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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 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Construction and performance characteristics of a prototype NBS/GPS receiver

The construction and performance characteristics of a low-cost, high-accuracy GPS C/A receiver are reviewed. The receiver takes advantage of a simultaneous common view of the same satellites, which could allow time transfer with accuracies on the order of 10 ns or less for baselines as large as 3000 km. Frequency can be measured to better than one part in 10 to the 14th. The software and the receiver are configured to be fully automatic with a Z80A microprocessor setting the amplitude for the lock loops of the receiver and setting the synthesizer with corrects for Doppler shift. The microprocessor can calibrate a 0.1 ns built-in time interval counter.

Davis, D. D.↗
NASA NTRS1984

Analysis of the electron-beam-induced current of a polycrystalline p-n junction when the diffusion lengths of the material on either side of a grain boundary differ

The short circuit current generated by the electron beam of a scanning electron microscope in p-n junctions is reduced by enhanced recombination at grain boundaries in polycrystalline material. Frequently, grain boundaries separate the semiconductor into regions possessing different minority carrier life times. This markedly affects the short circuit current I(sc) as a function of scanning distance from the grain boundary. It will be shown theoretically that (1) the minimum of the I(sc) in crossing the grain boundary with the scanning electron beam is shifted away from the grain boundary toward the region with smaller life time (shorter diffusion length), (2) the magnitude of the minimum differs markedly from those calculated under the assumption of equal diffusion lengths on either side of the grain boundary, and (3) the minimum disappears altogether for small surface recombination velocities (s less than 10,000 cm/s). These effects become negligible, however, for large recombination velocities s at grain boundaries. For p-type silicon this happens for s not less than 100,000 cm/s.

Von Roos, O.↗
NASA NTRSDate not supplied

A Remote, Human-in-the-Loop Evaluation of a Multiple-Drone Delivery Operation

Over time, advances in unmanned aircraft systems (UAS) have enabled a shift in the operational paradigm from one operator managing one aircraft to that of multiple operators working together to manage multiple aircraft. This shift has highlighted the need for effective human-autonomy teaming methods to maintain manageable workload levels for operators as well as high standards of system performance and safety. This paper presents a study aimed at evaluating whether automation can help operators manage workload during small UAS (sUAS) package delivery scenarios featuring contingency situations. These contingency situations, resulting from unplanned UAS Volume Reservations (UVRs), required flight path reroutes for multiple aircraft simultaneously. The study manipulated the number of aircraft affected by the UVRs and the level of automation support. The presence of terrain conflicts was also controlled within each scenario. Due to the COVID-19 pandemic, subjects were not able to gain direct access to the Ground Control System (GCS). Therefore, the study was conducted using a subject-surrogate paradigm that required subjects to relay commands through a verbal protocol from remote locations outside of the lab to a researcher surrogate who had direct control of the GCS interfaces at the lab location. Results show that the automated support condition was associated with faster reroute response times, more efficient reroute maneuvers, and significantly lower levels of perceived workload than the manual reroute condition. However, the automation support level did not significantly impact pilots’ ability to avoid the UVR successfully; pilots were overwhelmingly capable of avoiding the UVR in all conditions. The presence of terrain conflicts primarily impacted pilot performance by leading to multiple uploads per vehicle, which was not typically required when pilots only needed to maneuver laterally. Although subjects did not have direct control over the GCS, subjective ratings indicate that the displays under test provided them with sufficient information to manage their aircraft and promptly respond to the unplanned UVRs. Overall, the objective and subjective data strongly suggest that the verbal protocol and subject-surrogate paradigm were effective methods for collecting data remotely amid the COVID-19 pandemic.

multi-UAS↗
NASA NTRS1981

A motion picture presentation of magnetic pulsations

Using the data obtained from the IMS North American magnetometer network stations at high latitudes, a motion picture was made by a computer technique, describing time changes of Pc5 and Pi3 magnetic pulsation vectors. Examples of pulsation characteristics derived from this presentation are regional polarization changes including shifts of polarization demarcation lines, changes in the extent of an active region and its movement with time.

Suzuki, A.↗
NASA NTRS1989

Impaired driving performance in shiftworkers: the role of the circadian system in a multifactorial model

A substantial and growing percentage of the U.S. work force now works on a rotating shift schedule. The repeated changes in sleep-wake, meal and work times inherent in such schedules conflict with the dictates of the internal biological clock and have adverse consequences for the health of the shiftworker population. An important consequence of this conflict is impaired performance, both on and off the job, as indexed by the increased incidence of motor vehicle accidents in shift workers. In this paper we report the results of a survey administered to rotating shift and straight day workers at a manufacturing plant in the eastern U.S. This survey documents an increased incidence of motor vehicle accidents or "near misses" in which sleepiness was implicated as a cause by the respondent. Complaints of poor sleep and increased sleepiness were also significantly more common in shiftworkers than day workers. Last, shiftworkers reported higher caffeine and alcohol consumption, and were more likely to use alcohol as a sleep aid. Although causal links cannot be established using these associative observations alone, previously reported experience with alteration of shift schedules, improvement of levels of alertness, and reduction in adverse performance outcomes corroborate the possibility of a causal link and suggest potential interventions.

NASA Discipline Regulatory Physiology↗
NASA NTRS2006

Tunable Filter Made From Three Coupled WGM Resonators

A tunable third-order band-pass optical filter has been constructed as an assembly of three coupled, tunable, whispering-gallery-mode resonators similar to the one described in Whispering-Gallery-Mode Tunable Narrow-Band-Pass Filter (NPO-30896), NASA Tech Briefs, Vol. 28, No. 4 (April 2004), page 5a. This filter offers a combination of four characteristics that are desirable for potential applications in photonics: (1) wide real-time tunability accompanied by a high-order filter function, (2) narrowness of the passband, (3) relatively low loss between input and output coupling optical fibers, and (4) a sparse spectrum. In contrast, prior tunable band-pass optical filters have exhibited, at most, two of these four characteristics. As described in several prior NASA Tech Briefs articles, a whispering-gallery-mode (WGM) resonator is a spheroidal, disklike, or toroidal body made of a highly transparent material. It is so named because it is designed to exploit whispering-gallery electromagnetic modes, which are waveguide modes that propagate circumferentially and are concentrated in a narrow toroidal region centered on the equatorial plane and located near the outermost edge. Figure 1 depicts the optical layout of the present filter comprising an assembly of three coupled, tunable WGM resonators. Each WGM resonator is made from a disk of Z-cut LiNbO3 of 3.3-mm diameter and 50-m thickness. The perimeter of the disk is polished and rounded to a radius of curvature of 40 microns. The free spectral range of each WGM resonator is about 13.3 GHz. Gold coats on the flat faces of the disk serve as electrodes for exploiting the electro-optical effect in LiNbO3 for tuning. There is no metal coat on the rounded perimeter region, where the whispering-gallery modes propagate. Light is coupled from an input optical fiber into the whispering-gallery-modes of the first WGM resonator by means of a diamond prism. Another diamond prism is used to couple light from the whispering-gallery-modes of the third WGM resonator to an output optical fiber. The filter operates at a nominal wavelength of 1,550 nm and can be tuned over a frequency range of plus or minus 12 GHz by applying a potential in the range of plus or minus 150 V to the electrodes. The insertion loss (the loss between the input and output coupling optical fibers) was found to be repeatable at 6 dB. The resonance quality factor (Q) of the main sequence of resonator modes was found to be 5 x 10(exp 6), which corresponds to a bandwidth of 30 MHz. The filter can be shifted from one operating frequency to another within a tuning time less than or equal to 30 micro seconds. The transmission curve of the filter at frequencies near the middle of the passband closely approximates a theoretical third-order Butterworth filter profile, as shown in Figure 2.

Savchenkov, Anatoliy↗
NASA NTRS1987

The detection of global convection on the sun by an analysis of line shift data of the John M. Wilcox Solar Observatory at Stanford University

Signatures of the existence of the global convection in the sun were found in the absorption line shift data of the John M. Wilcox Solar Observatory at Stanford University. The signatures are characterized by persistent periodic time variations in the east-west component of the velocity fields defined by fitting a slope to the line shift data in a certain longitude window at a specified latitude and longitude by a least square method. The variations indicate that the amplitude of the velocity fields is about 100 m/s. It is suggested that several modes of global convection are coexisting in the solar convection zone.

Yoshimura, Hirokazu↗
NASA NTRS1983

Dawn-dusk electric field asymmetry of the Io plasma torus

The effects of a combined convection and corotation electric field across the Io plasma torus are considered. A dawn-to-dusk electric field E sub C will modify the orbits of charged particles shifting them toward dawn. The radial drift imposed by the perturbed orbits implies a local time-dependent modulation of low-energy ion and electron temperatures with particles hotter at dusk than at dawn. With E sub C approximately 4 mV/m, the orbits near 6 Jupiter radii would be shifted by approximately 0.2 Jupiter radius. Then the electron temperature would be 20% higher at dust than at dawn, an effect which could explain the local time asymmetry of EUV intensity found by the Voyager ultraviolet spectrometer. The source of the convection electric field is internal to the magnetosphere, and is attributed to the tailward escape of Iogenic and Jovian plasma beyond the Alfven surface.

Barbosa, D. D.↗
NASA NTRS1989

A two dimensional power spectral estimate for some nonstationary processes

A two dimensional estimate for the power spectral density of a nonstationary process is being developed. The estimate will be applied to helicopter noise data which is clearly nonstationary. The acoustic pressure from the isolated main rotor and isolated tail rotor is known to be periodically correlated (PC) and the combined noise from the main and tail rotors is assumed to be correlation autoregressive (CAR). The results of this nonstationary analysis will be compared with the current method of assuming that the data is stationary and analyzing it as such. Another method of analysis is to introduce a random phase shift into the data as shown by Papoulis to produce a time history which can then be accurately modeled as stationary. This method will also be investigated for the helicopter data. A method used to determine the period of a PC process when the period is not know is discussed. The period of a PC process must be known in order to produce an accurate spectral representation for the process. The spectral estimate is developed. The bias and variability of the estimate are also discussed. Finally, the current method for analyzing nonstationary data is compared to that of using a two dimensional spectral representation. In addition, the method of phase shifting the data is examined.

Smith, Gregory L.↗
NASA NTRS1992

Digital Extraction Of Doppler Shift In An Advanced Receiver

Report describes demonstration of ability of Advanced Receiver II (ARX II) to extract Doppler shifts in radio telemetry signals from spacecraft by digital processing. Frequency of sampling clock fixed and derived from frequency-and-timing subsystem. Although this can result in noninteger number of samples per symbol, it enables digital extraction of Doppler shift. ARX II operates with older receiver called "Block IV". ARX II performed at least as well as, and in most cases better than, Block IV.

Hinedi, Sami M.↗
NASA NTRS1970

Digital-voltage curve generator

Curve generator capable of producing precisely repeatable curve for any single-valued function of voltage versus time uses digital approach, implemented by means of clocked feedback shift register, large scale integrated circuit diode matrix comprising about 12,000 diodes, counter, and digital-to-analog converter.

Perlman, M.↗
NASA NTRS1974

Differential phase shift keyed communication system

A communication system using differential phase-shift-keying (DPSK) transmits and receives binary data without requiring timing or phase reference signals. The system encodes and modulates the data at the transmitter, and decodes and demodulates the data at the receiver, without ambiguity as to the data content.

Hopkins, P. M.↗
NASA NTRS1976

The fast decoding of Reed-Solomon codes using number theoretic transforms

It is shown that Reed-Solomon (RS) codes can be encoded and decoded by using a fast Fourier transform (FFT) algorithm over finite fields. The arithmetic utilized to perform these transforms requires only integer additions, circular shifts and a minimum number of integer multiplications. The computing time of this transform encoder-decoder for RS codes is less than the time of the standard method for RS codes. More generally, the field GF(q) is also considered, where q is a prime of the form K x 2 to the nth power + 1 and K and n are integers. GF(q) can be used to decode very long RS codes by an efficient FFT algorithm with an improvement in the number of symbols. It is shown that a radix-8 FFT algorithm over GF(q squared) can be utilized to encode and decode very long RS codes with a large number of symbols. For eight symbols in GF(q squared), this transform over GF(q squared) can be made simpler than any other known number theoretic transform with a similar capability. Of special interest is the decoding of a 16-tuple RS code with four errors.

Reed, I. S.↗
NASA NTRS1983

Quantitative histochemistry of rat lumbar vertebrae following spaceflight

The histochemical effects of the return to gravity immediately and 6 and 29 days following spaceflight on the bone of rat vertebral bodies were investigated. No significant change in the calcium salt content of the vertebrae was found immediately postflight, although 6 days later it was significantly decreased. The calcium content was found to have returned to normal by 29 days postflight. While postflight collagen content was not significantly altered, keratosulfate was found to be significantly higher in trabecular bone of rats immediately postflight and 6 days postflight. In addition, chondroitin sulfate was found to be increased in vertebral bone on days 6 and 29 postflight. These findings indicate that bone turnover slows in vertebrae during spaceflight allowing bone aging, which support the contention that a form of osteolysis begins immediately upon return to gravity to remove components of old bone at which time mineral levels decrease and levels of chondroitin and keratkosulfates shift. It was found that the osteolysis phase was quickly followed by new bone replacement which was completed before 29 days postspaceflight.

Eurell, J. A.↗
NASA NTRS1984

Frequency and time standards based on stored ions

The method of ion storage provides a basis for excellent time and frequency standards. This is due to the ability to confine ions for long periods of time without the usual perturbations associated with confinement (e.g., wall shifts). In addition, Doppler effects can be greatly suppressed. The use of stored ions for microwave frequency standards and the future possibilities for an optical frequency standard based on stored ions are addressed.

Bollinger, J. J.↗
NASA NTRS1989

Launch commit criteria performance trending analysis, phase 1, revision A. SRM and QA mission services

An assessment of quantitative methods and measures for measuring launch commit criteria (LCC) performance measurement trends is made. A statistical performance trending analysis pilot study was processed and compared to STS-26 mission data. This study used four selected shuttle measurement types (solid rocket booster, external tank, space shuttle main engine, and range safety switch safe and arm device) from the five missions prior to mission 51-L. After obtaining raw data coordinates, each set of measurements was processed to obtain statistical confidence bounds and mean data profiles for each of the selected measurement types. STS-26 measurements were compared to the statistical data base profiles to verify the statistical capability of assessing occurrences of data trend anomalies and abnormal time-varying operational conditions associated with data amplitude and phase shifts.

Source record↗
NASA NTRS1989

Advanced technology satellite demodulator development

Ford Aerospace has developed a proof-of-concept satellite 8 phase shift keying (PSK) modulation and coding system operating in the Time Division Multiple Access (TDMA) mode at a data range of 200 Mbps using rate 5/6 forward error correction coding. The 80 Msps 8 PSK modem was developed in a mostly digital form and is amenable to an ASIC realization in the next phase of development. The codec was developed as a paper design only. The power efficiency goal was to be within 2 dB of theoretical at a bit error rate (BER) of 5x10(exp 7) while the measured implementation loss was 4.5 dB. The bandwidth efficiency goal was 2 bits/sec/Hz while the realized bandwidth efficiency was 1.8 bits/sec/Hz. The burst format used a preamble of only 40 8 PSK symbol times including 32 symbols of all zeros and an eight symbol unique word. The modem and associated special test equipment (STE) were fabricated mostly on a specially designed stitch-weld board although a few of the highest rate circuits were built on printed circuit cards. All the digital circuits were ECL to support the clock rates of from 80 MHz to 360 MHz. The transmitter and receiver matched filters were square-root Nyquist bandpass filters realized at the 3.37 GHz i.f. The modem operated as a coherent system although no analog phase locked (PLL) loop was employed. Within the budgetary constraints of the program, the approach to the demodulator has been proven and is eligible to proceed to the next phase of development of a satellite demodulator engineering model. This would entail the development of an ASIC version of the digital portion of the demodulator, and MMIC version of the quadrature detector, and SAW Nyquist filters to realize the bandwidth efficiency.

Ames, Stephen A.↗
NASA NTRS1992

Fuel optimal propulsive reboost of flexible spacecraft

This paper presents for the first time an exact solution to the fuel optimal propulsive reboost problem for flexible spacecraft. The spacecraft undergoes rigid-body motion and flexible-body motion and reboost is achieved propulsively through the use of reaction control jets. The exact fuel optimal solution to the associated minimization problem is found numerically based on an adaptive grid bisection search. The reboost of the floating harmonic oscillator reveals properties of the fuel optimal solution. Nondimensional plots of minimum fuel versus maneuver time expose the nature of the solution classes depending on the maneuver time. Some very interesting properties are observed, among them, the shifting of impulses to the smaller oscillator mass, and comparisons are made with near fuel optimal solutions obtained by other investigators.

Silverberg, Larry↗