Nanosatellites in ISS orbits experience a fluctuation in the power available to the solar panels during the mission lifetime. If the satellite is continuously operating in Nadir pointing (NP) mode, the power generation presents minima resulting in a non-optimal use of the available power. This study proposes a new attitude mode, called pitch sun tracking (PST), to maximise the power received by the solar panels which can be employed when the minimum values of power production are foreseen. It is shown that a 2U-CubeSat equipped with a momentum wheel can acquire and maintain such an attitude mode with acceptable accuracy. The PST mode can maximise power production by tracking the projection of the Sun vector on the orbital plane. Simulations show that the extended Kalman filter estimator satisfies the required determination accuracy and a linear quadratic regulator controller designed for the NP mode can be adapted for the PST mode.
CubeSats provide affordable space access, but face control challenges due to their size and nonlinear dynamics, which conventional controllers struggle to address effectively. This study presents a finite-time sliding mode controller (FTSMC) for the attitude control of a 12U CubeSat for an ionospheric exploration mission. The FTSMC ensures finite-time equilibrium by defining a sliding surface and control law. The dynamic model is formulated using the Newton-Euler formulation, considering external disturbances from aerodynamic, residual magnetic dipole, and gravity gradient torques. Two actuator configurations were examined: reaction wheels in tetrahedral configuration and reaction wheels in an orthogonal configuration alongside three magnetorquers. The controller achieves accurate Euler angle tracking, with a rise time between 8.5 to 9.2 seconds and a settling time of around 23 seconds. Compared to the proportional-derivative (PD) controller, the proposed controller improves the settling time by 88.5%. FTSMC can provide better attitude control for CubeSats used in scientific missions.
Understanding the dynamics of high area-to-mass ratio (HAMR) objects in near-geostationary earth orbit (GEO) is essential for space situational awareness (SSA). This study develops a numerical propagator to model the long-term behaviour of HAMR objects, incorporating solar radiation pressure, Earth's oblateness, and third-body gravitational effects. The propagator's results were compared with Vimpel catalog ephemeris data, focusing on the orbital evolution of debris with varying area-to-mass ratios. The analysis revealed strong agreement between the propagator and ephemeris data, though some discrepancies regarding eccentricity and semi-major axis were identified. Findings show that HAMR debris in GEO can persist for decades, maintaining a mean motion near GEO while exhibiting significant variations in orbital parameters. These results enhance understanding of HAMR dynamics, offering insights for improving SSA and developing debris mitigation strategies.
This paper investigates the issue of attitude control for a flexible spacecraft subject to the vibrational effects of its flexible appendages. To handle this challenge, an efficient control technique is proposed based on an optimised mixed proportional-derivative (OMPD) controller. The proposed control design can be expressed as the combination of conventional proportional-derivative (PD) control law and auxiliary control terms (ACT) to mitigate the influence of the flexible appendages and ensure the overall stability of the spacecraft attitude. The stability of the closed loop system is proven theoretically via Lyapunov method. In addition, the controller parameters are fine-tuned using particle swarm optimisation (PSO) algorithm. Finally, numerical results are presented to show the performance of the developed controller.
