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NASA NTRS2005

Spatial Extent of a Deep Moonquake Nest: A Preliminary Report of Reexamination

Deep moonquakes, occurring at depths about halfway to the center of the Moon, were discovered during the Apollo lunar landing missions, 1969-1972. Their near-monthly occurrence with nearly identical waveforms at any given seismic station suggests that they are strongly influenced by tides, caused by the Earth and the Sun, acting on certain limited regions of the deep lunar interior. However, much about them is unknown, why they are restricted to certain depths and to limited source regions (nests), and what they tell us about the nature of the material and dynamics of the interior of the Moon. A piece of information helpful to decipher their true nature is the spatial extent and distribution of their hypocenters. The occurrence of nearly identical waveforms suggests groups of hypocenters appear in close proximity to one another, but can we tell how closely they are located and how they are distributed? The Apollo PSE (Passive Seismic Experiment) data from all stations of the seismic network were received in real time at a common receiving station on Earth in digital form. This provided extremely high inter-station timing accuracy not achievable for most earthquake data on Earth at that time. We took advantage of this to compute relative locations of waveform-matched events, and concluded that deep moonquake foci in the A1 moonquake nest were concentrated on a nearly horizontal plane of less than 1 km in diameter. This earlier study was based on deep moonquake events visually identified on seismograms. A recent reanalysis of earlier unidentified seismic events fully utilizing the high capability of present-day computers expanded the list of positively identified deep moonquakes by more than a factor of five. The new list contains many events that are not visually matched in waveforms, yet correlated at a significant level when cross-correlated with a computer. Thus it became imperative to reexamine the spatial distribution of deep moonquake hypocenters including the newly identified events. Additional information is included in the original extended abstract.

Nakamura, Yosio↗
NASA NTRS2005

A Prototype Flux-Plate Heat-Flow Sensor for Venus Surface Heat-Flow Determinations

Venus is the most Earth-like planet in the Solar System in terms of size, and the densities of the two planets are almost identical when selfcompression of the two planets is taken into account. Venus is the closest planet to Earth, and the simplest interpretation of their similar densities is that their bulk compositions are almost identical. Models of the thermal evolution of Venus predict interior temperatures very similar to those indicated for the regions of Earth subject to solid-state convection, but even global analyses of the coarse Pioneer Venus elevation data suggest Venus does not lose heat by the same primary heat loss mechanism as Earth, i.e., seafloor spreading. The comparative paucity of impact craters on Venus has been interpreted as evidence for relatively recent resurfacing of the planet associated with widespread volcanic and tectonic activity. The difference in the gross tectonic styles of Venus and Earth, and the origins of some of the enigmatic volcano-tectonic features on Venus, such as the coronae, appear to be intrinsically related to Venus heat loss mechanism(s). An important parameter in understanding Venus geological evolution, therefore, is its present surface heat flow. Before the complications of survival in the hostile Venus surface environment were tackled, a prototype fluxplate heat-flow sensor was built and tested for use under synthetic stable terrestrial surface conditions. The design parameters for this prototype were that it should operate on a conforming (sand) surface, with a small, self-contained power and recording system, capable of operating without servicing for at least several days. The precision and accuracy of the system should be < 5 mW/sq m. Additional information is included in the original extended abstract.

Morgan, Paul↗
NASA NTRS2006

Mineralogy of nakhlite Martian meteorites: Implications for their relative burial depths

Nakhlites are Martian cumulate rocks mainly composed of augite with variable amounts of olivine and groundmass (mesostasis). Currently seven samples are known: Nakhla (Nak), Governador Valadares (GV), Lafayette (Laf), NWA817, Y000593 (Y), NWA998 and MIL03346 (MIL). All the nakhlites show a similar unbrecciated cumulate texture, and their identical crystallization and exposure ages suggest that they originated from the same igneous body on Mars and were ejected by the same impact event. It is important to study difference of their mineralogy to reconstruct the igneous body from which nakhlites originated. Augite grains in all nakhlites have a nearly identical core composition (En39Fs22Wo39) and have thin Fe-rich rims. These Fe-rich rims are zoned to Ca-poor pyroxene compositions and the degree of chemical zoning varies from one sample to another. NWA998 has the most Mg-rich edge composition. The edge composition becomes more Fe-rich in the order of Laf, Nak/GV, Y and NWA817. Unlike other samples, the Fe-rich edge of MIL augite is zoned to the hedenbergite composition. Olivine grains in all samples except Laf and NWA998 show extensive chemical zoning whose degree is clearly related to the chemical zoning of pyroxenes. MIL and NWA817 have the widest compositional ranges (Fa54-93). Y has a slightly narrower compositional range of Fa58-85. Nak and GV have even narrower ranges (Fa58-72). In contrast to these samples, olivines in Laf and NWA998 are homogeneous (Fa66-67 and Fa61-62, respectively). Such chemical zoning (Fa and Ca) can be used to quantitatively estimate their cooling rates (burial depths) because it was clearly formed by interaction with the intercumulus melt. The obtained burial depths are 1-2 m for NWA817, 4 m for MIL, 7 m for Y, approx.10 m for Nak and GV, and >30 m for Laf and NWA998. This order is clearly related to the degree of pyroxene chemical zoning. The abundance and mineralogy of nakhlite groundmass are also consistent with this order. In Nak, GV and Laf, the groundmass abundance is about 7-8%. Y and NWA998 have a slightly higher abundance (10%), while NWA817 and MIL have much higher abundance (20-24%). The groundmass texture is also related to its abundance. The groundmass of Nak, GV, Laf and Y is mainly composed of feldspar laths. In contrast, NWA817 and MIL have glassy mesostasis without feldspar crystals. In NWA998, feldspar is a large blocky crystal with clear twinning, suggesting that it is even deeper than Laf.

Mikouchi, T.↗
NASA NTRS2002

Companions to isolated elliptical galaxies: revisiting the Bothun-Sullivan (1977) sample using the NASA/IPAC extragalactic database

We investigate the number of physical companion galaxies for a sample of relatively isolated elliptical galaxies. The NASA/IPAC Extragalactic Database (NED) has been usedto reinvestigate the incidence of satellite galaxies for a sample of 34 elliptical galaxies, firstinvestigated by Bothun & Sullivan (1977) using a visual inspection of Palomar Sky Survey prints out to a projected search radius of 75 kpc. We have repeated their original investigation usingdata cataloged data in NED. Nine of these ellipticals appear to be members of galaxy clusters:the remaining sample of 25 galaxies reveals an average of +1.0 f 0.5 apparent companions per galaxy within a projected search radius of 75 kpc, in excess of two equal-area comparisonregions displaced by 150-300 kpc. This is nearly an order of magnitude larger than the +0.12+/- 0.42 companions/galaxy found by Bothun & Sullivan for the identical sample. Making use of published radial velocities, mostly available since the completion of the Bothun-Sullivan study,identifies the physical companions and gives a somewhat lower estimate of +0.4 companions per elliptical. This is still a factor of 3x larger than the original statistical study, but giventhe incomplete and heterogeneous nature of the survey redshifts in NED, it still yields a firmlower limit on the number (and identity) of physical companions. An expansion of the searchradius out to 300 kpc, again restricted to sampling only those objects with known redshifts in NED, gives another lower limit of 4.3 physical companions per galaxy. (Excluding fiveelliptical galaxies in the Fornax cluster this average drops to 3.5 companions per elliptical.)These physical companions are individually identified and listed, and the ensemble-averagedradial density distribution of these associated galaxies is presented. For the ensemble, the radial density distribution is found to have a fall-off consistent with p c( R^-0.5 out to approximately150 kpc. For non-Fornax cluster companions the fall-off continues out to the 300-kpc limit of thesurvey. The velocity dispersion of these companions is found to be constant with projected radial distance from the central elliptical, holding at a value of approximately +/- 300-350 km/sec overall.

NED NASA/IPAC Extragalactic Database↗
NASA NTRS2005

Kinetic Studies of Iron Deposition Catalyzed by Recombinant Human Liver Heavy, and Light Ferritins and Azotobacter Vinelandii Bacterioferritin Using O2 and H2O2 as Oxidants

The discrepancy between predicted and measured H2O2 formation during iron deposition with recombinant heavy human liver ferritin (rHF) was attributed to reaction with the iron protein complex [Biochemistry 40 (2001) 10832-10838]. This proposal was examined by stopped-flow kinetic studies and analysis for H2O2 production using (1) rHF, and Azotobacter vinelandii bacterial ferritin (AvBF), each containing 24 identical subunits with ferroxidase centers; (2) site-altered rHF mutants with functional and dysfunctional ferroxidase centers; and (3) rccombinant human liver light ferritin (rLF), containing 110 ferroxidase center. For rHF, nearly identical pseudo-first-order rate constants of 0.18 per second at pH 7.5 were measured for Fe(2+) oxidation by both O2 and H2O2, but for rLF, the rate with O2 was 200-fold slower than that for H2O2 (k-0.22 per second). A Fe(2+)/O2 stoichiometry near 2.4 was measured for rHF and its site altered forms, suggesting formation of H2O2. Direct measurements revealed no H2O2 free in solution 0.5-10 min after all Fe(2+) was oxidized at pH 6.5 or 7.5. These results are consistent with initial H2O2 formation, which rapidly reacts in a secondary reaction with unidentified solution components. Using measured rate constants for rHF, simulations showed that steady-state H2O2 concentrations peaked at 14 pM at approx. 600 ms and decreased to zero at 10-30 s. rLF did not produce measurable H2O2 but apparently conducted the secondary reaction with H2O2. Fe(2+)/O2 values of 4.0 were measured for AvBF. Stopped-flow measurements with AvBF showed that both H2O2 and O2 react at the same rate (k=0.34 per second), that is faster than the reactions with rHF. Simulations suggest that AvBF reduces O2 directly to H2O without intermediate H2O2 formation.

Bunker, Jared↗
NASA NTRS2007

Methods of Attenuation Correction for Dual-Wavelength and Dual-Polarization Weather Radar Data

In writing the integral equations for the median mass diameter and number concentration, or comparable parameters of the raindrop size distribution, it is apparent that the forms of the equations for dual-polarization and dual-wavelength radar data are identical when attenuation effects are included. The differential backscattering and extinction coefficients appear in both sets of equations: for the dual-polarization equations, the differences are taken with respect to polarization at a fixed frequency while for the dual-wavelength equations, the differences are taken with respect to frequency at a fixed polarization. An alternative to the integral equation formulation is that based on the k-Z (attenuation coefficient-radar reflectivity factor) parameterization. This-technique was originally developed for attenuating single-wavelength radars, a variation of which has been applied to the TRMM Precipitation Radar data (PR). Extensions of this method have also been applied to dual-polarization data. In fact, it is not difficult to show that nearly identical equations are applicable as well to dualwavelength radar data. In this case, the equations for median mass diameter and number concentration take the form of coupled, but non-integral equations. Differences between this and the integral equation formulation are a consequence of the different ways in which attenuation correction is performed under the two formulations. For both techniques, the equations can be solved either forward from the radar outward or backward from the final range gate toward the radar. Although the forward-going solutions tend to be unstable as the attenuation out to the range of interest becomes large in some sense, an independent estimate of path attenuation is not required. This is analogous to the case of an attenuating single-wavelength radar where the forward solution to the Hitschfeld-Bordan equation becomes unstable as the attenuation increases. To circumvent this problem, the equations can be expressed in the form of a final-value problem so that the recursion begins at the far range gate and proceeds inward towards the radar. Solving the problem in this way traditionally requires estimates of path attenuation to the final gate: in the case of orthogonal linear polarizations, the attenuations at horizontal and vertical polarizations (same frequency) are required while in the dual-wavelength case, attenuations at the two frequencies (same polarization) are required.

Meneghini, R.↗
NASA NTRS2004

Wireless event-recording device with identification codes

A wireless recording device can be interrogated to determine its identity and its state. The state indicates whether a particular physical or chemical event has taken place. In effect, the physical or chemical event is recorded by the device. The identity of the device allows it to be distinguished from a number of similar devices. Thus the sensor device may be used in an array of devices that can be probed by a wireless interrogation unit. The device tells the interrogator who it is and what state it is in. The interrogator can thus easily identify particular items in an array that have reached a particular condition.

Watters, David G.↗
NASA NTRS2003

Event-recording devices with identification codes

A recording device allows wireless interrogation to determine its identity and its state. The state indicates whether one or more physical or chemical events have taken place. In effect, the one or more physical or chemical events are recorded by the device. The identity of the device allows it to be distinguished from a number of similar devices. The recording device may be used in an array of devices that allows wireless probing by an interrogation unit. When probed, each device tells the interrogator who it is and what state it is in. The devices allow multiple use and the interrogator may use a logical reset to determine the state of each device. The interrogator can thus easily identify particular items in an array that have reached a particular condition. The device may record the status of each device in a database to maintain a history for each.

Watters, David G.↗
NASA NTRS2006

Lightweight, low-cost solar energy collector

A lightweight solar concentrator of the reflecting parabolic or trough type is realized via a thin reflecting film, an inflatable structural housing and tensioned fibers. The reflector element itself is a thin, flexible, specularly-reflecting sheet or film. The film is maintained in the parabolic trough shape by means of a plurality of identical tensioned fibers arranged to be parallel to the longitudinal axis of the parabola. Fiber ends are terminated in two identical spaced anchorplates, each containing a plurality of holes which lie on the desired parabolic contour. In a preferred embodiment, these fibers are arrayed in pairs with one fiber contacting the front side of the reflecting film and the other contacting the back side of the reflecting film. The reflective surface is thereby slidably captured between arrays of fibers which control the shape and position of the reflective film. Gas pressure in the inflatable housing generates fiber tension to achieve a truer parabolic shape.

Hochberg, Eric B.↗
NASA NTRS1990

Multispectral glancing incidence X-ray telescope

A multispectral glancing incidence X-ray telescope is illustrated capable of broadband, high-resolution imaging of solar and stellar X-ray and extreme ultraviolet radiation sources which includes a primary optical system preferably of the Wolter I type having a primary mirror system (20, 22). The primary optical system further includes an optical axis (24) having a primary focus (F1) at which the incoming radiation is focused by the primary mirrors. A plurality of ellipsoidal mirrors (30a, 30b, 30cand 30d) are carried at an inclination to the optical axis behind the primary focus (F1). A rotating carrier (32) is provided on which the ellipsoidal mirrors are carried so that a desired one of the ellipsoidal mirrors may be selectively positioned in front of the incoming radiation beam (26). In the preferred embodiment, each of the ellipsoidal mirrors has an identical concave surface carrying a layered synthetic microstructure coating tailored to reflect a desired wavelength of 1.5 .ANG. or longer. Each of the identical ellipsoidal mirrors has a second focus (F2) at which a detector (16) is carried. Thus the different wavelength image is focused upon the detector irregardless of which mirror is positioned in front of the radiation beam. In this manner, a plurality of low wavelengths in a wavelength band generally less than 30 angstroms can be imaged with a high resolution.

Hoover, Richard B.↗
NASA NTRS2006

Containerless Processing of a Lithium Disilicate Glass

Glasses of Li2O.2SiO2 (LS2) and LS2 doped with 0.001 wt% platinum (LS2 + 0.001 wt% Pt) compositions were melted, cooled and re-heated at controlled rates while levitated (containerless) inside an Electrostatic Levitator (ESL) furnace at NASA Marshall Space Flight Center. The experiments were conducted in vacuum using spherical 2.5 - 3.0 mm diameter glass samples. The measured critical cooling rate for glass formation, Rc, for the LS2 and LS2 + 0.001 wt% Pt glasses processed at ESL were 14 plus or minus 2 C/min and 130 plus or minus 5 C/min, respectively. The values of Rc for the same LS2 and LS2 + 0.001 wt% Pt glasses processed in a container were 62 plus or minus 3 C/min and 162 plus or minus 5 C/min, respectively. The effective activation energy for crystallization, E, for the LS2 glass processed without a container at ESL was higher than that for an identical glass processed in a container. These results suggest that the glass formation tendency for a containerless LS2 melt is significantly increased compared to an identical melt in contact with a container. The absence of heterogeneous nucleation sites that are inherently present in all melts held in containers is believed to be the reason for the increased glass forming tendency of this containerless melt.

Ranasinghe, K. S.↗
NASA NTRS2008

Outcome of Recent Satellite Impact Experiments

This paper summarizes three satellite impact tests completed in early 2007 through collaboration between Kyushu University and the NASA Orbital Debris Program Office. The previous experiments completed in late 2005 aimed to compare low- and hyper-velocity impacts on identical target satellites, whereas the new tests used larger satellites as targets and aimed to investigate the effects of impact directions. Three identical micro satellites equipped with fully-functional electronic devices were prepared as targets. Their dimensions were 20 cm by 20 cm by 20 cm, and the mass of each was approximately 1.3 kilograms. Aluminum alloy solid spheres, with diameters of 3 cm and masses of 39 grams were prepared as projectiles. The impact velocity was approximately 1.7 km/s. The impact tests were carried out at the two-stage light gas gun facility at the Kyushu Institute of Technology. All three target satellites were completely fragmented, but there were noticeable differences among the three sets of fragments due to the different impact directions. More than 1000 fragments from each test were collected, measured, photographed, and documented with material descriptions. The analysis of the fragments is currently in progress. Preliminary results of the new data and comparisons with previous data will be included in the paper.

Hanada, Toshiya↗
NASA NTRS2006

Atmospheric Radiation Measurements Aerosol Intensive Operating Period: Comparison of Aerosol Scattering during Coordinated Flights

In May 2003, a Twin Otter airplane, equipped with instruments for making in situ measurements of aerosol optical properties, was deployed during the Atmospheric Radiation Measurements (ARM) Program s Aerosol Intensive Operational Period in Oklahoma. Several of the Twin Otter flights were flown in formation with an instrumented light aircraft (Cessna 172XP) that makes routine in situ aerosol profile flights over the site. This paper presents comparisons of measured scattering coefficients at 467 nm, 530 nm, and 675 nm between identical commercial nephelometers aboard each aircraft. Overall, the agreement between the two nephelometers decreases with longer wavelength. During the majority of the flights, the Twin Otter flew with a diffuser inlet while the Cessna had a 1 mm impactor, allowing for an estimation of the fine mode fraction aloft. The fine mode fraction aloft was then compared to the results of a ground-based nephelometer. Comparisons are also provided in which both nephelometers operated with identical 1 mm impactors. These scattering coefficient comparisons are favorable at the longer wavelengths (i.e., 530 nm and 675 nm), yet differed by approximately 30% at 467 nm. Mie scattering calculations were performed using size distribution measurements, made during the level flight legs. Results are also presented from Cadenza, a new continuous wave cavity ring-down (CW-CRD) instrument, which compared favorably (i.e., agreed within 2%) with data from other instruments aboard the Twin Otter. With this paper, we highlight the significant implications of coarse mode (larger than 1 mm) aerosol aloft with respect to aerosol optical properties.

Hallar, A. G.↗
NASA NTRS2008

Gaseous Surrogate Hydrocarbons for a Hifire Scramjet that Mimic Opposed Jet Extinction Limits for Cracked JP Fuels

This paper describes, first, the top-down methodology used to define simple gaseous surrogate hydrocarbon (HC) fuel mixtures for a hypersonic scramjet combustion subtask of the HiFIRE program. It then presents new and updated Opposed Jet Burner (OJB) extinction-limit Flame Strength (FS) data obtained from laminar non-premixed HC vs. air counterflow diffusion flames at 1-atm, which follow from earlier investigations. FS represents a strain-induced extinction limit based on cross-section-average air jet velocity, U(sub air), that sustains combustion of a counter jet of gaseous fuel just before extinction. FS uniquely characterizes a kinetically limited fuel combustion rate. More generally, Applied Stress Rates (ASRs) at extinction (U(sub air) normalized by nozzle or tube diameter, D(sub n or t) can directly be compared with extinction limits determined numerically using either a 1-D or (preferably) a 2-D Navier Stokes simulation with detailed transport and finite rate chemistry. The FS results help to characterize and define three candidate surrogate HC fuel mixtures that exhibit a common FS 70% greater than for vaporized JP-7 fuel. These include a binary fuel mixture of 64% ethylene + 36% methane, which is our primary recommendation. It is intended to mimic the critical flameholding limit of a thermally- or catalytically-cracked JP-7 like fuel in HiFIRE scramjet combustion tests. Our supporting experimental results include: (1) An idealized kinetically-limited ASR reactivity scale, which represents maximum strength non-premixed flames for several gaseous and vaporized liquid HCs; (2) FS characterizations of Colket and Spadaccini s suggested ternary surrogate, of 60% ethylene + 30% methane + 10% n-heptane, which matches the ignition delay of a typical cracked JP fuel; (3) Data showing how our recommended binary surrogate, of 64% ethylene + 36% methane, has an identical FS; (4) Data that characterize an alternate surrogate of 44% ethylene + 56% ethane with identical FS and nearly equal molecular weights; this could be useful when systematically varying the fuel composition. However, the mixture liquefies at much lower pressure, which limits on-board storage of gaseous fuel; (5) Dynamic Flame Weakening results that show how oscillations in OJB input flow (and composition) can weaken (extinguish) surrogate flames up to 200 Hz, but the weakening is 2.5x smaller compared to pure methane; and finally, (6) FS limits at 1-atm that compare with three published 1-D numerical OJB extinction results using four chemical kinetic models. The methane kinetics generally agree closely at 1-atm, whereas, the various ethylene models predict extinction limits that average ~ 45% high, which represents a significant problem for numerical simulation of surrogate-based flameholding in a scramjet cavity. Finally, we continue advocating the FS approach as more direct and fundamental for assessing idealized scramjet flameholding potentials than measurements of "unstrained" premixed laminar burning velocity or blowout in a Perfectly Stirred Reactor.

Pellett, Gerald L.↗
NASA NTRS2008

Fast Plasma Instrument for MMS: Data Compression Simulation Results

Magnetospheric Multiscale (MMS) mission will study small-scale reconnection structures and their rapid motions from closely spaced platforms using instruments capable of high angular, energy, and time resolution measurements. To meet these requirements, the Fast Plasma Instrument (FPI) consists of eight (8) identical half top-hat electron sensors and eights (8) identical ion sensors and an Instrument Data Processing Unit (IDPU). The sensors (electron or ion) are grouped into pairs whose 6 deg x 180 deg fields-of-view (FOV) are set 90 deg apart. Each sensor is equipped with electrostatic aperture steering to allow the sensor to scan a 45 deg x 180 deg fan about its nominal viewing (0 deg deflection) direction. Each pair of sensors, known as the Dual Electron Spectrometer (DES) and the Dual Ion Spectrometer (DIS), occupies a quadrant on the MMS spacecraft and the combination of the eight electron/ion sensors, employing aperture steering, image the full-sky every 30-ms (electrons) and 150-ms (ions), respectively. To probe the results in the DES complement of a given spacecraft generating 6.5-Mbs(exp -1) of electron data while the DIS generates 1.1-Mbs(exp -1) of ion data yielding an FPI total data rate of 6.6-MBs(exp -1). The FPI electron/ion data is collected by the IDPU then transmitted to the Central Data Instrument Processor (CIDP) on the spacecraft for science interest ranking. Only data sequences that contain the greatest amount of temporal/spatial structure will be intelligently down-linked by the spacecraft. Currently, the FPI data rate allocation to the CIDP is 1.5-Mbs(exp -1). Consequently, the FPI-IDPU must employ data/image compression to meet this CIDP telemetry allocation. Here, we present simulations of the CCSDS 122.0-B-1 algorithm-based compression of the FPI-DES electron data. Compression analysis is based upon a seed of re-processed Cluster/PEACE electron measurements. Topics to be discussed include: review of compression algorithm; data quality; data formatting/organization; and, implications for data/matrix pruning. To conclude a presentation of the base-lined FPI data compression approach is provided.

Barrie, A.↗
NASA NTRS2008

Investigation, Analysis, and Testing of Self-contained Oxygen Generators

Self Contained Oxygen Generators (SCOGs) have widespread use in providing emergency breathing oxygen in a variety of environments including mines, submarines, spacecraft, and aircraft. These devices have definite advantages over storing of gaseous or liquid oxygen. The oxygen is not generated until a chemical briquette containing a chlorate or perchlorate oxidizer and a solid metallic fuel such as iron is ignited starting a thermal decomposition process allowing gaseous oxygen to be produced. These devices are typically very safe to store, easy to operate, and have primarily only a thermal hazard to the operator that can be controlled by barriers or furnaces. Tens of thousands of these devices are operated worldwide every year without major incident. This report examines the rare case of a SCOG whose behavior was both abnormal and lethal. This particular type of SCOG reviewed is nearly identical to a flight qualified version of SCOG slated for use on manned space vehicles. This Investigative Report is a compilation of a NASA effort in conjunction with other interested parties including military and aerospace to understand the causes of the particular SCOG accident and what preventative measures can be taken to ensure this incident is not repeated. This report details the incident and examines the root causes of the observed SCOG behavior from forensic evidence. A summary of chemical and numerical analysis is provided as a background to physical testing of identical SCOG devices. The results and findings of both small scale and full scale testing are documented on a test-by-test basis along with observations and summaries. Finally, conclusions are presented on the findings of this investigation, analysis, and testing along with suggestions on preventative measures for any entity interested in the safe use of these devices.

Keddy, Christopher P.↗
NASA NTRS2000

Conditioning of the Stable, Discrete-time Lyapunov Operator

The Schatten p-norm condition of the discrete-time Lyapunov operator L(sub A) defined on matrices P is identical with R(sup n X n) by L(sub A) P is identical with P - APA(sup T) is studied for stable matrices A is a member of R(sup n X n). Bounds are obtained for the norm of L(sub A) and its inverse that depend on the spectrum, singular values and radius of stability of A. Since the solution P of the the discrete-time algebraic Lyapunov equation (DALE) L(sub A)P = Q can be ill-conditioned only when either L(sub A) or Q is ill-conditioned, these bounds are useful in determining whether P admits a low-rank approximation, which is important in the numerical solution of the DALE for large n.

Tippett, Michael K.↗
NASA NTRS2009

Reflectors Made from Membranes Stretched Between Beams

Lightweight cylindrical reflectors of a proposed type would be made from reflective membranes stretched between pairs of identically curved and identically oriented end rails. In each such reflector, the curvature of the two beams would define the reflector shape required for the intended application. For example, the beams could be curved to define a reflector of parabolic cross section, so that light incident along the axis of symmetry perpendicular to the cylindrical axis would be focused to a line. In addition, by applying suitable forces to the ends of the beams, one could bend the beams to adjust the reflector surface figure to within a precision of the order of the wavelength of the radiation to be reflected. The figure depicts an example of beams shaped so that in the absence of applied forces, each would be flat on one side and would have a radius of curvature R on the opposite side. Alternatively, the curvature of the reflector-membrane side could be other than circular. In general, the initial curvature would be chosen to optimize the final reflector shape. Then by applying forces F between the beam ends in the positions and orientations shown in the figure, one could bend beams to adjust their shape to a closer approximation of the desired precise circular or noncircular curvature.

Dooley, Jennifer↗