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

Reaction wheel configurations for high and middle inclination orbits

The purpose of this paper is to identify the low-power Reaction Wheel (RW) configuration for a 3-axis satellite attitude control at high and middle inclination orbits. All of the proposed RW configurations are evaluated through the numerical simulations with respect to an identical reference mission. The simulations are tested for two different orbit positions; first, at a high inclination (e.g., 83°), second, at a middle inclination (e.g., 53°). All configurations are analysed in terms of their total torques and attitude performances. The stable attitude accuracies (≈0.001°) are achieved in all the configurations either at 83° or 53° inclinations. Results also revealed that the change of orbit inclination slightly influences the determination of the low-power RW configurations. This research provides a quick summary on a possible low-power arrangement of reaction wheels onboard a small satellite

A fractional-order sliding mode control for nominal and underactuated satellite attitude controls

Sliding mode control (SMC) is widely used in many existing nonlinear control solutions due to its capability against external disturbances and uncertainties, while the fractional order control (FOC) is employed as it can further enhance the control performance due to its robustness. This paper attempts to implement a fractional-order sliding mode control (FOSMC) for a small satellite with reaction wheels (RWs). In this work, a conventional SMC was initially designed to cope with the uncertainties of satellite attitude dynamics. In order to improve the attitude control performance, the FOSMC was designed accordingly and the classical chattering problem was alleviated by using the hyperbolic tangent function. This current work is the maiden work on FOSMC especially for small satellites using RWs. The FOSMC was also tested for a satellite with only two functional RWs, in which the control allocation technique is proposed to solve the underactuated satellite attitude control problem. Since the angular momentum of the reaction wheel will become saturated over time, it will be managed using the momentum unloading technique with the unique fuzzy proportional-integral (FPI) control. All control algorithms were numerically treated and analysed. The results show that the FOSMC is effective in achieving the overall desired attitude control performance for nominal and underactuated satellites

The assessment of comparative advantage of the non-ruminant subsector through policy analysis matrix (PAM) in Peninsular Malaysia

The objective of this study was to assess comparative advantages of the non-ruminant subsector in selected states of Peninsular Malaysia. The study analysed livestock production, namely chicken meat and eggs in three states i.e. Negeri Sembilan, Perak and Selangor. This study used a Policy Analysis Matrix (PAM) to determine whether non-ruminant products have a comparative advantage for production under commercial, medium or small scale farm size. The study demonstrated that Malaysia has a strong comparative advantage in the production of chicken meat compared to the production of eggs. Chicken meat produced on a commercial scale has a DRC ratio of 0.24 while eggs produced on a medium scale have a DRC ratio of 0.26. Both farms have a comparative advantage because their ratio implies that the value added per unit of product is larger than the value of domestic resources used to produce in that unit. According to Tsakok (1990), the level of comparative advantage of each subsector is greatest if the DRC ratio is close to zero. As a result, broiler farms on commercial scale with a DRC ratio of 0.24 have a higher degree of comparative advantage compared to layer farms on a commercial scale with DRC ratio of 0.71

Enhanced attitude control structure for small satellites with reaction wheels

Purpose: This paper aims to describe a design enhancement for the satellite attitude control system using reaction wheels, and the wheel momentum unloading using magnetorquers. Design/methodology/approach: The proportional – integral–derivative-controller and active force control (AFC) schemes are developed together with their governing equations for closed loop system of attitude control. Four numerical simulations were carried out using the Matlab – Simulink™ software and results were compared. Findings: From the results, it is evident that the attitude accuracies for roll–pitch–yaw axes have improved significantly through the proportional – derivative (PD) – AFC controller for the attitude control and the wheel momentum can be well maintained during the momentum unloading scheme. The results show that the AFC has a high potential to be implemented in the satellite attitude control system. Practical implications: Using AFC, the actual disturbance torque is considered totally rejected by the system without having to have any direct prior knowledge on the actual disturbance itself. Originality/value: The results demonstrate the satellite attitude control using reaction wheel is enhanced by PD–AFC attitude controller

The Assessment of Comparative Advantage of the Non-Ruminant Subsector through Policy Analysis Matrix(PAM) in Peninsular Malaysia

The objective of this study was to assess comparative advantages of the non-ruminant subsector in selected states of Peninsular Malaysia. The study analysed livestock production, namely chicken meat and eggs in three states i.e. Negeri Sembilan, Perak and Selangor. This study used a Policy Analysis Matrix (PAM) to determine whether non-ruminant products have a comparative advantage for production under commercial, medium or small scale farm size. The study demonstrated that Malaysia has a strong comparative advantage in the production of chicken meat compared to the production of eggs. Chicken meat produced on a commercial scale has a DRC ratio of 0.24 while eggs produced on a medium scale have a DRC ratio of 0.26. Both farms have a comparative advantage because their ratio implies that the value added per unit of product is larger than the value of domestic resources used to produce in that unit. According to Tsakok (1990), the level of comparative advantage of each subsector is greatest if the DRC ratio is close to zero. As a result, broiler farms on commercial scale with a DRC ratio of 0.24 have a higher degree of comparative advantage compared to layer farms on a commercial scale with DRC ratio of 0.71

Enhanced attitude control structure for small satellites with reaction wheels

Attitude accuracies of a three-axis satellite are highly influenced by space environment disturbances and uncertainties. Similar to actuators, an attitude controller also plays an important role and must be robust enough to cope with any disturbances and uncertainties. Various controllers have been used for satellite attitude controls either linear or nonlinear control theories. This thesis presents an enhanced attitude control structure for a small satellite with reaction wheels (RWs) and the wheel angular momentum unloading control using magnetic torquers (MTQs). In order to improve the attitude control performances, a proportional derivative-active force control (PDAFC), and a Fuzzy PD-AFC are developed. For the momentum unloading control, a Fuzzy-proportional integral (Fuzzy-PI) is developed to remove the excess wheel momentum. Using the PD-AFC and Fuzzy PD-AFC, the actual disturbances torques are considered totally rejected by the system without having to have any direct prior knowledge on the actual disturbances itself. These days, however, satellites have become increasingly more complex, with many additional components, such as antennas, cameras, solar panels and mechanical manipulators. These components introduce flexible mode which results in a satellite dynamic system becoming highly nonlinear. Therefore, a robust nonlinear controller such as sliding mode control (SMC) is highly desirable. Besides, a number of studies have shown that, fractional order controller (FOC) could enhance the control system performance due to its extra degrees of freedom. In this thesis, a fractional order sliding mode control (FOSMC) is developed. In fact, this current work will be one of the maiden works on FOSMC for small satellites. All the proposed controllers were also tested for a satellite with only two functional RWs, in which the control allocation technique is proposed to solve the underactuated satellite attitude control problem. All the relevant attitude control architectures are developed together with their governing equations. Eventually, all control algorithms are numerically treated and analysed. The research results obtained proved that the PD-AFC, Fuzzy PD-AFC and FOSMC to be successful in achieving the overall stability attitude control system in the presence of external disturbances and uncertainties, i.e., PD-AFC (±0.0040° - 0.0055°) ; Fuzzy PD-AFC (±0.0010° - 0.0015°); FOSMC (±0.00020), and with the Fuzzy-PI for momentum unloading control whereby, the wheel momentum can be well maintained. Finally, the research for underactuated satellite attitude control performances using two RWs have been also successfully demonstrated and the research results proved that the control allocation technique provides a good performance in controlling the satellite attitude

Attitude control simulation of small satellites with reaction wheels

Nowadays, most of the designed satellites are dedicated for high performance missions, which require high attitude pointing accuracies. The reaction wheel is the most suitable satellite actuator that can provide high attitude pointing accuracies (0.1°-0.001°). Commonly, three or four reaction wheel configurations are used for a 3-axis satellite attitude control. In fact, higher power is consumed when multiple reaction wheels are employed. Thus, it is rather challenging to adopt multiple reaction wheels for the small satellite missions because of the power constraint. On the other hand, reaction wheels lack of the ability to remove the excess angular momentum and that the wheels have a limited capacity to store momentum. Without a momentum management control, the satellite may be uncontrollable. Therefore, to make the implementation of multiple reaction wheels reliable for a small satellite, it is necessary to find a way to minimize the wheel’s power consumption. Also, it is compulsory for a satellite to be equipped with a momentum management scheme in order to maintain the angular momentum within their allowable limits. Momentum management control using magnetic torquers are chosen in this work. Indeed, the wheel’s power consumption can be lowered by particularly arranging the reaction wheels’ orientation onboard the satellite. In this research, several configurations, based on three or four reaction wheels, are investigated in order to identify the most suitable orientation with the total minimum power. All the related mathematical models are implemented in Matlab-SimulinkTM software. Numerical simulations are performed for all the possible reaction wheel configurations with respect to an identical reference mission. Two simulation analyses are presented for their performance evaluations. First simulation focuses on the satellite attitude control only and the second simulation focuses on the satellite attitude control with momentum management control. Based on the simulations, the reaction wheel configuration that produces a minimum total control torque is identified, which also corresponds to the configuration with a minimum power intake. The wheel angular momentums and satellite attitude accuracies are also well maintained during the control task

Understanding Potential Heavy Metal Contamination, Absorption, Translocation and Accumulation in Rice and Human Health Risks

Rice is a worldwide staple food and heavy metal contamination is often reported in rice production. Heavy metal can originate from natural sources or be present through anthropogenic contamination. Therefore, this review summarizes the current status of heavy metal contamination in paddy soil and plants, highlighting the mechanism of uptake, bioaccumulation, and health risk assessment. A scoping search employing Google Scholar, Science Direct, Research Gate, Scopus, and Wiley Online was carried out to build up the review using the following keywords: heavy metals, absorption, translocation, accumulation, uptake, biotransformation, rice, and human risk with no restrictions being placed on the year of study. Cadmium (Cd), arsenic (As), and lead (Pb) have been identified as the most prevalent metals in rice cultivation. Mining and irrigation activities are primary sources, but chemical fertilizer and pesticide usage also contribute to heavy metal contamination of paddy soil worldwide. Further to their adverse effect on the paddy ecosystem by reducing the soil fertility and grain yield, heavy metal contamination represents a risk to human health. An in-depth discussion is further offered on health risk assessments by quantitative measurement to identify potential risk towards heavy metal exposure via rice consumption, which consisted of in vitro digestion models through a vital ingestion portion of rice