Space Environmental Disturbances Research Articles

Multi‐Instruments Observation of Ionospheric‐Thermospheric Dynamic Coupling Over Mohe (53.5°N, 122.3°E) During the April 2023 Geomagnetic Storm

AbstractThe state and variations of the Ionosphere‐Thermosphere (I‐T) system are strongly influenced by dynamical processes, with these effects being amplified during intense space environment disturbances such as geomagnetic storms, producing multi‐scale disturbance features in the I‐T system. The redistribution of energy and momentum through the dynamical processes is currently not well understood. Unfortunately, the dearth of thermospheric observations has yielded limited studies capable of monitoring and analyzing the I‐T dynamical coupling during storms using co‐located measurements. This work examines the responses of the I‐T system during the April 2023 geomagnetic storm based on high‐resolution continuous I‐T system observations at Mohe observatory, a middle latitude station. Both large‐scale features and short‐period oscillations were identified in multiple key parameters of the I‐T system. Similar disturbed patterns in thermospheric winds occurred during the main and recovery phases of the geomagnetic storm. However, the oscillation features in many parameters of the I‐T system are only observed during the main phase. The results of concurrent I‐T system observations unveil the oscillation features of thermospheric winds, temperatures, the ionospheric F2 peak height, electron density, and total electron content. These findings reveal the important influence of wind divergence on thermospheric temperature disturbances and its modulatory effect on ionospheric disturbances.

Detection and Analysis of Radiation Doses in Multiple Orbital Space during Solar Minimum

Based on orbit detection data acquired by a positive channel Metal Oxide Semiconductor (PMOS) dose detectors on FY4-A (GEO), BD3-M15 (MEO), and YH1-01A (LEO) between November 2018 and November 2022, investigations reveal variations in total dose and the mechanism of radiation dose increase within the geostationary earth orbit (GEO), medium earth orbit (MEO), and low earth orbit (LEO) during the transition from the 24th to the 25th solar cycles. It provides the radiation dose parameters for the study of the space environment from different altitude orbits, and also provides an important basis for studying the solar minimum activity and dose generation The data indicate directional disparities in radiation doses among the orbital regions, with the hierarchy being FY4-A > YH1-01A > BD3-M15. Furthermore, the results show that the total doses of FY4-A and BD3-M15 were higher than that of YH1-01A by two orders of magnitude, with BD3-M15 > FY4-A > YH1-01A. The monthly radiation dose rates of FY4-A in GEO and BD3-M15 in MEO exhibited positive correlation with their corresponding APs during the solar minimum. Notably, for FY4-A, the monthly radiation dose rate during geomagnetic disturbed periods exceeded that of the dose rate during geomagnetic quiet periods by one order of magnitude. This analysis revealed the substantial impact of geomagnetic storms and space environment disturbances on radiation doses detected by MEO and GEO orbital satellites. These perturbations, attributable to medium- and small-scale high-energy electron storms induced by reproducible coronal holes, emerged as key driving factors of the increase in radiation doses in MEO and GEO environments.

A Controller Design Method for Drag-Free Spacecraft Multiple Loops With Frequency Domain Constraints

Space-based gravitational wave detection requires a strict level of residual acceleration ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$10^{-15} \mathrm{~m/s}^{2} / \sqrt{\text{Hz}}$</tex-math></inline-formula> in the frequency band of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$0.1\text{mHz}\sim 1\text{Hz}$</tex-math></inline-formula> ) on the test masses along the sensitive axes. Because of the configuration of the detection spacecraft with two test masses, there are complex couplings between the spacecraft attitude, drag-free and suspension control loops in the drag-free and attitude control system. Moreover, the space environment disturbances and the limited noise levels of the actuators and sensors make it difficult for multiple control degrees of freedom to meet the index requirements at the same time. Currently, PID and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$H_\infty$</tex-math></inline-formula> methods are mainly used for its controller design, where the system is decoupled and divided into relatively independent control loops, and the controllers are designed to meet the requirements separately. However, parameter tuning usually requires empirical trial and error, leading to the low design efficiency. And the coupling relationships between loops cannot be well described and treated mathematically. Therefore, a controller design method for drag-free spacecraft multi loops is proposed in this paper, where the index requirements are transformed into frequency domain constraints and the optimization objectives are designed for better performances according to the control characteristics of different loops. Then the controllers are tuned by multi-population genetic algorithm improving the design efficiency. As mentioned, under the premise that the index requirements are all met, the couplings between loops are considered and some of the performances of the system can be optimized, such as the residual acceleration acting on the test masses. Numerical simulation and comparison verify the effectiveness of this method.

Design and Realization of LNA Prototype Frequency 1090 Mhz for ADS-B on Nano Satellite

The nanosatellite is a satellite with a weight of less than 10kg and an orbital height of 500km. Telkom University through Nano Satellite Laboratory is researching for many payloads on a nanosatellite. One of the nanosatellite payloads is Automatic Dependence Surveillance-Broadcast (ADS-B), an aircraft data transmission broadcast. The long-distance deliveries and space environmental disturbances can cause weak received signals. Therefore a Low Noise Amplifier (LNA) is needed to enhance the signal-to-noise ratio (SNR) of a received signal. This paper has successfully designed and prototyped a single-stage LNA with a gain of 12.7dB and it enhances coverage of ADS-B from 180 to 358km

Motion control of a space manipulator using fuzzy sliding mode control with reinforcement learning

The free-flying space manipulators present challenges in controlling the motions of both the spacecraft bus and the manipulator, because of the highly-coupling system dynamics and the unknown space environment disturbances. Although the sliding mode controllers are robust to the unknown disturbances and system uncertainties, the chattering effect could affect the pointing accuracy and the lifetime of the actuators. This paper first introduces the dynamics of a CuBot, which is a 3-rigid-link manipulator based on the CubeSat platform. To maintain the robustness while decreasing the chattering effect, an innovative reinforcement learning based fuzzy adaptive sliding mode controller is proposed. To maintain the robustness while reducing the chattering effect, an innovative reinforcement learning based fuzzy adaptive sliding mode controller is proposed. The switching gain is updated to estimate the lumped upper bound of the system uncertainties and the unknown disturbances, and then a new fuzzy logic adaptive law is applied on the switching gain to decrease the chattering effects. On top of that, the fuzzy logic rules are tuned by an innovative modified reinforcement learning mechanism to achieve the better tracking performance. The uniformly ultimately bounded tracking errors are guaranteed by the proposed control scheme, and the effectiveness is validated by the simulation results.

Super-twisting disturbance observer-based finite- time attitude stabilization of flexible spacecraft subject to complex disturbances

There exist complex disturbances in the attitude control system of flexible spacecrafts, such as space environmental disturbances, flexible vibrations, inertia uncertainties, payload motions, etc. To suppress the effects of these disturbances on the performance of attitude stabilization, a super-twisting disturbance observer (STDO)-based nonsingular terminal sliding mode controller (NTSMC) is proposed in this paper. First, STDO is designed for a second-order dynamical system constructed by applying the lumped disturbance and its integral as state variables, and applying the integral as virtual measurement. Since the virtual measurement is obtained by integrating the inverse attitude dynamics, STDO not only avoids the differential operation of angular velocity, but also fully utilizes the information of a nonlinear model. By combining STDO with NTSMC, a composite controller is designed to achieve high-accuracy spacecraft attitude stabilization. Since most of the disturbances are compensated for by a STDO-based feedforward compensator, only a small switching gain is required to deal with the residual disturbances and uncertainties. Thus, the chattering phenomenon of the controller can be alleviated to a great extent. Finally, numerical simulations for the comparison between STDO-based NTSMC and nonlinear disturbance observer-based NTSMC are carried out in the presence of complex disturbances to verify the effectiveness of the proposed approach.

Statistical Study of Magnetic Topology for Eruptive and Confined Solar Flares

AbstractLarge flares and halo coronal mass ejections (CMEs) can often cause strong space environment disturbances and sequently a series of space environment effects. The X‐class flares associated with halo CMEs are particular prone to these effects. In this paper, 58 X‐class flares were collected and studied with the source locations in 30° from the disk center, which were observed from 1996 to 2015. Among these events, 48 flares were associated with CMEs and defined as “eruptive” events. The other 10 flares without CMEs were defined as “confined” flares. By comparing the properties of flares and associated magnetic fields for the two sets of samples, we found the following: (1) magnetic free energy and overlying transverse fields play important roles in producing solar eruptions. Eruptive flares with high‐speed CMEs tend to occur in active regions with more free energy and larger decay index. (2) CME speeds are affected by magnetic free energy, which are described by parameters of the unsigned magnetic flux, the area of polarity inversion region, and the strength of transverse fields in the low altitude. These parameters have moderate positive correlations with CME speeds.

Attitude stabilization of flexible spacecrafts via extended disturbance observer based controller

To achieve the high-precision attitude stabilization for the flexible spacecraft in the presence of space environmental disturbances, unmodeled dynamics, and the disturbances caused by the elastic vibration of flexible appendages, an extended disturbance observer (EDO) based controller is proposed. The proposed controller is formulated by combining EDO and a backstepping feedback controller. EDO is used to estimate the disturbance, which is modeled as an unknown high-order differentiable equation and the rth-order derivative of the disturbance is assumed to be bounded. Compared to the conventional first-order disturbance observer, the higher order EDO offers improvement in estimate accuracy, if the absolute values of poles for EDO transfer function are chosen larger than the frequency content of the disturbance. Then, the output of EDO plus the backstepping feedback controller are applied to stabilize the attitude with high precision by rejecting disturbances for the flexible spacecraft. Finally, numerical simulations have been conducted to verify the effectiveness of the proposed controller.

Operational Space Weather Services in National Space Science Center of Chinese Academy of Sciences

Operational Space Weather Services in National Space Science Center of Chinese Academy of Sciences

Medium‐frequency disturbance attenuation for the spacecraft via virtual‐gimbal tilting of the magnetically suspended reaction wheel

A medium-frequency disturbance attenuation strategy based on the virtual-gimbal effect of the active magnetically suspended reaction wheels (MSRWs) is proposed to improve the pointing stability for the high-resolution observation of the spacecraft. The disturbances decreasing the pointing stability include not only the space environment disturbances with low frequency but also the flexible modes and vibrations with medium frequency which are excited by the flexible appendix and the rotating components. The model of the MSRW is constructed firstly and the model of the spacecraft with one MSRW is then developed. Furthermore, a hybrid three-loop control strategy is designed to stabilise the pointing of the spacecraft and the MSRW, where the compensation loop is used to attenuate the medium-frequency disturbances beyond the bandwidth of the attitude control loop. The bandwidth of the MSRW is expanded by tilting the rotor shaft, and the attitude angular velocity is directly feedback to the compensation loop. In addition, the cross feedback control is introduced to attenuate the medium-frequency disturbances. Finally, simulations are constructed and the results indicate the medium-frequency disturbances are effectively attenuated.

High spin rate magnetic controller for nanosatellites

This paper presents a study of a high rate closed-loop spin controller that uses only electromagnetic coils as actuators. The controller is able to perform spin rate control and simultaneously align the spin axis with the Earth's inertial reference frame. It is implemented, optimised and simulated for a 1-unit CubeSat ESTCube-1 to fulfil its mission requirements: spin the satellite up to 360degs−1 around the z-axis and align its spin axis with the Earth's polar axis with a pointing error of less than 3°. The attitude of the satellite is determined using a magnetic field vector, a Sun vector and angular velocity. It is estimated using an Unscented Kalman Filter and controlled using three electromagnetic coils. The algorithm is tested in a simulation environment that includes models of space environment and environmental disturbances, sensor and actuator emulation, attitude estimation, and a model to simulate the time delay caused by on-board calculations. In addition to the normal operation mode, analyses of reduced satellite functionality are performed: significant errors of attitude estimation due to non-operational Sun sensors; and limited actuator functionality due to two non-operational coils. A hardware-in-the-loop test is also performed to verify on-board software.

Space Weather Prediction and Exascale Computing

Space weather can have a great effect on Earth's climate. Predicting the impact of space environment disturbances on Earth presents a challenge to scientists. The authors present the ExaScience Lab's efforts, which use exascale computing and new visualization tools to predict the arrival and impact of space events on Earth.

Fault Tolerant Attitude Control for Flexible Satellite with Uncertainties and Actuator Saturation

A novel fault tolerant control scheme, using model-based control and time delay control theories, is proposed for flexible satellites with uncertainties and actuator saturation and the stability condition of the scheme is analysed. The moment–of-inertia uncertainty, actuator faults uncertainty, space environment disturbances and the actuator saturation are analysed. The computable control torques, including the space environmental torques, reaction wheel dynamics and the known flexible appendage dynamics, are formulated using the model-based control. The unknown flexible satellite dynamics is estimated according to its one-step previous value and employed to update the control command; this greatly reduces the conservativeness and enhances the pointing accuracy. Numerical simulations under different conditions demonstrate the advantages of the novel proposed controller compared to the conventional PD controller and a simplified fault tolerant controller.

Modified model-based fault-tolerant time-varying attitude tracking control of uncertain flexible satellites

A novel, modified model-based fault-tolerant attitude tracking control scheme is derived for the uncertain flexible satellites with four reaction wheels. The stability conditions of this type of satellite are also analyzed. The attitude tracking error dynamics is employed to derive the novel control scheme, which is formulated in the presence of actuator fault uncertainties, moment-of-inertia uncertainties, flexible appendage dynamics uncertainties, space environmental disturbances, and reaction wheel dynamics. The uncertainties are estimated to update the computed torque, which extremely enhances the pointing accuracy and reduces the conservativeness. The large-angle attitude tracking and time-varying attitude trajectory can be stabilized by the novel controller, which solves the constant desired trajectory restriction in most of other control schemes. Numerical results are presented to verify the advantages of the proposed control scheme in comparison with proportional–derivative controller, model-based controller, time delay controller, and modified time delay controller.

Space Weather Monitoring and Forecasting Activity in NICT

Disturbances of Space environment around the Earth (geospace) is controlled by the activity of the Sun and the solar wind. Disturbances in geospace sometimes cause serious problems to satellites, astronauts, and telecommunications. To minimize the effect of the problems, space weather forecasting is necessary. In Japan, NICT (National Institute of Information and Communications Technology) is in charge of space weather forecasting services as a regional warning center of International Space Environment Service. With help of geospace environment data exchanging among the international cooperation, NICT operates daily space weather forecast service every day to provide information on nowcasts and forecasts of solar flare, geomagnetic disturbances, solar proton event, and radio-wave propagation conditions in the ionosphere. For prompt reporting of space weather information, we also conduct our original observation networks from the Sun to the upper atmosphere: Hiraiso solar observatory, domestic ionosonde networks, magnetometer & HF radar observations in far-east Siberia and Alaska, and south-east Asia low-latitude ionospheric network (SEALION). ACE (Advanced Composition Explorer) and STEREO (Solar TErrestrial RElations Observatory) real-time beacon data are received using our antenna facilities to monitor the solar and solar wind conditions in near real-time. Our current activities and future perspective of space weather monitoring and forecasting will be introduced in this report.

Composite attitude control for flexible spacecraft with simultaneous disturbance attenuation and rejection performance

In this paper, a composite attitude control approach for orbiting spacecraft with rigid central hubs and flexible appendages is presented. The established attitude control model consists of the vibration modes excited by the rigid body, the space environment disturbances, the measurement noises, and the model uncertainty. The model is formulated into a dynamic system with two types of disturbance inputs. A composite control law with the simultaneous disturbance attenuation and rejection performance is presented for the flexible spacecraft system subject to multiple disturbances. The disturbance-observer-based control is designed for feedforward compensation of the elastic vibration. The H∞ state-feedback controller is designed to perform the robust attitude control in the presence of the space environment disturbances, measurement noises, and the model uncertainty. Numerical simulations show that the performance of the attitude control systems can be improved by combining the disturbance observer with H∞ state-feedback control.

An anti-disturbance PD control scheme for attitude control and stabilization of flexible spacecrafts

This paper studies the attitude control problem of spacecrafts with flexible appendages. It is well known that the unwanted vibration modes, model uncertainty and space environmental disturbances may cause degradation of the performance of attitude control systems for a flexible spacecraft. In this paper, the vibration from flexible appendages is modeled as a derivative-bounded disturbance to the attitude control system of the rigid hub. A disturbance-observer-based control (DOBC) is formulated for feedforward compensation of the elastic vibration. The model uncertainty and space environmental disturbances as well as other noises are merged into an “equivalent” disturbance. We design a composite controller with a hierarchical architecture by combining DOBC and PD control, where DOBC is used to reject the vibration effect from the flexible appendages. Numerical simulations are performed to demonstrate that by using the composite hierarchical control law, disturbances can be effectively attenuated and the robust dynamic performances be enhanced.

Geosynchronous Satellites Anomalies on Geosynchronous Magnetopause Crossing

The orbital radius of geosynchronous satellites in elliptical orbit above the equator is 6.6 times as long as the radius of the earth ‘Re’. Usually, geosynchronous satellites are inside the Earth's magnetopause the radius of which is greater than 10 Re from the Earth's center, the magnetosphere shields geosynchronous satellites from the solar wind. However, when the solar wind pressure increases, the magnetopause position approaches and crosses geosynchronous orbit. This phenomenon is called “Geosynchronous Magnetopause Crossing (GMC)”. We calculated the magnetopause position during three days before 81 satellite anomalies occurred from 1 January 1997 to 31 December 2007, and analyzed a relationship between GMCs and geosynchronous satellite anomalies. The magnetopause position will be used as an index to prevent geosynchronous satellite anomalies from space environment disturbances on geosynchronous satellite operation.

Multi-objective output-feedback control for microsatellite attitude control: An LMI approach

Mixed H 2 / H ∞ output-feedback controller with pole placement constraints against the internal uncertainty of moment-of-inertia variation and space environmental disturbances is proposed for mircosatellite attitude control. The multi-objective controller is designed based on linear model of attitude dynamics. The H ∞ performance takes into account both robustness stability against moments-of-inertia uncertainty and the disturbance rejection aspect. H 2 performance takes into account the LQG aspect which avoids the undesirable wheels’ saturation effect. In addition, the closed-loop poles can be forced into some sector of the stable half-plane to obtain well-damped transient responses. The problem is then reduced to a convex optimization involving linear matrix inequalities (LMIs), so it can be efficiently solved. The simulation results demonstrate that the presented mixed H 2 / H ∞ control system is robust stable and optimal in the sense of H 2 norm, and has good steady-state and dynamic performances against the parameter uncertainties and various disturbances for the microsatellite attitude control system.

Mixed H2/H∞ state-feedback design for microsatellite attitude control

Abstract Owing to a great decrease in size and weight, the pointing accuracy of microsatellite is vulnerable to space environmental disturbances and the internal uncertainty of moment-of-inertia variation. Mixed H 2 / H ∞ control, giving consideration to both stability robustness and root-mean-square (rms) performance, is particularly attractive for attitude controller design of microsatellites. By using linear matrix inequality method, the numerical solution of mixed H 2 / H ∞ state-feedback controller can be efficiently solved. The performance differences between mixed H 2 / H ∞ controller and its two extremes—pure H 2 controller and pure H ∞ controller—are discussed in detail. Mixed H 2 / H ∞ controller shows the remarkable capability of achieving a balanced compromise between H 2 and H ∞ performances.