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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1996

Jet Propulsion Laboratories in Space: The Production of Astrophysical Jets by Magnetic Accretion Disks, and a Super-Eddington Wind Model for the Early Stages of GROJ1455-40

Measurements of the properties of gravitational lenses have the power to tell us what sort of universe we live in. The brightest known radio Einstein ring/gravitational lens PKS 1830-211, whilst obscured by our galaxy at optical wavelengths, has recently provided a lensing galaxy redshift of 0.89 through the detection of a new absorption feature, most likely due to neutral hydrogen in a second redshift system at z=0.19.

PKS 1830-211↗
NASA NTRS2008

Recent Observations of the Early Stage of Solar Eruptions

We examine the onset of two solar eruptions, using data from Hinode STEREO, TRACE, and SOHO, and other sources. One eruption occurred on 2007 March 2, and the other occurred on 2007 May 20. The first eruption involves a filament that erupts, and motions of the filament begin at least 20 min prior to onset of the main eruption; magnetic cancellation occurs beneath the filament among opposite polarity magnetic elements for at least six hours prior to the eruption.. In the second case, a surge-like filament is ejected from a location north of the main erupting magnetic neutral line; in this case magnetic cancellation occurs both along the main neutral line and also at the sight of the surge source north of the main neutral line. Thus in both cases, magnetic cancellation prior to eruption plays a crucial role in releasing the magnetic energy responsible for the respective eruptions.

Sterling, Alphonse↗
NASA NTRS2023

Parameter Dependencies of Early-Stage Tangential Discontinuity-Driven Foreshock Bubbles in Local Hybrid Simulations

Foreshock bubbles (FBs) are significant foreshock transients that can accelerate particles and disturb the magnetosphere-ionosphere system. In the kinetic formation model, foreshock ions interact with the discontinuity by performing partial gyrations to generate currents that change the magnetic field topology around the discontinuity. However, how different foreshock ion properties affect the growth of the field variations is not well understood. Therefore, we use 2-D local hybrid simulations to study the effects of different foreshock ion distributions and properties on the growth of tangential discontinuity (TD)-driven FBs. We discover that for a gyrophase-bunched distribution with an initial phase where the guiding center is on the other side of the TD, the foreshock ions gyrate together across the TD, causing more foreshock ions to cross the TD and leading to a faster expansion of the structure than for a Maxwellian distribution. A ring distribution also yields higher expansion speeds because of the higher projected velocity into the new perpendicular direction. For Maxwellian distributions, there are positive and linear correlations of the FB expansion speeds with the initial foreshock ion densities, thermal speeds, parallel speeds, and sine of the TD magnetic shear angles. These parameter dependencies grow in strength as the structures evolve with time. The foreshock ion distributions and properties that lead to stronger currents produce more significant magnetic field variations and higher expansion speeds. Our study helps quantify the formation and expansion of FBs to forecast their space weather effects and contribution to shock acceleration.

Andrew Vu↗
NASA NTRSDate not supplied

Urban Air Mobility Airspace Dynamic Density

Airspace safety must be assured for Urban Air Mobility (UAM) to become reality. Emerging operations need to safely integrate with existing and future air traffic. UAM is anticipated to evolve in stages. Early stages, characterized by low-density operations, may be accommodated by traditional air traffic management approaches. However, to enable the scale of UAM operations necessary to reach ubiquitous integration into daily life, new paradigms that utilize collaborative and automated systems are being considered. Correspondingly, traditional approaches for determining a safe number of simultaneous operations in an airspace must be adapted to suit evolving traffic management paradigms. In this paper, we examine dynamic density as an approach to determine when an airspace is excessively populated, and safety may become compromised. We review previous work on dynamic density as it relates to air traffic controller workload and propose factors that may be more fitting for UAMs. Rather than considering controller workload, we propose factors that suggest increased likelihood of loss of separation and may lead to conflicts that require tactical avoidance maneuvers. In addition to monitoring dynamic density for tactical decision making, we endeavor to predict airspace dynamic density with adequate look-ahead to allow for strategic route selection.

UAM↗
NASA NTRS2022

Optimizing Screening for Preventable Blindness With Head-Mounted Visual Assessment Technology

Age-related macular degeneration (AMD) is a leading cause of blindness and is diagnosed as early-stage or late-stage. Early-stage AMD is usually asymptomatic and entails pigmentary changes of the retina (Ayoub & Patel, 2009). As the disorder progresses, there are atrophic or neovascular changes that distort vision, especially the central visual field (Ayoub & Patel, 2009). There are several genetic and non-genetic risk factors for AMD and no proven therapy to slow or reverse late-stage atrophic AMD, while anti-VEGF has effectively treated late-stage neovascular AMD. Several genes of interest have also been investigated thoroughly thus far in their connection to AMD and the CFH and ARMS2 genes have shown promise in understanding the genetic basis of the disorder (Awh et al., 2013). There are other epigenetic and environmental factors as well including smoking and low antioxidant levels (Cano et al., 2010). Ongoing investigations include antioxidant supplementation and a smoking cessation regimen to reverse early-stage AMD (Cano et al., 2010). Progress in treating AMD as a disorder across its varied stages requires newer therapeutics along with a more detailed understanding of the genetic and cellular pathways of pathophysiology is needed to better counter this prevalent disorder of the eye.

age-related macular degeneration↗
NASA NTRS1991

Late stages of accumulation and early evolution of the planets

Recently developed solutions of problems are discussed that were traditionally considered fundamental in classical solar system cosmogony: determination of planetary orbit distribution patterns, values for mean eccentricity and orbital inclinations of the planets, and rotation periods and rotation axis inclinations of the planets. Two important cosmochemical aspects of accumulation are examined: the time scale for gas loss from the terrestrial planet zone, and the composition of the planets in terms of isotope data. It was concluded that the early beginning of planet differentiation is a function of the heating of protoplanets during collisions with large (thousands of kilometers) bodies. Energetics, heat mass transfer processes, and characteristic time scales of these processes at the early stages of planet evolution are considered.

Vityazev, Andrey V.↗
NASA NTRS1978

Multiple-satellite studies of magnetospheric substorms - Plasma sheet recovery and the poleward leap of auroral zone activity

Particle observations from pairs of satellites (OGO 5 and Vela 4A and 5A) during 28 plasma sheet thickening events indicate that thickening of the nighttime plasma sheet during substorms occurs in two main stages. The early stage involves single or multiple expansions of the near-earth plasma sheet at the onset of substorm expansions (Pi 2 bursts) on the ground, while the later stage of plasma sheet recovery starts near the time of maximum auroral zone bay activity. This stage is characterized by a large-scale thickening toward higher latitudes that occurs over a broad azimuthal scale and at heights that range from the ionosphere to beyond the Vela orbit. A detailed analysis of two-satellite observations during eight plasma sheet recoveries is presented, and events that occurred within 5 min in widely separated locations at small distances from the tail's midplane as well as events that occurred concurrently in the Vela orbit and at high latitudes in the near-earth region are revealed.

Pytte, T.↗
NASA NTRS1987

Accumulation of the planets

In modeling the accumulation of planetesimals into planets, it is appropriate to distinguish between two stages: an early stage, during which approximately 10 km diameter planetesimals accumulate locally to form bodies approximate 10 to the 25th g in mass; and a later stage in which the approximately 10 to the 25th g planetesimals accumulate into the final planets. In the terrestrial planet region, an initial planetesimal swarm corresponding to the critical mass of dust layer gravitational instabilities is considered. In order to better understand the accumulation history of Mercury-sized bodies, 19 Monte-Carlo simulations of terrestrial planet growth were calculated. A Monte Carlo technique was used to investigate the orbital evolution of asteroidal collision debris produced interior to 2.6 AU. It was found that there are two regions primarily responsible for production of Earth-crossing meteoritic material and Apollo objects. The same techniques were extended to include the origin of Earth-approaching asteroidal bodies. It is found that these same two resonant mechanisms predict a steady-state number of Apollo-Amor about 1/2 that estimated based on astronomical observations.

Wetherill, G. W.↗
NASA NTRS2011

Early Oscillation Detection Technique for Hybrid DC/DC Converters

Oscillation or instability is a situation that must be avoided for reliable hybrid DC/DC converters. A real-time electronics measurement technique was developed to detect catastrophic oscillations at early stages for hybrid DC/DC converters. It is capable of identifying low-level oscillation and determining the degree of the oscillation at a unique frequency for every individual model of the converters without disturbing their normal operations. This technique is specially developed for space-used hybrid DC/DC converters, but it is also suitable for most of commercial and military switching-mode power supplies. This is a weak-electronic-signal detection technique to detect hybrid DC/DC converter oscillation presented as a specific noise signal at power input pins. It is based on principles of feedback control loop oscillation and RF signal modulations, and is realized by using signal power spectral analysis. On the power spectrum, a channel power amplitude at characteristic frequency (CPcf) and a channel power amplitude at switching frequency (CPsw) are chosen as oscillation level indicators. If the converter is stable, the CPcf is a very small pulse and the CPsw is a larger, clear, single pulse. At early stage of oscillation, the CPcf increases to a certain level and the CPsw shows a small pair of sideband pulses around it. If the converter oscillates, the CPcf reaches to a higher level and the CPsw shows more high-level sideband pulses. A comprehensive stability index (CSI) is adopted as a quantitative measure to accurately assign a degree of stability to a specific DC/DC converter. The CSI is a ratio of normal and abnormal power spectral density, and can be calculated using specified and measured CPcf and CPsw data. The novel and unique feature of this technique is the use of power channel amplitudes at characteristic frequency and switching frequency to evaluate stability and identify oscillations at an early stage without interfering with a DC/DC converter s normal operation. This technique eliminates the probing problem of a gain/phase margin method by connecting the power input to a spectral analyzer. Therefore, it is able to evaluate stability for all kinds of hybrid DC/DC converters with or without remote sense pins, and is suitable for real-time and in-circuit testing. This frequency-domain technique is more sensitive to detect oscillation at early stage than the time-domain method using an oscilloscope.

Wang, Bright L.↗
NASA NTRS2016

Productivity Challenges for Mars Rover Operations

Achieving consistently high levels of productivity for surface exploration missions has been a challenge for Mars missions. While the rovers have made major discoveries and accomplished a large number of objectives, they often require a great deal of effort from the operations teams and achievingobjectives can take longer than anticipated. This paper describes the early stages of a multi-year project to investigate solutions for enhancing surface mission productivity. A primary focus of this early stage is to conduct in-depth studies of Mars Science Laboratory science campaigns to gain a deeper understanding of the factors that impact productivity, and to use this understanding to identify potential changes to flight software and ground operations practices to increase productivity. We present the science campaigns we have selected along with a conceptual model of how surface missions achieve objectives that is used to guide the study. We also provide some early thoughts on the technologies, and their interactions, which we believe will play an important role in addressing surface mission productivity challenges.We are in the early stages of a multi-year project to studyand address productivity challenges of future surface missions. We have identified campaigns from the MSL missionfor study which we believe will yield valuable informationabout the nature of surface mission productivity challenges.Based on preliminary analysis from the data collected weanticipate that the lessons from these case studies will helpdevelop and mature our concepts for changes to flight andground systems to address these challenges.While the focus of our work is on Mars rover missions, webelieve the concepts in the work will be applicable to a variety of in-situ explorers, including Venus, and Titan, as wellas orbital missions, such as the Europa orbiter. These missions will also benefit from the ability to adapt and respondto the latest state of the spacecraft and its environment.

Gaines, Daniel↗
NASA NTRS2014

Coupling Damage-Sensing Particles to the Digitial Twin Concept

The research presented herein is a first step toward integrating two emerging structural health management paradigms: digital twin and sensory materials. Digital twin is an emerging life management and certification paradigm whereby models and simulations consist of as-built vehicle state, as-experienced loads and environments, and other vehicle-specific history to enable high-fidelity modeling of individual aerospace vehicles throughout their service lives. The digital twin concept spans many disciplines, and an extensive study on the full domain is out of the scope of this study. Therefore, as it pertains to the digital twin, this research focused on one major concept: modeling specifically the as-manufactured geometry of a component and its microstructure (to the degree possible). The second aspect of this research was to develop the concept of sensory materials such that they can be employed within the digital twin framework. Sensory materials are shape-memory alloys that undergo an audible phase transformation while experiencing sufficient strain. Upon embedding sensory materials with a structural alloy, this audible transformation helps improve the reliability of crack detection especially at the early stages of crack growth. By combining these two early-stage technologies, an automated approach to evidence-based inspection and maintenance of aerospace vehicles is sought.

Hochhalter, Jacob↗
NASA NTRS2010

Inversion Method for Early Detection of ARES-1 Case Breach Failure

A document describes research into the problem of detecting a case breach formation at an early stage of a rocket flight. An inversion algorithm for case breach allocation is proposed and analyzed. It is shown how the case breach can be allocated at an early stage of its development by using the rocket sensor data and the output data from the control block of the rocket navigation system. The results are simulated with MATLAB/Simulink software. The efficiency of an inversion algorithm for a case breach location is discussed. The research was devoted to the analysis of the ARES-l flight during the first 120 seconds after the launch and early prediction of case breach failure. During this time, the rocket is propelled by its first-stage Solid Rocket Booster (SRB). If a breach appears in SRB case, the gases escaping through it will produce the (side) thrust directed perpendicular to the rocket axis. The side thrust creates torque influencing the rocket attitude. The ARES-l control system will compensate for the side thrust until it reaches some critical value, after which the flight will be uncontrollable. The objective of this work was to obtain the start time of case breach development and its location using the rocket inertial navigation sensors and GNC data. The algorithm was effective for the detection and location of a breach in an SRB field joint at an early stage of its development.

Mackey, Ryan M.↗
NASA NTRS1990

Computation of instability and transition

The state of transition calculations in 1989 and desirable future trends are analyzed within the framework of aeronautical applications with emphasis on wall-bounded flows. A shift to studies of the early stages of transition, particularly to receptivity, from studies of the late stages in excessively confined periodic domains is proposed. It is pointed out that early-stage studies require a larger computational domain and more difficult boundary conditions but not a very fine grid. Intermediate strategies, more involved than the classical Orr-Sommerfeld equation but much more economical than full Navier-Stokes equations, are emphasized, along with the need for compressible calculations.

Spalart, P. R.↗
NASA NTRS1995

Studies on Equatorial Shock Formation During Plasmaspheric Refilling

During the grant period from August 1, 1994 to October 31, 1995 we have continued to investigate the effects of plasma wave instabilities on the early stage plasmaspheric refilling. Since ion beams are the primary feature of the interhemispheric plasma flows during the early stage refilling, ion-beam driven instabilities and associated waves are of primary interest. The major findings of this research are briefly summarized here. After a systematic examination of the relevant plasma instabilities, we realized that when the interhemispheric plasma flows begin to interpenetrate at the equator, the most relevant plasma instability is the electrostatic ion cyclotron wave instability. Only at later stages the ion-acoustic instability may be affecting the plasma flow. An interesting property of the electrostatic ion cyclotron wave is that it heats ions perpendicular to the magnetic field. When the ions in the field-aligned flows are transversely heated, they are trapped in the magnetic flux tube, thus affecting the refilling process. The eic wave instability is a microprocess with scale length of the order of ion Larmor radius and the corresponding time scale is the ion cyclotron period. We have attempted to tackle the problem for the plasmaspheric refilling by incorporating the effects of eic wave instability on the mesoscale plasma flow when the properties of the latter exceeds the critical conditions for the former. We have compared the results on refilling from the model with and without the eic instability effects.

Singh, Nagendra↗