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NASA NTRS1989

Atomic oxygen resistant protective coatings for the Hubble Space Telescope solar array in low earth orbit

The Hubble Space Telescope back-up solar array (BSFR-ATOX) was designed with atomic oxygen resistant materials to replace the original high efficiency cell (HEC) array. Pending qualification of the BSFR-ATOX array, protective coatings for application to the existing HEC array were evaluated. Three polysiloxane-type coating materials, SWS V-10, DC-100, and CV-1144 were evaluated with respect to atomic oxygen resistance, outgassing, contamination potential, stability under UV irradiation, electron-proton irradiation, thermal cycling, and long-term storage after application. Atomic oxygen testing included characterization of the atomic oxygen plasma using comparison of Kapton reaction to existing flight data, residual gas analysis, and temperature measurements. Results from these tests show DC-100 as a greater contamination concern if used in the vicinity of sensitive optical surfaces, i.e., solar cell cover glasses. The SWS V-10 and CV-1144 coatings met all acceptance criteria.

Burns, H. D.↗

NASA NTRS1992

Numerical study on mixing of sprayed liquid in an LNG storage tank

This paper presents a numerical method to simulate the mixing of heavier LNG sprayed on lighter layer. Numerical results for evolutions of flow field and density field are obtained in a rectangular computational domain which includes the vicinity of the liquid surface. At the surface boundary, uniform distributions of the fluid velocity and the density are assumed. Detail structure of flow caused by impingements of liquid drops are neglected. But, to trigger a realistic motion, a series of random numbers is employed. It is used as an initial distribution of the density near the surface. This method successfully gives a realistic simulation of the mixing process. Numerical results for mixing velocity shows good agreement with experimental data.

Uchida, Hiroyuki↗

NASA NTRS1994

Analysis of coseismic surface displacement gradients using radar interferometry: New insights into the Landers earthquake

The map of the coseismic displacement field generated by interferometric processing of synthetic aperture radar (SAR) images taken before and after the June 28, 1992, Landers earthquake sequence brings new insights into the nature of deformation caused by these earthquakes. We use the interferometric map generated by Massonnet et al. (1993) to analyze the surface displacement field in the vicinity of the fault trace. Complexities in the fringe pattern near the fault reflect short-wavelength variations of the surface rupture and slip distribution, and attest to large displacement gradients. Along two sections of the fault, characteristic fringe patterns can be recognized, contrasting in density and direction with patterns observed away from the rupture. In order to understand the observed fringe patterns, we compute synthetic interferograms in three simple cases: (1) rigid-body rotations about a vertical axis, (2) about a horizontal axis (tilt), and (3) distributed, simple shear. The orientation and spatial separation of interferometric fringes predicted by these models help constrain near-field deformation and rupture parameters. Where the Kickapoo fault connects with the Homestead Valley fault, the interferogram shows a clear pattern of parallel N20 deg W fringes separated by about 160 m. This pattern and vertical offsets measured along the Kickapoo fault suggest that the block between this fault and the Johnson Valley fault may have been tilted, down to the west. A 5-km block lifted by 1 m on one side would be tilted by an angle of 0.01 deg (190 microrad), producing fringes separated by about 160 m, parallel to the tilt axis. Such a tilt, parallel to a N20 deg W direction, would account for the gradual, northward increase of the vertical slip component observed along the Kickapoo fault. This tilt may also explain the 1 m of reverse slip observed along the 'slip gap' section of the Homestead Valley break. Between the southern end of the Johnson Valley fault and the Eureka Peak fault, where no surface rupture has been mapped, the dense pattern of fringes implies distributed shear, probably resulting from fault slip at depth. The density and direction of the fringes in the gap are consistent with a right-lateral slip of 1.2-3.8 m on a blind fault locked above the depth of 1.5-2 km. Such observations of small wavelength features in the SAR interferogram bring new insights into the near-field displacement gradient and thus on response of the uppermost crust to seismic rupture.

Peltzer, Gilles↗

NASA NTRS2001

Advanced Communication and Networking Technologies for Mars Exploration

Next-generation Mars communications networks will provide communications and navigation services to a wide variety of Mars science vehicles including: spacecraft that are arriving at Mars, spacecraft that are entering and descending in the Mars atmosphere, scientific orbiter spacecraft, spacecraft that return Mars samples to Earth, landers, rovers, aerobots, airplanes, and sensing pods. In the current architecture plans, the communication services will be provided using capabilities deployed on the science vehicles as well as dedicated communication satellites that will together make up the Mars network. This network will evolve as additional vehicles arrive, depart or end their useful missions. Cost savings and increased reliability will result from the ability to share communication services between missions. This paper discusses the basic architecture that is needed to support the Mars Communications Network part of NASA's Space Science Enterprise (SSE) communications architecture. The network may use various networking technologies such as those employed in the terrestrial Internet, as well as special purpose deep-space protocols to move data and commands autonomously between vehicles, at disparate Mars vicinity sites (on the surface or in near-Mars space) and between Mars vehicles and earthbound users. The architecture of the spacecraft on-board local communications is being reconsidered in light of these new networking requirements. The trend towards increasingly autonomous operation of the spacecraft is aimed at reducing the dependence on resource scheduling provided by Earth-based operators and increasing system fault tolerance. However, these benefits will result in increased communication and software development requirements. As a result, the envisioned Mars communications infrastructure requires both hardware and protocol technology advancements. This paper will describe a number of the critical technology needs and some of the ongoing research activities.

Bhasin, Kul↗

NASA NTRS2001

Monthly Report of the Meteorological Satellite Center: June 2001

The CD-ROM concerning the June 2001 Monthly Report of the Meteorological Satellite Center (MSC) contains the observation data derived from the Geostationary Meteorological Satellite (GMS) of Japan and the Polar Orbital Meteorological Satellites operated by NOAA. The CD-ROM contains the following observation data: Full Disk Earth's Cloud Image; Cloud Image of Japan and its vicinity; Cloud Amount; Sea Surface Temperature; Cloud Motion Wind; Water Vapor Motion Wind; Equivalent Blackbody Temperature; OLR (Out-going Longwave Radiation), Solar Radiation; Snow and Ice Index; Orbit Data; Attitude Data; VISSR Image Data Catalog (Cartridge Magnetic Tape (CMT), Micro Film); TOVS (TIROS Operational Vertical Sounder) Vertical Profile of Temperature and Precipitable Water; and TOVS Total Ozone Amount.

Source record↗

NASA NTRS2008

Passive Porous Treatment for Reducing Flap Side-Edge Noise

A passive porous treatment has been proposed as a means of suppressing noise generated by the airflow around the side edges of partial-span flaps on airplane wings when the flaps are extended in a high-lift configuration. The treatment proposed here does not incur any aerodynamic penalties and could easily be retrofit to existing airplanes. The treatment could also be applied to reduce noise generated by turbomachinery, including wind turbines. Innovative aspects of the proposed treatment include a minimum treatment area and physics-based procedure for treatment design. The efficacy of the treatment was confirmed during wind-tunnel experiments at NASA Ames, wherein the porous treatment was applied to a minute surface area in the vicinity of a flap edge on a 26-percent model of Boeing 777-200 wing.

Choudhari, Meelan M.↗

NASA NTRS2010

Fast X-Ray Timing: A Window into the Strong-Field Regime

The dynamical time-scales in the vicinity of neutron star surfaces and black hole horizons are in the millisecond range. Over the past decade, timing signatures on such scales, either quasi-periodic oscillations (QPOs) and/or coherent pulsations, have been discovered and studied from both neutron stars and black holes with NASA's Rossi X-ray Timing Explorer, Although theoretical interpretations are still hotly debated, these timing properties almost certainly reflect the dynamics of matter in regions dominated by relativistic gravity. I will survey our current understanding of these timing properties, with a focus on how they might he used as probes of fundamental physics.

Strohmayer, Tod↗

NASA NTRS2005

Program Computes Sound Pressures at Rocket Launches

Launch Vehicle External Sound Pressure is a computer program that predicts the ignition overpressure and the acoustic pressure on the surfaces and in the vicinity of a rocket and launch pad during launch. The program generates a graphical user interface (GUI) that gathers input data from the user. These data include the critical dimensions of the rocket and of any launch-pad structures that may act as acoustic reflectors, the size and shape of the exhaust duct or flame deflector, and geometrical and operational parameters of the rocket engine. For the ignition-overpressure calculations, histories of the chamber pressure and mass flow rate also are required. Once the GUI has gathered the input data, it feeds them to ignition-overpressure and launch-acoustics routines, which are based on several approximate mathematical models of distributed sources, transmission, and reflection of acoustic waves. The output of the program includes ignition overpressures and acoustic pressures at specified locations.

Ogg, Gary↗

NASA NTRS2013

Can Solution Supersaturation Affect Protein Crystal Quality?

The formation of large protein crystals of "high quality" is considered a characteristic manifestation of microgravity. The physical processes that predict the formation of large, high quality protein crystals in the microgravity environment of space are considered rooted in the existence of a "depletion zone" in the vicinity of crystal. Namely, it is considered reasonable that crystal quality suffers in earth-grown crystals as a result of the incorporation of large aggregates, micro-crystals and/or large molecular weight "impurities", processes which are aided by density driven convective flow or mixing at the crystal-liquid interface. Sedimentation and density driven convection produce unfavorable solution conditions in the vicinity of the crystal surface, which promotes rapid crystal growth to the detriment of crystal size and quality. In this effort, we shall further present the hypothesis that the solution supersaturatoin at the crystal surface determines the growth mechanism, or mode, by which protein crystals grow. It is further hypothesized that protein crystal quality is affected by the mechanism or mode of crystal growth. Hence the formation of a depletion zone in microgravity environment is beneficial due to inhibition of impurity incorporatoin as well as preventing a kinetic roughening transition. It should be noted that for many proteins the magnitude of neither protein crystal growth rates nor solution supersaturation are predictors of a kinetic roughening transition. That is, the kinetic roughening transition supersaturation must be dtermined for each individual protein.

Gorti, Sridhar↗

NASA NTRS2016

An Independent Orbit Determination Simulation for the OSIRIS-REx Asteroid Sample Return Mission

After arriving at the near-Earth asteroid (101955) Bennu in late 2018, the OSIRIS-REx spacecraft will execute a series of observation campaigns and orbit phases to accurately characterize Bennu and ultimately collect a sample of pristine regolith from its surface. While in the vicinity of Bennu, the OSIRIS-REx navigation team will rely on a combination of ground-based radiometric tracking data and optical navigation (OpNav) images to generate and deliver precision orbit determination products. Long before arrival at Bennu, the navigation team is performing multiple orbit determination simulations and thread tests to verify navigation performance and ensure interfaces between multiple software suites function properly. In this paper, we will summarize the results of an independent orbit determination simulation of the Orbit B phase of the mission performed to test the interface between the OpNav image processing and orbit determination software packages.

Orbit↗

NASA NTRS2020

Feasibility of “Weak GPS” Real-Time Positioning/Timing at Lunar Distance

There are multiple Global Navigation Satellite Systems (GNSS’s), comprising over 100 navigation satellites in the Earth’s medium and high orbits. Most of these satellites have antennas that point Nadir to earth, and transmit navigation signals so vehicles on Earth’s surface and in its vicinity can perform trilateration and estimate its 3-dimenional (3D) positioning. The sidelobes of these antennas can occasionally point to the Moon. It is postulated that a lunar vehicle carrying a large enough receiving antenna can occasionally detects and receives four or more sidelobes of these weak GNSS signals, thus enabling the vehicle to perform 3D positioning using an onboard GNSS receiver. We propagate the orbits of the GNSS satellites from United States’ Global Positioning Satellite (GPS) constellation, the Europe’s Galileo constellation, and the Russia’s GLONASS constellation, a total of 81 satellites. We simulate the visibility of these satellites by a lunar vehicle in a Near Rectilinear Halo Orbit (NRHO), based on the assumption that the lunar vehicle is “in-view” of a GNSS satellite as long as it falls within the 40- degree beam-width of the satellite. We also simulate the 3D positioning performance as a function of satellites’ ephemeris errors and pseudo-range errors. The preliminary results show that the lunar vehicle can “see” 5 – 13 satellites, and achieve a 3D positioning error (one-sigma) of 200 – 300 meters based on reasonable ephemeris and pseudo- range error assumptions. We also consider the case of using relative positioning to mitigate the GNSS satellites’ ephemeris biases. That is, by assuming a reference receiver with accurately known positioning that is close to the lunar vehicle, and computing the relative position of the lunar vehicle relative to the reference.

Cheung, Kar-Ming↗

NASA NTRS1977

Chemical and optical properties at the Apollo 15 and 16 sites

The bulk chemical composition, the surface chemical concentration of four major elements, and the optical albedo were determined for six core samples, for two sites and from four different depths below the lunar surface, and also for surface soil samples from the vicinity of the sites of the cores. The chemical composition of the core samples was found to be related to that of the surface samples from the same sites, and the correlation of the albedo with the surface iron plus titanium content that has previously been demonstrated for the surface samples was also verified for the core samples. A soil layer near the bottom of the Apollo 15 deep drill core was found to be unusual in two respects: the grain surface and the bulk chemical compositions were found to be more similar than is usual, and the albedo was exceptionally high, though still only 0.6 of the albedo of crushed rock of similar composition. The mechanism of darkening of lunar soil is discussed in the light of these observations.

Gold, T.↗

NASA NTRS1997

Aeroacoustic Measurements of a Wing-Flap Configuration

Aeroacoustic measurements are being conducted to investigate the mechanisms of sound generation in high-lift wing configurations, and initial results are presented. The model is approximately 6 percent of a full scale configuration, and consists of a main element NACA 63(sub 2) - 215 wing section and a 30 percent chord half-span flap. Flow speeds up to Mach 0.17 are tested at Reynolds number up to approximately 1.7 million. Results are presented for a main element at a 16 degree angle of attack, and flap deflection angles of 29 and 39 degrees. The measurement systems developed for this test include two directional arrays used to localize and characterize the noise sources, and an array of unsteady surface pressure transducers used to characterize wave number spectra and correlate with acoustic measurements. Sound source localization maps show that locally dominant noise sources exist on the flap-side edge. The spectral distribution of the noise sources along the flap-side edge shows a decrease in frequency of the locally dominant noise source with increasing distance downstream of the flap leading edge. Spectra are presented which show general spectral characteristics of Strouhal dependent flow-surface interaction noise. However, the appearance of multiple broadband tonal features at high frequency indicates the presence of aeroacoustic phenomenon following different scaling characteristics. The scaling of the high frequency aeroacoustic phenomenon is found to be different for the two flap deflection angles tested. Unsteady surface pressure measurements in the vicinity of the flap edge show high coherence levels between adjacent sensors on the flap-side edge and on the flap edge upper surface in a region which corresponds closely to where the flap-side edge vortex begins to spill over to the flap upper surface. The frequency ranges where these high levels of coherence occur on the flap surface are consistent with the frequency ranges in which dominant features appear in far field acoustic spectra. The consistency of strongly correlated unsteady surface pressures and far field pressure fluctuations suggests the importance of regions on the flap edge in generating sound.

Meadows, Kristine R.↗

NASA NTRS1973

Near-terminator and earthshine photography

Photographic results obtained during the Apollo 17 flight for the near terminator and earthshine conditions are discussed. Lunar surface photographs taken in the vicinity of the sunshine terminator provide important information that is not obtained on photographs taken at higher sun evaluation angles. Earthshine photography also provides data on low relief, crater morphology, and small scale structures. Examples of photographs of the lunar surface taken under both conditions are provided.

Head, J. W.↗

NASA NTRS1986

Identification of some key parameters limiting the performance of high-efficiency silicon solar cells

This paper presents, for the first time, a detailed sensitivity analysis of key cell parameters on silicon-cell efficiency by incorporating advanced solar cell physics in a sophisticated numerical simulation program. It delineates the true physical barriers to obtaining a high-efficiency silicon solar cell. Specific parameters presently limiting cell efficiency are identified to be the minority carrier lifetime and the recombination velocities at the front and back surfaces. Practical cell efficiencies in the vicinity of 22 percent are estimated to be attainable by using good quality silicon crystal and substantially reducing surface recombination velocities.

Mokashi, Anant R.↗

NASA NTRS2012

Aeroacoustic Study of a High-Fidelity Aircraft Model: Unsteady Surface Pressures - Part 2

In this paper, we present unsteady surface pressure measurements for an 18%-scale, semi-span Gulfstream aircraft model. This high-fidelity model is being used to perform detailed studies of airframe noise associated with main landing gear, flap components, and gear-flap interaction noise, as well as to evaluate novel noise reduction concepts. The aerodynamic segment of the tests, conducted in the NASA Langley Research Center 14- by 22-Foot Subsonic Tunnel, was completed in November 2010. To discern the characteristics of the surface pressure fluctuations in the vicinity of the prominent noise sources, unsteady sensors were installed on the inboard and outboard flap edges, and on the main gear wheels, struts, and door. Various configurations were tested, including flap deflections of 0?, 20?, and 39?, with and without the main landing gear. The majority of unsteady surface pressure measurements were acquired for the nominal landing configuration where the main gear was deployed and the flap was deflected 39?. To assess the Mach number variation of the surface pressure amplitudes, measurements were obtained at Mach numbers of 0.16, 0.20, and 0.24. Comparison of the unsteady surface pressures with the main gear on and off shows significant interaction between the gear wake and the inboard flap edge, resulting in higher amplitude fluctuations when the gear is present.

Khorrami, Mehdi R.↗

NASA NTRSDate not supplied

Artemis Internal Science Team Update: Crew Training

Astronauts will soon return to the Moon as part of Artemis — a campaign of crewed missions to explore the lunar surface. The first crewed Artemis missions include Artemis II, which will send four astronauts to lunar orbit to test the Orion spacecraft and observe the lunar surface; and Artemis III, the first human mission to land on the Moon in the vicinity of the South Pole. Artemis III surface objectives include lunar exploration through scientific traverses and observations, collection of lunar samples for Earth return, and deployment of scientific instruments. From this point, human missions to the lunar surface will continue under Artemis, with increasing exploration capability.

Artemis Science↗

NASA NTRS2018

Thermodynamic and Dynamic Aspects of Ice Nucleation

It is known that ice nucleating particles (INP) immersed within supercooled droplets promote the formation of ice. Common theoretical models used to represent this process assume that the immersed particle lowers the work of ice nucleation without significantly affecting the dynamics of water in the vicinity of the particle. This is contrary to evidence showing that immersed surfaces significantly affect the viscosity and diffusivity of vicinal water. To study how this may affect ice formation this work introduces a model linking the ice nucleation rate to the modification of the dynamics and thermodynamics of vicinal water by immersed particles. It is shown that INP that significantly reduce the work of ice nucleation also pose strong limitations to the growth of the nascent ice germs. This leads to the onset of a new ice nucleation regime, called spinodal ice nucleation, where the dynamics of ice germ growth instead of the ice germ size determines the nucleation rate. Nucleation in this regime is characterized by an enhanced sensitivity to particle area and cooling rate. Comparison of the predicted ice nucleation rate against experimental measurements for a diverse set of species relevant to cloud formation suggests that spinodal ice nucleation may be common in nature.

Barahona, Donifan↗