Pose and Shape Reconstruction of a Noncooperative Spacecraft Using Camera and Range Measurements

Recent interest in on-orbit proximity operations has pushed towards the development of autonomous GNC strategies. In this sense, optical navigation enables a wide variety of possibilities as it can provide information not only about the kinematic state but also about the shape of the observed object. Various mission architectures have been either tested in space or studied on Earth. The present study deals with on-orbit relative pose and shape estimation with the use of a monocular camera and a distance sensor. The goal is to develop a filter which estimates an observed satellite's relative position, velocity, attitude, and angular velocity, along with its shape, with the measurements obtained by a camera and a distance sensor mounted on board a chaser which is on a relative trajectory around the target. The filter's efficiency is proved with a simulation on a virtual target object. The results of the simulation, even though relevant to a simplified scenario, show that the estimation process is successful and can be considered a promising strategy for a correct and safe docking maneuver

Simultaneous Capture and Detumble of a Resident Space Object by a Free-Flying Spacecraft-Manipulator System

The article of record as published may be found at https://doi.org/10.3389/frobt.2019.00014A maneuver to capture and detumble an orbiting space object using a chaser spacecraft equipped with a robotic manipulator is presented. In the proposed maneuver, the capture and detumble objectives are integrated into a unified set of terminal constraints. Terminal constraints on the end-effector’s position and velocity ensure a successful capture, and a terminal constraint on the chaser’s momenta ensures a post-capture chaser-target system with zero angular momentum. The manipulator motion required to achieve a smooth, impact-free grasp is gradually stopped after capture, equalizing the momenta across all bodies, rigidly connecting the two vehicles, and completing the detumble of the newly formed chaser-target system without further actuation. To guide this maneuver, an optimization-based approach that enforces the capture and detumble terminal constraints, avoids collisions, and satisfies actuation limits is used. The solution to the guidance problem is obtained by solving a collection of convex programming problems, making the proposed guidance approach suitable for onboard implementation and real-time use. This simultaneous capture and detumble maneuver is evaluated through numerical simulations and hardware-in-the-loop experiments. Videos of the numerically simulated and experimentally demonstrated maneuvers are included as Supplementary Material

Simultaneous Capture and Detumble of a Resident Space Object by a Free-Flying Spacecraft-Manipulator System

A maneuver to capture and detumble an orbiting space object using a chaser spacecraft equipped with a robotic manipulator is presented. In the proposed maneuver, the capture and detumble objectives are integrated into a unified set of terminal constraints. Terminal constraints on the end-effector's position and velocity ensure a successful capture, and a terminal constraint on the chaser's momenta ensures a post-capture chaser-target system with zero angular momentum. The manipulator motion required to achieve a smooth, impact-free grasp is gradually stopped after capture, equalizing the momenta across all bodies, rigidly connecting the two vehicles, and completing the detumble of the newly formed chaser-target system without further actuation. To guide this maneuver, an optimization-based approach that enforces the capture and detumble terminal constraints, avoids collisions, and satisfies actuation limits is used. The solution to the guidance problem is obtained by solving a collection of convex programming problems, making the proposed guidance approach suitable for onboard implementation and real-time use. This simultaneous capture and detumble maneuver is evaluated through numerical simulations and hardware-in-the-loop experiments. Videos of the numerically simulated and experimentally demonstrated maneuvers are included as Supplementary Material

Autonomous Rendezvous with a non-cooperative satellite: trajectory planning and control

Con la nascita di nuove problematiche e nuove esigenze in ambito spaziale, le più importanti riguardanti il tema della mitigazione dei detriti spaziali o dell’assistenza e del servizio dei satelliti in orbita, lo scenario di rendez-vous autonomo tra un satellite inseguitore e un satellite target non cooperativo sta diventando sempre più centrale, ambizioso e accattivante. Il grande scoglio da superare, tuttavia, consiste nell’individuazione di una strategia di approccio robusta e vincente: mentre l’esecuzione di una manovra di rendez-vous e docking o cattura con satellite cooperativo è già stata collaudata e possiede una consolidata eredità di volo, il rendez-vous autonomo con satellite non cooperativo ed in stato di tombolamento è uno scenario agli albori, con pochi studi al riguardo. Lo scopo di questa tesi consiste nell’identificazione di una strategia di approccio che consideri le principali problematiche legate al tema in questione, ovvero la non-cooperazione e le scarse informazioni sullo stato di moto del target da raggiungere. Queste due complicazioni portano alla necessità di eseguire un moto di ispezione del satellite target e alla considerazione di numerosi vincoli nella progettazione della traiettoria di ispezione e di approccio. Un controllore adatto a trattare questo problema complesso e multi-vincolato è il Model Predictive Controller, in forma lineare o non lineare, abbinato ad un filtro di Kalman. La capacità di questo controllore di previsione e pianificazione di una traiettoria d’approccio, a partire da stime di posizione relativa tra target e inseguitore, permette di portare a termine la manovra in modo sicuro e robusto.According to the rise of new problems and new demands in the space field, the most important concerning the mitigation of space debris or the spacecraft on-orbit servicing and assistance themes, the Autonomous Rendezvous scenario between a chase satellite and a non-cooperative target satellite is becoming increasingly significant, ambitious, and attractive. The main issue to overcome, however, consists in the identification of a robust and successful approach strategy: while the execution of a rendezvous and docking or capture maneuver with a cooperative satellite has already been tested and holds a solid flight heritage, the autonomous rendezvous with a non-cooperative satellite in a state of tumbling motion is a scenario in the early days, with few studies about it and a not yet mature technology. The aim of this thesis consists in the identification of an approach strategy that deals with the main challenges related to the considered problem, namely non-cooperativeness and exiguous information about the target to be reached. These two issues lead to the need of performing an inspection motion and considering several constraints in the trajectory design. A controller suitable to handle this complex and multi-constrained problem is the Model Predictive Controller, in a linear or non-linear form, paired with a Kalman filter. The ability of this controller to predict and plan an approaching trajectory, starting from estimates of the relative position between the target and the chaser, allows to complete the approaching maneuver safely and in a robust way

Robotic Manipulation and Capture in Space: A Survey

Space exploration and exploitation depend on the development of on-orbit robotic capabilities for tasks such as servicing of satellites, removing of orbital debris, or construction and maintenance of orbital assets. Manipulation and capture of objects on-orbit are key enablers for these capabilities. This survey addresses fundamental aspects of manipulation and capture, such as the dynamics of space manipulator systems (SMS), i.e., satellites equipped with manipulators, the contact dynamics between manipulator grippers/payloads and targets, and the methods for identifying properties of SMSs and their targets. Also, it presents recent work of sensing pose and system states, of motion planning for capturing a target, and of feedback control methods for SMS during motion or interaction tasks. Finally, the paper reviews major ground testing testbeds for capture operations, and several notable missions and technologies developed for capture of targets on-orbit

Design and Operational Elements of the Robotic Subsystem for the e.deorbit Debris Removal Mission

This paper presents a robotic capture concept that was developed as part of the e.deorbit study by ESA. The defective and tumbling satellite ENVISAT was chosen as a potential target to be captured, stabilized, and subsequently de-orbited in a controlled manner. A robotic capture concept was developed that is based on a chaser satellite equipped with a seven degrees-of-freedom dexterous robotic manipulator, holding a dedicated linear two-bracket gripper. The satellite is also equipped with a clamping mechanism for achieving a stiff fixation with the grasped target, following their combined satellite-stack de-tumbling and prior to the execution of the de-orbit maneuver. Driving elements of the robotic design, operations and control are described and analyzed. These include pre and post-capture operations, the task-specific kinematics of the manipulator, the intrinsic mechanical arm flexibility and its effect on the arm's positioning accuracy, visual tracking, as well as the interaction between the manipulator controller and that of the chaser satellite. The kinematics analysis yielded robust reachability of the grasp point. The effects of intrinsic arm flexibility turned out to be noticeable but also effectively scalable through robot joint speed adaption throughout the maneuvers. During most of the critical robot arm operations, the internal robot joint torques are shown to be within the design limits. These limits are only reached for a limiting scenario of tumbling motion of ENVISAT, consisting of an initial pure spin of 5 deg/s about its unstable intermediate axis of inertia. The computer vision performance was found to be satisfactory with respect to positioning accuracy requirements. Further developments are necessary and are being pursued to meet the stringent mission-related robustness requirements. Overall, the analyses conducted in this study showed that the capture and de-orbiting of ENVISAT using the proposed robotic concept is feasible with respect to relevant mission requirements and for most of the operational scenarios considered. Future work aims at developing a combined chaser-robot system controller. This will include a visual servo to minimize the positioning errors during the contact phases of the mission (grasping and clamping). Further validation of the visual tracking in orbital lighting conditions will be pursued

Development and Testing of Hardware Simulator for Satellite Proximity Maneuvers and Formation Flying

Satellite Formation Flying (SFF) and Proximity Operations are applications that have increasingly gained interest over the years. These applications foresee the substitution of a single spacecraft with a system of multiple satellites that perform coordinated position and attitude control maneuvers, which in turn results in higher accuracy of payload measurement, higher flexibility, robustness to failure, and reduction of development costs. These systems present however higher difficulties in their design since they have not only absolute but also relative state requirements, which make them also liable to higher control action expense with respect to (wrt) the single satellite systems. Moreover, applications like Automated Rendez-Vous and Docking (RVD) and in general close proximity maneuvers present a high risk of impact between the satellites, which must be treated with an appropriate design of the on board Guidance Navigation and Control (GNC) system. These aspects justify the development and employment of a ground hardware simulator representative of two or more satellites performing coordinate maneuvers, allowing the investigation of these problems with an easily accessible system. The aim of my Ph.D. Activities has consisted in the development and testing of the cooperating SPAcecRaft Testbed for Autonomous proximity operatioNs experimentS (SPARTANS) hardware simulator, which is under development since 2010 at the Center of Studies and Activities for Space (CISAS) of the University of Padova. This ground simulator presents robotic units that allow the reproduction of the relative position and attitude motions of satellites in proximity or in formation, and can be therefore employed for the extensive study of control algorithms and strategies for these types of applications, allowing dedicated hardware in the loop to be tested in a controlled environment. At the beginning of my Ph.D., the testbed consisted in the first prototype of Attitude Module (AM), a platform with three rotational Degrees of Freedom (DOF) of Yaw, Pitch and Roll, controllable through a GNC system based on incremental encoders and air thrusters. A small contribution was initially given in support of the execution of a series of 3 DOF attitude control maneuvers tests with the AM. Subsequently, the first activity consisted in the design and development of the air suspension system that enables a low friction translational motion of the a whole Unit of the testbed over the test table, with the characterization of air skids available in laboratory. The subsequent activity consisted in the design and development of the Translation Module (TM), the lower section of the whole Unit, as modular structure supporting the air suspension system, the AM, and the on board localization system. After this activity the on board localization system for position and Azimuth estimation, based on Optical Flow Sensors (OFS), was developed and tested. The system was installed on a TM base prototype and it was calibrated and tested with the imposition of known motions through rotational and translational motorized stages wich were used in conjunction, presenting max deviations at the level of 0.1° for a total rotational range of 40°, and max deviations of 1 mm for a total translational range of 100 mm. Combined maneuvers, i.e. translational and rotational motions imposed in sequence, were subsequently performed, showing a drift trend, up to approximately 1 cm for a 90° rotation. Subsequently the OFS system was assembled in the TM and integrated with an external vision system, under development in parallel in the context of the SPARTANS project. Results showed a good general concordance between the two systems, but combined maneuvers with extended rotational range showed again a drift trend in the OFS system solution, not only in position but also in Azimuth. A parallel activity consisted in the design and development of the levellable test table for the Units with a modular structure. Another activity consisted in the development of a Matlab Software Simulator for Units tests planning. A series of preliminary standard and optimal control maneuvers were planned with the software simulator. The last activity of my Ph.D. consisted in the analysis of an inspection scenario for satellite removal purposes, with the goal of reproducing the relative dynamics in scale with the SPARTANS simulator. The chosen scenario foresaw the inspection, through a vision system on board an inspection satellite, of the currently freely tumbling Envisat spacecraft . The analysis performed with a Matlab software simulator was focused on the acquisition and maintainance of a circular relative orbit at close range starting from a flyaround orbit, through the employment of Model Predictive Control (MPC) and Linear Quadratic Regulator (LQR) optimal controllers. Simulations results showed a lower tracking error in position with the MPC controller wrt to the LQR controller, but with a higher control action expense: for a 6 hours inspection on a 41 m radius circular relative orbit, the max total delta-v component resulted of 3.3 m/s for MPC, while it resulted of 0.7 m/s for LQR. In the present configuration the SPARTANS testbed presents a first complete Unit and test table to be assembled in the immediate future for the execution of the first position and attitude control maneuvers. The final configuration of the testbed will present a minimum of two Units allowing to perform coordinate control maneuvers for the investigation and study of problems and strategies related to SFF, Automated Rendez-Vous and Docking, and in general proximity manevuers

Laboratory Experimentation of Guidance and Control of Spacecraft During On-Orbit Proximity Maneuvers

The article of record is available from http://www.intechopen.com/books/mechatronic-systems-simulation-modeling-and-control/laboratoryexperimentation-of-guidance-and-control-of-spacecraft-during-on-orbit-proximity-maneuversThe traditional spacecraft system is a monolithic structure with a single mission focused design and lengthy production and qualification schedules coupled with enormous cost. Additionally, there rarely, if ever, is any designed preventive maintenance plan or re-fueling capability. There has been much research in recent years into alternative options. One alternative option involves autonomous on-orbit servicing of current or future monolithic spacecraft systems. The U.S. Department of Defense (DoD) embarked on a highly successful venture to prove out such a concept with the Defense Advanced Research Projects Agency’s (DARPA’s) Orbital Express program. Orbital Express demonstrated all of the enabling technologies required for autonomous on-orbit servicing to include refueling, component transfer, autonomous satellite grappling and berthing, rendezvous, inspection, proximity operations, docking and undocking, and autonomous fault recognition and anomaly handling (Kennedy, 2008). Another potential option involves a paradigm shift from the monolithic spacecraft system to one involving multiple interacting spacecraft that can autonomously assemble and reconfigure. Numerous benefits are associated with autonomous spacecraft assemblies, ranging from a removal of significant intra-modular reliance that provides for parallel design, fabrication, assembly and validation processes to the inherent smaller nature of fractionated systems which allows for each module to be placed into orbit separately on more affordable launch platforms (Mathieu, 2005)

Suboptimal LQR-based spacecraft full motion control: Theory and experimentation

Abstract This work introduces a real time suboptimal control algorithm for six-degree-of-freedom spacecraft maneuvering based on a State-Dependent-Algebraic-Riccati-Equation (SDARE) approach and real-time linearization of the equations of motion. The control strategy is sub-optimal since the gains of the linear quadratic regulator (LQR) are re-computed at each sample time. The cost function of the proposed controller has been compared with the one obtained via a general purpose optimal control software, showing, on average, an increase in control effort of approximately 15%, compensated by real-time implementability. Lastly, the paper presents experimental tests on a hardware-in-the-loop six-degree-of-freedom spacecraft simulator, designed for testing new guidance, navigation, and control algorithms for nano-satellites in a one-g laboratory environment. The tests show the real-time feasibility of the proposed approach