Robustness Analysis and Robust Design of Uncertain Systems

Langley Research Center, Hampton, Virginia A methodology was developed for the analysis and design of systems subject to parametric uncertainty in which design requirements are specified via hard inequality constraints. Hard constraints are those that must be satisfied for all parameter realizations within a given uncertainty model. Uncertainty models are given by norm-bounded perturbations from a nominal parameter value (i.e., hyperspheres) and by sets of independently bounded uncertain variables (i.e., hyperrectangles). These models, which are also quite practical, allow for a rigorous mathematical treatment within the proposed framework. Hardconstraint feasibility is determined by sizing the largest uncertainty set for which the design requirements are satisfied.

Posted in: Briefs, Electronics & Computers, Software, Mathematical models, Durability


XDB3 Extension for Equality and Relational Operators

Ames Research Center, Moffett Field, California While keyword full-text searches work well for textual data, they do not work well for numeric, date, or other more highly structured information. In particular, Netmark/XDB could retrieve any record where the author contained “Knight” in the text, but could not return only those records from Calendar Year 2010 that have “Knight” in their author section. Traditional relational databases allow for rich comparison “relational” operators; for example, one can express a query such as “return all rows where the signature date is on January 1, 2010.” Netmark/XDB, being primarily targeted at XML processing and retrieving XML-structured data, was designed for full-text querying to find keywords. Most other XML indexing and querying systems also are designed with the assumption that content (“CDATA”) is textual or binary data that can be queried against, but not with relational comparison operators like “greater than a value.”

Posted in: Briefs, Electronics & Computers, Software, Computer software and hardware, Data acquisition and handling, Terminology


Simulator for a Self-Stabilizing Synchronization Protocol for Arbitrary Digraphs

Langley Research Center, Hampton, Virginia This work was conducted to create a means of simulating and visualizing the behavior of a self-stabilizing distributed clock synchronization protocol developed at LaRC (Langley Research Center). The protocol has many applications including projects that directly pertain to work being done at NASA. Time synchronization is a critical component of many projects, from computer networking and distributed systems, to autonomous flight. This easy-to-understand interface both displays accurate information concerning the protocol, and conveys its utility.

Posted in: Briefs, Electronics & Computers, Software, Computer simulation, Mathematical models, Displays


Testing Encapsulation of Internet, DTN, and LTP Traffic over AOS Space Data Link Protocol

NASA’s Jet Propulsion Laboratory, Pasadena, California The CCSDS ENCAP Over AOS Over UDP software engine encapsulates live Internet Protocol (IP), DTN Bundle Protocol (BP), or Licklider Transport Protocol (LTP) traffic over a Consultative Committee for Space Data Systems (CCSDS)-compliant Encapsulation Ser vice (ENCAP) running over an Advanced Orbiting Systems (AOS) data link protocol UDP stream. Many space missions currently use the AOS protocol, and this software is an implementation of a standard mechanism to encapsulate Internet Protocol traffic (including interactive Web applications and streaming video) and DTN Bundle Protocol traffic (for large file transfers over high latency links) over ENCAP over AOS.

Posted in: Briefs, Electronics & Computers, Software, Communication protocols, Data exchange, Internet, Satellite communications


Predicting Magnetospheric Relativistic >1 MeV Electrons

NASA’s Jet Propulsion Laboratory, Pasadena, California There is an association between High-Intensity Long-Duration Continuous AE (HILDCAA) activity intervals and the acceleration of relativistic >1 MeV electrons in the magnetosphere. All of the HILDCAAs that occurred in solar cycle 23 (SC23) from 1995 to 2008 led to the acceleration of E>0.6 MeV, >2.0 MeV, and >4.0 MeV electrons in the Earth’s outer radiation belts. What is particularly noteworthy is that the E>0.6 MeV electron acceleration was delayed ~1.0 day after the onset of the HILDCAA event, the E>2.0 MeV electrons delayed ~1.5 days after the onset of the HILDCAA event, and the E>4.0 MeV electrons delayed ~2.5 days after the onset of the HILDCAA event.

Posted in: Briefs, Software, Mathematical analysis, Measurements, Radiation, Spacecraft


Optimal Prioritized Actuator Allocation

This allocation could improve the safety and autonomy of missions where it is critical to match torque first to minimize disturbances to spacecraft pointing. NASA’s Jet Propulsion Laboratory, Pasadena, California For formation flying, rendezvous and docking, and proximity operations with small bodies of the solar system, spacecraft require simultaneous translational and rotational agility. The necessary agility is generally provided by combinations of multiple small thrusters and torque-only actuators. To use these actuators, an onboard control system first calculates desired forces and torques that cause a spacecraft to follow a desired trajectory. Then the commanded forces and torques are turned into individual commands to specific actuators such that the combined action of all the actuators realizes as closely as possible the commanded forces and torques. This problem is referred to as actuator (or control) allocation.

Posted in: Briefs, Software, Trajectory control, Sensors and actuators, Spacecraft guidance, Spacecraft


Terrain Model Registration

Model registration solves target tracking and target handoff problems. Ames Research Center, Moffett Field, California This technology is a method for registration of terrain models created using stereovision on a planetary rover. Most 3D model registration approaches use some variant of iterated closest point (ICP), which minimizes a norm based on the distances between corresponding points on an arbitrary 3D surface where closest points are taken to be corresponding points. The approach taken here instead projects the two surface models into a common viewpoint, rendering the models as they would be seen from a single range sensor. Correspondence is established by determining which points on the two surfaces project to the same location on the virtual range sensor image plane. The norm of the deviations in observed depth at all pixels is used as the objective function, and the algorithm finds the rigid transformation, which minimizes the norm. This recovered transformation can be used for visual odometry, rover pose estimation, and feature handoff.

Posted in: Briefs, Software, Mathematical models, Measurements, Imaging and visualization, Terrain, Spacecraft


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