Search NASA⌕ Search

SEARCH · Search NASA

Results for “Low Precision”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

In-flight simulation study of decoupled longitudinal controls for the approach and landing of a STOL aircraft

In this decoupled concept, the natural interactions of the flight variables were suppressed, and the pilot operated a separate controller for each (fore-and-aft control column for flight path angle without speed or pitch attitude change, for example). The handling qualities of the decoupled airplane were judged to be very favorable. The precise path control led to small touchdown point dispersion along with consistently low sink rates. The decoupled control system provided significantly better flying qualities than did conventional SAS applied to the same basic airframe.

Feinreich, B.↗
NASA NTRS1978

Subminiature hydraulic actuator

Subminiature, single-vane rotary actuator for wind-tunnel test-model control-surface actuation systems presents severe torque and system band-pass requirements with stringent space and weight limitations. Actuator has very low leakage of fluid from one side to other, permitting use in precision position servo-systems.

Sevart, F. D.↗
NASA NTRS1977

Cosmic ray investigation for the Voyager missions: Energetic particle studies in the outer heliosphere - and beyond

The Voyager mission cosmic ray detector system, consisting entirely of solid-state charged-particle detectors, is designed to measure the energy spectrum of electrons in the range 3 to 110 MeV and the energy spectra and elemental composition of cosmic ray nuclei from hydrogen through iron in the range 1 to 500 MeV/nuc; for isotopes of hydrogen through sulfur the range is approximately 2 to 75 MeV/nuc. The cosmic ray investigation deals with the energy content, origin and acceleration process, and dynamics of cosmic rays in the galaxy, with particular attention given to low-energy phenomena in interstellar space and the outer solar system. The precise measurement of three-dimensional stream patterns of nuclei from H to Fe, as well as electrons over a wide energy range, is the data acquisition program emphasized.

Stone, E. C.↗
NASA NTRS1979

Remote sensing using solid-state array technology

The paper describes the design features and capabilities of a remote sensor that uses solid-state linear arrays and operates in a 'pushbroom' scan mode to provide the required performance. Pushbroom scanning is a term describing the technique of using the forward motion of a satellite platform to sweep a linear array of detectors oriented perpendicular to the ground track across a scene being imaged. One array is typically used for each spectral channel. Satellite motion provides one direction of scan and electronic sampling of the detectors in the crosstrack dimension provides the orthogonal scan component to form an image. The detector array is sampled at the appropriate rate so that contiguous lines are produced. The performance of a pushbroom system is discussed relative to radiometric sensitivity, detector array geometric fidelity, and radiometric correction. System advantages are precision geometric positioning of the detectors, very high sensitivity and favorable SNR, low power consumption, and no moving optics.

Thompson, L. L.↗
NASA NTRS1980

Stabilization and control of the International Ultraviolet Explorer including a summary of flight performance

The paper discusses the International Ultraviolet Explorer Mission sequence, spacecraft equipment, and control laws. Flight data from the precision control modes are presented, to illustrate the performance achieved; the subarc second pointing at sources for 60 min periods is accomplished routinely. Two modes of precision control are available: one is of a bright guide star which is in the vicinity of the target source, so that the guidance mode includes a star tracker for position information and a gyro system for rate damping. When a guide star is not available, precision hold is accomplished solely on a well trimmed gyro reference with low frequency updates from a dim source. The three axis maneuvers, the maneuver angle, and the gyro data used are discussed, concluding that these data used in conjunction with star tracker data provide a good source of information for orbital performance evaluation.

Moore, J. V.↗
NASA NTRS1983

Airborne measurements of laser backscatter from the ocean surface

The data are taken with three different pulsed laser sources, one each in the ultraviolet (337.1 nm), visible (532.1 nm) and infrared (9.5 microns). The principal instrument is the airborne oceanographic lidar of the NASA Wallops Flight Facility. The data on mean laser backscatter and its variation with angle off nadir are found to be consistent with previous analytical work and some previous experimental work. The absolute calibration of this backscatter in terms of an effective Lambertian reflectance is less precise, but the data support values near nadir of approximately 0.20 for low wind speeds. It is noted that these values are 1 order of magnitude larger than the Fresnel reflectance for an air/water discontinuity in the refractive index. Whereas the normalized standard deviation (modulation factor) of backscatter is less well understood analytically, it is defined by these measurements to range from a few percent to over 50 percent at nadir and to increase off nadir as the tangent of theta or faster. The data are uncertain beyond 15 deg off nadir owing to a dynamic range limitation.

Bufton, J. L.↗
NASA NTRS1987

Integrated control and display research for transition and vertical flight on the NASA V/STOL Research Aircraft (VSRA)

Results of a substantial body of ground-based simulation experiments indicate that a high degree of precision of operation for recovery aboard small ships in heavy seas and low visibility with acceptable levels of effort by the pilot can be achieved by integrating the aircraft flight and propulsion controls. The availability of digital fly-by-wire controls makes it feasible to implement an integrated control design to achieve and demonstrate in flight the operational benefits promised by the simulation experience. It remains to validate these systems concepts in flight to establish their value for advanced short takeoff vertical landing (STOVL) aircraft designs. This paper summarizes analytical studies and simulation experiments which provide a basis for the flight research program that will develop and validate critical technologies for advanced STOVL aircraft through the development and evaluation of advanced, integrated control and display concepts, and lays out the plan for the flight program that will be conducted on NASA's V/STOL Research Aircraft (VSRA).

Foster, John D.↗
NASA NTRS1988

Integrated control and display research for transition and vertical flight on the NASA V/STOL Research Aircraft (VSRA)

Results of a substantial body of ground-based simulation experiments indicate that a high degree of precision of operation for recovery aboard small ships in heavy seas and low visibility with acceptable levels of effort by the pilot can be achieved by integrating the aircraft flight and propulsion controls. The availability of digital fly-by-wire controls makes it feasible to implement an integrated control design to achieve and demonstrate in flight the operational benefits promised by the simulation experience. It remains to validate these systems concepts in flight to establish their value for advanced short takeoff vertical landing (STOVL) aircraft designs. This paper summarizes analytical studies and simulation experiments which provide a basis for the flight research program that will develop and validate critical technologies for advanced STOVL aircraft through the development and evaluation of advanced, integrated control and display concepts, and lays out the plan for the flight program that will be conducted on NASA's V/STOL Research Aircraft (VSRA).

Foster, John D.↗
NASA NTRS1989

Optimal trajectories for hypervelocity flight

Optimal trajectories for hypervelocity flight of interest in aeroassisted orbital transfer are discussed. Both coplanar and noncoplanar transfer are studied. More precisely, the geosynchronous-earth-orbit-, high-earth orbit- and low-earth-orbit-to-low earth-orbit transfers are considered in connection with a spacecraft that is controlled during the atmospheric pass by the angle of attack (coplanar case) or by the angle of attack and the angle of bank (noncoplanar case). Within the framework of classical optimal control, the following problems are studied: minimize the energy required for orbital transfer; maximize the time of flight during the atmospheric portion of the trajectory; and minimize the time integral of the square of the path inclination. Within the framework of minimax optimal control, the problem studied is to minimize the peak rate. Numerical solutions for the problems are obtained by means of the sequential gradient-restoration algorithm. The engineering implications of the results are discussed.

Miele, A.↗
NASA NTRS1991

Chronology of early Archaean granite-greenstone evolution in the Barberton Mountain Land, South Africa, based on precise dating by single zircon evaporation

Precise Pb-207/Pb-206 single zircon evaporating ages are reported for low-grade felsic metavolcanic rocks within the Onverwacht and Fig Tree Groups of the Barberton Greenstone Belt (BGB), South Africa, as well as for granitoid plutons bordering the belt. Dacitic tuffs of the Hooggenoeg Formation in the upper part of the Onverwacht Group are shown to yield ages between 3445 + or - 3 and 3416 + or - 5 Ma and to contain older crustal components represented by a 3504 + or - 4 Ma old zircon xenocryst. Fig Tree dacitic tuffs and agglomerates have euhedral zircons between 3259 + or - 3 Ma in age which are interpreted to reflect the time of crystallization. The comagmatic relationships between greenstone felsic volcanic units and the surrounding plutonic suites are keynoted. The data adduced show that the Onverwacht and Fig Tree felsic units have distinctly different ages and thus do not constitute a single, tectonically repeated unit as proposed by others. It is argued that conventional multigrain zircon dating may not accurately identify the time of felsic volcanic activity in ancient greenstones, and that the BGB in the Kaapval craton of southern Africa and greenstones in the Pilbara Block of Western Australia may have been part of a larger crustal unit in early Archaean times.

Kruener, Alfred↗
NASA NTRS1991

Compensating sampling errors in stabilizing helmet-mounted displays using auxiliary acceleration measurements

A method based on complementary filtering is shown to be effective in compensating for the image stabilization error due to sampling delays of HMD position and orientation measurements. These delays would otherwise have prevented the stabilization of the image in HMDs. The method is also shown to improve the resolution of the head orientation measurement, particularly at low frequencies, thus providing smoother head control commands, which are essential for precise head pointing and teleoperation.

Merhav, S.↗
NASA NTRS1991

Gaseous oxygen detection using laser diodes

Transitions in the R-branch of the O2 A-band have been observed by modulating IR laser diode temperatures; on the basis of these transitions, O2 concentrations as low as 750 ppm can be determined. The transmission measurement's achievable precision correlates with an O2 concentration uncertainty of only 0.5 percent. Both the concentration and the static temperature of the gas are thereby determinable. Improved optics are being designed to improve these performance figures.

Fox, Curtis W.↗
NASA NTRS1994

An update on the development of a line-focus refractive concentrator array

Concentrator arrays offer a number of generic benefits for space (i.e. high array efficiency, protection from space radiation effects, minimized plasma interactions, etc.). The line-focus refractive concept, however, also offers two very important advantages: (1) relaxation of precise array tracking requirements to only a single axis and (2) low-cost mass production of the lens material. The linear refractive concentrator can be designed to provide an essentially flat response over a wide range of longitudinal errors for satellites having only single-axis tracking capability. New panel designs emphasize light weight, high stiffness, storability, and ease of manufacturing and assembly. This paper addresses the current status of the concentrator program with special emphasis on the design implications, and flexibility, of using a linear refractive concentrator lens as well as details recent fabrication of prototype hardware.

Piszczor, Michael F.↗
NASA NTRS1995

Hot bottom burning in asymptotic giant branch stars and its effect on oxygen isotopic abundances

A self-consistent calculation of asymptotic giant branch (AGB) evolution was carried out, including nucleosynthesis at the base of the convective envelope (hot bottom burning). Hot bottom burning was found to occur for stars between approximately 4.5 and approximately 7 solar mass, producing envelopes with O-18/O-16 less than or equal to 10(exp -6) and 10(exp -3) approximately less than or equal O-17/O-16 approximately less than or equal to 10(exp -1). The O-17 abundance depends sensitively on the nuclear O-17-destruction rate; this rate is only loosely constrained by the requirement that first and second dredge-up models match O-isotope observations of red giant branch (RGB) stars (Boothroyd, Sackmann, & Wasserburg 1994). In some cases, high mass-loss rates can terminate hot bottom burning before further O-17 enrichment takes place or even before all O-18 is destroyed. These predictions are in accord with the very limited stellar observations of J type carbon stars on the AGB and with some of the circumstellar Al2O3 grains from meteorites. In contrast, precise data from a number of grains and data from most low-mass S and C AGB stars (approximately less than 1.7 solar mass) lie in a region of the O-18/O-16 versus O-17/O-16 diagram that is not accessible by first and second dredge-up or by hot bottom burning. We conclude that for AGB stars, the standard models of stellar evolution are not in accord with these observations. We surmise that an additional mixing mechanism must exist that transports material from the cool bottom of the stellar convective envelope to a depth at which O-18 is destroyed. This 'cool bottom processing' mechanism on the AGB is similar to extra mixing mechanisms proposed to explain the excess C-13 (and depleted C-12) observed in the earlier RGB stage of evolution and the large Li-7 depletion observed in low-mass main-sequence stars.

Boothroyd, Arnold I.↗
NASA NTRS1994

An Update on the Development of a Line-Focus Refractive Concentrator Array

Concentrator arrays offer a number of generic benefits for space (i.e. high array efficiency, protection from space radiation effects, minimized plasma interactions, etc.). The line-focus refractive concentrator concept, however, also offers two very important advantages: (1) relaxation of precise array tracking requirements to only a single axis and (2) low-cost mass production of the lens material. The linear refractive concentrator can be designed to provide an essentially flat response over a wide range of longitudinal errors for satellites having only single-axis tracking capability. New panel designs emphasize light weight, high stiffness, stowability and ease of manufacturing and assembly. This paper will address the current status of the concentrator program with special emphasis on the design implications, and flexibility, of using a linear refractive concentrator lens as well as detail the recent fabrication of prototype hardware.

Piszczor, Michael F.↗
NASA NTRS2008

Development of Laser, Detector, and Receiver Systems for an Atmospheric CO2 Lidar Profiling System

A ground-based Differential Absorption Lidar (DIAL) is being developed with the capability to measure range-resolved and column amounts of atmospheric CO2. This system is also capable of providing high-resolution aerosol profiles and cloud distributions. It is being developed as part of the NASA Earth Science Technology Office s Instrument Incubator Program. This three year program involves the design, development, evaluation, and fielding of a ground-based CO2 profiling system. At the end of a three-year development this instrument is expected to be capable of making measurements in the lower troposphere and boundary layer where the sources and sinks of CO2 are located. It will be a valuable tool in the validation of NASA Orbiting Carbon Observatory (OCO) measurements of column CO2 and suitable for deployment in the North American Carbon Program (NACP) regional intensive field campaigns. The system can also be used as a test-bed for the evaluation of lidar technologies for space-application. This DIAL system leverages 2-micron laser technology developed under a number of NASA programs to develop new solid-state laser technology that provides high pulse energy, tunable, wavelength-stabilized, and double-pulsed lasers that are operable over pre-selected temperature insensitive strong CO2 absorption lines suitable for profiling of lower tropospheric CO2. It also incorporates new high quantum efficiency, high gain, and relatively low noise phototransistors, and a new receiver/signal processor system to achieve high precision DIAL measurements.

Ismail, Syed↗
NASA NTRS2010

Microwave Plasma Hydrogen Recovery System

A microwave plasma reactor was developed for the recovery of hydrogen contained within waste methane produced by Carbon Dioxide Reduction Assembly (CRA), which reclaims oxygen from CO2. Since half of the H2 reductant used by the CRA is lost as CH4, the ability to reclaim this valuable resource will simplify supply logistics for longterm manned missions. Microwave plasmas provide an extreme thermal environment within a very small and precisely controlled region of space, resulting in very high energy densities at low overall power, and thus can drive high-temperature reactions using equipment that is smaller, lighter, and less power-consuming than traditional fixed-bed and fluidized-bed catalytic reactors. The high energy density provides an economical means to conduct endothermic reactions that become thermodynamically favorable only at very high temperatures. Microwave plasma methods were developed for the effective recovery of H2 using two primary reaction schemes: (1) methane pyrolysis to H2 and solid-phase carbon, and (2) methane oligomerization to H2 and acetylene. While the carbon problem is substantially reduced using plasma methods, it is not completely eliminated. For this reason, advanced methods were developed to promote CH4 oligomerization, which recovers a maximum of 75 percent of the H2 content of methane in a single reactor pass, and virtually eliminates the carbon problem. These methods were embodied in a prototype H2 recovery system capable of sustained high-efficiency operation. NASA can incorporate the innovation into flight hardware systems for deployment in support of future long-duration exploration objectives such as a Space Station retrofit, Lunar outpost, Mars transit, or Mars base. The primary application will be for the recovery of hydrogen lost in the Sabatier process for CO2 reduction to produce water in Exploration Life Support systems. Secondarily, this process may also be used in conjunction with a Sabatier reactor employed to stockpile life-support oxygen as well as propellant and fuel production from Martian atmospheric CO2

Atwater, James↗
NASA NTRS2013

FPGA-Based X-Ray Detection and Measurement for an X-Ray Polarimeter

This technology enables detection and measurement of x-rays in an x-ray polarimeter using a field-programmable gate array (FPGA). The technology was developed for the Gravitational and Extreme Magnetism Small Explorer (GEMS) mission. It performs precision energy and timing measurements, as well as rejection of non-x-ray events. It enables the GEMS polarimeter to detect precisely when an event has taken place so that additional measurements can be made. The technology also enables this function to be performed in an FPGA using limited resources so that mass and power can be minimized while reliability for a space application is maximized and precise real-time operation is achieved. This design requires a low-noise, charge-sensitive preamplifier; a highspeed analog to digital converter (ADC); and an x-ray detector with a cathode terminal. It functions by computing a sum of differences for time-samples whose difference exceeds a programmable threshold. A state machine advances through states as a programmable number of consecutive samples exceeds or fails to exceed this threshold. The pulse height is recorded as the accumulated sum. The track length is also measured based on the time from the start to the end of accumulation. For track lengths longer than a certain length, the algorithm estimates the barycenter of charge deposit by comparing the accumulator value at the midpoint to the final accumulator value. The design also employs a number of techniques for rejecting background events. This innovation enables the function to be performed in space where it can operate autonomously with a rapid response time. This implementation combines advantages of computing system-based approaches with those of pure analog approaches. The result is an implementation that is highly reliable, performs in real-time, rejects background events, and consumes minimal power.

Gregory, Kyle↗