Two degree-of-freedom spacecraft attitude controller

Two degree-of-freedom controller is designed together with its governing equations for a spacecraft pitch attitude control. The attitude controller incorporates the Active Force Control (AFC) technique into the conventional Proportional-Derivative (PD) controller based spacecraft pitch attitude loop. The PD-AFC attitude controller is then employed to enhance the attitude pointing of the Combined Energy and Attitude Control System (CEACS). Numerical treatments are performed to validate the effectiveness of AFC, whereby the CEACS attitude performance is analysed from its accuracy point of view. The results show that the PD-AFC attitude control performance is superiorly better than that of the solely conventional PD type

Satellite attitude performance during the momentum dumping mode.

In this paper, the active magnetic control technique is applied for controlling the attitude and nutation of roll/yaw ares as well as unloading the excess wheel angular momentum for a small biased-momentum satellite in a nominal operation. Two control structures are configured using 2 and 3 magnetic torquers. The proportional controller is used for the attitude and nutation control of roll/yaw ares while the proportional-integral controller is used for the wheel momentum unloading task Both systems are evaluated through numerical treatments and compared particularly during the momentum unloading process. The performance from simulations exhibits that both systems fulfill the mission requirements. However, the system that uses 3 magnetic lorquers gives a better attitude performance

Optimal control for combined energy storage and attitude control system (CEACS) in small satellites

The combined energy storage and attitude control system (CEACS) combines both energy storage and attitude control modules via the flywheel technology. Previously only the conventional control methods were tested for CEACS. In this paper, H2 and H-infinity control methods are implemented in CEACS. The satellite attitude control performances show that both control options can be employed for a good attitude pointing accuracy

A study of reaction wheel configurations for a 3-axis satellite attitude control

The satellite reaction wheel’s configuration plays also an important role in providing the attitude control torques. Several configurations based on three or four reaction wheels are investigated in order to identify the most suitable orientation that consumes a minimum power. Such information in a coherent form is not summarized in any publication; and therefore, an extensive literature search is required to obtain these results. In addition, most of the available results are from different test conditions; hence, making them difficult for comparison purposes. In this work, the standard reaction wheel control and angular momentum unloading schemes are adopted for all the reaction wheel configurations. The schemes will be presented together with their governing equations, making them fully amenable to numerical treatments. Numerical simulations are then performed for all the possible reaction wheel configurations with respect to an identical reference mission. All the configurations are analyzed in terms of their torques, momentums and attitude control performances. Based on the simulations, the reaction wheel configuration that has a minimum total control torque level is identified, which also corresponds to the configuration with minimum power consumption

Solar power profile prediction for low earth orbit satellites

This paper presents the development of algorithms using MATLAB® codes to predict the in-orbit satellite power profile. Satellite power requirement is a crucial parameter for its in-orbit operation. In this case, it is best to identify the power profile which indicates the amount of power generated over a time frame of an orbit. However, the determination of the satellite power profile requires substantial amount of efforts to compute and this is largely due to the complex numerical treatments. Orbital parameters are deemed to affect the determination of the satellite power profile. Therefore, a computer program has been written to solve all the governing equations leading to the satellite power profile prediction for an orbit and eventually for a year. The power profile validation was done analytically using the governing equations before the profile is generated through the computer codes. This work contributes greatly towards the small satellite (<100 kg) power sizing effort and eliminates the need of a costly commercial power sizing software

An optimum magnetic control torque generation of a momentum bias satellite

This paper describes a comparison study of magnetic attitude control torque generation performance of a momentum bias satellite operated in Low Earth Orbit (LEO) with various orbit inclinations. The satellite is equipped with two magnetic torquers that are placed along the +x and +y axes where magnetic control torque is generated when these magnetic torquers couple with the geomagnetic fields and its vector direction is perpendicular to both the magnetic fields. The control algorithm was structured using a proportional (P) controller for satellite attitudes/nutation control and a proportional-integral (PI) controller for managing the excess angular momentum on the momentum wheel. The structured control algorithm is simulated for 23°, 53° and 83° orbit inclinations and the generated attitude torque performances are compared to see how the variation of the satellite orbit affects the satellite’s attitude torque generation as the magnitude and direction of the geomagnetic fields vary with respect to the altitude and latitude while the magnitude and direction of the magnetic fields generated by the magnetic torquers vary with respect to the orbital motion. Results from simulation show that the higher orbit inclination generates optimum magnetic attitude control torque. Note that this work is the extension of the previous work published in The International Journal of Multiphysics [1]

Sliding mode control techniques for combined energy and attitude control system

Combined Energy and Attitude Control System (CEACS) is an optimization approach that combines the energy storage system and the attitude control system. With a double counter rotating flywheel simultaneously serving as energy storage device and as attitude control actuator, CEACS requires an accurate control strategy to obtain the mission requirements. In addition, it is important to design the control law to be invariant to uncertainties and disturbances, and guarantee robustness as CEACS inherits these in-orbit uncertainties. This paper presents a nonlinear control employing sliding mode to enhance the CEACS attitude control capability. The mathematical model for the conventional and boundary layer sliding mode controls are developed herein for CEACS. The controller provides enhancement in pointing accuracies, reasonable transient responses and a robustness against uncertainties and in-orbit disturbances

A Study Of Coupled Magnetic Fields For An Optimum Torque Generation

Magnetic torquers are specifically designed to generate a magnetic field onboard the satellites for their attitude control. A control torque is generated when the magnetic fields generated by the magnetic torquers couple with the geomagnetic fields, whereby the vector of the generated torque is perpendicular to both the magnetic fields

Interlaminar stress analysis for carbon/epoxy composite space rotors

This paper extends the previous works that appears in the International Journal of Multiphysics, Varatharajoo, Salit and Goh (2010). An approach incorporating cohesive zone modelling technique is incorporated into an optimized flywheel to properly simulate the stresses at the layer interfaces. Investigation on several fiber stacking sequences are also conducted to demonstrate the effect of fiber orientations on the overall rotor stress as well as the interface stress behaviour. The results demonstrated that the rotor interlaminar stresses are within the rotor materials’ ultimate strength and that the fiber direction with a combination of 45°/-45°/0° offers the best triple layer rotor among the few combinations selected for this analysis. It was shown that the present approach can facilitate also further investigation on the interface stress behaviour of rotating rotors

H2 and H∞ control options for the combined attitude and thermal control system (CATCS)

The combined attitude and thermal control system (CATCS) combines the conventional attitude control and thermal control subsystems. Its principle is based on circulating a heat conducting fluid inside a closed duct wielding the excess onboard heat in order to produce the attitude control torques. Previously only the proportional-integral (PI) controller has been tested for CATCS. In this paper two other control options for CATCS were designed based on the H2 and H∞ control methods to improve the attitude control performance of a small satellite. The control gain matrix with the minimum cost function is obtained by solving the Riccati equation and fed back to the system in order to achieve the system’s performance. The designed controllers can efficiently control the roll, pitch and yaw satellite attitudes. Simulations for the two techniques were carried out using Matlab and Simulink for ideal and non-ideal system models. Results show that the H2 controller has a better attitude control performance over the H∞ controller and PI controller itself