Real-time dynamic simulation of the Cassini spacecraft using DARTS. Part 2: Parallel/vectorized real-time implementation

Part 1 of this paper presented the requirements for the real-time simulation of Cassini spacecraft along with some discussion of the DARTS algorithm. Here, in Part 2 we discuss the development and implementation of parallel/vectorized DARTS algorithm and architecture for real-time simulation. Development of the fast algorithms and architecture for real-time hardware-in-the-loop simulation of spacecraft dynamics is motivated by the fact that it represents a hard real-time problem, in the sense that the correctness of the simulation depends on both the numerical accuracy and the exact timing of the computation. For a given model fidelity, the computation should be computed within a predefined time period. Further reduction in computation time allows increasing the fidelity of the model (i.e., inclusion of more flexible modes) and the integration routine

Intelligent Elements for the ISHM Testbed and Prototypes (ITP) Project

Deep-space manned missions will require advanced automated health assessment capabilities. Requirements such as in-space assembly, long dormant periods and limited accessibility during flight, present significant challenges that should be addressed through Integrated System Health Management (ISHM). The ISHM approach will provide safety and reliability coverage for a complete system over its entire life cycle by determining and integrating health status and performance information from the subsystem and component levels. This paper will focus on the potential advanced diagnostic elements that will provide intelligent assessment of the subsystem health and the planned implementation of these elements in the ISHM Testbed and Prototypes (ITP) Project under the NASA Exploration Systems Research and Technology program

Simulation and experiments on friction and wear of diamond: a material for MEMS and NEMS application

To date most of the microelectromechanical system (MEMS) devices have been based on silicon. This is due to the technological know-how accumulated on the manipulation, machining and manufacturing of silicon. However, only very few devices involve moving parts. This is because of the rapid wear arising from high friction in these silicon-based systems. Recent tribometric experiments carried out by Gardos on silicon and polycrystalline diamond (PCD) show that this rapid wear is caused by a variety of factors, related both to surface chemistry and cohesive energy density of these likely MEMS bearing materials. In particular, the 1.8-times stronger C-C bond in diamond as opposed to the Si-Si bond in the bulk translates into a more than 104-times difference in wear rates, even though the difference in flexural strength is only 20-times, in hardness 10-times and in fracture toughness 5-times. It also has been shown that the wear rates of silicon and PCD are controlled by high-friction-induced surface cracking, and the friction is controlled by the number of dangling, reconstructed or adsorbate-passivated surface bonds. Therefore, theoretical and tribological characterization of Si and PCD surfaces is essential prior to device fabrication to assure reliable MEMS operation under various atmospheric environments, especially at elevated temperatures. As a part of the rational design and manufacturing of MEMS devices containing moving mechanical assemblies (MEMS-MMA) and especially nanoelectromechanical devices (NEMS), theory and simulation can play an important role. Predicting system properties such as friction and wear, and materials properties such as thermal conductivity is of critical importance for materials and components to be used in MEMS-MMAs. In this paper, we present theoretical studies of friction and wear processes on diamond surfaces using a steady state molecular dynamics method. We studied the atomic friction of the diamond-(100) surface using an extended bond-order-dependent potential for hydrocarbon systems. Unlike traditional empirical potentials, bond order potentials can simulate bond breaking and formation processes. Therefore, it is a natural choice to study surface dynamics under friction and wear. In order to calculate the material properties correctly, we have established a consistent approach to incorporate non-bond interactions into the bond order potentials. We have also developed an easy-to-use software to evaluate the atomic-level friction coefficient for an arbitrary system, and interfaced it into a third-party graphical software

BLUEPRINT OF AN EFFICIENT MODEL-BASED DIAGNOSIS ENGINE*

The most widely used approach to model-based diagnosis consists of a two-step process: (1) Generating conflict sets from symptoms; (2) Calculating minimal diagnosis set from the conflicts. Here a conflict set is a set of assumptions on the modes of some components that is not consistent with the model of the system and observations, and a minimal diagnosis is a set of the consistent assumptions of the modes of all components with minimal number of abnormal components. However, there are major drawbacks in the current model-based diagnosis techniques in efficiently performing the above two steps that severely limit their practical application to many systems of interest. For conflict generating problem, these techniques are usually based on different versions of Truth Maintenance (TM) method, which lead to exhaustive search in the space of possible modes of the components. The most common method for finding minimal diagnosis from the conflicts is based on Reiter’s algorithm [9], which requires both exponential time and exponential space (memory) to be implemented. In order to overcome these limitations, we propose a novel and two-fold approach: First, we propose a new approach for generating conflict sets based on mapping this problem onto the well-studied problem of finding paths in a graph [5]. This approach can significantly accelerate the conflict generation step by bounding the search space and thus avoiding unnecessary search. Second, we propose a novel algorithmic approach and a set of new algorithms for calculation of minimal diagnosis set, which is an inherently intractable (NP-complete) problem [3]. However, our new approach allows the development of new algorithms that enable more efficient solution for large and realistic problems. More specifically, our new approach allows us to calculate the lower and upper bounds on the size of the solution. Utilizing these new insights, we are able to develop a new version of the branch-and-bound method for solving the problem

Novel algorithm for computation of inverse kinematics and inverse dynamics of Gough-Stewart platform

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