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Stratospheric balloons serve as cost-effective platforms for wireless communication. However, these platforms encounter challenges stemming from their underactuation in the horizontal plane. Consequently, controllers must continually identify favorable wind conditions to optimize station-keeping performance while managing energy consumption. This study presents a receding horizon controller based on wind and balloon models. Two neural networks, PredRNN and ResNet, are utilized for short-term wind field forecast. Additionally, an online receding horizon controller, based on simultaneous optimistic optimization (SOO), is developed for action sequence planning and adapted to accommodate various constraints, which is especially suitable due to its gradient-free nature, high efficiency, and effectiveness in black-box function optimization. A reward function is formulated to balance power consumption and station-keeping performance. Simulations conducted across diverse positions and dates demonstrate the superior performance of the proposed method compared with traditional greedy and A* algorithms. [ABSTRACT FROM AUTHOR]

This study analyzes the performance of a tape-like bare electrodynamic tether as a promising propellant-free technology for the International Space Station (ISS) station-keeping, supporting the concept that the technology can provide significant mission benefits by reducing the ISS reliance on costly refueling operations for orbit maintenance. Convenient control laws for managing the electrical power supplied to the tether are proposed, exploring two distinct scenarios. The first involves using the electrodynamic tether continuously to counteract aerodynamic drag. The second adopts a cyclic approach, alternating between boosting the station with the tether and allowing for periods of natural decay. Optimal tether geometry, aimed at maximizing system efficiency, is also detailed. The study specifies an electrodynamic tether configuration featuring a 6-kilometer-long aluminum ribbon, 5 cm wide and 50 μ m thick, capable of overcoming aerodynamic drag ranging from 0.40 N to 0.80 N. Additionally, numerical simulations assess the tether performance under real environmental conditions. Furthermore, the study briefly introduces the potential of a photovoltaic tether as a fully autonomous system capable of supplying the necessary input power. • Electrodynamic tethers are proposed as a promising technology for ISS station-keeping • Air drag compensation and zig-zag are novel control strategies for orbit maintenance • Optimization codes are implemented for the identification of tether characteristics • The performances of the tether are investigated through numerical simulations • Bare Photovoltaic Tethers are proposed as autonomous systems for power harvesting [ABSTRACT FROM AUTHOR]

Abstract Control of the geographic location of high-altitude balloons has been desired for decades due to the cost and simplicity of the systems. These balloon systems rely on variations in wind direction with altitude so that when a balloon changes height, it also changes the direction of its horizontal motion. An altitude control system can thus also control the horizontal position by transitioning to a wind layer with favorable winds. The system’s ability to navigate successfully thus relies on the existence of certain wind conditions. In this paper, we explore how the ability of a balloon to station-keep varies based on the geographic location and season. We used spatially and temporally variant ERA5 wind data with a tree-search-based algorithm to traverse potential trajectories, and we selected the altitude transitions that maximize time within 50 km of a target. The simulation’s outputs show large variations in success across both latitude and season. Midlatitudes are particularly challenging for station-keeping, while lower latitudes are more favorable. Summer is typically more favorable than winter. This demonstrates that for all balloon systems, the ability to station-keep is highly variant and not universally possible.

Simple Summary: The European corn borer (Ostrinia nubilalis) is a major pest of corn, managed successfully in North America since 1996 with transgenic Bt-corn. However, practical field resistance and early-warning increases in frequency of resistance genes for all available insecticidal Bt proteins expressed in corn were detected recently at several locations in Canada. Given the high mobility of moths, design of containment and mitigation measures would have to be implemented at large spatial scales around a resistance hotspot to be successful. Effective strategies must account for high gene flow consistent with improved understandings of this species' complex movement ecology, including migratory behavior. The European corn borer (Ostrinia nubilalis, Hübner) has been managed successfully in North America since 1996 with transgenic Bt-corn. However, field-evolved resistance to all four available insecticidal Bt proteins has been detected in four provinces of Canada since 2018. Evidence suggests resistance may be spreading and evolving independently in scattered hotspots. Evolution and spread of resistance are functions of gene flow, and therefore dispersal, so design of effective resistance management and mitigation plans must take insect movement into account. Recent advances in characterizing European corn borer movement ecology have revealed a number of surprises, chief among them that a large percentage of adults disperse from the natal field via true migratory behavior, most before mating. This undermines a number of common key assumptions about adult behavior, patterns of movement, and gene flow, and stresses the need to reassess how ecological data are interpreted and how movement in models should be parameterized. While many questions remain concerning adult European corn borer movement ecology, the information currently available is coherent enough to construct a generalized framework useful for estimating the spatial scale required to implement possible Bt-resistance prevention, remediation, and mitigation strategies, and to assess their realistic chances of success. [ABSTRACT FROM AUTHOR]

A tag-recapture study was undertaken on the Natal seacatfish Galeichthys troworum in the Pondoland Marine Protected Area (PMPA) on the east coast of South Africa. A total of 473 fish were tagged over a period of 8 years, and 136 individuals (28.8%) were recaptured over a period of 16 years, some of them on multiple occasions. Most recaptures (82%) were caught within 200 m of their release site, with movements ranging between 0 and 617 m, and time-at-liberty ranging between 0 and 3 407 days (9.3 years). Data analysis showed that all recaptured fish remained in relatively small home ranges (of ∼360 m linear distance) and none of them abandoned their home range and moved out of the 2-km2 sampling blocks. While the no-take area of the PMPA provided effective protection for these fish, their relative abundance was similar in an adjacent exploited area. This is likely because G. troworum is not a desired linefish species, with most individuals caught being released, coupled with high post-release survival. [ABSTRACT FROM AUTHOR]

The solar sail spacecraft utilizing a hybrid approach of solar sail and solar electric propulsion in the heliocentric displaced orbit is affected by external disturbances, internal unmodeled dynamics, initial injection errors, and input saturation. To solve the station-keeping control problem under such complex conditions, an adaptive control strategy is proposed. First, the dynamical equations of the spacecraft utilizing hybrid low-thrust propulsion in the cylindrical coordinate system are derived. Second, the combined disturbance acceleration introduced by external disturbances and internal unmodeled dynamics is constructed, and a radial basis function neural network estimator is designed to estimate it online in real time. Third, an adaptive high-performance station-keeping controller based on an improved integral sliding surface and multivariate super-twisting sliding mode approaching law is designed. Then, stability analysis is conducted using Lyapunov theory, adaptive laws are designed, and the introduced virtual control accelerations are converted into actual control variables. Finally, simulations are conducted under different simulation conditions based on the disturbance sources. The results show that although the use of hybrid low-thrust propulsion breaks the symmetry of the solar sail in configuration, the proposed control strategy can effectively achieve the station-keeping and disturbance estimation of the spacecraft with only a small amount of propellant consumed and position tracking errors up to decimeters. [ABSTRACT FROM AUTHOR]

• The strategy of capturing asteroids using a lunar flyby and station-keeping maneuvers is proposed. • Station-keeping maneuvers of LPOs with different amplitudes and durations are investigated. • Analytic expressions of the non-planar Hohmann transfer are used to select candidate asteroids. • A lunar flyby can reduce the fuel consumption of capturing asteroids, even when the station-keeping maneuvers are considered. Long-term capture of near-Earth asteroids to Sun-Earth L 1 /L 2 libration point orbits using a lunar flyby and station-keeping maneuvers is investigated in this paper. The model of the circular restricted three-body problem (CR3BP) provides reference L 1 /L 2 libration point orbits and stable manifolds to capture asteroids. A station-keeping method using target points is employed to maintain the final periodic orbits under the Moon's perturbation. Then the stable manifold with the Moon's perturbation is applied to achieve transfers for capturing candidate asteroids. After candidate asteroids are selected using the non-planar Hohmann transfer, optimizations of capturing asteroids are carried out by minimizing the sum of transfer costs and station-keeping maneuvers. Simulation results show that the lunar flyby can reduce the fuel consumption of capturing asteroids, even when the station-keeping maneuvers are taken into account. [ABSTRACT FROM AUTHOR]

Remotely Operated Vehicles (ROVs) working close to the sea surface are subjected to wave disturbances that affect their positioning. To treat this problem, we present a control scheme for the dynamic positioning of ROVs under wave disturbances and at low operation depths. The approach is composed of an Augmented Wave Filter (AWF) based on the Extended Kalman Filter (EKF) algorithm and an Adaptive-Model Predictive Control (A-MPC). The filter provides the optimal motion states and wave height estimation to the A-MPC, which calculates the control efforts based on the receding horizon approach. The scheme is tested through numerical simulations on the depth control of the Mandi II-ROV at the diving plane. The results are compared to those of a standard Proportional-Integral-Derivative (PID) controller. To perform realistic simulations, a detailed mathematical model is presented, considering the rigid body-motion, hydrodynamic and hydrostatic forces, thrusters dynamics, and onboard sensor measurements. The simulations are performed for different scenarios, considering the dynamic positioning in still waters and the station-keeping under wave disturbances for significant heights of 1 and 2 m. The controller robustness to parameter variation is assessed by using Monte-Carlo simulation. Results have shown improved performance for the A-MPC in terms of positioning errors, motion oscillations, and drift attenuation in comparison to a PID controller. The Monte-Carlo simulation reveals enhanced robustness to the A-MPC, which is associated with the greater variance for the control forces. Also, the filter performed very well in all the tests, producing an accurate estimate of the wave-induced height and providing an off-set free control. [ABSTRACT FROM AUTHOR]

• Define in-plane and out-of plane station-keeping strategies for Sun-synchronous orbits. • The strategies are suited to extremely low thrust level (a few hundreds of μ N) and nano-satellites, where chemical propulsion fails to scale down. • In-plane control features a new alternating two-legs strategy that scales up to chemical propulsion level. • Out-of-plane control features a new no-deadband method. Traditional station-keeping for Earth observation satellites with chemical thrusters generally involves maneuvers every couple months that are able to change significantly the semi-major axis and the inclination. These strategies do not scale down to very low thrust level (a few hundreds of μN) electrical thrusters. This paper presents both in-plane and out-of-plane strategies that spread corrections over very long arcs and discretize them to tiny maneuvers every couple orbits, taking into account mission-constraints on maneuvers locations. These strategies scale up to medium thrust strategies, filling the gap between propulsion technologies. The out-of-plane strategy although features a new no-deadband property and controls the full orbital momentum. All strategies allow control very close to the reference (a few hundreds meters in osculating parameters) and very low cost. [ABSTRACT FROM AUTHOR]

The wave glider (WG) is an autonom surface vehicle (ASV) that is driven only by waves without propellers, and it maintains the power consumption of the control system and various payloads through solar power generation. To cope with the power shortages caused by extreme weather and sudden failures, a station-keeping strategy in emergency mode for WGs is proposed in this paper, so that the WG can remain in the current area with extremely low power consumption. More specifically, according to the power consumption mechanism of the WG, a partition control method is designed to set different operating modes in different areas. Also, an event-triggered (ET) motion control algorithm is proposed to reduce the execution rate of the rudder, which introduces adjustment factors to dynamically adjust the trigger threshold to further cut down rudder steering power consumption. Additionally, an online heading prediction system is developed to predict the submerged glider heading (SGH) of the WG through the float heading (FH) when the rudder management system shuts down. Through simulation and experimental analysis, the strategy in emergency mode can achieve positioning control with extremely low power consumption. [ABSTRACT FROM AUTHOR]

• A partitioning control method based on distance error is designed to distinguish risk levels of WGs, which is divided into three areas: warning area, escape area and obstacle area. Different navigation methods are designed in different areas. • An AILOS algorithm is designed to make the WG follow the required circular path, and the lookahead distance can adaptively be adjusted based on external disturbances. A tan-type BLF is introduced into the AILOS algorithm to determine the warning area boundary. • Considering the extreme situation of WG within a period, the escape area navigation method is designed to prevent the WG entering the obstacle area. An obstacle mode station-keeping strategy that considers obstacles in the station-keeping center area is proposed for wave gliders (WGs) to cope with special applications such as oil spill monitoring on drilling platforms and observation around the island. Different from the traditional station-keeping strategy which requires closing in the preset position as much as possible, this strategy uses the adaptive integral line of sight (AILOS) algorithm to make the WG sail around the preset obstacle area. A partitioning control strategy based on distance error is introduced to divide three areas according to the risk level: warning area, escape area and obstacle area. A tan-type barrier Lyapunov function (BLF) is introduced into the warning area control method to determine the boundary. To avoid the potential risk of collision, the escape area control strategy is to make the WG move away from the obstacle area as quickly as possible. Simulation and sea trial results verified the capability of the proposed station-keeping strategy in a stable ocean environment and the station-keeping safety of the WG using this strategy under extreme situations. [ABSTRACT FROM AUTHOR]

GEO satellites require precise station-keeping and ensuring collision avoidance to maintain their desired orbital positions and ensure uninterrupted communication services. However, maneuvering these satellites poses significant challenges due to various geophysical factors and orbital perturbations. This work proposes a model predictive control for planned maneuver station-keeping and collision avoidance of GEO satellites using south, east, and west maneuvers. These maneuvers have been achieved using on/off chemical thrusters with a short firing time. The station-keeping problem is reformulated as an optimization problem using mixed-integer linear programming. MILP-MPC formulation simultaneously considers multiple objectives and constraints such as fuel consumption, maneuver planning, and collision avoidance for mitigating collision risks. Simulation results demonstrate the effectiveness of the proposed MILP-MPC framework compared to the real-time telemetry in achieving accurate station-keeping and collision-free operation while optimizing fuel consumption. The proposed controller increases the satellite lifetime by reducing the thruster firing time. [ABSTRACT FROM AUTHOR]

• Two simple novel station-keeping stategies around triangular libration points in the realistic Earth-Moon system are proposed. • Both strategies do not require a pre-determined nominal orbit, and both can be extended to the case of a pre-determined nominal orbit. • The robustness of the two strategies is tested by considering errors from the force model, the maneuvers, and the orbit determination process. Concerning the unstable motions around triangular libration points in the Earth-Moon system, two simple station-keeping strategies are proposed. One is based on continuous low-thrust maneuvers, and the other is based on impulsive maneuvers. For the first strategy, its advantage is that the station-keeping process is completely decoupled from the orbit determination process. For the second strategy, the annual station-keeping cost can be as low as less than 4 m/s while maintaining a reasonably small orbit. For both strategies, the maneuvers are computed either by reference to the libration point itself, or by reference to a pre-determined nominal orbit. The two strategies are firstly proposed in the simple ephemerides model, and then verified in a simulated realistic model which considers force model uncertainties, maneuver errors, and orbit determination errors. [ABSTRACT FROM AUTHOR]

For a few years now, CNES has been developing ASTERIA, an on-board autonomy concept combining autonomous station-keeping and collision risks management for Low Earth Orbit (LEO) satellites. ASTERIA, acronym for Autonomous Station-keeping Technology with Embedded collision RIsk Avoidance system, enables both in-track and cross-track control for different LEO missions. The on-board collision risk management process is fully integrated into the autonomous station-keeping in order to maintain the satellite orbit as best as possible and to minimize mission unavailability resulting from the avoidance maneuvers. Collision risk management requires the best possible knowledge of the future trajectory of the primary satellite, up-to-date information on secondary objects, as well as a calculation process with a large amount of data and the propagation of orbital states and covariance. That is why, so far, collision risk management has always been a ground segment activity. But this strongly limits on-board autonomy by imposing a timing and a knowledge of the station-keeping maneuvers not very suitable with a reactive Autonomous Orbit Control (AOC) system. On the contrary, management by the spacecraft itself offers interesting prospects for responsiveness and increased autonomy, but requires to carry out on-board risk calculation, to identify relevant risk assessments and to implement efficient avoidance solutions. The paper aims to show the completeness of the ASTERIA concept. First, the principles of on-board collision risk management are described. Then, the paper presents the study of the on-board computational load, the accuracy of risk estimation and the performance of risk avoidance strategies. The ability to operate such a system is then demonstrated through the study of the related operational management process. The concept has been tested and validated by in flight experiments on the ESOC OPS-SAT 3-Units CubeSat. Some preliminary results of this experiment are presented. Finally, the issues related to an autonomous system are discussed, particularly those concerning space traffic management. • Autonomous orbit control method including station keeping strategy and collision risk mitigation. • Definition of a ground and on-board filtering process for the space objects catalog. • Conclusive validation through in-flight experiments on the OPS-SAT satellite. • Relevant estimate of the level of collision risk calculated on-board. • On-board determination of avoidance solutions compatible with low-thrusts. [ABSTRACT FROM AUTHOR]

A remotely operated underwater vehicle (ROV) is crucial in ocean exploration and underwater missions. An ROV is manipulated through a tether cable by an operator on shore or mother boat, and it can be used for underwater observations or as a robotic arm to take samples back. The position control and movement of an ROV are not stable due to buoyancy, ocean current, and surge waves. To overcome the influence of these disturbances on the ROV, we propose a switch proportional-integral (PI) controller combined with a buck-boost converter (BBC) to process the ROV's position following. In this paper, a six-axis ROV was designed and implemented. The ROV controller was designed by a NI-roboRIO-based embedded system, which includes a pressure sensor, an accelerometer, six thrusters, and two webcams. The LabVIEW human–machine interface was designed to integrate the control system, sensors, and thrusters. The PI controller was employed to perform the station-keeping and trajectory following. Different PI control parameters were used for the ROV floating-up and diving-down in the sine-wave trajectory following. Experimental results showed that the proposed switch PI control scheme is robust for the position tracking of the underwater robot. The contribution of this study is that we proposed a novel switch proportional-integral controller combined with a buck-boost converter and applied the controller to a natural underwater vehicle, not a mathematical model. The experiments showed that the proposed controller can resist the disturbance of the aquatic environment. [ABSTRACT FROM AUTHOR]

The solar sail spacecraft utilizing a hybrid approach of solar sail and solar electric propulsion in the heliocentric displaced orbit is affected by external disturbances, internal unmodeled dynamics, initial injection errors, and input saturation. To solve the station-keeping control problem under such complex conditions, an adaptive control strategy is proposed. First, the dynamical equations of the spacecraft utilizing hybrid low-thrust propulsion in the cylindrical coordinate system are derived. Second, the combined disturbance acceleration introduced by external disturbances and internal unmodeled dynamics is constructed, and a radial basis function neural network estimator is designed to estimate it online in real time. Third, an adaptive high-performance station-keeping controller based on an improved integral sliding surface and multivariate super-twisting sliding mode approaching law is designed. Then, stability analysis is conducted using Lyapunov theory, adaptive laws are designed, and the introduced virtual control accelerations are converted into actual control variables. Finally, simulations are conducted under different simulation conditions based on the disturbance sources. The results show that although the use of hybrid low-thrust propulsion breaks the symmetry of the solar sail in configuration, the proposed control strategy can effectively achieve the station-keeping and disturbance estimation of the spacecraft with only a small amount of propellant consumed and position tracking errors up to decimeters.

Future long-term lunar missions, such as cis -lunar space stations and communication/navigation constellations, have been proposed by different space agencies. For such long-term missions, reliable station-keeping strategies are of great importance to counteract unfavourable effects of perturbations, navigation errors, etc. In this study, representative cis -lunar orbits with favourable characteristics, including near rectilinear halo orbits (NRHOs), distant retrograde orbits (DROs), and halo orbits, are considered as nominal orbits of long-term lunar missions for station-keeping analysis. Both the target point method and the discrete linear quadrant regulator (DLQR) control are applied to these nominal orbits in the ephemeris model. Under some practical constraints caused by the navigation and orbital control systems, Monte-Carlo simulations are carried out to evaluate performances of the station-keeping strategies. Then, effects of solar radiation pressure (SRP) and nonspherical lunar gravity on the station-keeping performances are demonstrated by Monte-Carlo simulations with low-fidelity nominal orbits constructed in ephemeris models without SRP or nonspherical lunar gravity. Finally, comparisons between different impulse intervals are made to find the balance between the station-keeping cost and position deviation. It is found that the stability index of the nominal orbit has no direct effect on the station-keeping cost, but plays an important role in the selection of the impulse interval. The DROs and NRHOs allow a much longer impulse interval than the unstable halo orbits. The results can provide useful references for selections of the nominal orbit and station-keeping strategy in future long-term lunar missions. • Station-keeping problems of DROs, NRHOs and halo orbits are investigated. • Different station-keeping strategies are verified by Monte-Carlo simulations. • The station-keeping with different impulse intervals are compared. • Orbital stability has no direct effect on station-keeping cost, but has effects on impulse interval. • DROs and NRHOs allow much longer impulse intervals than halo orbits. [ABSTRACT FROM AUTHOR]

Due to the latest technological breakthroughs, High-Altitude Pseudo Satellites (HAPS) have recently become a feasible solution with great potential in the aerospace industry for Earth observation and communications, among other applications. Minimizing the energy consumption of these solar powered platforms is critical and, in the case of lighter than air vehicles, leads to smaller and more manageable platforms. When stratospheric airships perform a station-keeping mission, a certain displacement from the Earth surface reference point is usually admissible. This flexibility makes it possible to define an optimal control law for the airship that minimizes the energy required to fly in a 24-hour cycle, leading to a sprint and drift trajectory. This study analyzes the impact on the energy balance of the mission that stems from the changes in the allowed station-keeping radius. It also considers the effects of the daylight hours, the wind intensity, and the characteristics of the onboard energy system. The associated optimal control problems are rigorously solved numerically by means of a transcription method with regularization. The results define the optimal sprint and drift trajectories adapted to every scenario, providing the time evolution of the available power that controls the flight. The analysis indicates that following the optimal trajectory leads to weight savings in the energy system of about 5.4 kilograms per kilometer of the station-keeping radius. It entails that, for example, if a 20 kilometer radius is allowed, the energy required decreases more than 6% and the payload capacity increases about a 43% when compared to the fixed-point flight. [ABSTRACT FROM AUTHOR]

The use of autonomous underwater vehicles (AUVs) has expanded in recent years to include inspection, maintenance, and repair missions. For these tasks, the vehicle must maintain its position while inspections or manipulations are performed. Some station-keeping controllers for AUVs can be found in the literature that exhibits robust performance against external disturbances. However, they are either model-based or require an observer to deal with the disturbances. Moreover, most of them have been evaluated only by numerical simulations. In this paper, the feasibility of a model-free high-order sliding mode controller for the station-keeping problem is validated. The proposed controller was evaluated through numerical simulations and experiments in a semi-Olympic swimming pool, introducing external disturbances that remained unknown to the controller. Results have shown robust performance in terms of the root mean square error (RMSE) of the vehicle position. The simulation resulted in the outstanding station-keeping of the BlueROV2 vehicle, as the tracking errors were kept to zero throughout the simulation, even in the presence of strong ocean currents. The experimental results demonstrated the robustness of the controller, which was able to maintain the RMSE in the range of 1–4 cm for the depth of the vehicle, outperforming related work, even when the disturbance was large enough to produce thruster saturation. [ABSTRACT FROM AUTHOR]

This paper proposes a novel electric thruster configuration design optimization scheme to implement efficient station-keeping operations for geostationary satellites. In this work, the electric thrusters are equipped with 4-DOF robotic manipulators to provide flexible control thrust in space, which consumes much less propellant than the conventional station-keeping process using fixed-position electric thrusters. To effectively determine the firing right ascensions and firing durations of each electric thruster during the station-keeping process, a novel station-keeping control strategy is developed in view of the low-thrust feature of electric thrusters and the flexible pointing capacity of robotic manipulators. A low-thrust station-keeping period includes one two-day orbit determination period and six two-day control periods, where the initial orbital elements are determined in the orbit determination period, and the electric thrusters fire to compensate the perturbations in the control periods. Based on the control strategy, the electric thruster configuration design optimization problem is formulated to minimize the total propellant consumption via optimizing the robotic manipulator joint swivel angles and firing durations simultaneously, subject to several practical engineering constraints including the station-keeping accuracy, angular momentum dumping, collision between electric thruster and solar array, and electric thruster plume. Finally, the proposed electric thruster configuration design optimization scheme is applied to real-world station-keeping problems. The simulation results show that the geostationary satellites can be successfully maintained in an assigned station-keeping window using the robotic manipulators based low-thrust station-keeping control strategy. Moreover, the optimized electric thruster configuration with robotic manipulators can save 31.58% propellant consumption compared with that of the conventional configuration owing to the favorable flexibility of control thrust, which demonstrates the effectiveness and practicality of this work. [ABSTRACT FROM AUTHOR]

The dynamics of an AUV, which can perform manoeuvres with pitch angles in the range of 90° is investigated in this paper. The purpose of the AUV is to perform a station-keeping manoeuvre at about 90° pitch angle by varying propeller revolution. The AUV is launched in horizontal orientation. Quaternion mathematics, 4 quadrant propeller open water characteristics, and PID controller for propeller revolution are incorporated in manoeuvring mathematical model for this purpose. A procedure for optimizing the gain coefficients for the PID controller is developed using the 7 DoF manoeuvring mathematical model. Two design configurations of the AUV are investigated, positively buoyant and negatively buoyant. The design objective is, the AUV shall travel as far away as possible from the parent vehicle using minimum energy and time. It is shown that both the optimal gain coefficients for the PID controller for propeller revolution and the dynamic response of the AUV is different for each design configuration. The methodology developed in the paper can be used in the design and propeller revolution control system for certain categories of AUVs. The study shows that prime mover torque/ shaft revolution and 7 DoF manoeuvring mathematical model are important in predicting the attitude and trajectory in space and station-keeping manoeuvring capability of an AUV launched from a parent vehicle. [ABSTRACT FROM AUTHOR]

In this paper, a control effort minimizing optimal station-keeping guidance is designed and implemented to regulate a spacecraft around an L 1 quasi-halo orbit in the Sun–Earth–Moon elliptic four-body problem. The station-keeping guidance is formulated as a finite time, non-linear optimal control problem with hard terminal output constraints and Impulsive Model Predictive Static Programming (I-MPSP) is used to obtain station-keeping maneuvers. The algorithm is iterative, where the guessed station-keeping maneuvers are optimally updated by a simple closed-form equation until an output terminal constraint is satisfied and an optimal cost function is obtained. The technique involves the calculation of sensitivity matrices that is done in a computationally efficient manner owing to their recursive nature. Through extensive simulations, in the presence of disturbance forces and uncertainties, a closed-loop application of I-MPSP guidance results in a trajectory that remains tightly bound to the reference orbit over a long-duration mission. • Impulsive MPSP guidance is proposed for station keeping on quasi-halo orbits. • This computational guidance ensures control energy minimization. • It exhibits rapid convergence and demands minimal computational time. • Robustness analysis shows it can effectively handle disturbances and uncertainties. • Spacecraft trajectories are tightly bound to the reference orbit during the entire mission. [ABSTRACT FROM AUTHOR]

High circular polar orbits around the Moon are considered as one of the options for placing a prospective lunar station. Due to gravitational perturbations from the Earth, such orbits are subject to the Lidov–Kozai effect. This effect results in the increase in the average value of the eccentricity, which eventually leads to the collision of the spacecraft with the lunar surface. Therefore, when used in lunar missions, these orbits require periodic corrections. The work proposes a station-keeping technique for high near-circular polar lunar orbits based on the dynamical structures of the double-averaged equations of motion that include the central gravitational fields of the Earth and the Moon. The annual station-keeping delta-v for a 10,000 km polar orbit is presented considering navigation errors and maneuver execution errors. The nominal parameters of the orbit are selected to increase its lifetime. • Stability properties of high lunar orbits are investigated. • We use the double-averaged equations of motion to predict the orbital evolution. • A two-impulse station-keeping technique for high polar lunar orbits is proposed. • The stable manifold of the zero-eccentricity equilibrium is targeted. • The annual station-keeping cost for a 10,000 km polar lunar orbit is about 20 m/s. [ABSTRACT FROM AUTHOR]

To detect and forecast solar weather in advance is of great importance for humankind to protect power infrastructure on ground and communication satellites in orbit from damaging. In this regard, a large space platform consisting of a solar weather detector, long space tether and a sailcraft with actively adjustable lightness number is constructed. Within the elliptic Sun-Earth restricted three-body system (ESERTBS), merely the motion of the platform along the Sun-Earth line is focused on, full nonlinear dimensional and dimensionless dynamics of the system is established with a massless, taut and rigid/flexible tether. A sliding mode controller is developed to make the closed-loop dynamics asymptotically stable and the prescribed constant dimensional distance between the Sun and detector is maintained thereby. The time histories of some critical variables of the closed-loop system are presented to verify the performance of the developed controller, to check the lightness number of the sailcraft required, to show the internal tension/strain within the tether etc. Moreover, the steady-state responses of the closed-loop dynamic system are also presented to give more information. The lightness number of a single sailcraft used for performing the mission is compared to the lightness number of the sailcraft of the proposed platform. Some discussions and suggestions for selecting the tether's length and elasticity are presented from the aspect of the lightness number required, the internal tension and strain based on numerical simulations. [ABSTRACT FROM AUTHOR]

• The longitude maneuvers for space objects are studied based on dynamical model. • Single maneuver model and dual maneuver model are proposed. • Two maneuver detection methods are derived by solving these two maneuver models. There are approximately 2900 active space objects cataloged, and the number will increase continually in future. All these space objects may maneuver for some purpose occasionally, including highly elliptical orbit (HEO) transfer, station-keeping, orbit altitude adjustment, etc. Hence maneuver detection is very important for space situational awareness (SSA). It also plays an important role in the catalog maintenance by correlating the orbits before and after maneuver. In the paper, the maneuver detection methods based on orbital dynamical model are proposed. Firstly, the perturbations before and after maneuver are analyzed. Then two kinds of maneuver models are derived using the relative dynamical equations. Finally, several kinds of maneuver cases are performed to verify the models proposed. It is demonstrated that these two models are feasible and effective for the detection of longitude maneuvers. [ABSTRACT FROM AUTHOR]

• The relationship between the buoyancy and gravity is analyzed when the thermal effects are considered. • Three station-keeping scenarios are proposed and compared for the stratospheric airship. • The significance of pressure control and altitude control is revealed by the calculation and analysis. • An effective way to specify the helium's mass is presented when the thermal effects are considered. • The airspeed control is shown as an efficient way to cut down the energy consumption during the long-endurance flight. The ability to achieve long-endurance station-keeping flights makes stratospheric airships desirable platforms for the provision of communication and surveillance services. To maintain long-endurance flights, it is necessary to consider the problem of energy consumption. In this paper, we discuss long-endurance flight scenarios of stratospheric airships in the presence of thermal effects. The balance between buoyancy and gravity is influenced by thermal effects during the diurnal cycle. We perform a theoretical analysis based on the helium's mass, pressure differential, and altitude as the main factors. To verify the effectiveness of the control over the pressure differential and the altitude, three long-endurance flight scenarios are proposed and compared. Then, the corresponding optimization problems are constructed to determine the energy-minimum flight. Finally, further efforts are made to reduce energy consumption. The realization and limitations of two strategies for improvement are analyzed. A comparison with other scenarios shows the effectiveness of energy conservation. The study in this paper thus provides a reference for station-keeping applications of stratospheric airships. [ABSTRACT FROM AUTHOR]

• Solar sail station-keeping in the circular restricted three-body problem with optical degradation. • Reference orbit update using in situ parameter estimation and numerical continuation. • A robust integrated guidance and control algorithm is designed for station-keeping. • Simulations for station-keeping on halo orbits with optical degradation are demonstrated. Current control approaches for solar sail station-keeping on libration point orbits have not considered the degradation of the sail's optical properties. However, significant optical degradation could lead to poor station-keeping performance or even complete failure. This paper presents an integrated guidance and control strategy to address this problem by updating the reference orbit based on in situ estimation. An exponential optical degradation model is incorporated into the solar radiation acceleration model, and an on-line reference orbit update approach is incorporated into the station-keeping, coupled with an active disturbance rejection controller. The reflection coefficient is estimated on-line and the reference orbit is updated discretely when the optical properties have degraded by a prescribed amount. This strategy provides discrete updates to the reference orbits such that the perturbation due to the optical degradation is maintained within a small range. These smaller perturbations can be dealt with by the controller's robustness and station-keeping can be sustained for long durations even in the presence of large optical degradation. [ABSTRACT FROM AUTHOR]

The use of autonomous underwater vehicles (AUVs) has expanded in recent years to include inspection, maintenance, and repair missions. For these tasks, the vehicle must maintain its position while inspections or manipulations are performed. Some station-keeping controllers for AUVs can be found in the literature that exhibits robust performance against external disturbances. However, they are either model-based or require an observer to deal with the disturbances. Moreover, most of them have been evaluated only by numerical simulations. In this paper, the feasibility of a model-free high-order sliding mode controller for the station-keeping problem is validated. The proposed controller was evaluated through numerical simulations and experiments in a semi-Olympic swimming pool, introducing external disturbances that remained unknown to the controller. Results have shown robust performance in terms of the root mean square error (RMSE) of the vehicle position. The simulation resulted in the outstanding station-keeping of the BlueROV2 vehicle, as the tracking errors were kept to zero throughout the simulation, even in the presence of strong ocean currents. The experimental results demonstrated the robustness of the controller, which was able to maintain the RMSE in the range of 1–4 cm for the depth of the vehicle, outperforming related work, even when the disturbance was large enough to produce thruster saturation.

Recently, the station-keeping of the stratospheric airship is an attractive topic due to its application to provide long-endurance communication and surveillance services. The motion of the stratospheric airship is sensitive to the wind because of the characteristics of large volume and low airspeed. When the wind speed exceeds the maximum airspeed, the airship may float out of the given station-keeping region. In such a case, how to recover to the station-keeping site is a necessary problem to consider. In this paper, the recovery trajectory optimization of the stratospheric airship is discussed and the purpose is to find the economical recovery flight trajectory to the station-keeping site. The trajectory optimization model is established by considering the motion model of the stratospheric airship, the atmospheric model, the wind field model, the solar radiation model, and the thermal model. To represent the exploitation of solar energy during the flight, the solar radiation collection problem is modeled for the airship whose hull is approximated by the double-ellipsoid geometry. Then the recovery trajectory optimization problem is formulated with constraints consideration and three recovery flight scenarios are put forward. The trajectory optimization problem is transformed into the nonlinear programming problem (NLP) by the orthogonal collocation and can be solved by the off-the-shelf NLP solver. The accuracy of the solution is improved by a modified ph -adaptive mesh refinement method. Two study cases are carried out to make a profound study of the recovery flight problem. In the first case, the basic characteristics of the flight trajectories using different recovery flight scenarios are compared and analyzed. Then the influence of the solar position on the recovery trajectory is discussed in the second case, which also gives some insights on the flight characteristics of the solar-powered stratospheric airship. The results of this paper may provide some important references for the station-keeping application of the stratospheric airship. • The recovery flight problem of the stratospheric airship for the station-keeping mission is formulated in detail. • The solar collection model is developed for the stratospheric airship with the double-ellipsoid geometry hull.. • Based on the characteristics of the station-keeping mission, three recovery flight scenarios are proposed and compared. • A modified ph -adaptive pseudospectral is adopted to solve the recovery trajectory optimization problem. • The influence of the wind and solar radiation on the optimal recovery flight trajectory is analyzed. [ABSTRACT FROM AUTHOR]

In recent years, with the reduction of the cost of microsatellites, the development of commercial rockets and the multi-satellite launching technology, the construction of large-scale constellations in low-Earth orbit (Mega-Constellations) has become a development trend. Since the motion of LEO satellites is affected by perturbations such as non-spherical gravitational fields and atmospheric drag, as well as the uncertainty of actuators, measurement systems, and dynamic models, it is easy to cause divergence of constellation configurations. The station-keeping control of the satellites is crucial for the stable operation of the mega-constellation. Aiming at this problem, this paper proposes an uncertainty propagation approach based on semi-analytical and Monte Carlo for LEO Mega-Constellations. Under the assumption that initial uncertainty on the osculating trajectory is Gaussian distribution, through hypothesis testing analysis, the uncertainty propagation simulations of a single satellite suggest that the satellite argument of latitude and the relative phase of co-plane satellites can be both considered as Gaussian distributions with zero means. Multi-group Monte Carlo simulations with product-based least-squares surface fitting establish an approximate mapping between initial and terminal errors. The mapping provides an efficient method for deviation prediction and can be used to design the station-keeping control strategy.

The combination of solar array and rechargeable battery is the main trend of energy system for scientific balloon station-keeping, when the performances of station-keeping strategies are evaluated, energy problem should be considered. In this paper, the performances of air ballast system and double balloon system are evaluated with the consideration of energy management strategy. The theoretical model consisting of thermal model, solar array power model, energy consumption model and energy evaluation model is proposed. The energy management strategy containing solar array and lithium battery is designed. Based on the theoretical model and energy management strategy, a MATLAB program is developed. The feasibility is verified by comparison analysis. The energy harvesting characteristics, effects of the station-keeping duration and effects of the station-keeping region radius are analyzed carefully. The results show that the double balloon is superior than air ballast system from the perspective of energy. The air ballast system requires more energy than double balloon system and the energy difference increases over time. Air ballast system lithium battery capacity requirement is higher than double balloon system, the total energy consumption and the energy differences decrease with expected radius increasing. It would be helpful in selecting station-keeping strategies for scientific balloon mission. • Station-keeping strategies are evaluated. • Calculation model and program are proposed. • Energy speaking, double balloon system is superior. [ABSTRACT FROM AUTHOR]

• Yearly station-keeping cost for small Sun-Venus L2 Lissajous orbits is about 1 m/s. • Any mean illumination level can be achieved by properly selecting a Lissajous orbit. • The X-axis control requires 10% less fuel but less accurate than the 3-axis control. • Orbit insertion errors below 100 km in position and 10 cm/s in velocity are advised. • Navigation uncertainty of 10 km in position and 1 cm/s in velocity is satisfactory. In this study, the choice of a nominal space telescope orbit in the vicinity of the Sun–Venus L 2 libration point is discussed from the viewpoint of illumination conditions and station-keeping costs. Such a location for the space telescope is especially appealing for the observation of potentially hazardous asteroids approaching the Earth from the daytime side of the sky. In contrast to the case of a telescope placed near the Sun–Earth L 1 point, a significantly longer warning time can be achieved. Moreover, a Lissajous-type quasi-periodic orbit can be selected so that a predefined percentage of the orbit is shadowed. When a nominal orbit is allowed to be permanently sunlit, a large halo orbit is preferred due to the lower station-keeping cost. For two sets of unstable halo and Lissajous orbits, the station-keeping cost is evaluated by conducting Monte Carlo simulations in the ephemeris model of motion. Two modifications of the target point station-keeping technique are examined: the X -axis control and the 3-axis control. The simulation scenario includes orbit insertion and navigation errors, impulse execution errors, and constraints on the minimum imparted Δ v. Dependence of the station-keeping cost on orbit insertion and navigation errors is analyzed. Some of the large halo orbits appear to be linearly stable. The corresponding central manifold location in the phase space is determined, which makes a simple targeting strategy possible. [ABSTRACT FROM AUTHOR]

• Families of halo orbits in the solar sail elliptic restricted three-body problem are generated. • Multi-revolution halo orbits are designed to satisfy the constraint on period. • Stability is analyzed and a bifurcation is identified. • Station-keeping is demonstrated using RCD technology. Solar sail halo orbits designed in the Sun-Earth circular restricted three-body problem (CR3BP) provide inefficient reference orbits for station-keeping since the disturbance due to the eccentricity of the Earth's orbit has to be compensated for. This paper presents a strategy to compute families of halo orbits around the collinear artificial equilibrium points in the Sun-Earth elliptic restricted three-body problem (ER3BP) for a solar sail with reflectivity control devices (RCDs). In this non-autonomous model, periodic halo orbits only exist when their periods are equal to integer multiples of one year. Here multi-revolution halo orbits with periods equal to integer multiples of one year are constructed in the CR3BP and then used as seeds to numerically continue the halo orbits in the ER3BP. The linear stability of the orbits is analyzed which shows that the in-plane motion is unstable while the out-of-plane motion is neutrally stable and a bifurcation is identified. Finally, station-keeping is performed which shows that a reference orbit designed in the ER3BP is significantly more efficient than that designed in the CR3BP, while the addition of RCDs improve station-keeping performance and robustness to uncertainty in the sail lightness number. [ABSTRACT FROM AUTHOR]

Designing long-duration lunar orbiter missions is challenging due to the Moon's highly nonlinear gravity field and the third-body perturbations induced by the Earth, Sun and other large bodies. The absence of a Lunar atmosphere has offered the possibility for mission designers to search for extremely low-altitude, quasi-stable lunar orbits. In addition to the reduced amount of propellant required for station-keeping maneuvers, these orbits present great opportunities for unique scientific studies such as high resolution imaging and characterization of the polar ice deposits in deep craters. Prior to the GRAIL mission, mission planning for Lunar orbiters had suffered from inaccuracies, mainly due to the lack of an accurate Lunar gravity model, which resulted in severe deviations with respect to the spacecraft's nominal orbit. We study station-keeping feasibility for spacecraft in near-polar and extremely low-altitude, quasi-frozen orbits around the Moon, that are perturbed by a high-fidelity lunar gravity model and third-body effects from the Earth and Sun. For several candidate orbits, we compare the trade-space between mission duration and Δ V budget, considering impulsive maneuvers applied once every ' N ∈ { 2,6,10,14,18 } ' orbits at periselene or aposelene. Additionally, we investigate the propulsive cost for different orbit insertion dates, the location of impulsive corrections for arresting argument of periselene (ω) drift, and controlling periselene altitude. • Analytical insights on ω variation drawn and specific trends for polar orbits reported. • Six extremely low-altitude (Periselene alt. ~ 20 km), quasi-frozen polar orbits are presented. • Investigation on optimal gravity of the Moon's fidelity model is conducted. • High-fidelity GRAIL model and third-body effects from Earth and Sun are considered. • Station-keeping analyses performed for different orbit insertion dates and maneuver points. [ABSTRACT FROM AUTHOR]

The Argo Global Ocean Observing Network has remained the preeminent ocean observation network worldwide. Since the Argo buoys lack freedom of lateral movement, their wave-following working characteristics prevent them from completing the long-term observations in the designated sea area. Long-term monitoring of designated waters is often required, for example, to study the impacts of seabed mining on the marine environment in the surrounding sea area. To solve this problem, a portable underwater profiler (PUP) that combines the functionalities of profiling buoys and underwater gliders was devised. The PUP employs a center of gravity adjustment mechanism utilizing the double-weight block approach, enabling the pitch angle adjustment within -90° to 0°. Remarkably, the PUP weighs only 11.25 kg, meeting the requirements for rapid deployment. Furthermore, the prediction method of the ocean current velocity was optimized by employing the full-depth-averaged ocean current velocity instead of the depth-averaged ocean current velocity. To ensure continuous observation operations of the PUP within designated sea areas, a horizontal displacement correction strategy (HDCS) based on the virtual mooring concept is proposed. The effectiveness of the HDCS has been preliminarily validated through simulations and further confirmed through lake trials conducted in Qiandao Lake. [ABSTRACT FROM AUTHOR]

The strategy developed by the authors in previous works for recovering halo orbit missions in case of contingent station-keeping maneuver delay is now applied to quasi-halo orbit missions. Monte Carlo trials are used to estimate recovery Δ v costs and their scattering for each delay time. Families of orbits around the Earth–Moon L 1 point are considered. • The problem of quasi-halo orbit mission recovery is considered. • Optimal transfers to the reference and best backup quasi-halo orbits are compared. • The adaptation scheme to the ephemeris model of motion is given. • In the ephemeris model, the results change significantly and depend on the dates. • Best target orbit in the CR3BP model can be not optimal in the ephemeris model. [ABSTRACT FROM AUTHOR]

There are many different types of (quasi)periodic orbits in the vicinity of collinear libration points. These libration point orbits (LPOs) are inherently unstable and must be controlled. This paper studies general station-keeping strategies that are suitable for various types of LPOs. Two complementary methods are proposed by exploiting the hyperbolic dynamics of the collinear libration points. One main advantage of these methods is that no information of the nominal orbit is needed in order to do the station-keeping. The first is a semi-analytical projection method which is based on the high order polynomial approximation of the center manifold. After the transformation from synodic coordinates to center manifold coordinates is derived, the error state can be projected to center manifold or its stable manifold by introducing a station-keeping Delta-V, effectively eliminating the unstable component. The second is a fully numerical method. An escape time algorithm is designed to find the intersection of stable and unstable manifolds, effectively projecting the error state to the center manifold. By applying these techniques to the collinear libration points of Earth–Moon system, it has been demonstrated that these proposed methods can achieve better maneuver cost performance and they can handle station-keeping problems of various types of LPOs in a unified manner. • Two ad hoc station-keeping strategies of collinear libration point orbits are proposed. • Station-keeping is realized by projecting error state to center manifold or its stable manifold. • No information of the nominal orbit is needed in order to do the station-keeping. • These strategies are suitable for various types of libration point orbits. [ABSTRACT FROM AUTHOR]

Station-keeping endurance of high altitude balloon is the foundation of the assignments of environmental monitoring and communicational relaying. Exploiting the natural wind-field that varies with altitude by the altitude control system to extend the station-keeping endurance is proposed in this paper. A Matlab program is developed based on the theoretical model to simulate the station-keeping performance of the balloon in the real wind field. The trajectories of the balloon in different wind fields and the states of the balloon caused by the venting and pumping processes are discussed in detail. The results show that with the altitude control system it is possible to retain the balloon within the designated district for few days to a week. This can serve as a guideline for the design and initial flight tests of the serviceable high altitude balloon. [ABSTRACT FROM AUTHOR]

Abstract Having a reliable and fast estimation of states regardless of prior knowledge about environmental conditions is a major goal to be achieved in application of Dynamic Positioning (DP). One way to have a faster estimation is to reduce state size which is studied in this research. The reduced elements belong to Wave Frequency (WF) model of estimation. Implemented estimation method is a new robust nonlinear extension of Kalman Filter called Square-Root Unscented Kalman Filter (SRUKF). Station-Keeping (SK) as one of the most common DP operations for supply vessels is considered as a case study in this research. Wind, wave and ocean current are considered as disturbing environmental loading. Computational efficiency and accuracy of 9 elements model is studied and compared with 15 elements counterpart in different sea Beaufort numbers (BN). Results show that in average 9 elements model is 37% faster than 15 elements model. However 15 elements model is generally more accurate, particularly in WF elements. The final results show that by assuming proper bounds for state Root-Mean Square Error (RMSE), using 9 elements model for BNs below 6 is a better choice. [ABSTRACT FROM AUTHOR]

Abstract For the absence of the propeller system to resist wind load, the balloon will float everywhere with unstable position. In order to fix the balloon within a specific district and extend the station-keeping endurance, an effective approach that utilizes the wind from different directions by altering the float altitude was proposed. A program was developed to simulate the flight performance and the station-keeping endurance of the stratospheric super-pressure balloon in the real wind field. The influences of the initial Helium volume ratio and the float altitude on the traveled horizontal distance of the balloon were analyzed. The results indicate that the altitude of the balloon fluctuates with the change of the volume of the balloon during the day-night cycle, providing the possibility to catch the wind from different directions. By choosing the appropriate Helium volume ratio and float altitude, the traveled horizontal distance of the balloon can be shortened greatly. Our study can provide guidance for investigation on active control algorithm for station-keeping of the balloon that can fix the balloon within the desired district for months and years. [ABSTRACT FROM AUTHOR]

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The problem of propellant-efficient station-keeping using a hybrid sail in the Earth–Moon system is investigated in this paper. To achieve high-precision station-keeping and minimize propellant consumption, the problem is addressed from perspectives of reference orbits design and control strategy design. A high-fidelity model of a hybrid sail, which consists of a solar electric propulsion (SEP) system and a solar sail covered by reflectivity control devices (RCDs), is exploited for reference orbits design in the Earth–Moon system using numerical methods. These hybrid-sail perturbed halo and Lyapunov orbits are parameterized by the sail's reflectivity and are inherent unstable. An orbit-attitude control strategy is proposed for station-keeping which is composed of three parts: a nonlinear disturbance observer (NDO)-based optimal periodic orbital controller, SEP acceleration optimization, and a NDO-based robust backstepping attitude controller. In particular, RCDs are used in both orbital control and attitude control. Numerical results show that the proposed control strategy can guarantee high-precision station-keeping and effective reduction in propellant consumption. [ABSTRACT FROM AUTHOR]