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.
The space plasma is one of the environmental components impinging on the materials used for spacecraft surface structure and configuration. Therefore, ground-based experimental simulations are carried out on samples of materials to study the variation of the characteristics and morphological structures of the materials due to plasma effects. In the experiments, discharging and arcs inception has been investigated. The experimental procedures are performed at different test conditions and plasma parameters. Morphological and arc images analyses have been carried out using the Python and Maxim DL programs. The results have shown the variation of the structure and sample characteristics due to plasma exposure and arc effects.
In Bolivia, like in most Latin American countries space projects are increasing, and this phenomenon leads to the need to train new professionals in space issues. For this reason, universities and academic centres require specialised equipment in this area. Unfortunately, this equipment has high costs (equipment such as CubeSat kit, educational satellites, satellite kit, etc.). Due to this, the design and construction of an educational and low-cost picosatellite kit with its respective signal reception equipment were necessary. The kit consists of an educational picosatellite, with a ground station, that is intended to become the perfect tool for practical training in space engineering at different levels. Potential users range from primary schools, where STEM skills development is pursued, to university engineering courses and, even, engineering companies. Additionally, this real satellite simulator offers a wide variety of educational activities without compromising cost.
This paper addresses the attitude control problem in spacecraft systems subjected to multiple sources of disturbances. To estimate these disturbances, it is important to consider factors such as vibration torque from solar panels, environmental disturbance torques, and unmodelled dynamics of the flexible spacecraft. We propose an enhanced sliding mode attitude control (SMC) with a disturbance observer (DO). Based on the estimates provided by this observer, we employ a SMC law optimised for spacecraft stabilisation using the particle swarm optimisation (PSO) algorithm. Lyapunov stability theory proves closed-loop system stability and estimation error convergence. Comparative simulations between the proposed control scheme and proportional-derivative (PD) control optimised with PSO highlight the superior performance of our approach. The results show that the PSO-optimised controller enables rapid convergence of the flexible spacecraft's attitude. To evaluate the controller's accuracy, the root mean square error (RMSE) of the attitude error is used as the performance method.
Space deployable truss is an important component in the spacecraft system, its smooth deployment is significant to ensure the normal operation of the spacecraft. The parts in truss are connected by joints and clearance inevitably exists in joints. As the growing of truss scales, the proliferation of joints amplifies the impact of clearance on truss mobility, thereby influencing spacecraft operation. Firstly, in this paper, based on the Cartesian method of multi-body system, the variable topology fast algorithm is introduced to solve the locking problem of space deployable truss. Then we establish contact dynamics model for clearance joint, obtaining normal contact force and tangential friction force by applying Hertz contact theory and Coulomb friction model, respectively. Finally, numerical simulations are conducted to analyse the effects of clearance, driving force, and friction on truss mobility. The results indicate that reducing joint clearance and driving force, along with increasing joint friction, diminishes truss mobility.
In this work, the problem of attitude control of flexible satellites is addressed by applying a composite controller (PD-DOBC) that incorporates a disturbance observer to estimate the appendix vibrations and then compensate for them by integrating the estimated disturbance in the control law of the composite controller. To further enhance the controller's performance, we introduce a nonlinear proportional derivative controller (NPD) and optimise the controller/observer gains using the grey wolf optimisation (GWO). Simulation results demonstrate the feasibility and effectiveness of the proposed methods, with significant improvements in the control performance. In particular, the optimised nonlinear PD-DOBC method outperforms other methods, confirming its superior effectiveness in addressing the challenges of attitude control in flexible satellites with flexible appendages. Our findings have important implications for the design of future space missions and highlight the potential for enhancing the attitude precision and the pointing accuracy of flexible satellites attitude control.
In this paper, we propose a novel approach for detecting and predicting satellite failures using machine learning, with a focus on the Algerian satellite Alsat-1B. Analysing five years of event data, comprising over seven million occurrences and 3,000 event types, we evaluate four sequence-to-sequence prediction models and eight classification models. Our key contribution combines a Markov chain for sequence prediction and a logistic regression model for classification, proving highly effective with 97.7% accuracy, precision of 1.0, recall of 0.84, and an f-score of 0.91. This approach showcases the potential of intelligent systems in satellite control, underscoring the imperative for further exploration and development in this promising field.
Space junk is particularly common in Earth's orbit and includes abandoned spacecraft, stranded launch vehicle stages, mission-related waste, and disintegration debris from the destruction of uninhibited missile launchers and spacecraft. Striping off this debris will be more effective than performing collision avoidance manoeuvres that would take hours and need a substantial amount of propellant since the optimisation of tracking and location prediction of debris is obscure. In this paper, a comprehensive study of space debris is presented which includes serious threats offered by space junk, and working techniques developed in the past eight years to remove space waste. The recent techniques of debris removal and all their possible deviations are investigated and explained with illustrations. The purpose of this paper is to incorporate in a single platform all the efficient strategies of debris removal adopted in the last 8 years, and the techniques used till 2015 are tabulated.
In this paper, aerospace target tracking of multiple targets moving in space has been done based on symmetrical transformation of measurements using different nonlinear Gaussian filters. The targets' positions and velocities have been estimated using traditional extended Kalman filter (EKF), unscented Kalman filter (UKF) and advanced cubature quadrature Kalman filter (CQKF) for three types of symmetrical measurement, namely sum of power, sum of product and homogeneous symmetric form. The results of EKF, UKF and CQKF for those symmetrical measurements with optimal linear Kalman filter have been compared in terms of root mean square error (RMSE). It has been observed that RMSEs of position and velocity are distinctly smaller in sum of product than sum of power, whereas performance for homogeneous symmetric form is comparable to sum of product and sometimes better. Further investigation reveals that UKF and CQKF with homogeneous symmetric form reduce RMSEs of position and velocity significantly.
Inclination change manoeuvre is widely performed to correct the inclination to the desired value. However, inclination manoeuvres studied or performed so far assumed that the thrust profile is constant maximum. In fact, for inclination change manoeuvre, the satellite position in orbit affects the ?i/?t efficiency and the manoeuvre will be best performed at nodes. This research investigated the optimum profile thrust for inclination change manoeuvre for small inclination changes only on a case study of LAPAN-A4 satellite. The optimisation involved several methods: using GMAT software and using genetic algorithm which is divided further into general and special perturbation. The results showed a good agreement that the most optimum thrust profile for this case is a constant maximum thrust profile.
In this work, well known existing estimation algorithms like extended Kalman filter (EKF) and unscented Kalman filter (UKF) with different adaptive extensions are implemented on target tracking problem for passive tracking. To deal with model uncertainty and uncertain noises, the process and measurement noise covariances are adapted based on innovation and residual sequences. Different adaptation rules for adjusting the noise covariance are examined. For the robustness performance analysis of each algorithm, target loss that occurred at last time of simulation is accounted for with consideration of a 2% estimation error. The effectiveness of filter performance is evaluated on the basis of root mean square error, average target loss and relative computational time with Monte Carlo simulation. Simulation results demonstrate that adaptive version of traditional filters have improved tracking performance with a significant computational burden in terms of estimation accuracy and track loss.
Earth observation (EO) is a popular mission objective of satellite systems. A typical optical EO satellite occupies a LEO orbit which allows to achieve resolutions required for their applications with optics that fits in a medium-sized bus. One of the alternatives is a small satellite with a propulsion module operating on a very low Earth orbit (VLEO.) While this approach has a number of challenges, it can result in small, low-price satellites capable of achieving resolutions comparable with standard EO satellites on LEO orbit. This paper describes the satellite platform that can potentially be used in the VLEO orbit. Image quality and observation instrument aspects as well as an impact of VLEO orbit on a mission design and its cost are discussed. Justification of a propulsion concept follows, and a parametric model of propulsion module is described. A mission analysis estimating mission durations at VLEO is described and results are discussed.
This project aims to develop a remote sensing satellite for observing Mars. Microsatellites will be incompetent to traverse Mars autonomously; hence an alternate fail-proof is to deploy multiple microsatellites using a mothership with adequate fuel. The microsatellite performs its operation in a polar orbit that integrates Mars colour camera and thermal infrared imaging spectrometers as payloads and utilises components off the shelf to serve individual subsystem requirements. The chemical propulsion subsystem utilises a monopropellant employing a 1-N thruster. The power subsystem generates and distributes the necessary power to function efficiently using its 18 solar panels. The communication subsystem enables signal transmission between Earth and Mars through its short and long-range broadcast equipment. The unique structural frame of the microsatellite offers a high strength-to-weight ratio during the entirety of the mission. The microsatellite proposes an opportunity for university students to observe Mars at an economically low cost by employing current technology.
In the present study, shock waves produced over different blunt bodies moving at Mach 2.0 at zero angle of attack have been captured and analysed using computational investigations. Forebodies of distinct bluntness (hemisphere, ellipse, and ogive) are adopted, and the effect of the forebody geometry on the flow parameters is investigated. The flow parameters such as shock stand-off distance and shock strength have been captured over various forebody geometries and correlated with the forebody drag coefficient. With the reduction in the forebody bluntness, the shock stand-off distance and the shock strength are found to be decreasing, resulting in a decrease in the forebody drag coefficient values. The effect of the free-stream supersonic Mach number over a typical blunt body (hemisphere) was also investigated. With increasing freestream Mach number, the shock wave generated ahead the blunt hemisphere moved closer to the forebody and an increase in the forebody drag was observed.
This paper studies the attitude control of a satellite in three-axis using only four thrusters. The mathematical model of the attitude is represented as a switched system with 16 subsystems. Each subsystem is defined based on the thruster's on/off status. The dynamic programming is utilised to find the optimal switching between subsystems such that a cost function is optimised. Furthermore, to generalise the solution for a specific domain of interest, neural network is employed for offline training and approximating the cost function. An offline training algorithm is suggested to find the optimal weights of the neurons and determine optimal switching. It is shown that the proposed method can execute a manoeuvre within fixed final time. Moreover, the control is robust against uncertainties in the system modelling. Finally, the system modelling and control approach is suggested as a framework to design low-cost attitude control system unit, suitable for microsatellite-class.
