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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Asymptotic unbounded root loci - Formulas and computation

A new geometric way of computing the asymptotic behavior of unbounded root loci of a strictly proper linear time-invariant control system as loop gain goes to infinity is presented. Properties of certain restricted linear maps and nested restrictions of linear maps are developed, and formulas are obtained for the leading coefficient of the asymptotic values of the unbounded multivariable root loci are obtained in terms of eigenvalues of those maps. Published results and a certain simple null structure assumption are used to relate these asymptotic values to the structure at infinity of the Smith-McMillan form of the open loop transfer function. Explicit matrix formulas for the more abstract derived formulas are given and additional geometric insights are developed with orthogonal projections and singular value decomposition. Formulas for the pivots of the unbounded root loci are calculated and shown to have the same form as the coefficients of the unbounded asymptotic root loci.

Sastry, S. S.↗
NASA NTRS2014

Addressing the Hard Factors for Command File Errors by Probabilistic Reasoning

Command File Errors (CFE) are managed using standard risk management approaches at the Jet Propulsion Laboratory. Over the last few years, more emphasis has been made on the collection, organization, and analysis of these errors for the purpose of reducing the CFE rates. More recently, probabilistic modeling techniques have been used for more in depth analysis of the perceived error rates of the DAWN mission and for managing the soft factors in the upcoming phases of the mission. We broadly classify the factors that can lead to CFE's as soft factors, which relate to the cognition of the operators and hard factors which relate to the Mission System which is composed of the hardware, software and procedures used for the generation, verification & validation and execution of commands. The focus of this paper is to use probabilistic models that represent multiple missions at JPL to determine the root cause and sensitivities of the various components of the mission system and develop recommendations and techniques for addressing them. The customization of these multi-mission models to a sample interplanetary spacecraft is done for this purpose.

Meshkat, Leila↗
NASA NTRS2021

Performance Assessment of a Western Range 915-MHz Doppler Radar Wind Profiler

Please find enclosed the performance assessment for a Western Range 915-MHz Doppler Radar Wind Profiler (DRWP). This assessment was conducted following the installation of the new DRWP systems at the Western and Eastern Ranges. DRWP profiles were compared to Automated Meteorological Profiling System balloons launched from Vandenberg Space Force Base. Balloon data was collected from both normal synoptic and launch operations as well as some releases at the DRWP site. These results will include errors due to the spatial separation of winds. Root Mean Square wind speed deltas between the balloons and DRWP system mainly ranged between 1.0 and 2.3 m/s. Mean wind direction deltas mainly ranged between 10 and 28 degrees for wind speeds greater than or equal to 4 m/s. Data availability at discrete altitudes ranged from 20% to 94% with the least amount of available profiles being in the lower altitude ranges between 100 m and 500 m. The effective vertical resolution was determined to be approximately 250 m. The results from this analysis were requested by the United States Space Force for use of the acceptance of the DRWP system and for internal EV44 reference.

B J Barbre↗
NASA NTRS2009

Root Cause Assessment of Pressure Drop Rise of a Packed Bed of Lithium Hydroxide in the International Space Station Trace Contaminant Control System

The trace contaminant control system (TCCS) located in the International Space Station s (ISS) U.S. laboratory module employs physical adsorption, thermal catalytic oxidation, and chemical adsorption to remove trace chemical contamination produced by equipment offgassing and anthropogenic sources from the cabin atmosphere. The chemical adsorption stage, consisting of a packed bed of granular lithium hydroxide (LiOH), is located after the thermal catalytic oxidation stage and is designed to remove acid gas byproducts that may be formed in the upstream oxidation stage. While in service on board the ISS, the LiOH bed exhibited a change in flow resistance that leading to flow control difficulties in the TCCS. Post flight evaluation revealed LiOH granule size attrition among other changes. An experimental program was employed to investigate mechanisms hypothesized to contribute to the change in the packed bed s flow resistance. Background on the problem is summarized, including a discussion of likely mechanisms. The experimental program is described, results are presented, and implications for the future are discussed.

Aguilera, Tatiana↗
NASA NTRS1986

Analysis of growth patterns during gravitropic curvature in roots of Zea mays by use of a computer-based video digitizer

A computer-based video digitizer system is described which allows automated tracking of markers placed on a plant surface. The system uses customized software to calculate relative growth rates at selected positions along the plant surface and to determine rates of gravitropic curvature based on the changing pattern of distribution of the surface markers. The system was used to study the time course of gravitropic curvature and changes in relative growth rate along the upper and lower surface of horizontally-oriented roots of maize (Zea mays L.). The growing region of the root was found to extend from about 1 mm behind the tip to approximately 6 mm behind the tip. In vertically-oriented roots the relative growth rate was maximal at about 2.5 mm behind the tip and declined smoothly on either side of the maximum. Curvature was initiated approximately 30 min after horizontal orientation with maximal (50 degrees) curvature being attained in 3 h. Analysis of surface extension patterns during the response indicated that curvature results from a reduction in growth rate along both the upper and lower surfaces with stronger reduction along the lower surface.

NASA Discipline Plant Biology↗
NASA NTRS1985

Aquatic Plants Aid Sewage Filter

Method of wastewater treatment combines micro-organisms and aquatic plant roots in filter bed. Treatment occurs as liquid flows up through system. Micro-organisms, attached themselves to rocky base material of filter, act in several steps to decompose organic matter in wastewater. Vascular aquatic plants (typically, reeds, rushes, cattails, or water hyacinths) absorb nitrogen, phosphorus, other nutrients, and heavy metals from water through finely divided roots.

Wolverton, B. C.↗
NASA NTRS1993

Octave: A MARSYAS post-processor for computer-aideed control system design

MARSYAS is a computer-aided control system analysis package for the simulation and analysis of dynamic systems. In the summer of 1991 MARSYAS was updated to allow for the analysis of sampled-data systems in terms of frequency response, stability, etc. This update was continued during the summer of 1992 in order to extend further MARSYAS commands to the study of sampled data systems. Further work was done to examine the computation of openat transfer functions, root-locii and omega-plane frequency response plots. At the conclusion of the summer of 1992 work, it was proposed that control-system design capability be incorporated into the MARSYAS package. It was decided at that time to develop a separate 'stand-alone' computer-aided control system design (CACSD) package. This report is a brief description of such a package.

Hodel, A. Scottedward↗
NASA NTRS1985

The Capillary Pumped Loop (CPL) GAS experiment G-471

The Capillary Pumped Loop (CPL) experiment, 6-471 is a thermal control system with high density heat acquisition and transport capability. The CPL consists of two capillary pumped evaporators with integral heaters, a fluid loop charged with ammonia (NH3), a condenser plate (heat sink), and various control electronics. The purpose of the experiment is to demonstrate the capability of a capillary pumped system under zero gravity conditions for use in the thermal control of large scientific instruments, advanced orbiting spacecraft, and space station components. A unique feature of the CPL is the capillary pumps, which contain no moving parts. Each pump contains a wick of porous material which is saturated with the working fluid (anhydrous ammonia). As heat is added to the fluid, it evaporates and travels to the condenser, thus transporting the heat (via the latent heat of vaporization) from the heat source to its sink at nearly a constant temperature. The evaporation process produces the pressure gradient or pumping action that circulates the fluid. This is the same principal that plants and trees use to transport water and nutrients from their roots to their leaves against gravity. The difference is that the CPL employs a closed system to return the fluid directly to the pumps, whereas "Mother Nature'' has an open system where the fluid is indirectly returned to the roots by condensation of water from the clouds in the form of rain. It should be noted that the CPL experiment was the first flight of a thermal control system of this type. It was also the first shuttle experiment from the Space Station Advanced Development Program.

Dan Butler↗
NASA NTRS1974

A movable-mass attitude stabilization system for cable-connected artificial-g space stations

The development of an active, momentum-exchange system to be used for attitude stabilization of a class of cable-connected artificial-g space stations is studied. A system which employs a single movable control mass is examined for the control of a space station which has the physical appearance of two cylinders connected axially by cables. The dynamic model for the space station includes its aggregate rigid body rotation and relative torsional rotation between the bodies. A zero torsional stiffness design (one cable) and a maximum torsional stiffness design (eight cables) are examined in various stages of deployment, for selected spin velocities ranging from 4 rpm upwards. A linear, time-invariant, feed-back control system is employed, with gains calculated via a root-specification procedure. The movable mass controller provides critical wobble-damping capability for the crew quarters for all configurations and spin velocity.

Childs, D. W.↗
NASA NTRS1977

Systems for measuring response statistics of gigahertz bandwidth photomultipliers

New systems have been developed for measuring the average impulse response, the pulse-height spectrum, the transit-time statistics as a function of signal level, and the dark-count spectrum of gigahertz bandwidth photomultipliers. Measurements showed that the 0.53 microns pulse used as an optical test source had a 30 picoseconds and less than 70 ps pulse width. Calibration data showed the system resolution to be less than 20 ps for root mean square transit-time measurements. Test data for a static crossed-field photomultiplier showed 2-photoelectron resolution and less than 30-ps time jitter over the 1- to 100-photoelectron range.

Abshire, J. B.↗
NASA NTRS1985

The experimental results of a self tuning adaptive controller using online frequency identification

A fourth-order laboratory dynamic system featuring very low structural damping and a noncolocated actuator-sensor pair has been used to test a novel real-time adaptive controller, implemented in a minicomputer, which consists of a state estimator, a set of state feedback gains, and a frequency-locked loop for real-time parameter identification. The adaptation algorithm employed can correct controller error and stabilize the system for more than 50 percent variation in the plant's natural frequency, compared with a 10 percent stability margin in frequency variation for a fixed gain controller having the same performance as the nominal plant condition. The very rapid convergence achievable by this adaptive system is demonstrated experimentally, and proven with simple, root-locus methods.

Chiang, W.-W.↗
NASA NTRS1988

Strain accumulation in quasicrystalline solids

The relaxation of two-dimensional quasicrystalline elastic networks when their constituent bonds are perturbed homogeneously is studied. Whereas ideal, quasi-periodic networks are stable against such perturbations, significant accumulations of strain in a class of disordered networks generated by a growth process are found. The grown networks are characterized by root mean square phason fluctuations which grow linearly with system size. The strain accumulation observed in these networks also grows linearly with system size. Finally, dependence of strain accumulation on cooling rate is found.

Nori, Franco↗
NASA NTRS1991

Stability of Intershaft Squeeze Film Dampers

Intershaft squeeze film dampers were investigated for damping of dual rotor aircraft jet engines. It was thought that the intershaft damper would enhance the stability of the rotor-bearing system. Unfortunately, it was determined that the intershaft squeeze film damper was unstable above the engine's first critical speed. Here, a stability analysis of rotors incorporating intershaft squeeze film dampers is discussed. A rotor model consisting of two Jeffcott rotors with two intershaft squeeze film dampers was investigated. Examining the system characteristic equation for the conditions at which the roots indicate an ever-growing unstable motion results in the stability conditions. The cause of the instability is identified as the rotation of the oil in the damper clearance. Several proposed configurations of intershaft squeeze film dampers are discussed, and it is shown that the intershaft dampers are stable supercritically only with a configuration in which the oil film does not rotate.

El-Shafei, A.↗
NASA NTRS1994

Application of the GEM-T2 gravity field to altimetric satellite orbit computation

As part of a continuing effort to provide improved orbits for use with existing altimeter data, we have recomputed ephemerides for both the Seasat and Geosat Exact Repeat altimeter missions. The orbits were computed in a consistent fashion, using the Goddard Earth Model T2 (GEM-T2) gravity field along with available ground-based tracking data. Such an approach allows direct comparisons of sea level between the two altimeter systems. Evaluation of the resulting ephemerides indicates that root-mean-square accuracies of 30-50 cm have been achieved for the radial component of the orbits for both satellites. An exception occurs for the last year of the Geosat Exact Repeat Mission, when the rms radial orbit accuracy degrades to the 1-m level at times owing to the inability to adequately model the drag force arising from the increased solar activity.

Haines, Bruce J.↗
NASA NTRS1989

Precision Segmented Reflectors (PSR)

Current Precision Segmented Reflectors (PSR) technology development is intended for LDR-like applications: (1) Large segmented reflector systems; (2) Lightweight composite panels at 3 micron root-mean-square (RMS); (3) Precision lightweight structure at 500 microns; (4) Active figure control at 1 micron RMS accuracy; and (5) 5 micron RMS overall surface accuracy. Development of PSR technologies to date has demonstrated the potential of: (1) Lightweight composite panels at 0.1 micron RMS via polishing and re-finishing; (2) Shape control of composite panels by imbedded actuators; (3) Precision lightweight structure at 100 microns or better; and (4) Smart structure strut that can suppress vibrations and change its length.

Lin, Richard Y.↗
NASA NTRS2004

Development of a Self-calibrating Dissolved Oxygen Microsensor Array for the Monitoring and Control of Plant Growth in a Space Environment

Plant experiments in space will require active nutrient delivery concepts in which water and nutrients are replenished on a continuous basis for long-term growth. The goal of this study is to develop a novel microsensor array to provide information on the dissolved oxygen environment in the plant root zone for the optimum control of plant cultivation systems in the space environment. Control of water and oxygen is limited by the current state-of-the-art in sensor technology. Two capabilities of the new microsensor array were tested. First, a novel in situ self-diagnosis/self-calibration capability for the microsensor was explored by dynamically controlling the oxygen microenvironment in close proximity to an amperometric dissolved oxygen microsensors. A pair of integrated electrochemical actuator electrodes provided the microenvironments based on water electrolysis. Miniaturized thin film dissolved oxygen microsensors on a flexible polyimide (Kapton(Registered Trademark)? substrate were fabricated and their performances were tested. Secondly, measurements of dissolved oxygen in two representative plant growth systems were made, which had not been performed previously due to lack of proper sensing technology. The responses of the oxygen microsensor array on a flexible polymer substrate properly reflected the oxygen contents on the surface of a porous tube nutrient delivery system and within a particulate substrate system. Additionally, we demonstrated the feasibility of using a 4-point thin film microprobe for water contents measurements for both plant growth systems. mechanical flexibility, and self-diagnosis. The proposed technology is anticipated to provide a reliable sensor feedback plant growth nutrient delivery systems in both terrestrial environment and the microgravity environment during long term space missions. The unique features of the sensor include small size and volume, multiple-point sensing,

Kim, Chang-Soo↗
NASA NTRS2012

Automated Sequence Processor: Something Old, Something New

High productivity required for operations teams to meet schedules Risk must be minimized. Scripting used to automate processes. Scripts perform essential operations functions. Automated Sequence Processor (ASP) was a grass-roots task built to automate the command uplink process System engineering task for ASP revitalization organized. ASP is a set of approximately 200 scripts written in Perl, C Shell, AWK and other scripting languages.. ASP processes/checks/packages non-interactive commands automatically.. Non-interactive commands are guaranteed to be safe and have been checked by hardware or software simulators.. ASP checks that commands are non-interactive.. ASP processes the commands through a command. simulator and then packages them if there are no errors.. ASP must be active 24 hours/day, 7 days/week..

Automated↗