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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 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
NASA NTRS2018

CLAS-ACT: Conformal, Lightweight Antennas for Aeronautical Communications Technology

The growing demand for Unmanned Aerial Vehicles (UAVs) and operating them beyond the line of sight (BLOS) has resulted in an increased interest in using existing satellite communication capabilities for command, control, and telemetry (CC&T). As the user base in this allocated portion of the spectrum expands, there is an increased potential for interference with existing terrestrial fixed-point communication systems. As secondary users, UAVs must seek out new solutions to avoid interfering with these existing ground sites while maintaining good links with satellite constellations. In this presentation, a novel lightweight conformal phased array antenna currently under development is presented that can use null steering and/or beam shaping to avoid ground interference while simultaneously providing strong satellite microwave links for communications. The reduced weight of this design and ability to integrate into the fuselage of smaller UAV platforms will also be discussed as a potential solution to provide BLOS operation via spectrum sharing for an expanding user base.

Meador, Mary Ann↗
NASA NTRS1993

Modeling Non-Gravitational Forces Acting on Topex/Poseidon: The Early Days

Topex/Poseidon is a satellite mission that will use altimetry to make precise measurements of sea-level with unprecedented acuracy such that small-amplitude, basin wide sea-level with unprecedented accuracy such that small-amplitude, basin wide sea-level changes caused by large-scale ocean circulation can be detected.

Topex/Poseidon↗
NASA NTRS2021

Subcommittee on Space and Aeronautics Committee on Science, Space, and Technology: Statement by Dr. Gavin A. Schmidt Senior Advisor on Climate to the Administrator (Acting) National Aeronautics and Space Administration 117th Congress

NASA has long recognized that climate science and climate change are fundamental parts of our mandate, and for decades we have worked on fundamental and applied research in these areas. With the increasing evidence for serious impacts and the elevation of this topic by the Administration, it is time for a renewed focus on all the aspects of climate change that NASA works on and a commitment to ensure that the data and understanding that NASA has and will continue to accumulate will be used for the benefit of society.

Gavin A Schmidt↗
NASA NTRS2019

Measurement of the Splashback Feature Around SZ-Selected Galaxy Clusters With DES, SPT, and ACT

We present a detection of the splashback feature around galaxy clusters selected using the Sunyaev–Zel’dovich (SZ) signal. Recent measurements of the splashback feature around optically selected galaxy clusters have found that the splashback radius, rsp, is smaller than predicted by N-body simulations. A possible explanation for this discrepancy is that rsp inferred from the observed radial distribution of galaxies is affected by selection effects related to the optical cluster-finding algorithms. We test this possibility by measuring the splashback feature in clusters selected via the SZ effect in data from the South Pole Telescope SZ survey and the Atacama Cosmology Telescope Polarimeter survey. The measurement is accomplished by correlating these cluster samples with galaxies detected in the Dark Energy Survey Year 3data. The SZ observable used to select clusters in this analysis is expected to have a tighter correlation with halo mass and to be more immune to projection effects and aperture-induced biases, potentially ameliorating causes of systematic error for optically selected clusters. We find that the measured rsp for SZ-selected clusters is consistent with the expectations from simulations, although the small number of SZ-selected clusters makes a precise comparison difficult. In agreement with previous work, when using optically selected red MaPPer clusters with similar mass and redshift distributions,rspis∼2σsmaller than in the simulations. These results motivate detailed investigations of selection biases in optically selected cluster catalogues and exploration of the splashback feature around larger samples of SZ-selected clusters. Additionally, we investigate trends in the galaxy profile and splashback feature as a function of galaxy colour, finding that blue galaxies have profiles close to a power law with no discernible splashback feature, which is consistent with them being on their first in fall into the cluster.

T Shin↗
NASA NTRS2021

Probing Galaxy Evolution in Massive Clusters Using ACT and DES: Splashback as a Cosmic Clock

We measure the projected number density profiles of galaxies and the splashback feature in clusters selected by the Sunyaev–Zel'dovich effect from the Advanced Atacama Cosmology Telescope (AdvACT) survey using galaxies observed by the Dark Energy Survey (DES). The splashback radius is consistent with CDM-only simulations and is located at-+-h2.4 Mpc0.40.31. We split the galaxies on color and find significant differences in their profile shapes. Red and green-valley galaxies show a splashback-like minimum in their slope profile consistent with theory, while the bluest galaxies show a weak feature at a smaller radius. We develop a mapping of galaxies to subhalos in simulations and assign colors based on infall time onto their hosts. We find that the shift in location of the steepest slope and different profile shapes can be mapped to the average time of infall of galaxies of different colors. The steepest slope traces a discontinuity in the phase space of dark matter halos. By relating spatial profiles to infall time, we can use splashback as a clock to understand galaxy quenching. We find that red galaxies have on average been in clusters over 3.2 Gyr, green galaxies about 2.2 Gyr, while blue galaxies have been accreted most recently and have not reached apocenter. Using the full radial profiles, we fit a simple quenching model and find that the onset of galaxy quenching occurs after a delay of about a gigayear and that galaxies quench rapidly thereafter with an exponential timescale of 0.6 Gyr.

Galaxy clusters↗