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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Advanced communication system time domain modeling techniques ASYSTD software description. Volume 2: Program support documentation

The theoretical basis for the ASYSTD program is discussed in detail. In addition, the extensive bibliography given in this document illustrates some of the extensive work accomplished in the area of time domain simulation. Additions have been in the areas of modeling and language program enhancements, orthogonal transform modeling, error analysis, general filter models, BER measurements, etc. Several models have been developed which utilize the COMSAT generated orthogonal transform algorithms.

Source record↗
NASA NTRS1976

Analysis and application of minimum variance discrete time system identification

An on-line minimum variance parameter identifier was developed which embodies both accuracy and computational efficiency. The new formulation resulted in a linear estimation problem with both additive and multiplicative noise. The resulting filter is shown to utilize both the covariance of the parameter vector itself and the covariance of the error in identification. It is proven that the identification filter is mean square covergent and mean square consistent. The MV parameter identification scheme is then used to construct a stable state and parameter estimation algorithm.

Kotob, S.↗
NASA NTRS1975

Analysis and application of minimum variance discrete time system identification

An on-line minimum variance parameter identifier is developed which embodies both accuracy and computational efficiency. The formulation results in a linear estimation problem with both additive and multiplicative noise. The resulting filter which utilizes both the covariance of the parameter vector itself and the covariance of the error in identification is proven to be mean square convergent and mean square consistent. The MV parameter identification scheme is then used to construct a stable state and parameter estimation algorithm.

Kaufman, H.↗
NASA NTRS1976

Analysis and application of minimum variance discrete time system identification

An on-line minimum variance parameter identifier is developed which embodies both accuracy and computational efficiency. The formulation results in a linear estimation problem with both additive and multiplicative noise. The resulting filter which utilizes both the covariance of the parameter vector itself and the covariance of the error in identification is proven to be mean square convergent and mean square consistent. The MV parameter identification scheme is then used to construct a stable state and parameter estimation algorithm.

Kotob, S.↗
NASA NTRS1989

Gravitational biology and the mammalian circadian timing system

Using published reports, this paper compares and contrasts results on the effects of altered gravitational fields on the regulation in mammals of several physiological and behavioral variables with the circadian regulation of the same variables. The variables considered include the temperature regulation, heart rate, activity, food intake, and calcium balance. It is shown that, in rats, the homeostatic regulation of the body temperature, heart rate, and activity becomes depressed following exposure to a 2 G hyperdynamic field, and recovers within 6 days of 1 G condition. In addition, the circadian rhythms of these variables exhibit a depression of the rhythm amplitude; a recovery of this condition requires a minimum of 7 days.

Fuller, Charles A.↗
NASA NTRS1991

A design approach for ultrareliable real-time systems

A design approach developed over the past few years to formalize redundancy management and validation is described. Redundant elements are partitioned into individual fault-containment regions (FCRs). An FCR is a collection of components that operates correctly regardless of any arbitrary logical or electrical fault outside the region. Conversely, a fault in an FCR cannot cause hardware outside the region to fail. The outputs of all channels are required to agree bit-for-bit under no-fault conditions (exact bitwise consensus). Synchronization, input agreement, and input validity conditions are discussed. The Advanced Information Processing System (AIPS), which is a fault-tolerant distributed architecture based on this approach, is described. A brief overview of recent applications of these systems and current research is presented.

Lala, Jaynarayan H.↗
NASA NTRS1973

Modeling of linear time-varying systems by linear time-invariant systems of lower order.

A method for modeling linear time-varying differential systems by linear time-invariant systems of lower order is proposed, extending the results obtained by Bierman (1972) by resolving such qualities as the model stability, various possible models of differing dimensions, and the uniqueness or nonuniqueness of the model coefficient matrix. In addition to the advantages cited by Heffes and Sarachik (1969) and Bierman, often by modeling a subsystem of a larger system it is possible to analyze the overall system behavior more easily, with resulting savings in computation time.

Nosrati, H.↗
NASA NTRS1987

Timing Control System

A timing control system is disclosed which is particularly useful in connection with simulated mortar shells. Special circuitry is provided to assure that the shell does not over shoot, but rather detonates early in case of an improper condition; this ensures that ground personnel will not be harmed by a delayed detonation. The system responds to an externally applied frequency control code which is configured to avoid any confusion between different control modes. A premature detonation routine is entered in case an improper time-setting signal is entered, or if the shell is launched before completion of the time-setting sequence. Special provisions are also made for very early launch situations and improper detonator connections. An alternate abort mode is provided to discharge the internal power supply without a detonation in a manner that can be externally monitored, thereby providing a mechanism for non-destructive testing. The abort mode also accelerates the timing function for rapid testing.

Wiker, Gordon A.↗
NASA NTRS1989

Timing control system

A timing control system is disclosed which is particularly useful in connection with simulated mortar shells. Special circuitry is provided to assure that the shell does not overshoot, but rather detonates early in case of an improper condition; this ensures that ground personnel will not be harmed by a delayed detonation. The system responds to an externally applied frequency control code which is configured to avoid any confusion between different control modes. A premature detonation routine is entered in case an improper time-setting signal is entered, or if the shell is launched before completion of the time-setting sequence. Special provisions are also made for very early launch situations and improper detonator connections. An alternate abort mode is provided to discharge the internal power supply without a detonation in a manner that can be externally monitored, thereby providing a mechanism for non-destructive testing. The abort mode also accelerates the timing function for rapid testing.

Wiker, Gordon A.↗
NASA NTRS1985

Satellite Time- and Frequency-Transfer System

Time synchronized at distant points within nanosecond. Report describes satellite-borne time-and frequency-transfer system proposed for synchronization of clocks at stations around Earth. Orbiting hydrogen-maser clock and frequency standard communicate by microwave links with Earth stations using hydrogen masers as local clocks. Pulsed-laser time-transfer sub-system also operated concurrently, either synchronized or unsynchronized with microwave subsystems.

Vessot, R. F. C.↗
NASA NTRS1994

Performance results of cooperating expert systems in a distributed real-time monitoring system

There are numerous definitions for real-time systems, the most stringent of which involve guaranteeing correct system response within a domain-dependent or situationally defined period of time. For applications such as diagnosis, in which the time required to produce a solution can be non-deterministic, this requirement poses a unique set of challenges in dynamic modification of solution strategy that conforms with maximum possible latencies. However, another definition of real time is relevant in the case of monitoring systems where failure to supply a response in the proper (and often infinitesimal) amount of time allowed does not make the solution less useful (or, in the extreme example of a monitoring system responsible for detecting and deflecting enemy missiles, completely irrelevant). This more casual definition involves responding to data at the same rate at which it is produced, and is more appropriate for monitoring applications with softer real-time constraints, such as interplanetary exploration, which results in massive quantities of data transmitted at the speed of light for a number of hours before it even reaches the monitoring system. The latter definition of real time has been applied to the MARVEL system for automated monitoring and diagnosis of spacecraft telemetry. An early version of this system has been in continuous operational use since it was first deployed in 1989 for the Voyager encounter with Neptune. This system remained under incremental development until 1991 and has been under routine maintenance in operations since then, while continuing to serve as an artificial intelligence (AI) testbed in the laboratory. The system architecture has been designed to facilitate concurrent and cooperative processing by multiple diagnostic expert systems in a hierarchical organization. The diagnostic modules adhere to concepts of data-driven reasoning, constrained but complete nonoverlapping domains, metaknowledge of global consequences of anomalous data, hierarchical reporting of problems that extend beyond a single domain, and shared responsibility for problems that overlap domains. The system enables efficient diagnosis of complex system failures in real-time environments with high data volumes and moderate failure rates, as indicated by extensive performance measurements.

Schwuttke, U. M.↗