Search NASA⌕ Search

SEARCH · Search NASA

Results for “phase delays”

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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

Circadian regulation of human sleep and age-related changes in its timing, consolidation and EEG characteristics

The light-entrainable circadian pacemaker located in the suprachiasmatic nucleus of the hypothalamus regulates the timing and consolidation of sleep by generating a paradoxical rhythm of sleep propensity; the circadian drive for wakefulness peaks at the end of the day spent awake, ie close to the onset of melatonin secretion at 21.00-22.00 h and the circadian drive for sleep crests shortly before habitual waking-up time. With advancing age, ie after early adulthood, sleep consolidation declines, and time of awakening and the rhythms of body temperature, plasma melatonin and cortisol shift to an earlier clock hour. The variability of the phase relationship between the sleep-wake cycle and circadian rhythms increases, and in old age sleep is more susceptible to internal arousing stimuli associated with circadian misalignment. The propensity to awaken from sleep advances relative to the body temperature nadir in older people, a change that is opposite to the phase delay of awakening relative to internal circadian rhythms associated with morningness in young people. Age-related changes do not appear to be associated with a shortening of the circadian period or a reduction of the circadian drive for wake maintenance. These changes may be related to changes in the sleep process itself, such as reductions in slow-wave sleep and sleep spindles as well as a reduced strength of the circadian signal promoting sleep in the early morning hours. Putative mediators and modulators of circadian sleep regulation are discussed.

Review, Tutorial↗
NASA NTRS1988

Monolithic electro-optic modulator array

A PIN GaAlAs diode structure is provided with parameters for index guiding of light in a single mode. The index of refraction of the central layer I (which in practice may be lightly doped .pi. or .nu.) is greater than the p- and n-layers to create a slab waveguide in the transverse direction. Stripe contacts define separate waveguide channels that are separated electrically and optically by implanting protons or etching grooves between the stripe contacts in the upper layer. Separate reverse biasing voltages may be applied to the stripe contacts for modulation of the light in proportions to the voltage, either with absorption modulation, if the light wavelength is within about 500.ANG. of the bandgap of the .pi.-material, or phase-delay modulation, if the wavelength is separated from the bandgap of the .pi.-material by at least 900.ANG..

Robinson, Deborah L.↗
NASA NTRS2008

Altimetry Using GPS-Reflection/Occultation Interferometry

A Global Positioning System (GPS)- reflection/occultation interferometry was examined as a means of altimetry of water and ice surfaces in polar regions. In GPS-reflection/occultation interferometry, a GPS receiver aboard a satellite in a low orbit around the Earth is used to determine the temporally varying carrier- phase delay between (1) one component of a signal from a GPS transmitter propagating directly through the atmosphere just as the GPS transmitter falls below the horizon and (2) another component of the same signal, propagating along a slightly different path, reflected at glancing incidence upon the water or ice surface.

Cardellach, Estel↗
NASA NTRS2009

FPGA-Based Networked Phasemeter for a Heterodyne Interferometer

A document discusses a component of a laser metrology system designed to measure displacements along the line of sight with precision on the order of a tenth the diameter of an atom. This component, the phasemeter, measures the relative phase of two electrical signals and transfers that information to a computer. Because the metrology system measures the differences between two optical paths, the phasemeter has two inputs, called measure and reference. The reference signal is nominally a perfect square wave with a 50- percent duty cycle (though only rising edges are used). As the metrology system detects motion, the difference between the reference and measure signal phases is proportional to the displacement of the motion. The phasemeter, therefore, counts the elapsed time between rising edges in the two signals, and converts the time into an estimate of phase delay. The hardware consists of a circuit board that plugs into a COTS (commercial, off-the- shelf) Spartan-III FPGA (field-programmable gate array) evaluation board. It has two BNC inputs, (reference and measure), a CMOS logic chip to buffer the inputs, and an Ethernet jack for transmitting reduced-data to a PC. Two extra BNC connectors can be attached for future expandability, such as external synchronization. Each phasemeter handles one metrology channel. A bank of six phasemeters (and two zero-crossing detector cards) with an Ethernet switch can monitor the rigid body motion of an object. This device is smaller and cheaper than existing zero-crossing phasemeters. Also, because it uses Ethernet for communication with a computer, instead of a VME bridge, it is much easier to use. The phasemeter is a key part of the Precision Deployable Apertures and Structures strategic R&D effort to design large, deployable, segmented space telescopes.

Rao, Shanti↗
NASA NTRS2008

Fast Switching and Precision Relative Astrometry at the DSN

A) We are developing new techniques to improve astrometric accuracy: 1) Reducing switching time (approx. 60s) and angular separation (approx.1deg) between quasars; 2) Use of phase delay & bandpass calibration; 3) Techniques also applicable with future DSN Array. B) Initial set of observations carried out at the DSN show great promise. C) Continue DSN observations using fainter calibrators to study robustness and to verify and validate error estimates. (Eventually demo technique with spacecraft measurements). D) Viability of technique depends on existence of sufficient number of calibrators. (Determining what fraction of radio sources are compact at the VLBA) E) May be able to use calibrators with flux density approx. 50 mJy with calibrator 1deg. G) Relative precision of approx.0.5 nrad may be achievable. E) Absolute measurement always depends on knowledge of calibrator position. (Catalog maintained and improved).

Deep Space Network (DSN)↗
NASA NTRS2004

The Development of Large Inflatable Antenna for Deep-Space Communications

NASA/JPL's deep-space exploration program has been placing emphasis on reducing the mass and stowage volume of its spacecraft's high-gain and large-aperture antennas. To achieve these goals, the concept of deployable flat reflectarray antenna using an inflatable/thin-membrane structure was introduced at JPL several years ago. A reflectarray is a flat array antenna space-fed by a low-gain feed located at its focal point in a fashion similar to that of a parabolic reflector. The ref1ectarray's elements, using microstrip technology, can be printed onto a flat thin-membrane surface and are each uniquely designed to compensate for the different phase delays due to different path lengths from the feed. Although the reflectarray suffers from limited bandwidth (typically < 10%), it offers a more reliably deployed and maintained flat "natural" surface. A recent hardware development at JPL has demonstrated that a 0.2mm rms surface tolerance (l/50th of a wavelength) was achieved on a 3-meter Ka-band inflatable reflectarray. Another recent development, to combat the reflectarray's narrow band characteristic, demonstrated that dual-band performance, such as X- and Ka-bands, with an aperture efficiency of above 50 percent is achievable by the reflectarray antenna. To mechanically deploy the antenna, the reflectarray's thin membrane aperture surface is supported, tensioned and deployed by an inflatable tubular structure. There are several critical elements and challenging issues associated with the inflatable tube structure. First, the inflatable tube must be made rigidizable so that, once the tube is fully deployed in space, it rigidizes itself and the inflation system is no longer needed. In addition, if the tube is penetrated by small space debris, the tube will maintain its rigidity and not cause deformation to the antenna structure. To support large apertures (e.g. 10m or beyond) without causing any buckling to the small-diameter inflatable tube during vibration, the tube, in addition to rigidization, is also reinforced by circumferential thin blades, as well as axial blades. Second, a controlled deployment mechanism, such as by using Velcro strips, must also be implemented into the system so that, for very large structures, the long inflatable tubes can be deployed in a time-controlled fashion and not get tangled with each other. Third, the thermal analysis is another critical element and must be performed for the tube design in order to assure that the inflated tube, under extreme space thermal conditions, will not deform significantly. Finally, the dynamic vibration analysis must also be performed on the inflatable structure. This will investigate the response of the structure due to excitation introduced by the spacecraft maneuvering and thus determine any necessary damping. Several reflectarray antennas have been developed at JPL to demonstrate the technology. These include an earlier 1-meter X-band inflatable reflectarray, a 3-meter Ka-band inflatable reflectarray, a half-meter dual-band (X and Ka) reflectarray, and the current on-going 10-meter inflatable structure development. The detailed RF and mechanical descriptions of these antennas, as well as their performances, will be presented during the conference.

inflatable antenna↗
NASA NTRS2012

A Translational Polarization Rotator

We explore a free-space polarization modulator in which a variable phase introduction between right- and left-handed circular polarization components is used to rotate the linear polarization of the outgoing beam relative to that of the incoming beam. In this device, the polarization states are separated by a circular polarizer that consists of a quarter-wave plate in combination with a wire grid. A movable mirror is positioned behind and parallel to the circular polarizer. As the polarizer-mirror distance is separated, an incident liear polarization will be rotated through an angle that is proportional to the introduced phase delay. We demonstrate a prototype device that modulates Stokes Q and U over a 20% bandwidth.

Chuss, David T.↗
NASA NTRS2013

NASA Tech Briefs, Februrary 2013

Topics covered include: Measurements of Ultra-Stable Oscillator (USO) Allan Deviations in Space; Gaseous Nitrogen Orifice Mass Flow Calculator; Validation of Proposed Metrics for Two-Body Abrasion Scratch Test Analysis Standards; Rover Low Gain Antenna Qualification for Deep Space Thermal Environments; Automated, Ultra-Sterile Solid Sample Handling and Analysis on a Chip; Measuring and Estimating Normalized Contrast in Infrared Flash Thermography; Spectrally and Radiometrically Stable, Wideband, Onboard Calibration Source; High-Reliability Waveguide Vacuum/Pressure Window; Methods of Fabricating Scintillators With Radioisotopes for Beta Battery Applications; Magnetic Shield for Adiabatic Demagnetization Refrigerators (ADR); CMOS-Compatible SOI MESFETS for Radiation-Hardened DC-to-DC Converters; Silicon Heat Pipe Array; Adaptive Phase Delay Generator; High-Temperature, Lightweight, Self-Healing Ceramic Composites for Aircraft Engine Applications; Treatment to Control Adhesion of Silicone-Based Elastomers; High-Temperature Adhesives for Thermally Stable Aero-Assist Technologies; Rockballer Sample Acquisition Tool; Rock Gripper for Sampling, Mobility, Anchoring, and Manipulation; Advanced Magnetic Materials Methods and Numerical Models for Fluidization in Microgravity and Hypogravity; Data Transfer for Multiple Sensor Networks Over a Broad Temperature Range; Using Combustion Synthesis to Reinforce Berms and Other Regolith Structures; Visible-Infrared Hyperspectral Image Projector; Three-Axis Attitude Estimation With a High-Bandwidth Angular Rate Sensor Change_Detection.m; AGATE: Adversarial Game Analysis for Tactical Evaluation; Ionospheric Simulation System for Satellite Observations and Global Assimilative; Modeling Experiments (ISOGAME); An Extensible, User- Modifiable Framework for Planning Activities; Mission Operations Center (MOC) - Precipitation Processing System (PPS) Interface Software System (MPISS); Automated 3D Damaged Cavity Model Builder for Lower Surface Acreage Tile on Orbiter; Mixed Linear/Square-Root Encoded Single-Slope Ramp Provides Low-Noise ADC with High Linearity for Focal Plane Arrays; RUSHMAPS: Real-Time Uploadable Spherical Harmonic Moment Analysis for Particle Spectrometers; Powered Descent Guidance with General Thrust-Pointing Constraints; X-Ray Detection and Processing Models for Spacecraft Navigation and Timing; and Extreme Ionizing-Radiation-Resistant Bacterium

Source record↗
NASA NTRS2013

Combined Global Navigation Satellite Systems in the Space Service Volume

Besides providing position, velocity, and timing (PVT) for terrestrial users, the Global Positioning System (GPS) is also being used to provide PVT information for earth orbiting satellites. In 2006, F. H. Bauer, et. al., defined the Space Service Volume in the paper GPS in the Space Service Volume , presented at ION s 19th international Technical Meeting of the Satellite Division, and looked at GPS coverage for orbiting satellites. With GLONASS already operational, and the first satellites of the Galileo and Beidou/COMPASS constellations already in orbit, it is time to look at the use of the new Global Navigation Satellite Systems (GNSS) coming into service to provide PVT information for earth orbiting satellites. This presentation extends GPS in the Space Service Volume by examining the coverage capability of combinations of the new constellations with GPS GPS was first explored as a system for refining the position, velocity, and timing of other spacecraft equipped with GPS receivers in the early eighties. Because of this, a new GPS utility developed beyond the original purpose of providing position, velocity, and timing services for land, maritime, and aerial applications. GPS signals are now received and processed by spacecraft both above and below the GPS constellation, including signals that spill over the limb of the earth. Support of GPS space applications is now part of the system plan for GPS, and support of the Space Service Volume by other GNSS providers has been proposed to the UN International Committee on GNSS (ICG). GPS has been demonstrated to provide decimeter level position accuracy in real-time for satellites in low Earth orbit (centimeter level in non-real-time applications). GPS has been proven useful for satellites in geosynchronous orbit, and also for satellites in highly elliptical orbits. Depending on how many satellites are in view, one can keep time locked to the GNSS standard, and through that to Universal Time as long as at least one satellite is in view (the longest duration with no satellites in view is important in determining the maximum clock drift from GNSS time). Instantaneous position requires four satellites in view, but because orbital motion is predictable, it is possible to build up knowledge of the orbital position gradually through time without a need for constant four satellite coverage. However, it is desirable to have four satellite coverage when performing satellite maneuvers, since there can be significant changes in velocity, leading to large changes in orbit parameter, causing substantial divergence in position over time. The Space Service Volume has been defined as the volume between three thousand km altitude and geosynchronous altitude, and can be divided into medium orbit services between three thousand km altitude and eight thousand km altitude, and high orbit services above eight thousand km. The Terrestrial Service Volume includes the Earth s surface, the atmosphere, and space below the altitude of three thousand km. The Terrestrial Service Volume is the volume within which the GNSS systems will have very similar performance to the Earth surface, and satellites need only use the signals specified to provide terrestrial performance. Above three thousand km the use of signals passing by the Earth s limb becomes important, so it is desirable to have additional information on signal strength, phase delay, and group delay covering wider beam angles than are needed for terrestrial service (and which can be obtained by monitoring GNSS signals from the Earth s surface). This presentation will look at each of the new GNSS constellations in combination with GPS (GLONASS with GPS, Galileo with GPS, Beidou/COMPASS with GPS), and also at the combination of all four GNSS systems. The presentation will largely follow the format of GPS in the Space Service Volume , presenting data on the availability of one, two, three, or four of the various combinations of GNSS constellation satelles at approximately two thousand grid points evenly spaced and fixed in longitude and latitude, the duration of the longest single-fold outages (intervals when no satellites are available), and the duration of the longest four-fold outages (intervals when fewer than four satellites are available) at several altitudes. Following the original paper, we will use the altitudes of three hundred km (typical LEO satellite, and within the Terrestrial Service Volume), at three thousand km (border between Terrestrial Service Volume and Space Service Volume), at eight thousand km (the border between medium and high orbit service within the Space Service Volume), at fifteen thousand km (just below the GNSS constellations), at twenty five thousand km (just above the GNSS constellations), at thirty six thousand, five hundred km (limit of Space Service Volume definition, geosynchronous altitude), and at seventy thousand km (to show the potential usefulness of GNSS beyond geosynchronous altitude).

Force, Dale A.↗
NASA NTRS2013

Navigation Performance of Global Navigation Satellite Systems in the Space Service Volume

GPS has been used for spacecraft navigation for many years center dot In support of this, the US has committed that future GPS satellites will continue to provide signals in the Space Service Volume center dot NASA is working with international agencies to obtain similar commitments from other providers center dot In support of this effort, I simulated multi-constellation navigation in the Space Service Volume In this presentation, I extend the work to examine the navigational benefits and drawbacks of the new constellations center dot A major benefit is the reduced geometric dilution of precision (GDOP). I show that there is a substantial reduction in GDOP by using all of the GNSS constellations center dot The increased number of GNSS satellites broadcasting does produce mutual interference, raising the noise floor. A near/far signal problem can also occur where a nearby satellite drowns out satellites that are far away. - In these simulations, no major effect was observed Typically, the use of multi-constellation GNSS navigation improves GDOP by a factor of two or more over GPS alone center dot In addition, at the higher altitudes, four satellite solutions can be obtained much more often center dot This show the value of having commitments to provide signals in the Space Service Volume Besides a commitment to provide a minimum signal in the Space Service Volume, detailed signal gain information is useful for mission planning center dot Knowledge of group and phase delay over the pattern would also reduce the navigational uncertainty

Force, Dale A.↗
NASA NTRS2015

Overview of the Design, Fabrication and Performance Requirements of Micro-Spec, an Integrated Submillimeter Spectrometer

Micro-Spec is a compact submillimeter (350-700 GHz) spectrometer which uses low loss superconducting niobium microstrip transmission lines and a single-crystal silicon dielectric to integrate all of the components of a grating-analog spectrometer onto a single chip. Here we present details of the fabrication and design of a prototype Micro-Spec spectrometer with resolution, R64, where we use a high-yield single-flip wafer bonding process to realize instrument components on a 0.45 m single-crystal silicon dielectric. We discuss some of the electromagnetic design concerns (such as loss, stray-light, cross-talk, and fabrication tolerances) for each of the spectrometer components and their integration into the instrument as a whole. These components include a slot antenna with a silicon lens for optical coupling, a phase delay transmission line network, parallel plate waveguide interference region, and aluminum microstrip transmission line kinetic inductance detectors with extremely low cross-talk and immunity to stray light. We have demonstrated this prototype spectrometer with design resolution of R64. Given the optical performance of this prototype, we will also discuss the extension of this design to higher resolutions suitable for balloon-flight.

spectrometer↗
NASA NTRS2021

Non-Causal Controller Approximation Methodology Augmented with Model Reference Control – Robust Design

This paper describes the development of a new control design methodology based on a non-causal controller structure and its approximation. The non-causal controller design is based on a loop shaping approach. Partial fraction decomposition is used, along with derivative approximations, to derive a proper transfer function design for a causal control structure. The premise for this non-causal control methodology is that the phase delay as a function of frequency ideally remains within approximately -90o, which tends to make the system robustly stable to uncertainties in the plant dynamics. To have a predictable control system response in lieu of the tolerance of this methodology to relatively large uncertainty in the plant dynamics, the approach is augmented with model reference control. The addition of model reference control can potentially further enhance the robustness of the design. A control system design example is presented in this paper, along with simulation results, to demonstrate the high degree of robustness of this non-causal methodology and its augmentation.

Control Systems↗
NASA NTRSDate not supplied

Astronaut Sleep Duration Varies by Timing of Scheduled Sleep

INTRODUCTION: Studies find that humans average approximately six hours of sleep per night in space, which is less than they sleep on Earth. Such short sleep duration has been associated with reduced alertness and performance in space. It is unclear whether this sleep loss is related to modifiable factors, such as irregular scheduling, poor sleep environment, and excessive workload or due to features of spaceflight that alter physiology (e.g., microgravity). Recent missions have afforded crew better, more stable sleep and work schedules, and an improved sleep environment. Despite these improvements, schedules do still vary enough to cause decrements in sleep duration. METHODS: Crewmembers (n = 19) who volunteered for the NASA Standard Measures protocol between January 2019 and March 2022 were provided with actiwatches (Phillips, Respironics, Bend OR) that they wore for two bouts of data collection lasting two weeks each before flight (at approximately L-270 and L-180), either continuously (n = 9) or for two weeks every two months while in space (n = 10), and for seven days postflight, immediately upon return to Earth (R+0). A regularly scheduled (or “nominal”) sleep episode would take place between the hours of 9:30pm and 6:00am. We looked at sleep outcomes (sleep duration, wake after sleep onset [WASO], sleep efficiency) depending on the distance from nominal sleep offset to see whether scheduled sleep period affected sleep durations and other metrics of sleep quality. RESULTS: Crewmembers provided data from 402 nights preflight, 2,137 nights inflight, and 275 nights postflight. They averaged 7.33 hours of sleep per night (± 1.16, SD) in space. Though this was significantly less sleep than they achieved preflight (7.87 ± 1.10) or postflight (7.75 ± 1.43, p < .01), this duration of sleep meets the recommended amount for optimal human health and well-being. For every hour after the nominal sleep period a crewmember woke up, their total sleep increased by 25 minutes (up to 5 hours). CONCLUSIONS: We conclude that humans are capable of achieving sufficient sleep in space, especially when their schedules afford adequate sleep (namely, schedules that phase delay rather than advance). Future studies are needed to determine whether microgravity impacts sleep architecture and sleep quality. Going forward, it is imperative that crewmembers are provided with stable schedules, with moderate workload, and environments that are conducive to sleep.

fatigue↗
NASA NTRSDate not supplied

Impact of Sleep Shifting Strategies on the International Space Station

Astronaut crews have historically averaged around six hours of sleep per night, especially during missions that required a high tempo work environment, confined spacecraft without crew quarters, and frequent sleep schedule changes. In recent years, crew aboard the ISS have had much more stable schedules, with a consistent bedtime at 2130 and wake time at 0600 Greenwich Mean Time. Despite these improvements to sleep conditions on the ISS, sleep schedules are disrupted by visiting vehicles that arrive or leave the ISS or when uncontrollable operational events require the crewmembers to shift their sleep. We characterized the approaches to sleep shifting, including shifting sleep earlier and later and split sleep to determine the impact on sleep duration and quality. METHODS Data were gathered though the Spaceflight Standard Measures protocol. These consisted of objective measures of sleep duration (calculated via a wrist-worn accelerometer) collected by 19 crewmembers (7 females; mean age 46 ± 7 years) throughout their tenure aboard the ISS. We first categorized episodes of “split sleep” whereby a person attempts sleep on two separate occasions in a 24-hour period that are similar in length. For example, they might have a 4-hour sleep opportunity followed by a night awake, followed by another 4-hour sleep opportunity the next morning. RESULTS Out of the 19 crewmembers, a total of 8 engaged in 11 episodes of split sleep while inflight. These periods all surrounded visiting vehicle events that interfered with their nominal sleep window, including docking, relocation, and undocking events. The first sleep opportunity typically took place during the afternoon before the disrupting event (all sleep periods were contained between 1151 and 2009), while the second episode took place the following morning (between 0343 and 1325) On average, the time in bed of the first sleep opportunity was shorter than the second (M1=2.89±0.82 vs. M2=4.30±1.41). DISCUSSION Next in our analysis, we will compare the crewmembers’ split sleep outcomes to those from other strategies (e.g., phase delays). We aim to determine which strategies yield the best sleep outcomes and to determine whether the sleep shifting strategy has consequences to subsequent sleep. Understanding these impacts will aid in decision making for future ISS operations and will also help us better understand the impacts of various strategies to adjust sleep and help guide scheduling in future missions where consistent schedules may not be possible.

sleep↗
NASA NTRS1980

Phase and group delay calibration of a very long baseline interferometer by East Coast VLBI Group

Precisely timed pulses injected into the input of each receiver are used to calibrate the phase and group delay through each interferometer terminal. The short duration pulses are generated at a 1 MHz rate directly from the output of the frequency standard. The pulses are injected into the receiver at a level low enough to produce less than one percent increase in system temperature, yet can be extracted during processing with a high enough signal to noise ratio to determine the phase of the calibration rails within 1 degree in 1 second of integration. The calibration system also includes precise cable measurement electronics and a pulse echo for clock synchronization.

Rogers, A. E. E.↗
DOE OSTI2022

Status of the Slide Rule Update - Phase 4 Plutonium Configurations – Delayed Gamma [Slides]

The fourth phase of Slide-Rule update gives a calculation scheme for DFG doses and its application to five plutonium material, as well as comparisons between radiation transport and depletion codes such as MCNP, SCALE, COG and FISPACT. Overall, DFG dose rates calculated by each laboratory led to consistent results. Extra effort is under way to identify the cause of the remaining differences, especially for case 2, by comparing precisely the gamma source, and particularly nuclides inventories.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1981

An analysis of radio interferometry with the block O system

The form and flow of information from signal reception to recorded bits at each station, through cross-correlation, phase-tracking, phase calibration, and bandwidth synthesis, to final observable formation are traced. In this process the data volume is greatly compressed for each observation, from approx. 10 to the 9th power bits on the station tapes to only four final observables: amplitude, delay, phase-delay rate and RF phase. After phase calibration and propagation media calibrations, the final delay observable is shown to be the sum of a geometric delay and a clock synchronization offset.

Thomas, J. B.↗