Servicing Spacecraft Research Articles

Towards a standardized grasping and refuelling on-orbit servicing for geo spacecraft

Exploitation of space must benefit from the latest advances in robotics. On-orbit servicing is a clear candidate for the application of autonomous rendezvous and docking mechanisms. However, during the last three decades most of the trials took place combining extravehicular activities (EVAs) with telemanipulated robotic arms. The European Space Agency (ESA) considers that grasping and refuelling are promising near-mid-term capabilities that could be performed by servicing spacecraft. Minimal add-ons on spacecraft to enhance their serviceability may protect them for a changing future in which satellite servicing may become mainstream.ESA aims to conceive and promote standard refuelling provisions that can be installed in present and future European commercial geostationary orbit (GEO) satellite platforms and scientific spacecraft. For this purpose ESA has started the ASSIST activity addressing the analysis, design and validation of internal provisions (such as modifications to fuel, gas, electrical and data architecture to allow servicing) and external provisions (such as integrated berthing fixtures with peripheral electrical, gas, liquid connectors, leak check systems and corresponding optical and radio markers for cooperative rendezvous and docking). This refuelling approach is being agreed with European industry (OHB, Thales Alenia Space) and expected to be consolidated with European commercial operators as a first step to become an international standard; this approach is also being considered for on-orbit servicing spacecraft, such as the SpaceTug, by Airbus DS.This paper describes in detail the operational means, structure, geometry and accommodation of the system. Internal and external provisions will be designed with the minimum possible impact on the current architecture of GEO satellites without introducing additional risks in the development and commissioning of the satellite. End-effector and berthing fixtures are being designed in the range of few kilos and linear dimensions around 15cm. A central mechanical part is expected to perform first a soft docking followed by a motorized retraction ending during a hard docking phase using aligning pins. Mating and de-mating will be exhaustively analysed to ensure robustness of operations. Leakage-free valves would allow for the transfer of fuel to the serviced spacecraft. The validation of the ASSIST system through dedicated environmental tests in a vacuum chamber together with dynamic testing using an air-bearing table will allow for the demonstration of concept feasibility and its suitability for becoming a standard of the on-orbit space industry.

Automatic trajectory planning for low-thrust active removal mission in low-earth orbit

In this paper two strategies are proposed to de-orbit up to 10 non-cooperative objects per year from the region within 800 and 1400km altitude in Low Earth Orbit (LEO). The underlying idea is to use a single servicing spacecraft to de-orbit several objects applying two different approaches. The first strategy is analogous to the Traveling Salesman Problem: the servicing spacecraft rendezvous with multiple objects in order to physically attach a de-orbiting kit that reduces the perigee of the orbit. The second strategy is analogous to the Vehicle Routing Problem: the servicing spacecraft rendezvous and docks with an object, spirals it down to a lower altitude orbit, undocks, and then spirals up to the next target.In order to maximise the number of de-orbited objects with minimum propellant consumption, an optimal sequence of targets is identified using a bio-inspired incremental automatic planning and scheduling discrete optimisation algorithm. The optimisation of the resulting sequence is realised using a direct transcription method based on an asymptotic analytical solution of the perturbed Keplerian motion. The analytical model takes into account the perturbations deriving from the J2 gravitational effect and the atmospheric drag.

Spacecraft power supply system using additional low-power sources of energy

The article analyzes modern spacecraft power supply systems and possible options for extending their possibilities through the use of low-power electric energy sources (the energy of solar radiation reflected from the Earth and the energy of the magnetic field of the Earth). A conclusion is made as to the most appropriate type of spacecraft power supply systems for the use of additional low-power sources of energy. The peculiarities of operation of the proposed power supply system are discussed. A method of producing additional electric energy on board the spacecraft due to its rotation in the Earth's magnetic field is described. Mathematical models of the Earth's magnetic field are analyzed. A model of description of the geomagnetic field using a series of spherical harmonics (number of Gauss) was applied on the basis of the results of the analysis of these models to assess the magnitude of the magnetic induction in spacecraft low orbits. Based on the evaluation of the magnetic induction, the set parameters of the spacecraft and the orbit the average power of electrical energy generated by low-power sources for on-board power consumers in one orbit pass was calculated. A variant of using additional electrical energy on board a spaceship is proposed. The use of the proposed scheme will make it possible to expand the possibilities of spacecraft to receive, transform and accumulate electrical energy from primary low-power sources, which will make the spacecraft service life longer and improve its power supply capacity.

Parameter Identification–Based Attitude Stabilization Control of Spacecraft with Multiaccessories during Orbital Maneuver

AbstractTargeted at one kind of on-orbit servicing spacecraft that contains flue containers, momentum actuators, space manipulators, and captured unknown objects, a specific attitude control proble...

LEO cooperative multi-spacecraft refueling mission optimization considering J2 perturbation and target’s surplus propellant constraint

The optimization of an LEO cooperative multi-spacecraft refueling mission considering the J2 perturbation and target’s surplus propellant constraint is studied in the paper. First, a mission scenario is introduced. One service spacecraft and several target spacecraft run on an LEO near-circular orbit, the service spacecraft rendezvouses with some service positions one by one, and target spacecraft transfer to corresponding service positions respectively. Each target spacecraft returns to its original position after obtaining required propellant and the service spacecraft returns to its original position after refueling all target spacecraft. Next, an optimization model of this mission is built. The service sequence, orbital transfer time, and service position are used as deign variables, whereas the propellant cost is used as the design objective. The J2 perturbation, time constraint and the target spacecraft’s surplus propellant capability constraint are taken into account. Then, a hybrid two-level optimization approach is presented to solve the formulated mixed integer nonlinear programming (MINLP) problem. A hybrid-encoding genetic algorithm is adopted to seek the near optimal solution in the up-level optimization, while a linear relative dynamic equation considering the J2 perturbation is used to obtain the impulses of orbital transfer in the low-level optimization. Finally, the effectiveness of the proposed model and method is validated by numerical examples.

Optimal Capture of a Tumbling Object in Orbit Using a Space Manipulator

This paper introduces an optimal capture strategy for a manipulator based on a servicing spacecraft to approach an arbitrarily rotating object, such as a malfunctioning satellite or a piece of orbital debris, for capturing with minimal impact to the robot's base spacecraft. The method consists of two steps. The first step is to determine an optimal future time and the target object's corresponding motion state for the robot to capture the tumbling object, so that, at the time when the gripper of the robot intercepts the target the very first instant, the resulting impact or disturbance to the attitude of the base spacecraft will be minimal. The second step is to control the robot to reach the tumbling object at the predicted optimal time along an optimal trajectory. The optimal control problem is solved with random uncertainties in the initial and final boundary conditions. Uncertainties are introduced because sensor and estimation errors inevitably exist in the first step, i.e., determination process of the initial and final boundary conditions. The application of the method is demonstrated using a dynamics simulation example.

Attitude Coordinated Control for Docked Spacecraft Based on Estimated Coupling Torque

AbstractWhen a service spacecraft docks successfully with its target spacecraft and forms a docked spacecraft, it will cause a large shift in the dynamics of the docked spacecraft. Not only do the mass properties change, but so do the reaction wheels’ configuration. Meanwhile, the attitude of the docked spacecraft will inevitably change, under the influence of contact and impact, and it may lead to instability of the entire system. Due to the limited control torque and saturation, the control system of the reaction wheel may not guarantee the system stability, and the thruster can generate large control torque, but it consumes valuable jet fuel. Since the space manipulator may generate a greater coupling torque by movement, this paper proposes an attitude coordinated control method for docked spacecraft based on the estimated coupling torque. The method adopts the chaotic particle swarm optimization (CPSO) algorithm to plan the coordinated motion trajectory of space manipulator, and then designs a coordin...

Multi-objective planning of a multiple geostationary spacecraft refuelling mission

ABSTRACTThe multi-objective optimization of multiple geostationary spacecraft refuelling is investigated in this article. A servicing spacecraft (SSc) and a propellant depot (PD), both parked initially in geostationary Earth orbit (GEO), are utilized to refuel multiple GEO targets of known propellant demand. The capacitated SSc is expected to rendezvous with fuel-deficient GEO targets or the PD for the purpose of refuelling or getting refuelled. The multiple geostationary spacecraft refuelling problem is treated as a multi-variable combinatorial optimization problem with the principal objective of minimizing the propellant consumption and the mission duration. A two-level optimization model is built, and the design variables are the refuelling order X, the refuelling time T and the binary decision variable S. The non-dominated sorting genetic algorithm is employed to solve the up-level optimization problem. For the low-level optimization, an exact algorithm is proposed. Finally, numerical simulations are presented to illustrate the effectiveness and validity of the proposed approach.

Reconfigurable spacecraft attitude takeover control in post-capture of target by space manipulators

Most current research on reconfigurable control system puts emphasis on reconfiguration for adapting to actuator failures. However, the reconfigurable control system is necessitated for spacecraft attitude takeover control in the application of capturing target spacecraft whose fuel is exhausted to extend its operational lifetime by supplying them propulsion, navigation and guidance services. In this scenario, the capture of target spacecraft by space manipulators will cause a large shift in the dynamics of the service spacecraft. Not only do the mass properties change, but also does the thruster configuration. The changes in the mass, center of mass and inertia of the combined spacecraft will cause changes in the equivalent force exerted by each thruster. In this paper, considering the changes of thruster configuration and the control reallocation, a reconfigurable control system is designed for spacecraft attitude takeover control in post-capture of target by space manipulators in order to adapt to changes in the mass properties. The unknown inertia properties of target spacecraft in the system constitute a formidable technical challenge for controller design. Therefore, a modified adaptive dynamic inverse controller is proposed to provide global asymptotic stability in the presence of model uncertainties and nonlinearities. Moreover, by the null-space intersections control reallocation method, the thrust forces of service spacecraft can be redistributed and satisfy some constraints. Numerical simulations validate the feasibility of reconfigurable spacecraft attitude takeover control with large center of mass shifts and unknown inertia properties.

Attitude takeover control for post-capture of target spacecraft using space robot

When the spacecraft reaches the end of life, its payload will still be able to work in most cases. Due to the loss of attitude control ability, these failed satellites had to be abandoned. The technology of attitude takeover control can be used to extend the operational lifetime of these failed satellites. Post-capture of target spacecraft using space robot will cause a large shift in the dynamics of combined spacecraft. Not only do the mass properties change, but also does the reaction wheels' configuration. Designing a reconfigurable control system can account for these changes. In this paper, a reconfigurable control system is designed for attitude takeover control of target spacecraft, which considers the changes of the mass properties and reaction wheels' configuration. Firstly, a modified SDRE (Sate-Dependent Riccati Equation) optimal controller is proposed to guarantee the convergence of the steady-state position errors and velocity errors, and meanwhile move the closed-loop poles of system in order to provide a sufficient stability margin. Then, a θ–D suboptimal control solving technique is adopted to solve an approximate solution of the modified SDRE optimal controller. Moreover, the control torques of reaction wheels of service spacecraft can be reallocated and satisfy some constraints using the dynamic control allocation method. Numerical simulations validate the feasibility of the reconfigurable control systems with large mass properties changes.

Time–frequency analysis of nonstationary vibration signals for deployable structures by using the constant-Q nonstationary gabor transform

Deployable structures have been widely used in on-orbit servicing spacecrafts, and the vibration properties of such structures have become increasingly important in the aerospace industry. The constant-Q nonstationary Gabor transform (CQ-NSGT) is introduced in this paper to accurately evaluate the variation in the frequency and amplitude of vibration signals along with time. First, an example signal is constructed on the basis of the vibration properties of deployable structures and is processed by the short-time Fourier transform, Wigner–Ville distribution, Hilbert–Huang transform, and CQ-NSGT. Results show that time and frequency resolutions are simultaneously fine only by employing CQ-NSGT. Subsequently, a zero padding operation is conducted to correct the calculation error at the end of the transform results. Finally, a set of experimental devices is constructed. The vibration signal of the experimental mode is processed by CQ-NSGT. On this basis, the experimental signal properties are discussed. This time–frequency method may be useful for formulating the dynamics for complex deployable structures.

Close-Range 3D Collision Prediction under Attitude Uncertainty for On-Orbit Servicing Missions

With a large and increasing number of satellites, not least because of expected falling prices due to new private space companies entering the market, the number of space assets requiring on-orbit maintenance is rising faster than ever. Advanced safety concepts which prevent collision between servicer and potentially valuable client spacecrafts in case of loss-of-control of the servicer spacecraft are necessary. Prediction of collision probability based on current state and navigation uncertainty is essential for safety evaluationand validation. An algorithm for prediction of the collision probability for the close range phase of satellite rendezvous is presented in this paper. 3d satellite geometry, relative attitude and relative position information and state uncertainty are taken into account during the calculation, resulting in an accurate and conservative collision probability estimate.

Modified super twisting controller for servicing to uncontrolled spacecraft

A relative position and attitude coupled sliding mode controller is proposed by combining the standard super twisting (ST) control and basic linear algorithm for autonomous rendezvous and docking. It is schemed for on-orbit servicing to a tumbling noncooperative target spacecraft subjected to external disturbances. A coupled dynamic model is established including both kinematical and dynamic coupled effect of relative rotation on relative translation, which illustrates the relative movement between the docking port located in target spacecraft and another in service spacecraft. The modified super twisting (MST) control algorithm containing linear compensation items is schemed to manipulate the relative position and attitude synchronously. The correction provides more robustness and convergence velocity for dealing with linearly growing perturbations than the ST control algorithm. Moreover, the stability characteristic of closed-loop system is analyzed by Lyapunov method. Numerical simulations are adopted to verify the analysis with the comparison between MST and ST control algorithms. Simulation results demonstrate that the proposed MST controller is characterized by high precision, strong robustness and fast convergence velocity to attenuate the linearly increasing perturbations.

Optimal planning of LEO active debris removal based on hybrid optimal control theory

The mission planning of Low Earth Orbit (LEO) active debris removal problem is studied in this paper. Specifically, the Servicing Spacecraft (SSc) and several debris exist on near-circular near-coplanar LEOs. The SSc should repeatedly rendezvous with the debris, and de-orbit them until all debris are removed. Considering the long-duration effect of J2 perturbation, a linear dynamics model is used for each rendezvous. The purpose of this paper is to find the optimal service sequence and rendezvous path with minimum total rendezvous cost (Δv) for the whole mission, and some complex constraints (communication time window constraint, terminal state constraint, and time distribution constraint) should be satisfied meanwhile. Considering this mission as a hybrid optimal control problem, a mathematical model is proposed, as well as the solution method. The proposed approach is demonstrated by a typical active debris removal problem. Numerical experiments show that (1) the model and solution method proposed in this paper can effectively address the planning problem of LEO debris removal; (2) the communication time window constraint and the J2 perturbation have considerable influences on the optimization results; and (3) under the same configuration, some suboptimal sequences are equivalent to the optimal one since their difference in Δv cost is very small.

Super twisting controller for on-orbit servicing to non-cooperative target

A relative position and attitude coupled controller is proposed for rendezvous and docking between two docking ports located in different spacecraft. It is concerned with servicing to a tumbling non-cooperative target spacecraft in arbitrary orbit subjected to external disturbances. By considering both kinematic and dynamical coupled effects of relative rotation on relative translation, a coupled dynamic model is established to represent the relative motion of docking port on target spacecraft with respect to another on the service spacecraft. The spacecraft control is based on the second order sliding mode algorithm of super twisting (ST). It is schemed to manipulate the relative position and attitude synchronously. A formal proof of the finite time convergence property of the closed-loop system is derived theoretically by the second method of Lyapunov. Numerical simulations with the designed ST controller are presented to validate the analytic analysis by contrast with the twisting control algorithm. Simulation results demonstrate that the proposed relative position and attitude integrated controller is characterized by high precision, strong robustness and high reliability.

Biobjective planning of GEO debris removal mission with multiple servicing spacecrafts

The mission planning of GEO debris removal with multiple servicing spacecrafts (SScs) is studied in this paper. Specifically, the SScs are considered to be initially on the GEO belt, and they should rendezvous with debris of different orbital slots and different inclinations, remove them to the graveyard orbit and finally return to their initial locations. Three key problems should be resolved here: task assignment, mission sequence planning and transfer trajectory optimization for each SSc. The minimum-cost, two-impulse phasing maneuver is used for each rendezvous. The objective is to find a set of optimal planning schemes with minimum fuel cost and travel duration. Considering this mission as a hybrid optimal control problem, a mathematical model is proposed. A modified multi-objective particle swarm optimization is employed to address the model. Numerous examples are carried out to demonstrate the effectiveness of the model and solution method. In this paper, single-SSc and multiple-SSc scenarios with the same amount of fuel are compared. Numerous experiments indicate that for a definite GEO debris removal mission, that which alternative (single-SSc or multiple-SSc) is better (cost less fuel and consume less travel time) is determined by many factors. Although in some cases, multiple-SSc scenarios may perform worse than single-SSc scenarios, the extra costs are considered worth the gain in mission safety and robustness.

Design and Modeling of Three Joint Mechanical Arm Based on the Free Floating Space Robot Project

The frequence and complex of space exploration activeities makes the life of the spacecraft and on-orbit service technologies becoming research hotspot in recent years. But the limitation of non-renewable fuels makes exploration mission costly and maintenance difficult, so the free floating space robot has its unique advantages. Because the research level and control technology is not maturity, study on the free floating space robot control method is the key theory and technology which is the difficulty that our country now needs to overcome, also, the research is of great theoretical and practical significance. This paper introduct an experiment scara mechanical arm based on the free floating space robot project. Main research contents of this paper include the mechanical structure design, and combining with the characteristic of the free floating mechanical arm , it makes kinematics and dynamics modals of the mechanical arm system, additional, it conduct statics test and dynamic modal analysis, which is to make sure that the mechanical arm could satisfy needs and to study its dynamic characteristics.This topic focus on structure design and mathematical modeling of the mechanical arm, it makes the research of control method and trajectory planning no longer stay on the paper, and makes the research more authenticity and accuracy.

Visual Modeling and Simulation Research of a Kind of On-Orbit Servicing Spacecraft

On-orbit servicing technology is a novel aerospace technology, which has important economic and military value. Reference to two on-orbit servicing programs named Orbital Express and Phoenix, the paper provides visual modeling and on-orbit module replacement simulation approach for a type of spacecraft based on satellite tool kit (STK). A kind of universal method for STK model building is presented, which includes multi-software model transformation and manual encoding. Some key problems about model integration and post processing, that helps complex STK model building, has also been summarized. An on-orbit replacement task simulation system based on co-simulation of MATLAB and STK can provide effective technical support for the aerospace program.

Angles-Only Navigation to a Noncooperative Satellite Using Relative Orbital Elements

This work addresses the design and implementation of a prototype relative navigation tool that uses camera-based measurements collected by a servicer spacecraft to perform far-range rendezvous with a noncooperative client in low Earth orbit. The development serves the needs of future on-orbit servicing missions planned by the German Aerospace Center. The focus of the paper is on the design of the navigation algorithms and the assessment of the expected performance and robustness under real-world operational scenarios. The tool validation is accomplished through a high-fidelity simulation environment based on the Multi Satellite Simulator in combination with the experience gained from actual flight data from the GPS and camera systems onboard the Prototype Research Instruments and Space Mission Technology Advancement mission.

Autonomous Release of a Snagged Solar Array: Technologies and Laboratory Demonstration

This paper describes a novel concept of operations, payload hardware, terminal navigation strategy, and localized vision scheme for autonomous release of a snagged solar array using a robotic servicing spacecraft. The hardware suite on the servicer consists of two robot arms, end effector cameras, a scanning laser sensor, two local fixed lasers, an end effector fiducial tool, and various active light sources for long-range and localized target illumination. The concept of operations consists of a terminal approach phase, a servicer preparation phase, and an array release phase. The scanning laser sensor is used throughout all phases to determine target pose, whereas the end effector cameras are used during the approach phase for variable baseline stereo ranging and during the release phase for localized scene imaging and arm guidance. Realistic full-scale laboratory tests in a six-degree-of-freedom relative navigation and control testbed demonstrate the complex integration and interaction of close-range autonomous relative navigation, cooperative dual-arm robotics, and localized machine vision necessary to perform such a task.