Attitude Control Strategies for Underactuated Spacecraft

Underactuated spacecraft are platforms with fewer independent control actuators than the three rotational degrees of freedom they must manage. This constraint often arises through actuator failure or deliberate design choices to reduce mass and complexity. Attitude control strategies for such vehicles must reconcile nonlinearity, actuator saturation and underactuation by exploiting intrinsic dynamics or external torques. Approaches range from energy‐shaping and pseudo‐linearisation of nonlinear models to hybrid schemes that combine traditional reaction wheels with environmental actuators such as solar radiation pressure. Key challenges include ensuring global stabilisation, avoiding singular configurations and accommodating model uncertainty. Recent advances have refined model predictive controls, sliding‐mode techniques and manifold switching laws to deliver robust pointing accuracy and agile reorientation, even when a torque axis is unresponsive. Practical applications span Earth observation, deep‐space exploration and agile communication satellites, where fault tolerance and minimised propellant usage are critical.

Research from Nature Portfolio

A novel extension of Lyapunov linearisation introduces the concept of an equilibrium space, enabling systems with infinitely many equilibrium points to be handled within a unified framework. By applying pseudo‐linearisation, researchers derived a discrete‐time representation for a control moment gyroscope system that preserves stability characteristics of the original continuous model even under large sampling intervals. This advance offers a more accurate, tractable foundation for designing attitude controllers on underactuated platforms equipped with gyroscopic actuators, reducing discretisation error and enhancing robustness against torque saturation.

Attitude Control Strategies for Underactuated Spacecraft publication trend

The graph below shows the total number of articles in attitude control strategies for underactuated spacecraft across all publications each year (not limited to Nature Index journals).

Technical terms

Underactuated spacecraft: A spacecraft whose number of independent control actuators is fewer than its rotational degrees of freedom.

Equilibrium space: A generalisation of equilibrium points in nonlinear systems accommodating infinite sets of steady states.

Pseudo‐linearisation: A technique to derive a linear model from a nonlinear system around an equilibrium space while preserving stability properties.

Model predictive control: A control strategy that optimises future control inputs over a moving time horizon subject to system and actuator constraints.

Sliding‐mode control: A robust control method that drives system trajectories to a designed manifold and maintains motion along it despite uncertainties.

Solar radiation pressure torque: An environmental torque generated by photon momentum on solar panels, used as a non‐propulsive actuation mechanism.

Control moment gyroscope: A spinning rotor whose gimbal motions produce aerial or space vehicle torque through gyroscopic coupling.

References

1. Equilibrium space and a pseudo linearization of nonlinear systems. Scientific Reports (2022).
2. Model Predictive Control-Based Attitude Control of Under-Actuated Spacecraft Using Solar Radiation Pressure. Aerospace (2022).
3. Adaptive Integral-Sliding-Mode Control for Spacecraft Single-Axis Pointing Using Two Torques. IEEE Access (2020).
4. Reorientation of Asymmetric Rigid Body Using Two Controls. Mathematical Problems in Engineering (2013).