Space Station Remote Manipulator Research Articles

Inverse kinematics and multi-objective configuration optimization of the SSRMS manipulator

The Space Station Remote Manipulator System (SSRMS) type redundant manipulator with higher flexibility and foldability is widely used in the space environment. Inverse kinematics and multi-objective configuration optimization are analyzed in this paper. An arm angle parameterized inverse kinematics method using the approximate solution and error compensation scheme is proposed, which has the advantages of not requiring a selection of initial estimates of joint variables, being insensitive to Jacobian matrix singularities, having no pose error, and finding multiple solutions. In addition, Multiple Objective Particle Swarm Optimization (MOPSO) scheme is adopted to optimize the arm angle trajectory in null space, and the optimization index is set as joint torque and manipulability. Unlike traditional trajectory planning methods, we synthesize null space and configuration control to provide a novel perspective for trajectory planning. Finally, the experiments prove that the inverse kinematics algorithm is efficient and reliable, and the effectiveness of the configuration optimization method is verified by the numerical simulation of single objective and multi-objective optimization.

Inverse kinematics and workspace analysis of a novel SSRMS-type reconfigurable space manipulator with two lockable passive telescopic links

This study proposes a novel space station remote manipulator system (SSRMS)-type reconfigurable space manipulator to enhance the adaptability of the traditional SSRMS-type manipulators in complex on-orbit tasks. The proposed manipulator has two lockable passive telescopic links (LPTLs) and allows changing their lengths to achieve reconfigurability. The inverse kinematics (IK) and the workspace for this manipulator are minutely analyzed. We develop a new CCDJAP-IK method to solve the IK problem by combining the cyclic coordinate descent (CCD) and joint angle parameterization (JAP) methods. This new method addresses the CCD method's convergence instability and the JAP method's high dependence on the pre-set value of the redundancy parameter. In particular, our approach is insensitive to the initial and singular configurations and can generate multiple exact solutions that satisfy the joint limit constraints. A reachability sphere map captures the proposed manipulator's kinematic capability for the workspace analysis. Then the effects of the two LPTLs on this capability are deeply explored. Based on the results, we propose an information-driven optimal configuration search method. Several typical simulations validate the proposed methods’ effectiveness.

Grappling Spacecraft

This article provides a survey overview of the techniques, mechanisms, algorithms, and test and validation strategies required for the design of robotic grappling vehicles intended to approach and grapple free-flying client satellites. We concentrate on using a robotic arm to grapple a free-floating spacecraft, as distinct from spacecraft docking and berthing, where two spacecraft directly mate with each other. Robotic grappling of client spacecraft is a deceptively complex problem: It entails designing a robotic system that functions robustly in the visually stark, thermally extreme orbital environment, operating near massive and extremely expensive yet fragile client hardware, using relatively slow flight computers with limited and laggy communications. Spaceflight robotic systems are challenging to test and validate prior to deployment and extremely expensive to launch, which significantly limits opportunities to experiment with new techniques. These factors make the design and operation of orbital robotic systems significantly different from those of their terrestrial counterparts, and as a result, only a relative handful of systems have been demonstrated on orbit. Nevertheless, there is increasing interest in on-orbit robotic servicing and assembly missions, and grappling is the core requirement for these systems. Although existing systems such as the Space Station Remote Manipulator System have demonstrated extremely reliable operation, upcoming missions will attempt to expand the types of spacecraft that can be safely and dependably grappled and berthed.

Precise semi-analytical inverse kinematic solution for 7-DOF offset manipulator with arm angle optimization

Seven-degree-of-freedom redundant manipulators with link offset have many advantages, including obvious geometric significance and suitability for configuration control. Their configuration is similar to that of the experimental module manipulator (EMM) in the Chinese Space Station Remote Manipulator System. However, finding the analytical solution of an EMM on the basis of arm angle parameterization is difficult. This study proposes a high-precision, semi-analytical inverse method for EMMs. Firstly, the analytical inverse kinematic solution is established based on joint angle parameterization. Secondly, the analytical inverse kinematic solution for a non-offset spherical-roll-spherical (SRS) redundant manipulator is derived based on arm angle parameterization. The approximate solution of the EMM is calculated in accordance with the relationship between the joint angles of the EMM and the SRS manipulator. Thirdly, the error is corrected using a numerical method through the analytical inverse solution based on joint angle parameterization. After selecting the stride and termination condition, the precise inverse solution is computed for the EMM based on arm angle parameterization. Lastly, case solutions confirm that this method has high precision, and the arm angle parameterization method is superior to the joint angle parameterization method in terms of parameter selection.

A Novel Analytical Inverse Kinematics Method for SSRMS-Type Space Manipulators Based on the POE Formula and the Paden-Kahan Subproblem

Space manipulators which have a similar symmetrical structure with seven revolute joints, such as the space station remote manipulator system (SSRMS), can be called SSRMS-type space manipulators. The analytical inverse kinematics of an SSRMS-type manipulator can be solved by locking a single joint; the locked joint (joint 1, 2, 6, or 7) can be determined by configuration analysis. Although widely used in establishing the kinematics of SSRMS-type manipulators, the Denavit-Hartenberg (DH) method has a singular problem when two adjacent joint axes are nearly parallel. To avoid this problem, this paper proposes a novel analytical inverse kinematics method for SSRMS-type manipulators based on the product of exponentials (POE) formula and the Paden-Kahan subproblem. Because of the symmetrical structure, an SSRMS-type manipulator degrades to two kinds of 6-degree-of-freedom (DOF) manipulators when locking a single joint (joint 1, 2, 6, or 7). The analytical inverse kinematics of these two kinds of 6-DOF manipulators is solved by combining the Paden-Kahan subproblems and geometric and algebraic methods, respectively. The proposed approach is not only singularity free compared with the traditional DH-based methods but also more accurate than the POE-based numerical solution. The simulation results verify the efficiency of the proposed approach.

Charging of the H-II Transfer Vehicle at Rendezvous and Docking Phase

The Japan Aerospace Exploration Agency developed an instrument consisting of a potential monitor and a plasma current sensor to measure the potential of the H-II transfer vehicle (HTV) against ambient plasma and the plasma environment around the HTV. In this first report on the charging measurements on the HTV-6 (sixth flight of H-II transfer vehicle), the onorbit data obtained during the rendezvous and docking phase are discussed, as well as the subsequent releasing phase. The trends observed during docking and releasing suggest the worst potential in terms of values never seen before over the full lifetime of the HTV-6. The cause is inferred to be resistance of the space station remote manipulator system as a result of numerical calculations based on simplified models of the HTV and the International Space Station.

A review of the end-effector of large space manipulator with capabilities of misalignment tolerance and soft capture

The space manipulator which has advantages of high dexterity and universality, is used to the space capturing usually. According to the different types of mechanical interfaces of targets, the on orbit capturing operation includes capturing of cooperative target and capturing of uncooperative target. The performances of the famous large space manipulators named space shuttle remote manipulator system (SRMS), the space station remote manipulator system (SSRMS) and the Europe robotic arm (ERA) are reviewed and studied respectively. Moreover, the space manipulators being developed by China for space station is also surveyed. Based on the performance analysis of the large space manipulators and end-effectors, which are adapted to the construction and daily maintenance for the large space structure such as the space station, the basic requirements of large misalignment tolerance capability, soft capturing capability and hard docking capability for the end-effector of large space manipulator are proposed in this paper. According to these requirements, the capture mechanism and methods that can enable the end-effector to have the capability of misalignment tolerance and soft capturing are presented. The development trend and key technologies of the large space manipulators and the end-effectors are also reviewed.

Fault-tolerant analysis and control of SSRMS-type manipulators with single-joint failure

Several space manipulators, whose configurations are similar to that of the Space Station Remote Manipulator System (SSRMS, also called Canadarm2), are playing important roles in the construction and maintenance of the International Space Station. Working in the harsh orbital environment, they are at high risk of single-joint failure. Fault-tolerant capability is critical for those manipulators to complete their on-orbital tasks.In this paper, we analysed and compared the manipulation capability of SSRMS-type manipulators with joints locked at arbitrary positions, and proposed efficient path planning via a fault-tolerant control method. First, a unified kinematic model of this type of manipulators was established. Second, the manipulation capability of the original 7-DOF (degrees of freedom) redundant manipulator was analysed and compared with its degraded 6-DOF counterparts formed by different joint locking configurations. Then, we identified those joints with large sensitivity to fault tolerance performance. The influences of different positions of all joints were also determined by numerical computation. Based on the analysis, the relatively safe and dangerous regions for each joint failure were identified. Finally, we proposed a path planning strategy and realized by a H∞ controller which enables the failure joint locked in the safe region, and simulations were carried on a degraded 3-DOF planar redundant manipulator to verify the planning strategy and control approach. This paper provided important analysis results and efficient methods to address the possible problems of SSRMS-type manipulators caused by single-joint failure that can be extended to other types of manipulators. Moreover, the proposed method is useful for designing the optimal configuration of a redundant manipulator.

Thermodynamic analysis of a space station remote manipulator with a harmonic drive that considers an integrated thermal protection layer

To eliminate anomalies and improve the performance of a space station remote manipulator (SSRM) used in a dynamically changeable thermal environment, we analyze the thermodynamic behavior of an SSRM that considers an integrated thermal protection system (ITPS). Solar radiative heat gain and loss become equally significant as conductive heat transfers through the interior of the SSRM on orbit. A thermodynamic model of the SSRM with a sandwich ITPS structure is established on the coupling between harmonic drive and changeable thermal environment. A motion precision is proposed to evaluate thermodynamic behavior under continuously changeable thermal circumstances. Simulation results indicate that the ITPS with a corrugated sandwich structure reduces the maximum amplitude of angular position errors to 41.6%, which helps improve the motion precision of the SSRM. The feasible regions for the SSRM in the Low Earth Orbit (LEO) and Geostationary Earth Orbit (GEO) are analyzed, which shows that the proportion of feasible region in LEO is significantly larger than that in GEO.

Analytical and semi-analytical inverse kinematics of SSRMS-type manipulators with single joint locked failure

Redundant space manipulators, including Space Station Remote Manipulator System (SSRMS), Special Purpose Dexterous Manipulator (SPDM) and European Robotic Arm (ERA), have been playing important roles in the construction and maintenance of International Space Station (ISS). They all have 7 revolute joints arranged in similar configurations, and are referred to as SSRMS-type manipulators.When a joint is locked in an arbitrary position due to some failures, a 7R manipulator degrades to a 6R manipulator. Without a spherical wrist or three consecutive parallel joints, the inverse kinematics of the 6R manipulator is very complex. In this paper, we propose effective methods to resolve the inverse kinematics for different cases of any joint locked in an arbitrary position. Firstly, configuration characteristics of the SSRMS-type redundant manipulators are analyzed. Then, an existing of closed-form inverse kinematics is discussed for locking different joints. Secondly, D–H frames and corresponding D–H parameters of the new 6-DOF manipulator formed by locking a joint in an arbitrary position are re-constructed. A unified table is then created to describe the kinematics for all possible cases of single joint locking failure. Thirdly, completely analytical and semi-analytical methods are presented to solve the inverse kinematics equations, and the former is used for locking joint 1, 2, 6 or 7 while the latter for locking joint 3, 4 or 5. Finally, typical cases for single joint locking are studied. The results verify the proposed methods.

Development and verification of ground-based tele-robotics operations concept for Dextre

The Special Purpose Dextreous Manipulator (Dextre) is the latest addition to the on-orbit segment of the Mobile Servicing System (MSS); Canada's contribution to the International Space Station (ISS). Launched in March 2008, the advanced two-armed robot is designed to perform various ISS maintenance tasks on robotically compatible elements and on-orbit replaceable units using a wide variety of tools and interfaces. The addition of Dextre has increased the capabilities of the MSS, and has introduced significant complexity to ISS robotics operations. While the initial operations concept for Dextre was based on human-in-the-loop control by the on-orbit astronauts, the complexities of robotic maintenance and the associated costs of training and maintaining the operator skills required for Dextre operations demanded a reexamination of the old concepts. A new approach to ISS robotic maintenance was developed in order to utilize the capabilities of Dextre safely and efficiently, while at the same time reducing the costs of on-orbit operations. This paper will describe the development, validation, and on-orbit demonstration of the operations concept for ground-based tele-robotics control of Dextre. It will describe the evolution of the new concepts from the experience gained from the development and implementation of the ground control capability for the Space Station Remote Manipulator System; Canadarm 2. It will discuss the various technical challenges faced during the development effort, such as requirements for high positioning accuracy, force/moment sensing and accommodation, failure tolerance, complex tool operations, and the novel operational tools and techniques developed to overcome them. The paper will also describe the work performed to validate the new concepts on orbit and will discuss the results and lessons learned from the on-orbit checkout and commissioning of Dextre using the newly developed tele-robotics techniques and capabilities.

1A2-J07 宇宙大型マニピュレータによる宇宙ステーション補給機「こうのとり」捕獲時の運動解析(【宇宙工学部門】宇宙工学とロボティクス・メカトロニクス(1))

1A2-J07 宇宙大型マニピュレータによる宇宙ステーション補給機「こうのとり」捕獲時の運動解析(【宇宙工学部門】宇宙工学とロボティクス・メカトロニクス(1))

An Intelligent Simulator for Telerobotics Training

Roman Tutor is a tutoring system that uses sophisticated domain knowledge to monitor the progress of students and advise them while they are learning how to operate a space telerobotic system. It is intended to help train operators of the Space Station Remote Manipulator System (SSRMS) including astronauts, operators involved in ground-based control of SSRMS and technical support staff. Currently, there is only a single training facility for SSRMS operations and it is heavily scheduled. The training staff time is in heavy demand for teaching students, planning training tasks, developing teaching material, and new teaching tools. For example, all SSRMS simulation exercises are developed by hand and this process requires a lot of staff time. Once in an orbit ISS astronauts currently have only simple web-based material for skill development and maintenance. For long duration space flights, astronauts will require sophisticated simulation tools to maintain skills. Roman Tutor addresses these challenges by providing a portable training tool that can be installed anywhere and anytime to provide “just in time” training. It incorporates a model of the system operations curriculum, a kinematic simulation of the robotics equipment, and the ISS, a high performance path planner and an automatic task demonstration generator. For each element of the curriculum that the student is supposed to master, Roman Tutor generates example tasks for the student to accomplish within the simulation environment and then monitors its progression to provide relevant feedback when needed. Although motivated by the SSRMS application, Roman Tutor remains applicable to any telerobotics system application.

1A2-L05 宇宙ステーション搭載アームによる補給機HTVの捕獲ハイブリッドシミュレータの構築(宇宙ロボティクス・メカトロニクス)

In orbital work like a capturing a target in space, a safety must be guaranteed at all times. In order to capture a target automatically, it is essential to figure out the behavior of target after contact. At first, we clarify the dangerous condition of contact by analyzing the behavior. The goal of this study is to propose the way of safe caputuring with consideration for the condition. This paper describes the capturing simulator for analyzing the behavior of target, especially the mission for capturing H-II Transfer Vehicle(HTV) by Space Station Remote Manipulator System(SSRMS).

Review of the Development of Robotic Manipulator for International Space Station

In extreme environment of the space,most of Extra-Vehicular Activity(EVA) has to depend on the aid of robotic manipulator.As a main part of International Space Station(ISS), robotic manipulator is playing a crucial role in the on-orbit assembly,external maintenance and the operations of ISS,and it therefore allays the working time and frequency of astronauts EVA.This paper reviews the development of the robotic manipulator based on ISS member countries' research, including shuttle remote manipulator,space station remote manipulator,European robotic arm, Japanese experiment module remote manipulator and German manipulator.It is expected that the concerning research will provide some references for the design of Chinese robotic manipulator.

Lessons learned from the STS-120/ISS 10A robotics operations

The STS-120/ISS 10A assembly mission was an unprecedented period during the life of the International Space Stations (ISS). The successful completion of the mission laid the foundation for the launch of the European and Japanese laboratories and continued assembly of the station. Unlike previous missions that concluded when the Space Shuttle undocked from the ISS, the 10A mission required critical assembly operations to continue after the Shuttle's departure to relocate the Harmony module to its permanent location and activate its systems. The end-to-end mission lasted for almost a month and required the execution of seven space walks, over 20 major robotics operations, and countless hours of ground commanding. The Canadian built mobile servicing system (MSS) and its robotics space station remote manipulator system (SSRMS) played a key a role in the success of the assembly operations. The mission presented the ISS robotics flight control team (ROBO) with unique challenges during the pre-mission planning and real-time execution of complex assembly tasks. The mission included the relocation of the P6 truss segment from the Z1 Node to its permanent location on the P5 truss; a three day marathon of highly choreographed sequence of robotics operations and space walks, and the reconfiguration of ISS structure to attach Harmony (Node 2) to the US destiny laboratory module; a six day sequence of complex robotics operations the majority of which was executed after the departure of the shuttle and included an unprecedented amount of ground commanded robotics operations. Of all the robotics operations executed during the mission, none were more challenging than supporting the repair of a torn P6 solar array that was damaged during its deployment; a dramatic space walk that pushed the MSS and the robotics flight control team to new limits and required the real-time planning and execution of an intricate series of operations that spanned two days. This paper will present an analysis of the robotics operations executed during the STS-120 and 10A stage mission. The paper will highlight the unique challenges associated with the planning and execution of the P6 truss and Node 2 module relocation tasks, as well as the robotics issues faced during the planning and execution of the solar array repair space walk. The analysis will address the operational techniques and mission planning guideline used to deal with tight timelines, structural loads issues, ISS attitude control issues, and complex interdependencies between various ISS systems during the assembly and solar array repair operations. A discussion of the lessons learned from the planning and execution of these complex robotics tasks will also be presented.

Technology of H-II Transfer Vehicle Rendezvous System

The H-II Transfer Vehicle (HTV), which is a Japanese unmanned cargo transfer spacecraft, will deliver supplies to the International Space Station (ISS). The first HTV will be launched in 2009 from the Tanegashima Space Center aboard an H-IIB launch vehicle with up to 6,000kg of supplies. HTV approaches to the ISS and the Space Station Remote Manipulator System (SSRMS), known as Canadarm2, will grapple the HTV and berth it to the ISS. After the supplies, the HTV will then be loaded with waste materials and then separated from the ISS by SSRMS. HTV conducts departure sequence from ISS after release from SSRMS and reentry to the atmosphere. In this paper, technology of HTV automated Guidance, Navigation and Control (GN&C) system is presented.

Dextre: Improving maintenance operations on the International Space Station

The Special Purpose Dexterous Manipulator (SPDM), known as “Dextre”, is currently slated to launch in February 2008 for deployment on the International Space Station (ISS) as the final component of Canada's Mobile Servicing System (MSS). Dextre's primary role on the Space Station is to perform repair and replacement (R&R) maintenance tasks on robotically compatible hardware such as Orbital Replaceable Units (ORUs), thereby eventually easing the burden on the ISS crew. This burden on the on-orbit crew translates practically into crew time being a limited resource on the ISS, and as such, finding ways to assist the crew in performing their tasks or offloading the crew completely when appropriate is a bonus to the ISS program. This is already accomplished very effectively by commanding as many non-critical robotics tasks as possible, such as powering up and free-space maneuvering of the Space Station Remote Manipulator System (SSRMS), known as “Canadarm2”, from the Ground. Thus, beyond its primary role, and based on an increasing clarity regarding the challenges of external maintenance on the ISS, Dextre is being considered for use in a number of ways with the objective of improving ISS operations while reducing and optimizing the use of crew time through the use of ground control for various tasks, pre-positioning hardware, acting as a temporary storage platform to break an Extra Vehicular Activity (EVA) day into manageable timelines, and extending the physical reach and range of the Canadarm2. This paper discusses the planned activities and operations for Dextre an rationale for how these will help optimize the use of crew resources on the ISS.

Singularity analysis of the Canadarm2

The determination of the singular or velocity-degenerate configurations of the Canadian Space Agency (CSA) Canadarm2 is presented. The Canadarm2 or space station remote manipulator system (SSRMS) is a 7-joint serial manipulator used on the International Space Station (ISS). A reciprocity-based based methodology for identifying 1-DOF (degree-of-freedom) loss singular configurations of joint-redundant manipulators is applied to a modified layout of the Canadarm2 (denoted modified Canadarm2). The modified Canadarm2 incorporates two additional link lengths not found in the Canadarm2. The results for the modified Canadarm2 are extended to the Canadarm2 by setting the two extra link lengths in the modified Canadarm2 to zero. It is shown that five sets of conditions defining families of singular configurations resulting in a single-motion DOF loss exist for manipulators having layouts kinematically equivalent to the Canadarm2 or modified Canadarm2. In addition, reciprocal screws characterizing the lost motion are found for each singular configuration.

The Neptec Three-Dimensional Laser Camera System: From Space Mission STS-105 to Terrestrial Applications

Neptec Design Group has developed the Laser Camera System (LCS), a three-dimensional auto-synchronized laser scanner based on a principle originating from the National Research Council of Canada. In imaging mode, the LCS raster scans objects and captures reflections from their surface features. In centroid acquisition mode, the LCS determines the position of discrete target points on an object. Neptec Design Group first developed the LCS for space applications. In August 2001, the LCS flew successfully onboard space shuttle Discovery during mission STS-105 to the International Space Station (ISS). During the mission, the LCS took four high-resolution (1024 × 1024 voxels) images of elements of the ISS during orbital day and night, demonstrating its immunity to dynamic lighting conditions. The LCS also tracked targets affixed to the Multi-Purpose Logistics Module (MPLM) while in motion, more than 10 m away. Comparison with Space Station Remote Manipulator System (SSRMS) data confirmed that the LCS tracked these targets with millimetre precision. continued on page 116