Fault tolerant kinematic control of hyper-redundant manipulators

Hyper-redundant spatial manipulators possess fault-tolerant features because of their redundant structure. The kinematic control of these manipulators is investigated with special emphasis on fault-tolerant control. The manipulator tasks are viewed in the end-effector space while actuator commands are in joint-space, requiring an inverse kinematic algorithm to generate joint-angle commands from the end-effector ones. The rate-inverse kinematic control algorithm presented in this paper utilizes the pseudoinverse to accommodate for joint motor failures. An optimal scale factor for the robust inverse is derived

XNsim: Internet-Enabled Collaborative Distributed Simulation via an Extensible Network

In this paper, the XNsim approach to achieve Internet-enabled, dynamically scalable collaborative distributed simulation capabilities is presented. With this approach, a complete simulation can be assembled from shared component subsystems written in different formats, that run on different computing platforms, with different sampling rates, in different geographic locations, and over singlelmultiple networks. The subsystems interact securely with each other via the Internet. Furthermore, the simulation topology can be dynamically modified. The distributed simulation uses a combination of hub-and-spoke and peer-topeer network topology. A proof-of-concept demonstrator is also presented. The XNsim demonstrator can be accessed at http://www.jsc.draver.corn/xn that hosts various examples of Internet enabled simulations

Zero-propellant maneuver guidance

To maintain its orbit and control its attitude, the International Space Station (ISS) is equipped with thrusters as well as four control moment gyroscopes (CMGs). The CMGs can be used only for attitude control, while the thrusters can be used for either attitude control or orbit corrections. For attitude control, thrusters can complete reorientations much more rapidly than the CMGs since the torque capability of the thrusters is at least an order of magnitude larger than the torque capability of the CMGs. However, using thrusters has signifi cant disadvantages, such as consumption of propellant, solar array contamination, and stressing of the ISS structure. CMGs can avoid these disadvantages as long as they operate within their angular momentum capacity because they are powered by electricity generated by the ISS solar arrays. If the CMG momentum becomes saturated, that is, the total angular momentum of the CMGs reaches its maximum value, the control authority of the CMGs is considered lost. For further information about CMGs and saturation, see “CMGs, Momentum Saturation, and Robotics Analogy.” Even at a slow rate of rotation, large-angle ISS maneuvers performed with CMGs can result in momentum saturation because the CMGs must compensate for the environmental disturbance torques on the ISS along the fl ight-software-generated attitude trajectory. As a result, until 2006 all large-angle ISS rotations were performed using thrusters.NASA Glenn Research CenterThe Charles Stark Draper Laboratory, Inc.NASA contract NNJ06HC37

Pseudospectral Optimal Control for Military and Industrial Applications

Abstract—During the last decade, pseudospectral methods for optimal control, the focus of this tutorial session, have been rapidly developed as a powerful tool to enable new applications that were previously considered impossible due to the complicated nature of these problems. The purpose of this tutorial section is to introduce this advanced technology to a wider community of control system engineering. We bring in experts of pseudospectral methods from academia, industry, and military and DoD to present topics covering a large spectrum of pseudospectral methods, including the theoretical foundation, numerical techniques of pseudospectral optimal control, and military/industry applications. Over the last few years, pseudospectral (PS) methods for solving optimal control problems have moved rapidly from mathematical theory to real-world applications. For example