Orbit Control Research Articles

Optically Driven Janus Microengine with Full Orbital Motion Control.

Microengines have shown promise for a variety of applications in nanotechnology, microfluidics, and nanomedicine, including targeted drug delivery, microscale pumping, and environmental remediation. However, achieving precise control over their dynamics remains a significant challenge. In this study, we introduce a microengine that exploits both optical and thermal effects to achieve a high degree of controllability. We find that in the presence of a strongly focused light beam, a gold-silica Janus particle becomes confined at the stationary point where the optical and thermal forces balance. By using circularly polarized light, we can transfer angular momentum to the particle, breaking the symmetry between the two forces and resulting in a tangential force that drives directed orbital motion. We can simultaneously control the velocity and direction of rotation of the particle changing the ellipticity of the incoming light beam while tuning the radius of the orbit with laser power. Our experimental results are validated using a geometrical optics phenomenological model that considers the optical force, the absorption of optical power, and the resulting heating of the particle. The demonstrated enhanced flexibility in the control of microengines opens up new possibilities for their utilization in a wide range of applications, including microscale transport, sensing, and actuation.

Low-Thrust Lunar Capture Leveraging Nonlinear Orbit Control

Nonlinear orbit control with the use of low-thrust propulsion is proposed as an effective strategy for autonomous guidance of a space vehicle directed toward the Moon. Orbital motion is described in an ephemeris model, with the inclusion of the most relevant perturbations. Unfavorable initial conditions, associated with weak, temporary lunar capture, are considered, as representative conditions that may be encountered in real mission scenarios. These may occur when the spacecraft is released in nonnominal flight conditions, which would naturally lead it to impact the Moon or escape the lunar gravitational attraction. To avoid this, low-thrust propulsion, in conjunction with nonlinear orbit control, is employed, to drive the space vehicle toward two different, prescribed, low-altitude lunar orbits. Nonlinear orbit control leads to identifying a saturated feedback law (for the low-thrust magnitude and direction) that is proven to enjoy global stability properties. The guidance strategy at hand is successfully tested on three different mission scenarios. Then, the capture region is identified, and includes a large set of initial conditions for which nonlinear orbit control with low-thrust propulsion is effective to achieve lunar capture and final orbit acquisition. For the purpose of achieving lunar capture, low-thrust propulsion is shown to be more effective if ignited at aposelenium.

A Fast Star-Detection Algorithm under Stray-Light Interference

The interference caused by stray light leads to the invalid attitude of star sensors in orbit, thus affecting the attitude control of satellites. In order to overcome this problem, this paper proposes a fast star-detection algorithm with strong stray-light suppression ability. The first step in the proposed method is stray-light suppression. The highlighted pixels are unified and then erosion and dilation operations based on a large template are performed. Using the background image only, which is filled with stray light, the cleaner star image is obtained by subtracting the background from the unified image. The second step in the proposed method is binarization. The binary star image is obtained by using a line-segment strategy combined with a local threshold. The third step in the proposed method is star labeling. It comprises connected-domain labeling based on the preordering of pixels and the calculation of centroid coordinates of stars in each connected domain. The experimental results show that the proposed algorithm extracts the stars stably under the interference of different stray lights. The proposed method consumes less resources, and the output delay is only 18.256 us. Moreover, the successful identification rate is 98% and the attitude accuracy of the X and Y axes is better than 5″(3σ) when the star sensor works at the speed of zero.

Sliding-Mode Control Under Denial-of-Service Attacks: An Event-Triggered Quantized State Feedback Approach

This brief is concerned with the robust stabilization issue of cyber-physical systems (CPSs) under periodic Denial-of-Service (DoS) attacks with quantized feedback sliding-mode control (SMC) based on event-triggered mechanism(ETM). The ETM is introduced for reducing the load of network communication, and states generated by the ETM are quantized to construct the available information of the design of sliding-mode controller. Sufficient conditions for robust stabilization of the system under periodic DoS attacks are proposed to ensure the reachability of sliding manifold. In addition, a lower bound of the quantized measurement saturation parameter is derived to guarantee the quantizer capture system states in only one step under periodic DoS attacks. After that, this brief proves that the execution time interval of the ETM has a positive lower bound and thus no Zeno behaviors occur. The effectiveness of this proposed method is finally verified by an example of a satellite control system.

A random error estimation method for satellites being launched into orbit based on ellipsoid theory

Accurate and fast random error estimation is essential to improve satellite control. In this paper, the random error of the satellite being launched into orbit is explored. According to the uncertainty matrix of six satellite orbit parameters associated with the project, the uncertainty of the orbit position in the three axes of the geocentric inertial frame of reference is calculated via the propagation rate of the covariance matrix. Then, the random error probability density of the satellite position is constructed for normal distribution. The surface of the error with the same probability density is approximated as an ellipsoid, the size is deduced along with the ellipsoid's shape and direction, and the satellite's spatial position probability is obtained. Monte Carlo method and STK software were employed to simulate low-earth orbit micro-nano satellite launching into the same orbital position. It is confirmed that the results obtained via the theoretical model are in line with practice. Therefore, the ellipsoid theory proposed in this paper can be used to describe the satellite random position error.

Optimized Controller Provisioning in Software-Defined LEO Satellite Networks

The controller provisioning, which adjusts the number, locations, and members of satellite controllers adaptive to the dynamic network load and topology, fundamentally impacts the performance of software-defined satellite networks (SDSNs). An ideal provisioning strategy should achieve a low total control overhead throughout the entire satellite operation period, which is extremely challenging since the network load can only be predicted in a short time scale. Existing methods can hardly achieve this goal for they greedily configure controllers in each time slot, where switches have to frequently migrate from one controller to another. In this paper, we focus on achieving globally optimized strategies with only current network load information. We firstly propose a comprehensive control overhead model and formulate the Controller Provisioning Problem (CPP) in SDSNs as a non-convex integer programming problem. To solve the problem, we propose an approximate algorithm named AROA by introducing a regularization framework and based on randomized rounding. We theoretically derive its competitive ratio. To produce strategies in time for future large satellite constellations, we further propose a more efficient heuristic algorithm HROA. Evaluations on our built simulation system show that our proposed methods significantly outperform related schemes in control overhead, latency, and scalability.

Spatial Full Degree‐Of‐Freedom Scattered Optical Field Modulation

AbstractScattered optical field modulations can enable the function of traditional optical technologies, such as the dynamic holographic display, in a scattering environment. Nonetheless, only part of the degrees of freedom in the optical field can be effectively modulated so far. Here, this work proposes spatial full degree‐of‐freedom scattered optical field modulation (SF‐SOM) to impose a control on the amplitude, phase, and polarization of the optical field. To do so, this method independently modulates the complex amplitude of two orthogonally polarized components. It also contains a full degree‐of‐freedom vector transmission matrix model to describe the transformation from the incident field to the scattered field. Compared with the single degree‐of‐freedom modulation methods against the same scattering environment, SF‐SOM increases the contrast of focus by a factor of five. Furthermore, the experiments demonstrate a holographic display and orbital angular momentum control with SF‐SOM to show its ubiquitous utility in optics.

Low-Thrust Transfer to Quasi-Synchronous Martian Elliptic Orbit via Nonlinear Feedback Control

This study considers the problem of injecting a spacecraft into an elliptic, repeating-ground-track orbit about Mars, starting from a 4-sol highly elliptical orbit, which is a typical Martian capture orbit, entered at the end of the interplanetary transfer. The final operational orbit has apoares corresponding to the maximum (or minimum) latitude, and nine nodal periods are flown in 5 Martian nodal days. The orbit at hand is proven to guarantee coverage properties similar to the Molniya orbit about Earth; therefore, it is especially suitable for satellites that form constellations. Low-thrust nonlinear orbit control is proposed as an affordable and effective option for orbit injection, capable of attaining significant propellant reduction if compared to alternative strategies based on chemical propulsion. This work introduces a new, saturated feedback law for the low-thrust direction and magnitude that is capable of driving the spacecraft of interest toward the operational orbit. Remarkable stability properties are proven to hold using the Lyapunov stability theory. Because no reference path is to be identified a priori, this technique represents a viable autonomous guidance strategy, even in the case of temporary unavailability of the low-thrust propulsion system or in the presence of widely dispersed initial conditions and errors on estimating orbit perturbations. Monte Carlo simulations prove that the feedback guidance strategy at hand is effective and accurate for injecting a spacecraft into the desired, repeating-ground-track operational orbit without requiring any reference transfer path.

Mars orbit injection via aerocapture and low-thrust nonlinear orbit control

This research proposes a new strategy for Mars orbit injection, based on aerocapture and low-thrust nonlinear orbit control. The range of periapse altitudes that allow aerocapture is identified as a function of the hyperbolic excess velocity at Mars arrival, with reference to a large variety of atmospheric density profiles and different ballistic coefficients. This analysis proves that a safe periares altitudinal range leading to aerocapture in all atmospheric conditions does not exist. Three different correction maneuvers, aimed at avoiding both impact and escape, are identified. After the atmospheric arc, the spacecraft orbit exhibits large dispersions in terms of orbit elements. Therefore, the identification of an effective autonomous guidance strategy, capable of driving the spacecraft toward the desired operational orbit, is mandatory. To do this, low-thrust nonlinear orbit control is proposed as an effective option. A feedback law for the low-thrust direction and magnitude, with saturation of the thrust magnitude, is defined, and is proven to enjoy global stability properties. As a result, the spacecraft travels toward the operational orbit of interest, i.e. either (a) an areostationary orbit, (b) a quasi-synchronous inclined orbit, or (c) a low-altitude, sunsynchronous orbit. Monte Carlo simulations, with stochastic density profiles and uncertain initial conditions, point out that the strategy at hand is successful and allows reducing the overall propellant budget in comparison to direct orbit injection based on chemical propulsion. Moreover, the overall time of flight typically ranges from 45 to 140 days, and therefore it is much shorter than that required with the use of aerobraking. As a last advantage, low-thrust nonlinear orbit control allows achievement of a variety of operational orbits, with great accuracy.

Collision Avoidance Second Order Sliding Mode Control of Satellite Formation with Air-Floated Platform Semi-Physical Simulation

As the number of satellites in orbit increases, the issue of flight safety in spacecraft formation orbit control has become increasingly prominent. With this in mind, this paper designs a second-order terminal sliding mode controller for spacecraft formation obstacle avoidance based on an artificial potential function (APF). To demonstrate the effectiveness of the controller, this paper first constructs a Lyapunov function to prove its stability and then verifies its theoretical validity through numerical simulation. Finally, a satellite simulator is used for semi-physical simulation to verify the practical effectiveness of the controller proposed in this paper.

Acute and Sub-acute Toxicity Studies of a <i>Siddha</i> Medicine <i>Ganthaga Mezhugu</i> by Oral Administration in Sprague Dawley Rats

Psoriasis, a chronic auto-immune skin disease, is troubling 1-3 % of the world population with a 0.44-2.8% prevalence rate in India affecting more males than females. It is considered a dermatologist’s menace as it is challenging to treat the condition. Siddha, one of the traditional systems of medicine practised more in South India, includes a wide range of medicines that are used to treat or manage various ailments, including psoriasis. One such medicine is Ganthaga Mezhugu (GM) used in treating skin diseases like psoriasis. This present study deals with the evaluation of the safety of GM as per the Organization for Economic Co-operation and Development (OECD) Guidelines 423 and 407 in Sprague Dawley (SD) rats. In the Acute Toxicity study, SD female rats were grouped into five, in which Groups I and II received elemental Sulphur in two different doses, Groups III and IV received Sulphur ‘purified’ with two different Siddha processes and Group V received GM (2000mg/kg b.wt.). In the subacute toxicity study, SD rats of both sexes were grouped into six in which Group 1 served as vehicle control, Groups 2, 3, and 4 as low, mid, and high dose groups and the last two (Groups 5 and 6) as satellite control and satellite high-dose groups. In the acute study, no mortality, toxic signs or any gross pathological changes were noted. Hence, the LD50 value of GM was found to be greater than 2000mg/kg b.wt. In the sub-acute toxicity study, no mortality or morbidity occurred. There was a gradual increase in body weight with normal food and water intake indicating normalcy in its metabolism. There were no significant changes in hematological and biochemical parameters, serum electrolytes and gross pathology. Also, no pathological changes were found in the histopathology of organs in treated animals when compared with control group animals. Based on the results, regarding the Globally Harmonized System of Classification and Labelling of chemicals, GM can be classified as Category−5, which implies its safety for human consumption. Moreover, the results of the sub-acute study also confirm the safety of GM up to the dose of 400mg/kg b.wt.

ATTITUDE CONTROL OF THE NANOSATELLITE USING A HYBRID FUZZY ALGORITHM BY MEANS OF THE REACTION WHEELS

Numerous application fields of automation the industrial processes have demonstrated favorable outcomes with modern control algorithms that rely on artificial intelligence. Therefore, some researchers have endeavored to implement these algorithms in the attitude control of satellites by evaluating their performance in simulated scenarios. However, due to the associated cost and risks, there is a scarcity of experimental data available for testing new attitude control algorithms on a real satellite. To address this issue, simulation of satellite positioning based on the dynamic model of the satellite with reaction wheels was carried out to perform a comparative analysis of a hybrid proportional integral and derivative (PID) fuzzy control algorithm and a classical PID control algorithm, regarding the analysis of the obtained performances. The obtained results indicate that using a Hybrid Fuzzy PID control algorithm produces better performances, than the PID control algorithm.

Switched Event-Triggered $\mathcal {H}_{\infty }$ Security Control for Networked Systems Vulnerable to Aperiodic DoS Attacks

This paper investigates switched event-triggered <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathcal {H}_{\infty }$</tex-math></inline-formula> security control for networked systems vulnerable to aperiodic denial-of-service (ADoS) attacks. An anti-attack switched event-triggered mechanism (ATASETM) is designed by considering the impact of ADoS attacks on the systems. Based on the mechanism, the entire time interval is split into rest intervals, continuous detection intervals, residual intervals, and ADoS active-attack intervals. The closed-loop system (CLS) is represented as a three-mode switched system by merging these intervals. Subsequently, a three-piecewise Lyapunov function is constructed for fewer conservative criteria to ensure that the CLS is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathcal {H}_{\infty }$</tex-math></inline-formula> exponentially stable. An exact expression of the relationship between the decay rate and length of the dormant- and active-attack intervals is obtained. On the basis of the proposed criteria, a joint-design strategy is developed in terms of linear matrix inequalities for the desired trigger matrix and feedback gain. Lastly, a satellite control system and an inverted pendulum model are used to validate the ATASETM-based stability analysis and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathcal {H}_{\infty }$</tex-math></inline-formula> security control approaches. Numerical results demonstrate that the maximum allowable exponential decay rate decreases with increasing attack time, and vice versa. Furthermore, the optimal <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathcal {H}_\infty$</tex-math></inline-formula> performance level becomes worse as the attack time or the difficulty of the event triggering increases.

The inner barrier mediated spin–orbit control in stepped quantum wells

The inner barrier in stepped quantum wells, which embrace an intrinsic structural inversion asymmetry (SIA), offers more possibilities for the multi-band spin–orbit (SO) control. By varying the inner band offset [Formula: see text], which adjusts the quantum confinement for electrons and also the SIA, we reveal that both the Rashba ([Formula: see text]) and Dresselhaus ([Formula: see text]) SO coeffcients of the two subbands exhibit contrasting dependence on [Formula: see text]. Also, [Formula: see text] and [Formula: see text] may have opposite signs, depending on the value of [Formula: see text]. By fine tuning the inner offset, there may even exist a scenario in which [Formula: see text] identically vanishes but [Formula: see text] is finite, offering a knob on how to subband-selectively suppress spin relaxation induced by SO coupling. In addition, by resorting to an external gate [Formula: see text], we reveal that in the regime of [Formula: see text] and [Formula: see text] having opposite signs, their magnitudes also vary with [Formula: see text] in an opposite manner. This, together with the engineered inner barrier of stepped wells, will facilitate flexible spin manipulation. Finally, the interband SO couplings, which depend on the spatial overlap of wave functions of distinct subbands and the corresponding parities, are also discussed.

Active disturbance rejection control of drag-free satellites considering the effect of micro-propulsion noise

The space gravitational wave detection mission requires a super "static and precise" scientific experiment environment. In order to solve the non-conservative force disturbance variation and the actuator noise and measurement noise, this paper designs a drag-free control scheme based on active disturbance rejection control (ADRC) framework to achieve the high-precision index. According to the ultra-high accuracy, low bandwidth limitation, and robustness requirements of drag-free satellite, the H∞ controller satisfying the robustness constraint is designed as an active disturbance rejection feedback controller to achieve the high-precision index. Meanwhile, the non-conservative force disturbance with a wide range of variations is estimated and feedforward compensated by an extended state observer to improve the system robustness. Simulation results show that the control system can achieve the relative displacement of 2nm/Hznm/Hz1/2 for the drag-free satellite platform and the residual acceleration of 1×10-15 m/sm/s2/Hz1/2 for the test mass.

Negative imaginary feedback control of satellite orbit dynamical model

This article presents observer-based negative imaginary positive feedback control of satellite orbit dynamical model. In this article, satellite orbital model is transformed into a strongly strict negative imaginary system using observer-based transformation scheme, and then, negative imaginary control theory is applied to achieve stability and robustness in orbit control system in the presence of multiplicative uncertainty. The solutions of orbit control problem are investigated with two thrusters input as well as one thruster input. According to the numerical simulation findings reported in this study, the investigated control approach guarantees the robust stabilization of the satellite orbital system.

Random Error Estimation and Propagation Analysis for Satellites’ Initial Positions

An increasing number of satellites are currently being launched into orbit to work in the form of clusters or constellations. However, the initial orbit position is accompanied by random errors, which will propagate during their running. Therefore, the orbit precision of the satellites directly affects space safety, network accuracy, and operating efficiency. Hence, accurate and fast random error estimation is essential to improve satellite control. The traditional method will take much time and cost, and it is associated with complex calculations or low accuracy, especially for large-scale constellations. In this paper, a random error evaluation model based on the ellipsoid is proposed. It can be used to estimate initial positions and error propagation for any orbit satellites. By comparing with the experiment results using the Monte Carlo method, it is proved that the proposed model is relatively simple, highly effective, and good at accuracy.

Modulated multi-sliding-surface attitude tracking control for all-electric propulsion satellites

This work presents an attitude tracking control method suitable for satellites only using on–off electric thrusters of constant magnitude. It is practically a globally stable finite-time controller modulated by the Pulse-Width-Pulse-Frequency (PWPF) algorithm. Two sliding surfaces are designed to insure a finite-time convergence property. An automatic generator for producing the time-related key parameter is proposed, leaving only two scalar parameters to fine tune values. Typical satellite control modes are used to validate the effectiveness of the proposed method. Results show that it is feasible not only for attitude tracking problem with various errors taken into account, but also for six degree-of-freedom control. Flexibility of trading-off the control accuracy and number of thruster firings can be achieved by the PWPF parameter tuning, which makes it a promising candidate for future use in real practise.

Attitude control and on-orbit performance evaluation of spacecraft with variable shape function

The variable shape function enables attitude and orbit control by actively changing the shape of a spacecraft on orbit. In order to demonstrate this function on orbit, we developed the “HIBARI” satellite equipped with drivable solar array paddles and demonstrated the world’s first in-orbit variable shape attitude control in FY2021. The present study first compares the behavior of the paddle drive on the ground and on orbit to evaluate its performance. In addition, attitude change angle data from paddle drive on orbit is used for comparison with analytical values and evaluation control performance.

Magnetometer-Only Kalman Filter Based Algorithms for High Accuracy Spacecraft Attitude Estimation (A Comparative Analysis)

Kalman Filter (KF) based algorithms are the most frequently employed attitude estimation algorithms. Typically, a fully observable system necessitates the use of two distinct sensor types. Therefore, relying on a single sensor, such as a magnetometer, for spacecraft attitude estimation is deemed to be a challenge. The present investigation centers on utilizing magnetometers as the exclusive sensor. Several KF based estimation algorithms have been designed and evaluated to give the designer of spacecraft Attitude and Orbit Control System (AOCS) the choice of a suitable algorithm for his mission based on quantitative measures. These algorithms are capable of effectively addressing nonlinearity in both process and measurement models. The algorithms under examination encompass the Extended Kalman Filter (EKF), Sequential Extended Kalman Filter (SEKF), Pseudo Linear Kalman Filter (PSELIKA), Unscented Kalman Filter (USKF), and Derivative Free Extended Kalman Filter (DFEKF). The comparison of the distinct algorithms hinges on key performance metrics, such as estimation error for each axis, computation time, and convergence rate. The resulting algorithms provide numerous benefits, such as diverse levels of high estimation accuracy (with estimation errors ranging from 0.014o to 0.14o), varying computational demands (execution time ranges from 0.0536s to 0.0584s), and the capability to converge despite large initial attitude estimation errors (which reached 170o). These properties render the algorithms appropriate for utilization by spacecraft designers in all operational modes, supplying high-precision attitude estimations better than (0.5o) despite high magnetometer noise levels, which reached (200 nT).