Non-cooperative Satellite Research Articles

Embedded State Estimation for Optimization of Cislunar Space Domain Awareness Constellation Design

The traffic in cislunar space is expected to increase over the coming years, leading to a higher likelihood of conjunction events among active satellites, orbital debris, and noncooperative satellites. This increase necessitates enhanced space domain awareness (SDA) capabilities that include state estimation for targets of interest. Both Earth surface-based and space-based observation platforms in geosynchronous orbit or below face challenges such as range, exclusion, and occlusion that hinder observation. Motivated by the need to place space-based observers in the cislunar space regime to overcome these challenges, this paper proposes a cislunar SDA constellation design and analysis framework that integrates state estimation into an optimization problem for determining the placement of observers for optimal state estimation performance on a set of targets. The proposed multiobserver placement optimization problem samples from a range of possible target orbits. Upon convergence, the optimized constellation is validated against a broader set of targets to assess its effectiveness. Two comparative analyses are presented to evaluate the effects of changes in the sensor tasking procedure and sensor fidelity on the optimized constellation, comparing these to a single observer baseline case. The results demonstrate that the optimized constellations can provide accurate state estimation for various orbit families.

A comprehensive study on PnP-based pipeline for pose estimation of noncooperative satellite

The monocular 6D pose estimation of a noncooperative satellite is essential in various on-orbit automatic operations. Nevertheless, the application of this technology still faces challenges, such as heavy model parameters and high latency. In this study, we comprehensively explored the critical components of satellite pose estimation, including landmark description, localisation, and the PnP algorithm, and we introduce a high-precision, real-time, and robust pipeline. Existing methods adopt external convex landmarks, such as 11 landmarks for the SPEED dataset, which are insufficient to describe the geometric structure of the satellite. This study adopted a wireframe-based landmark description, encompassing all visually prominent satellite joints connected directly into the satellite’s wireframe model. In addition, unlike most existing methods that rely on heatmap-based landmark localisation, which incurs high computational costs and quantisation errors, we adopt direct coordinate classification for satellite landmark localisation, which is lightweight, fast, and accurate. Experimental results on the SPEED dataset demonstrate that our method outperforms the current state-of-the-art technique, with an accuracy increase of 28% and parameter number decrease of 78%. In particular, our method is very lightweight and robust, and it runs in real-time, making it well-suited for on-orbit real-time satellite pose estimation.

Simulated annealing-particle swarm optimization initial orbit determination method for too-short-arcs

The initial orbit determination (IOD) of a non-cooperative satellite through space-based optical angle-only measurement data is a fundamental task. However, due to the lack of relative distance information of the targets, traditional methods have problems with poor accuracy and robustness in orbit determination results. The application of particle swarm optimization algorithm for IOD under optical too-short-arcs (TSA) measurement data has achieved good results. However, there is still a problem of convergence to local extremum. This article proposes a simulated annealing-particle swarm optimization (SA-PSO) hierarchical algorithm, which combines the efficient searchability of particle swarm optimization with the fine searchability of simulated annealing algorithm to achieve robust and precise optimization of non-cooperative targets orbit elements. The experimental results show the SA-PSO algorithm significantly improves the accuracy of orbit elements prediction compared to the particle swarm optimization algorithm and proves its effectiveness.

Two-phase visual servoing for capturing tumbling non-cooperative satellites with a space manipulator

In this paper, a visual servoing approach is developed to capture the docking rings of tumbling non-cooperative satellites with a space manipulator. The primary challenge addressed is the potential for the docking ring to leave the monocular camera’s field-of-view as the manipulator approaches the target, due to the ring’s large size. To solve this issue, a two-phase visual servoing scheme combining a monocular camera and a three-line structured light vision system is proposed. In an effort to augment the success rate and safety of capture operations, several constraints are formulated, encompassing manipulator’s kinematics, monocular camera’s field-of-view, obstacle avoidance, structured light’s breakpoints and smooth capture. Subsequently, a nonlinear model predictive controller is proposed to manage these constraints in real-time and regulate the system. System models are established based on image moments and pose for each phase, selecting these features as visual feedback to simplify the formulation of servo constraints and avoid the complex circle-based pose measurement. Furthermore, to ensure unbiased predictions, the model disturbances arising from the imprecise estimation of target motion parameter are observed using an extended Kalman filter, which are then incorporated into the predictive control framework. The simulation results demonstrate the effectiveness of this scheme.

Circular-Feature-Based Pose Estimation of Noncooperative Satellite Using Time-of-Flight Sensor

This paper develops an end-to-end circular-feature-based pose estimation using the time-of-flight (TOF) camera for capturing serviced satellite. First, the docking ring is chosen as the recognized object for pose measurement. Second, a new ellipse detection method is proposed to detect the docking ring. Third, the circular feature is used to estimate the six-degrees-of-freedom pose with the aid of a reflective block. Combined with the range at each pixel location from TOF, the pose duality can be eliminated, and the roll angle is recovered through the geometric constraint. Ground physical experiments validate the effectiveness and efficiency of the proposed method. The on-orbit application demonstrates that the proposed algorithm can accurately and robustly estimate the relative pose of the noncooperative satellite, providing reliable navigation information for the chaser spacecraft with the relative pose estimation errors less than 2 deg and 5 cm.

Real-time Pose Determination of Ultra-Close Non-Cooperative Satellite based on Time-of-Flight Camera

Real-time Pose Determination of Ultra-Close Non-Cooperative Satellite based on Time-of-Flight Camera

Active 6 DoF Force/Torque Control Based on Dynamic Jacobian for Free-Floating Space Manipulator

Abstract In-orbit capture of a non-cooperative satellite will be a major challenge in the proposed servicing and active debris removal missions. The contact forces between the manipulator end-effector and the elements of the target object will occur in the grasping phase. In this paper, an active 6 Degrees of Freedom (DoF) force/torque control method for manipulator mounted on a free-floating servicing satellite is proposed. The main aim of the presented method is to balance the relation between end-effector position and force along each direction in the Cartesian space. The control law is based on the Dynamic Jacobian, which takes into account the influence of the manipulator motion on the state of the servicing satellite. The proposed approach is validated in numerical simulations with a simplified model of contact. Comparison with the classical Cartesian control shows that the active 6 DoF force/torque control method allows to obtain better positioning accuracy of the end-effector and lower control torques in manipulator joints in the presence of external forces.

Retrieval of Subsurface Soil Moisture and Vegetation Water Content From Multifrequency SoOp Reflectometry: Sensitivity Analysis

Signals of opportunity reflectometry (SoOp-R), the re-utilization of non-cooperative satellite transmissions for communication and navigation, is a promising approach to remote sensing of root-zone soil moisture (RZSM). Satellite transmissions in the frequency ranges of 137–138, 240–270, and 360–380 MHz are of interest due to the increased penetration depth. These can be combined with Global Navigation Satellite System Reflectometry (GNSS-R) in L-band (1575.42 MHz) to estimate the subsurface SM profile. The objective is to define requirements (e.g. frequency and polarization combinations, observation error, and temporal coincidence of multi-source observations) for satellite-based remote sensing of RZSM. Our approach is to use synthetic observations generated from multi-year time series of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in-situ</i> SM measurements from seven United States Climate Reference Network (USCRN) sites and dynamic vegetation structure based on a simple scaling method. A multi-frequency/polarimetric retrieval algorithm is developed and applied to these synthetic observations and used to predict retrieval errors for a range of changes in system parameters. We found that the use of both high and low frequencies improves retrieval accuracy by limiting uncertainties from vegetation and surface SM and providing sensitivity to deeper layers. Moreover, the retrieval errors were found to increase linearly with the reflectivity error and inter-frequency time delays. A bivariate model derived from this linear relationship will be useful for developing requirements on reflectivity precision based upon science requirements for SM/VWC retrievals. Although orbits of specific transmitter constellations were used to generate realistic distributions of incidence angle combinations, the method and results could be applied more generally.

Pose measurement and motion estimation of non-cooperative satellite based on spatial circle feature

Malfunctioned satellites have seriously threatened orbital safety, and the capture of these satellites is of great significance. The pose measurement and the motion estimation of the tumbling satellite is the premise of capture. In this paper, the docking ring of the satellite is identified, which is equivalent to a spatial circle. Combined with the nozzle feature, the pose duality of the spatial circle can be eliminated. And the measurement accuracy is improved by minimizing the reprojection error of the docking ring and the nozzle. Due to the symmetry of the docking ring, the measured pose has only five degrees of freedom, losing the degree of freedom of rotation around the normal vector. In the motion estimation algorithm, the observability of the tumbling motion is firstly analyzed, then an error-state Kalman filter with inertia ratio constraints is designed. To improve the convergence speed and stability of the filter, a rough estimation algorithm of filter initial value based on linear term extraction and particle swarm optimization is proposed. The effectiveness of the pose measurement and motion estimation method is verified by simulations.

Capture and detumble of a non-cooperative target without a specific gripping point by a dual-arm space robot

This paper focuses on the control strategy of a dual-arm space robot to capture and detumble a non-cooperative satellite without a specific gripping point. First, an elastic hemispherical claw was designed to reduce the collision impacts and adjust the capture position, and its contact dynamics and capture ability were verified by ground experiments. Analysis of the position constraints led to the proposal of a compliant control scheme to achieve stable capture without a contact-force sensor. Subsequently, a modified adaptive sliding mode based prescribed trajectory tracking control (PTTC) and null space intersection approach was proposed to achieve target detumbling under the actuator constraints. The control system stability was analyzed via the Lyapunov method. Finally, numerical simulations were employed to validate the effectiveness and correctness of the strategy. Results showed that, a large inertia target could be steadily captured and detumbled within 80 s.

Ranging technology using signals of opportunity of non-cooperative communication satellites

AbstractThe positioning technique employing the ubiquitous signals of opportunity of non-cooperative satellites does not send special navigation signals, instead it passively receives satellite signals as noise, presenting advantages of concealment and difficulty for potential attackers. Thus, this study investigates the ranging principle and model using non-cooperative communication satellites and a time difference estimation algorithm. The technology of time difference measurement under non-cooperative observation mode was determined and simulated. A test platform for time difference measurement was built to receive the signal from an unknown geostationary Earth orbit communication satellite and verify the ranging feasibility and performance. The ranging accuracy was found to be smaller than 6 m, as demonstrated by experimental data, which shows the viability of the proposed positioning technique for ranging technology.

A Modular MIMO Millimeter-Wave Imaging Radar System for Space Applications and Its Components

This article presents the design and prototyping of components for a modular multiple-input-multiple-output (MIMO) millimeter-wave radar for space applications. A single radar panel consists of 8 transmitters (TX) and 8 receivers (RX), which can be placed several times on the satellite to realize application-specific radar apertures and hence different cross-range resolutions. The radar chirp signals are generated by SiGe:C BiCMOS direct-digital-synthesizers (DDS) in the frequency range of 1 to 10.5GHz with a chirp repetition rate of 30dB gain with noise figure values of 9dB, respectively. The MIMO radar utilizes patch antenna arrays on organic multilayer printed circuit boards (PCB) with 18dBi gain and 18∘ half power beamwidth (HPBW). Generation of power supply and control signals, analog-to-digital conversion (ADC), and radar signal processing are provided centrally to each panel. The radar supports detection and tracking of satellites in distances up to 1000m and image generation up to 20m, which is required to support orbital maneuvers like satellite rendezvous and docking for non-cooperative satellites.

BUFFER AND COMPLIANT DYNAMIC SURFACE CONTROL OF SPACE ROBOT CAPTURING SATELLITE BASED ON COMPLIANT MECHANISM

The buffer and compliant control for space robot to avoid joint damage during on-orbit capture non-cooperative satellite are studied. For the reason, a compliant mechanism is mounted between the joint motor and space manipulator, its functions are: first, the deformation of internal spring in compliant mechanism can absorb the impact torque of the captured satellite acting on the joint of the space robot; second, the joint impact torque can be limited to a safe range by reasonably designing the buffer and compliant control scheme. First of all, the dynamic models of the space robot system and the target satellite system before capture are derived by multi-body theory. After that, based on the law of conservation of momentum, the constraints of kinematics and the law of force transfer, the integrated dynamic model of the combined system is derived. At the same time, the impact effect and impact force are calculated. For the stabilization control of post-capture unstable combined system, a buffer and compliant control scheme based on dynamic surface is proposed. The proposed control scheme can not only effectively absorb the impact torque generated by the on-orbit capture process, but also timely open or close the joint motor when the impact torque is too large, which can avoid overload and damage of the joint motor. In addition, the dynamic surface control scheme is utilized to avoid calculation expansion caused by backstepping method and to reduce the calculation effectively. The stability of the system is proved by Lyapunov theorem, and numerical simulation verifies the effectiveness of the proposed buffer and compliant control method.

Inertia Parameter Identification for an Unknown Satellite in Precapture Scenario

The problem of dynamics and control using a space robot to capture a noncooperative satellite is an important issue for on-orbit services. Inertia parameters of the satellite should be identified before capturing such that the robot can design an active controller to finish the capturing task. In this paper, a new identification scheme is proposed for parameter identification of a noncooperative satellite. In this scheme, the space robot is controlled to contact softly and then maintain contact with the noncooperative target firstly, then the variation of momentum of the target during the contact-maintaining phase is calculated using the control force and torque acting on the base of the space robot and the kinematic information of the space robot, and finally, the momentum-conservation-based identification method is used to estimate inertia parameters of the target. To realize soft contact and then maintain contact, a damping contact controller is designed in this paper, in which a mass-damping system is designed to control the contact between the robot and the target. Soft contact and then contact maintenance can be realized by utilizing the buffering characteristics of the mass-damping system. The effectiveness of the proposed identification scheme is verified through numerical simulations at the end of this paper. Simulation results indicate that the proposed scheme can achieve high-precision identification results.

A new approach for the estimation of non-cooperative satellites based on circular feature extraction

Pose estimation of non-cooperative satellites has been a hot topic in the study of astronautics as the visual feedback will highly enhance the safety of on-orbit services. A stereo vision system is proposed in this paper. It works as an eye-to-hand vision camera in the final approach phase Based on circular feature extraction, a closed-form solution is presented. The position and orientation of the adapter ring can be figured out in real-time as well as the unknown radius. Neither additional sensors nor prior knowledge is required, and the orientation-duality problem has been solved. It works well on the partial ellipses and is robust to outliers, noise and occlusions. Experimental results on both synthetic and real images have demonstrated the effectiveness and efficiency of the proposed method.

Contact control for grasping a non-cooperative satellite by a space robot

In this paper, the contact control problem of a space robot to grasp a non-cooperative satellite is investigated in detail, and a new capture control strategy is proposed. Firstly, the dynamic equation of the robot system is derived based on the multibody dynamics theory, and a modified Hertz model is used to describe the contact force between the robot end-effector and the target satellite. Then, a novel position-based impedance control strategy for capturing the target satellite is proposed. This control strategy is to capture the target satellite by realizing soft contact between the end-effector and the target satellite, thus the target satellite will not depart from the end-effector after their contact. Different from the other existing capture control strategies, the proposed strategy needs only the kinematic information of the space robot, so the control performance requirement is lower and is easier to implement in practice. To verify the validity of the proposed capture control strategy, simulations are conducted at the end of this paper, and the results indicate that the target satellite can be grasped effectively using the proposed capture control strategy if the motion of the target satellite is translational or tumbling.

Hybrid Control Scheme for Grasping a Non-Cooperative Tumbling Satellite

Grasping a non-cooperative “customer satellite” with a robotic arm is a challenging task for on-orbit services of spacecraft since the collision between the robot and the target is inevitable and the dynamic behaviors of the two objects are hard to control after the collision. To grasp successfully, the contact between the space robot and the target is hoped to be maintained after the collision. In this paper, the contact control problem for grasping a non-cooperative satellite is studied. First, to simulate the contact conditions as realistic as possible, the multibody dynamics, the modified Hertz contact, and the contact detection theory are employed to establish a grasping dynamics model. Then, based on the study on the dynamic behavior of the two-ball collision problem, a hybrid control scheme with damping and attitude tracking controllers is proposed. By this scheme, the control goal, i.e. maintaining the contact between the robot and the target, can be realized after multiple collisions. Finally, numerical simulations are performed to validate the proposed control scheme, and the results demonstrate its effectiveness in grasping a non-cooperative tumbling satellite.

Three-line structured light vision system for non-cooperative satellites in proximity operations

Adapter ring is a commonly used component in non-cooperative satellites, which has high strength and is suitable to be recognized and grasped by the space manipulator. During proximity operations, this circle feature may be occluded by the robot arm or limited field of view. Moreover, the captured images may be underexposed when there is not enough illumination. To address these problems, this paper presents a structured light vision system with three line lasers and a monocular camera. The lasers project lines onto the surface of the satellite, and six break points are formed along both sides of the adapter ring. A closed-form solution for real-time pose estimation is given using these break points. Then, a virtual structured light platform is constructed to simulate synthetic images of the target satellite. Compared with the predefined camera parameters and relative positions, the proposed method is demonstrated to be more effective, especially at a close distance. Besides, a physical space verification system is set up to prove the effectiveness and robustness of our method under different light conditions. Experimental results indicate that it is a practical and effective method for the pose measurement of on-orbit tasks.

Docking mechanism design and dynamic analysis for the GEO tumbling satellite

Purpose According to the requirements of servicing and deorbiting the failure satellites, especially the tumbling ones on geosynchronous orbit, this paper aims to design a docking mechanism to capture these tumbling satellites in orbit, to analyze the dynamics of the docking system and to develop a new collision force-limited control method in various docking speeds. Design/methodology/approach The mechanism includes a cone-rod mechanism which captures the apogee engine with a full consideration of despinning and damping characteristics and a locking and releasing mechanism which rigidly connects the international standard interface ring (Marman rings, such as 937B, 1194 and 1194A mechanical interface). The docking mechanism was designed under-actuated, aimed to greatly reduce the difficulty of control and ensure the continuity, synchronization and force uniformity under the process of repeatedly capturing, despinning, locking and releasing the tumbling satellite. The dynamic model of docking mechanism was established, and the impact force was analyzed in the docking process. Furthermore, a collision detection and compliance control method is proposed by using the active force-limited Cartesian impedance control and passive damping mechanism design. Findings A variety of conditions were set for the docking kinematics and dynamics simulation. The simulation and low-speed docking experiment results showed that the force translation in the docking phase was stable, the mechanism design scheme was reasonable and feasible and the proposed force-limited Cartesian impedance control could detect the collision and keep the external force within the desired value. Originality/value The paper presents a universal docking mechanism and force-limited Cartesian impedance control approach to capture the tumbling non-cooperative satellite. The docking mechanism was designed under-actuated to greatly reduce the difficulty of control and ensure the continuity, synchronization and force uniformity. The dynamic model of docking mechanism was established. The impact force was controlled within desired value by using a combination of active force-limited control approach and passive damping mechanism.

Investigation on GEO satellite orbit determination based on CEI measurements of short baselines

Connected-Element Interferometry (CEI) is a technique for measuring the phase delay of difference of Time Of Arrival (TOA) of a downlink radio signal to two antennae on a short baseline. This technique can use an atomic clock for time-frequency transmission and achieve intermediate accuracy angular tracking. Owing to the relatively short length of the baseline, the passive reception mode, and near real-time operation, CEI can be used to continuously monitor the orbit variations of both cooperative and non-cooperative satellites. In this paper, a small-scale CEI system of two orthogonal baselines (75 m × 35 m) is investigated to track a Geostationary Earth Orbit (GEO) Television (TV) satellite at 110·5°E. The phases are extracted from correlation results. The results show that the Root Mean Square (RMS) of the phase fitting residuals, if not calibrated, is within 2° at night and up to 10° in the daytime. After applying the calibration signal, the RMS of the phase fitting residuals in the daytime decreases to the same level at night. Comparing the phase delay with the a priori phase delay using Two-Line-Element (TLE) data, the integer ambiguity is successfully resolved. Finally, a batch algorithm is used to estimate the orbit of the GEO satellite, and the orbit determination accuracy is evaluated using the precise orbits provided by the China National Time Service Centre (NTSC). The results show that the accuracies in the radial direction and the cross-track direction are less than 1 km, and the Three-Dimensional (3D) position accuracy reaches the 2 km order of magnitude.