Orbital Replacement Unit Research Articles

Dual-arm supervisory and shared control task description and execution

A unified control method for description and execution of cooperative dual-arm telerobotic supervisory and shared control tasks with multiple sensory inputs is presented. A general task execution primitive provides the capability. The desired behavior of execution is described by a large input parameter set to the primitive. The method provides a wide range of capabilities within the projected constraints for near-term space telerobotics systems such as limited computational power and safety. Move-squeeze decomposition is utilized to decompose forces sensed at the wrists of the two manipulators into forces in the move subspace, which cause system motion, and forces in the squeeze subspaces, which cause internal forces. The move and squeeze forces are then separately controlled. Each sensor control source is provided with its own task space for control before merging the inputs in a common move space frame. Bounded behavior control is used to ensure execution within safety bounds as specified a priori to task execution. Several space servicing tasks utilizing the cooperative dual-arm control capability are described and experimental results from the tasks are given. The supervisory and shared control tasks include capture of a rotating satellite, orbital replacement unit changeout, fluid coupler seating and locking, and contour following.

Simulating the Replacement of Spacecraft Modules by Means of a Telerobot

An experiment was conducted to simulate executing a proposed on-orbit Space Station maintenance task by means of a telerobotic system. A battery Orbital Replacement Unit (ORU) changeout task was simulated in the laboratory. This task was performed by 5 experienced robot operators using full-scale mockups of the ORU battery module and its interfaces. The space telerobot was emulated by a pair of Kraft robot arms mounted on a Cimcorp gantry robot. The results of the experiment demonstrated that the preliminary flight procedures defining the ORU changeout task worked well. The results also showed that the basic hardware design for the battery ORU could be manipulated by the telerobot. The effects of operator training were significant. Average task completion times improved almost 40 percent over 8 trials. The effects of training were not as pronounced on measures of performance quality, either in terms of errors made or forces and torques exerted on the ORU. Certain operator interface improvements were suggested.

Sensor-based space robotics-ROTEX and its telerobotic features

In early 1993 the space robot technology experiment ROTEX was flown with space-shuttle Columbia. A multisensory robot onboard the spacecraft successfully worked in autonomous modes, teleoperated by astronauts, as well as in different telerobotic ground control modes. These included online teleoperational and telesensor-programming: a task-level oriented programming technique involving learning-by-showing concepts in a virtual environment. The robot's key features were its multisensory gripper and the local sensory feedback schemes that are the basis for shared autonomy. The corresponding man-machine interface concepts, which use a six-degree-of-freedom non-force-reflecting control ball and visual feedback to the human operator, are explained. Stereographic simulation on the ground was used to predict not only the robot's free motion but even the sensor-based path refinement onboard. Prototype tasks performed by this space robot were the assembly of a truss structure, connecting/disconnecting an electrical plug (orbit replaceable unit exchange), and grasping free-floating objects. >

Autonomous single arm ORU changeout — strategies, control issues, and implementation

A preliminary strategy for autonomous single arm orbital replacement unit (ORU) changeout, the associated compliance and force control issues, and implementation results are described. The changeout operation is separated into subtasks, e.g. bolt-turn, compliant-grasp, and dual-pin-insertion/removal. Compliance and force control are done in Cartesian space and the selection of appropriate locations for the Cartesian control frame is discussed. The dual-pin-insertion/removal subtask requires a decision based strategy in conjunction with compliant control to prevent jamming. Actual implementation was done with a PUMA 560 6 degree of freedom manipulator although the control strategies could be implemented on any manipulator with at least 6 degrees of freedom.

Servicing of the future European stations/platforms through European means

In order to get a better knowledge of servicing problems and scenarii of the future European In Orbit Infrastructure, CNES (French Space Agency) decided to fund two separate servicing analysis, respectively conducted by Aérospatiale and MATRA. Aérospatiale work deals with several possible manned stations, taking into account a previous study, while MATRA work deals with polar platform aspects. The first part (Servicing of manned Space Stations) deals with a possible optimization of the roles to be played both by the future Ariane 5 launcher in automatic mode and by the Hermes Spaceplane for the servicing of some future manned space stations: the Columbus pressurized module on the U.S. Space Station, a non-evolutive one-module autonomous station and a multi-module one with a growth capability. After having identified the potential cargoes required for the maintenance and servicing of these stations (analysis of payloads, maintenance ORUs, consumales, crew exchange) and the possible frequencies of such a servicing, it is intended to show how it can be achieved through European means. Established scenarii make use of the Ariane 5 launcher combined either with the Hermes vehicle or with an automated payload. Solutions using payload carriers and/or logistic modules are examined, and possible impacts on stations and/or vehicles are identified further, following investigations on orbital transfer operations. The second part (Servicing of polar platforms) describes the possible scenarii of in-orbit implementation and servicing of a polar platform (number of Ariane 5 launches, modes of transfer, type of service vehicles, servicing orbit, …). This part is focused on the in-orbit operation to exchange on ORU (Orbital Replaceable Unit), once both platform and Hermes (or other servicing vehicle) are attached. After a review of the main tasks to be performed and the possible means to be used as manipulator or EVA, the paper describes the scenario (extraction of an ORU, integration of a new one). Moreover, some ORUs, such as sensors and instrumentation payloads, may require a specific in-orbit alignment; the main problems raised by such a requirement are identified.

A situated reasoning architecture for space-based repair and replace tasks

An area of increasing interest within AI and Robotics is the integration of techniques from both fields to the problem of controlling autonomous systems. Space-based systems, such as NASA's EVA Retriever, provide complex, realistic domains for this integration research. Space is a dynamic environment, where information is imperfect, and unexpected events are commonplace. As such, space-based robots need low level control for collision detection and avoidance, short-term load management, fine-grained motion, and other physical tasks. In addition, higher level control is required to focus strategic decision making as missions are assigned and carried out. Throughout the system, reasoning and control must be responsive to ongoing change taking place in the environment. This paper reports on current MITRE research aimed at bridging the gap between high level AI planning techniques and task-level robot programming for telerobotic systems. Our approach is based on incorporating situated reasoning into AI and Robotics systems in order to coordinate a robot's activity within its environment. Thus, the focus of this research is on controlling a robot embedded in an environment, as opposed to the generation and execution of lengthy robot plans. We present an integrated system under development in a “component maintenance” domain geared towards repair and replacement of Orbital Replacement Units (ORUs) designed for use aboard NASA's Space Station Freedom. The domain consists of a component-cell containing ORU components and a robot (manipulator and vision system) replacing worn and/or failed components based on the collection of components available at a given time. High level control reasons in “component space” in order to maximize the number operational component-cells over time, while the task-level controls sensors and effectors, detects collisions, and carries out pick and place tasks in “physical space.” Situated reasoning is used throughout the system to cope with, for example, nondeterministic component failures, the uncertain effects of task-level actions, and the actions of external agents operating in the domain.

European retrievable carrier Eureca servicing by Hermes

It has been demonstrated that HERMES with a cargo bay configuration as depicted in figure 1 (5 m length, 3 m diam.) with Handling and Positioning Aid (HPA) and HERMES Robotic Arm (HERA) is capable to service a small platform like EURECA, which is an NSTS quarter payload. Only 1 3 of the HERMES cargo bay volume and payload mass is required for the accommodation of the payload Orbital Replaceable Units. By implementing two additional hydrazine tanks refuelling can be avoided for a two-years EURECA mission. The overall servicing configuration is described as follows: The European Retrievable Carrier EURECA-B is mechanically attached through its -y-side sill trunnion to the HERMES berthing port. The HERMES cargo bay doors with radiators are opened and oriented to earth. The HERMES Robotic Arm is equipped with a Module Service Tool (MST) ready for Orbital Replaceable Unit (ORU) exchange. The HERMES berthing port is located at the rear side of the cargo bay in order to achieve best visibility, clearance and accessibility of the HERMES Robotic Arm operation within the cargo bay and the EURECA payload area. The EURECA solar arrays and antennas remain deployed. During the servicing operation, power will be provided by the fully deployed solar arrays. In order to minimize the plume impingement effect, the solar array edge is directed to the HERMES wing.

Telerobotic Control of a Dextrous Manipulator Using Master and Six-Dof Hand Controllers for Space Assembly and Servicing Tasks

Two studies were conducted evaluating methods of controlling a telerobot: bilateral force reflecting master controllers and proportional rate six degrees of freedom (DOF) hand controllers. The first study compared the controllers on performance of single manipulator arm tasks, a peg-in-the-hole task, and simulated satellite orbital replacement unit changeout. The second study, a Space Station truss assembly task, required simultaneous operation of both manipulator arms (all 12 DOFs) and complex multiaxis slave arm movements. Task times were significantly longer and fewer errors were committed with the hand controllers. The hand controllers were also rated significantly higher in cognitive and manual control workload on the two-arm task. The master controllers were rated significantly higher in physical workload. There were no significant differences in ratings of manipulator control quality.

Space-based servicing

On-orbit servicing of spacecraft and payloads is one of the most viable economic justification for a permanent, manned space station. Services include the changeout of Orbital Replaceable Units (ORU's), the replenishment of consumables, general maintenance, on-orbit assembly and repair of failures. Among economic and operational advantages are: longer spacecraft operational lifetime; lower acquisition cost of satellites; improved spacecraft performance. A comparison is made between space station and shuttle-based servicing.