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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 1,081 records · Page 60
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Power system state estimation for a spacecraft power system

An application of the maximum likelihood state estimator to a space-based power system is presented. The state estimator uses current and voltage measurements to generate estimates of node voltages for an electrical power distribution system for the Space Shuttle. Preliminary results on the effect of noisy measurements on estimated parameters are reported. The software used in generating these results is part of an overall package being developed at Louisiana Tech University. Intended applications of this package include the analysis of power systems and real-time parallel processing on the Space Shuttle.

Berry, F. C.↗
NASA NTRS1992

Method and apparatus for using magneto-acoustic remanence to determine embrittlement

A method and apparatus for testing steel components for temperature embrittlement uses magneto-acoustic emission to nondestructively evaluate the component are presented. Acoustic emission signals occur more frequently at higher levels in embrittled components. A pair of electromagnets are used to create magnetic induction in the test component. Magneto-acoustic emission signals may be generated by applying an AC current to the electromagnets. The acoustic emission signals are analyzed to provide a comparison between a component known to be unembrittled and a test component. Magnetic remanence is determined by applying a DC current to the electromagnets and then by turning the magnets off and observing the residual magnetic induction.

Allison, Sidney G.↗
NASA NTRS1992

Comparative investigation of multiplane thrust vectoring nozzles

The inflight aerodynamic performance of multiplane vectoring nozzles is critical to development of advanced aircraft and flight control systems utilizing thrust vectoring. To investigate vectoring nozzle performance, subscale models of two second-generation thrust vectoring nozzle concepts currently under development for advanced fighters were integrated into an axisymmetric test pod. Installed drag and vectoring performance characteristics of both concepts were experimentally determined in wind tunnel testing. CFD analyses were conducted to understand the impact of internal flow turning on thrust vectoring characteristics. Both nozzles exhibited drag comparable with current nonvectoring axisymmetric nozzles. During vectored-thrust operations, forces produced by external flow effects amounted to about 25 percent of the total force measured.

Capone, F.↗
NASA NTRS1992

Study of plasma environments for the integrated Space Station electromagnetic analysis system

The final report includes an analysis of various plasma effects on the electromagnetic environment of the Space Station Freedom. Effects of arcing are presented. Concerns of control of arcing by a plasma contactor are highlighted. Generation of waves by contaminant ions are studied and amplitude levels of the waves are estimated. Generation of electromagnetic waves by currents in the structure of the space station, driven by motional EMF, is analyzed and the radiation level is estimated.

Singh, Nagendra↗
NASA NTRS1993

Gravitational microlensing of gamma-ray bursts

A Monte Carlo code is developed to calculate gravitational microlensing in three dimensions when the lensing optical depth is low or moderate (not greater than 0.25). The code calculates positions of microimages and time delays between the microimages. The majority of lensed gamma-ray bursts should show a simple double-burst structure, as predicted by a single point mass lens model. A small fraction should show complicated multiple events due to the collective effects of several point masses (black holes). Cosmological models with a significant fraction of mass density in massive compact objects can be tested by searching for microlensing events in the current BATSE data. Our catalog generated by 10,000 Monte Carlo models is accessible through the computer network. The catalog can be used to take realistic selection effects into account.

Mao, Shude↗
NASA NTRS1993

Incorporation of a hierarchical grid component structure into GRIDGEN

The underlying framework of the GRIDGEN multiple block grid generation system has been refined so that grid components are now stored within a hierarchical data structure. This restructuring has enhanced the usability of the software by allowing grids to be generated on a more intuitive level. This new framework also provides a means by which the multiple block system can be edited at most any level in the grid generation process. Editing tools are currently being added to GRIDGEN so that a change to the grid can be propagated backward and forward in the data hierarchy. The new data structure, the editing tools, and other recent GRIDGEN improvements are described in this paper.

Steinbrenner, John P.↗
NASA NTRS1991

BALLIST: A computer program to empirically predict the bumper thickness required to prevent perforation of the Space Station by orbital debris

A computer program called BALLIST that is intended to be a design tool for engineers is described. BALLlST empirically predicts the bumper thickness required to prevent perforation of the Space Station pressure wall by a projectile (such as orbital debris) as a function of the projectile's velocity. 'Ballistic' limit curves (bumper thickness vs. projectile velocity) are calculated and are displayed on the screen as well as being stored in an ASCII file. A Whipple style of spacecraft wall configuration is assumed. The predictions are based on a database of impact test results. NASA/Marshall Space Flight Center currently has the capability to generate such test results. Numerical simulation results of impact conditions that can not be tested (high velocities or large particles) can also be used for predictions.

Rule, William Keith↗
NASA NTRS1992

High efficiency low cost monolithic module for SARSAT distress beacons

The program objectives were to develop a highly efficient, low cost RF module for SARSAT beacons; achieve significantly lower battery current drain, amount of heat generated, and size of battery required; utilize MMIC technology to improve efficiency, reliability, packaging, and cost; and provide a technology database for GaAs based UHF RF circuit architectures. Presented in viewgraph form are functional block diagrams of the SARSAT distress beacon and beacon RF module as well as performance goals, schematic diagrams, predicted performances, and measured performances for the phase modulator and power amplifier.

Petersen, Wendell C.↗
NASA NTRS1995

Improved reduced-resolution satellite imagery

The resolution of satellite imagery is often traded-off to satisfy transmission time and bandwidth, memory, and display limitations. Although there are many ways to achieve the same reduction in resolution, algorithms vary in their ability to preserve the visual quality of the original imagery. These issues are investigated in the context of the Landsat browse system, which permits the user to preview a reduced resolution version of a Landsat image. Wavelets-based techniques for resolution reduction are proposed as alternatives to subsampling used in the current system. Experts judged imagery generated by the wavelets-based methods visually superior, confirming initial quantitative results. In particular, compared to subsampling, the wavelets-based techniques were much less likely to obscure roads, transmission lines, and other linear features present in the original image, introduce artifacts and noise, and otherwise reduce the usefulness of the image. The wavelets-based techniques afford multiple levels of resolution reduction and computational speed. This study is applicable to a wide range of reduced resolution applications in satellite imaging systems, including low resolution display, spaceborne browse, emergency image transmission, and real-time video downlinking.

Ellison, James↗
NASA NTRS1995

Alternative packet switch architectures for a 30/20 GHz FDMA/TDMA geostationary communication satellite network

This study has investigated alternatives for realizing a packet-based network switch for deployment on a communication satellite. The emphasis was on the avoidance of contention problems that can occur due to the simultaneous arrival of an excessive number of packets destined for the same downlink dwell. The study was to look ahead, beyond the current Advanced Communications Technology Satellite (ACTS) capability, to the next generation of satellites. The study has not been limited by currently available technology, but has used university and commercial research efforts as a basis for designs that can be readily constructed and launched within the next five years. Tradeoffs in memory requirement, power requirement, and architecture have been considered as a part of our study.

Stehle, Roy↗
NASA NTRS1995

Propagation of beam-driven VLF waves from the ionosphere toward the ground

As part of the Cooperative High Altitude Rocket Gun Experiment (CHARGE-2B) rocket mission, an electron beam was injected into the ionosphere with a modulated beam current in an effort to generate very low frequency (VLF) waves. The propagation of the beam-driven VLF waves through the ionosphere is examined here to determine whether it is possible to detect these wave emissions with ground receivers. The paths of the VLF waves from where they were generated near the rocket were followed to the bottom of the ionosphere and the decrease in wave amplitude due to wave-particle resonance and collisional damping was calculated. It was found that due to collisional damping, which for these VLF waves becomes large at altitudes below about 150 km, wave amplitudes were decreased below the background atmospheric noise level. A number of different beam injection events have been examined and in all of these cases studied the waves were sufficiently damped such that detection on the ground would not be possible. This is in agreement with observations on the ground in which no wave emissions were observed during the CHARGE-2B mission. Control parameters that would be more favorable for beam-generated VLF propagation to the ground are discussed for future experiments of this type.

Schriver, David↗
NASA NTRS1996

Large Format Multifunction 2-Terabyte Optical Disk Storage System

The Kodak Digital Science OD System 2000E automated disk library (ADL) base module and write-once drive are being developed as the next generation commercial product to the currently available System 2000 ADL. Under government sponsorship with the Air Force's Rome Laboratory, Kodak is developing magneto-optic (M-O) subsystems compatible with the Kodak Digital Science ODW25 drive architecture, which will result in a multifunction (MF) drive capable of reading and writing 25 gigabyte (GB) WORM media and 15 GB erasable media. In an OD system 2000 E ADL configuration with 4 MF drives and 100 total disks with a 50% ration of WORM and M-O media, 2.0 terabytes (TB) of versatile near line mass storage is available.

Kaiser, David R.↗
NASA NTRS1996

An Independent Evaluation of the FMEA/CIL Hazard Analysis Alternative Study

The present instruments of safety and reliability risk control for a majority of the National Aeronautics and Space Administration (NASA) programs/projects consist of Failure Mode and Effects Analysis (FMEA), Hazard Analysis (HA), Critical Items List (CIL), and Hazard Report (HR). This extensive analytical approach was introduced in the early 1970's and was implemented for the Space Shuttle Program by NHB 5300.4 (1D-2. Since the Challenger accident in 1986, the process has been expanded considerably and resulted in introduction of similar and/or duplicated activities in the safety/reliability risk analysis. A study initiated in 1995, to search for an alternative to the current FMEA/CIL Hazard Analysis methodology generated a proposed method on April 30, 1996. The objective of this Summer Faculty Study was to participate in and conduct an independent evaluation of the proposed alternative to simplify the present safety and reliability risk control procedure.

Ray, Paul S.↗
NASA NTRS1996

Scattering and the Point Spread Function of the New Generation Space Telescope

Preliminary design work on the New Generation Space Telescope (NGST) is currently under way. This telescope is envisioned as a lightweight, deployable Cassegrain reflector with an aperture of 8 meters, and an effective focal length of 80 meters. It is to be folded into a small-diameter package for launch by an Atlas booster, and unfolded in orbit. The primary is to consist of an octagon with a hole at the center, and with eight segments arranged in a flower petal configuration about the octagon. The comers of the petal-shaped segments are to be trimmed so that the package will fit atop the Atlas booster. This mirror, along with its secondary will focus the light from a point source into an image which is spread from a point by diffraction effects, figure errors, and scattering of light from the surface. The distribution of light in the image of a point source is called a point spread function (PSF). The obstruction of the incident light by the secondary mirror and its support structure, the trimmed corners of the petals, and the grooves between the segments all cause the diffraction pattern characterizing an ideal point spread function to be changed, with the trimmed comers causing the rings of the Airy pattern to become broken up, and the linear grooves causing diffraction spikes running radially away from the central spot, or Airy disk. Any figure errors the mirror segments may have, or any errors in aligning the petals with the central octagon will also spread the light out from the ideal point spread function. A point spread function for a mirror the size of the NGST and having an incident wavelength of 900 nm is considered. Most of the light is confined in a circle with a diameter of 0.05 arc seconds. The ring pattern ranges in intensity from 10(exp -2) near the center to 10(exp -6) near the edge of the plotted field, and can be clearly discerned in a log plot of the intensity. The total fraction of the light scattered from this point spread function is called the total integrated scattering (TIS), and the fraction remaining is called the Strehl ratio. The angular distribution of the scattered light is called the angle resolved scattering (ARS), and it shows a strong spike centered on a scattering angle of zero, and a broad , less intense distribution at larger angles. It is this scattered light, and its effect on the point spread function which is the focus of this study.

Schreur, Julian J.↗
NASA NTRS1998

Design of Large Lightweight Space Telescope Optical Systems for the Next Generation Space Telescope

The Next Generation Space Telescope (NGST) is currently in a Pre Phase A study effort to prove feasibility of design and to show that the design can be implemented within cost constraint guidelines and meet the requirements of the science community. In an effort to achieve the science communities goals as outlined in "HST and Beyond" the NGST team has developed a government "yardstick" design of an eight meter diameter segmented telescope which would be launched in an Atlas IIAS launch vehicle to a L2 (Lagrange Point) orbit. This paper will discuss the design of the Optical Telescope Assembly (OTA) and the various issues and complications of designing lightweight optics to be placed in the environment that the NGST will encounter both during launch and during its operational mission at L2. The OTA must be lightweight but structurally must withstand the launch environment and transfer to its final L2 orbit. The OTA must be stable at L2 to provide high quality science at the cryogenic temperatures it will experience. The OTA segmented petal concept is to develop lightweight optics which can either be manipulated to achieve and maintain a desired figure or be rigid enough so that change in shape is only necessary for phasing and alignment. The secondary mirror structural mast must also be rigid with frequency responses which are not coupled to spacecraft modes in order to maintain and decenter and despace requirements.

Jacobson, Dave↗
NASA NTRS2000

Southern Ocean Response to NADW Changes

The possibility of North Atlantic Deep Water (NADW) changes in both past and future climates has raised the issue of how the Southern Ocean would respond. Recent experiments with the GISS coupled atmosphere-ocean model have shown that a "bipolar see-saw" between NADW production and Antarctic Bottom Water (AABW) production in the Weddell Sea can occur in conjunction with freshening of the North Atlantic. However, this effect operates not through a slow ocean response but via a rapid atmospheric mechanism. As NADW reduces, colder temperatures in the North Atlantic, and Northern Hemisphere in general, are associated with higher surface pressure (increased atmospheric mass). Reduced mass in the Southern Hemisphere occurs in response, with lower pressure over the South Pole (an EOF #1 effect, the "high phase" of the Antarctic Oscillation).The lower pressure is associated with stronger west winds that generate an intensified Antarctic Circumpolar Current (ACC), which leads to longitudinal heat divergence in the South Atlantic (and heat convergence in the Southern Indian Ocean). Colder temperatures in the Weddell Sea region lead to sea ice growth, increased salinity and surface water density, and greater Weddell Sea Bottom Water production. Increased poleward transport of heat occurs in the South Atlantic in conjunction with increased bottom water production, but its convergence at high latitudes is not sufficient to offset the longitudinal heat divergence due to the intensified ACC. The colder temperatures at high latitudes in the South Atlantic increase the latitudinal temperature gradient, baroclinic instability, eddy energy and eddy poleward transport of momentum, helping to maintain the lower pressure over the pole in an interactive manner. The heat flux convergence in the Indian Ocean provides a warming tendency in that region, and overall global production of AABW remains unchanged. These results have implications for the interpretation of the ice core records of the last deglaciation, but may also be relevant for changes during the Holocene and perhaps even in response to increased CO2 forcing,

Rind, David↗
NASA NTRS2001

Life Testing of the Hollow Cathode Plasma Contactor for the ProSEDS Mission

The Propulsive Small Expendable Deployer System (ProSEDS) mission is designed to provide an on-orbit demonstration of the electrodynamic propulsion capabilities of tethers in space. The ProSEDS experiment will be a secondary payload on a Delta 11 unmanned expendable booster. A 5-km conductive tether is attached to the Delta 11 second stage and collects current from the low Earth orbit (LEO) plasma. A hollow cathode plasma contactor emits the collected electrons from the Delta II, completing the electrical circuit with the ambient plasma. The current flowing through the tether generates thrust based on the Lorentz Force Law. The thrust will be generated opposite to the velocity vector, slowing down the spacecraft and causing it to de-orbit in approximately 14 days compared to the normal 6 months. A 10-km non-conductive tether is between the conductive tether and an endmass containing several scientific instruments. The ProSEDS mission lifetime was set at I day because most of the primary objectives can be met in that time. The extended ProSEDS mission will be for as many days as possible, until the Delta 11 second stage burns up or the tether is severed by a micrometeoroid or space debris particle. The Hollow Cathode Plasma Contactor (HCPC) unit has been designed for a 12-day mission. Because of the science requirements to measure the background ambient plasma, the HCPC must operate on a duty cycle. Later in the ProSEDS mission, the HCPC is operated in a manner to allow charging of the secondary battery. Due to the unusual operating requirements by the ProSEDS mission, a development unit of the HCPC was built for thorough testing. This developmental unit was tested for a simulated ProSEDS mission, with measurements of the ability to start and stop during the duty cycle. These tests also provided valuable data for the ProSEDS software requirements. Qualification tests of the HCPC flight hardware are also discussed.

Vaughn, Jason A.↗
NASA NTRS2001

A Global Electric Circuit on Mars

We describe conditions on the surface of Mars conducive to the formation of a martian global electric circuit, in a direct analogy to the terrestrial case where atmospheric currents and electric fields are generated worldwide through the charging in thunderstorms. Additional information is contained in the original extended abstract.

Delory, G. T.↗