft attitude control refers to the practice of controlling the orientation of a spacecraft with respect to an inertial frame of reference. To accomplish this goal, sensors are required to measure its current attitude while actuators apply torques in order to orient it properly. Guidance, navigation and control (GN&C) studies the entire field that encompasses these systems together.
Geometric adaptive control methods utilize potential functions to generate mathematically traceable control laws that asymptotically converge to desired attitudes while avoiding pointing constraints. These techniques have proven resilient in the face of unknown disturbances and can work with any number of conic constraints; additionally RL trained agents have also been used successfully for attitude control on reaction wheel and higher-fidelity momentum exchange ACS systems.
An attitude control system on a spacecraft is critical for maintaining payloads such as high-gain antennas and onboard experiments, while maintaining stability for operations and experiments onboard. This system includes sensors which measure motion reference as well as actuators providing torques needed for orientation of the vehicle, plus algorithms which command these actuators based on these sensor measurements – this field of study known as GNC (Guidance, Navigation and Control).
Attitude control involves employing various sensors such as control moment gyros, momentum wheels and spin stabilization devices. Magnetometers can track how Earth’s magnetic fields affect satellite attitudes as well as sun/moon sensors/horizon detectors/star trackers for tracking purposes.
Spacecraft attitude stabilisation and control is necessary for multiple reasons, including aligning its high gain antenna accurately towards Earth, performing experiments that require precise pointing for data collection purposes, avoiding heating/cooling effects of sunlight exposure, controlling propellusive maneuvers and maintaining propulsive maneuvers. Sensors must measure vehicle orientation while actuators apply torques to align it – this combination of sensor measurements, actuator torques, algorithms and control methods is known as guidance, navigation and control (GN&C).
Spacecraft attitude may be expressed using various models, including rotation matrices, Euler angles or quaternions. A quaternion model may be more efficient as it does not suffer from the problem of gimbal lock and requires only four values to fully describe an attitude.
As opposed to position and velocity, attitude refers to the rotational motion of a spacecraft’s center of mass. Acknowledging its position can assist with navigation, control and other systems onboard the vehicle.
Attitude descriptions include Euler angles, Rotation matrices and Quaternions as the three primary methods to represent spacecraft behavior. Euler angles provide the easiest visualization, however they often suffer from an undesirable phenomenon called Gimbal Lock; Rotation Matrices provide more complete descriptions but may require additional work; Quaternions provide a good compromise without experiencing Gimbal Lock issues.
Celestial reference devices can also help determine a spacecraft’s attitude. Examples include star trackers, sun sensors and planetary limb and solar array trackers.
A gyroscope is an apparatus that keeps spacecraft oriented by exchanging angular momentum with an external torque source, similar to how skaters exchange their angular velocity with friction from their wheels as they spin.
This field provides an optional way of specifying the level of interpolation used on attitude ephemeris data immediately following this metadata block. This parameter must take an integer value.
GMAT uses this value to configure steady-state precession motion of spacecraft within Attitude model PrecessingSpinner.
Residual atmospheric presence at orbital altitude causes atmospheric disturbance torques which may interfere with spacecraft attitude. These force perturbations may become particularly significant when dealing with low Earth orbit (LEO) satellites; even this could result in their shifting from one desired orientation to the other.
Magnetic stabilization systems provide an effective solution to overcome aerodynamic torques caused by secular aerodynamic forces, providing significant relief.
These use magnets to align spacecraft along Earth’s magnetic field. While these systems can withstand strong dynamic disturbances, their accuracy of pointing may be limited; to improve it, passive dampers such as hysteretic material or viscous damper dampers are sometimes combined for greater pointing precision.