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NASA NTRS2020

Comparison of Extreme Value Distributions for Electrostatic Discharge Magnitudes in Spacecraft Charging Tests

Electrostatic Discharge (ESD) induced by the accumulation of charge in the space environment is known to cause spacecraft anomalies and failures. While it is critical to estimate the worst-case expected ESD, sensitive radar instruments can be impacted by high rates of occurrence of very small ESD. To estimate the correct extreme behavior, it is important to select the correct extreme value distribution for extrapolation of test results limited in time and sensitivity. Quantile-quantile (Q-Q) analysis is used to compare electron beam-induced ESD test data to several statistical distributions used in the published literature. The best-fit distribution is shown to vary from between tests on different materials; however, it is clear that power law distributions are not good approximations for low amplitude events. Q-Q analysis is a convenient graphical method for evaluating multiple theoretical extreme-value distributions simultaneously.

Kim, Wousik↗
NASA NTRS2025

Sealing Europa’s Vents By Vapor Deposition: An Order-of-Magnitude Study

Fractures and vents in the ice crust of Europa, exposing the sub-surface ocean or liquid-water inclusions to the vacuum, might be responsible for the generation of planetary-scale water-vapor plumes. During its passage through the ice, the plume vapor is expected to partially condense on the cold ice walls. Together with other effects (water spillage, compression forces, etc.) this mechanism likely contributes to sealing the vent. In this work, we develop a lumped-parameter model to analyze the sealing timescales associated to water-vapor deposition alone. Neglecting all other possible mechanisms, we find shutting-off times roughly compatible with the 7-hour plume observed in 2012 by the Hubble Space Telescope, suggesting that vapor deposition might have played a major role in sealing the vent. A map of sealing times vs. plume density, mass flow rate and aperture areas is given. Plume quantities from the literature are analyzed and compared to our results. For a given plume density/mass flow rate, small apertures would be sealed quickly by vapor deposition and are thus incompatible with observations.

Europa↗
NASA NTRS2000

Influence of central set on anticipatory and triggered grip-force adjustments

The effects of predictability of load magnitude on anticipatory and triggered grip-force adjustments were studied as nine normal subjects used a precision grip to lift, hold, and replace an instrumented test object. Experience with a predictable stimulus has been shown to enhance magnitude scaling of triggered postural responses to different amplitudes of perturbations. However, this phenomenon, known as a central-set effect, has not been tested systematically for grip-force responses in the hand. In our study, predictability was manipulated by applying load perturbations of different magnitudes to the test object under conditions in which the upcoming load magnitude was presented repeatedly or under conditions in which the load magnitudes were presented randomly, each with two different pre-load grip conditions (unconstrained and constrained). In constrained conditions, initial grip forces were maintained near the minimum level necessary to prevent pre-loaded object slippage, while in unconstrained conditions, no initial grip force restrictions were imposed. The effect of predictable (blocked) and unpredictable (random) load presentations on scaling of anticipatory and triggered grip responses was tested by comparing the slopes of linear regressions between the imposed load and grip response magnitude. Anticipatory and triggered grip force responses were scaled to load magnitude in all conditions. However, regardless of pre-load grip force constraint, the gains (slopes) of grip responses relative to load magnitudes were greater when the magnitude of the upcoming load was predictable than when the load increase was unpredictable. In addition, a central-set effect was evidenced by the fewer number of drop trials in the predictable relative to unpredictable load conditions. Pre-load grip forces showed the greatest set effects. However, grip responses showed larger set effects, based on prediction, when pre-load grip force was constrained to lower levels. These results suggest that anticipatory processes pertaining to load magnitude permit the response gain of both voluntary and triggered rapid grip force adjustments to be set, at least partially, prior to perturbation onset. Comparison of anticipatory set effects for reactive torque and lower extremity EMG postural responses triggered by surface translation perturbations suggests a more general rule governing anticipatory processes.

Non-NASA Center↗
NASA NTRS2011

Michigan Orbital DEbris Survey Telescope Observations of the Geosynchronous Orbital Debris Environment. Observing Years: 2007-2009

NASA uses the Michigan Orbital DEbris Survey Telescope (MODEST), the University of Michigan's 0.61-m aperture Curtis-Schmidt telescope at the Cerro Tololo Inter-American Observatory in Chile, to help characterize the debris environment in geosynchronous orbit; this began in February 2001 and continues to the present day. Detected objects that are found to be on the U.S. Space Surveillance Network cataloged objects list are termed correlated targets (CTs), while those not found on the list are called uncorrelated targets (UCTs). This Johnson Space Center report provides details of observational and data-reduction processes for the entire MODEST dataset acquired in calendar years (CYs) 2007, 2008, and 2009. Specifically, this report describes the collection and analysis of 36 nights of data collected in CY 2007, 43 nights of data collected in CY 2008, and 43 nights of data collected in CY 2009. MODEST is equipped with a 2048 x 2048-pixel charged coupled device camera with a 1.3 by 1.3 deg field of view. This system is capable of detecting objects fainter than 18th magnitude (R filter) using a 5-s integration. This corresponds to a 20-cm diameter, 0.175-albedo object at 36,000 km altitude assuming a diffuse Lambertian phase function. The average number of detections each night over all 3 years was 26. The percentage of this number that represented the UCT population ranged from 34% to 18%, depending on the observing strategy and the field center location. Due to the short orbital arc over which observations are made, the eccentricity of the object s orbit is extremely difficult to measure accurately. Therefore, a circular orbit was assumed when calculating the orbital elements. A comparison of the measured inclination (INC), right ascension of ascending node (RAAN), and mean motion to the quantities for CTs from the U.S. Space Surveillance Network shows acceptable errors. This analysis lends credibility to the determination of the UCT orbital distributions. Figure 1 shows the size distribution of 3,143 objects detected in the data processed for CYs 2007, 2008, and 2009. The actual peak of the absolute magnitude distribution for the functional correlated targets is 10th magnitude, whereas the peak was 11th magnitude in 2002 2003 and 10th magnitude for 2004-2006. An absolute magnitude of 10.5 corresponds to objects with average diameters of 6.3 m, assuming an albedo of 0.175 and a diffuse Lambertian phase function. This result generally agrees with the known sizes of intact satellites. The absolute magnitude distribution for the UCTs is broad, but starts to roll off near 25 cm diameter or 17.5 magnitude. This roll off in the distribution reflects the detection capability of MODEST, not the true nature of the population. The true population is believed to continue at the same slope through fainter magnitudes based on comparisons with the LEO break-up law.

Abercromby, K. J.↗
NASA NTRS1994

The Hubble Space Telescope extragalactic distance scale key project. 2: Photometry of WFC images of M81

The Extragalactic Distance Scale (H(sub o)) Key Project for Hubble Space Telescope (HST) aims to employ the Cepheid period-luminosity (P-L) relation to measure galaxy distances out as far as the Virgo Cluster. The vital steps in this program are (1) to obtain precise photometry of stellar images from the Wide Field Camera (WFC) exposures of selected galaxies, and (2) to calibrate this photometry to obtain reliable distances to these galaxies from the Cepheid P-L relation. We have used the DAOPHOT II and ALLFRAME programs to determine 28 instrumental magnitudes -- 22 of F555W (of about V) and six of F785LP (of about I) -- of all stars brighter than V of about 25 in each of two 2.56 arcmin x 2.56 arcmin WFC fields of M81. The reductions use a varying point-spread function to account for the field effects in the WFC optics and yield instrumental magnitudes with single epoch precision ranging from 0.09 to 0.24 mag, at V of about 21.8 to 23.8 -- the magnitude range of the 30 Cepheids that we have now identified in M81. For brighter stars (V of about 22), single epoch magnitudes are precise to 0.09 mag. The photometric calibration onto the Johnson V and Kron-Cousins I systems was determined from independent ground-based CCD observing at the Canada-France-Hawaii Telescope (CFHT) 3.6 m (confirmed by the Kitt Peak National Observatory (KPNO) 4.0 m) and from the Palomar 5.0 m (using the wide-field COSMIC camera) and 1.5 m telescopes. Secondary standards, taken from the COSMIC and CFHT frames, were established in each of the WFC fields in V and I, allowing a direct transformation from ALLFRAME magnitudes to calibrated V and I magnitudes, giving mean V of about 23 magnitudes accurate to of about +/- 0.1 mag. The stellar populations in M81 have been analyzed in terms of the luminosity functions and color magnitude diagrams (CMD) derived from these data, from which we identify numerous supergiants, and a CMD morphology similar to M33.

Hughes, Shaun M. G.↗
NASA NTRS1975

A comparison of electric and magnetic field data from the OGO 6 spacecraft

Previous studies of OGO 6 electric-field data and magnetic-field magnitude observations have indicated a distinct dependence of disturbance characteristics on interplanetary-sector polarity. Examination of simultaneous data below 600 km over the summer polar cap shows that changes in electric-field patterns and the disturbance patterns in magnetic-field magnitude are highly correlated. This correlation extends to pattern shapes, boundary locations, and the amplitudes of the correlated quantities. In the winter hemisphere at altitudes above 800 km, correlations between boundaries exist, pattern correlations are present but not as strong as at low altitudes in summer, and amplitude correlations are essentially absent. These studies verify that below 600 km, the region of positive magnetic-field magnitude, from 2200 to 1000 magnetic local time (MLT), receives a significant contribution from both ionospheric and nonionospheric sources. Above 800 km, the nonionospheric sources dominate. These data are also consistent with the existence of a latitudinally broad current system at sunlit magnetic local times as the source of the negative-magnitude region between 1000 and 2200 MLT. In this region, broad structures in electric-field patterns and in magnetic-field magnitude patterns are highly correlated. Multiple peaks in the negative-magnitude, presumably identified with the multiple peaks in negative electric-field magnitude found by Langel (1973) in average surface data, occur when the electric-field pattern has multiple reversals near dusk.

Langel, R. A.↗
NASA NTRS1988

Pressure-strain-rate events in homogeneous turbulent shear flow

A detailed study of the intercomponent energy transfer processes by the pressure-strain-rate in homogeneous turbulent shear flow is presented. Probability density functions (pdf's) and contour plots of the rapid and slow pressure-strain-rate show that the energy transfer processes are extremely peaky, with high-magnitude events dominating low-magnitude fluctuations, as reflected by very high flatness factors of the pressure-strain-rate. A concept of the energy transfer class was applied to investigate details of the direction as well as magnitude of the energy transfer processes. In incompressible flow, six disjoint energy transfer classes exist. Examination of contours in instantaneous fields, pdf's and weighted pdf's of the pressure-strain-rate indicates that in the low magnitude regions all six classes play an important role, but in the high magnitude regions four classes of transfer processes, dominate. The contribution to the average slow pressure-strain-rate from the high magnitude fluctuations is only 50 percent or less. The relative significance of high and low magnitude transfer events is discussed.

Brasseur, James G.↗
NASA NTRS1993

Bonner Durchmusterung (Southern Durchmusterung)

The Southern Durchmusterung (SD, Schoenfeld 1886, Becker 1949, Schmidt 1967) is a visual survey of stars in the declination zones -02 to -23 deg, completed as an extension to Argelander's (1859-62) monumental Bonner Durchmusterung (BD). Schoenfeld's survey was carried out using the same methods as had been used for the BD. The procedure consisted of allowing the telescope to drift along the mean declination of each zone and recording the positions and magnitudes of stars crossing the transit line of each field. The goal of the survey was to extend the BD to declination -23 deg (a plan originally adopted by Argelander) with approximately the same magnitude limits, although the primary instrument was of larger aperture (159 mm) than the 78-mm telescope used for the BD. Thus, whereas the BD magnitude estimates extend to 9.4 mag with all fainter stars assigned a magnitude of 9.5, the SD magnitude estimates extend to 9.9 mag with all fainter stars assigned a magnitude of 10. The SD contains a number of stars fainter than 10.0 mag and even some as faint as 11 mag. Lists of all corrections made to the original data as a result of published corrigenda, stars deleted according to overstriking in the printed catalogs or their inclusion in lists of 'missing' stars, and stars inserted in later editions are given. No other corrections or changes have been incorporated into the original data, e.g., from more modern positions and magnitudes or from comparison with other catalogs.

Source record↗
NASA NTRS1995

Ultraviolet and optical observations of OB associations in M31

Images of the central and southern parts of the local group Sb spiral galaxy M31 were obtained by the Ultraviolet Imaging Telescope during the Astro-1 Spacelab mission. Stellar photometry is obtained for 611 stars in 59 van den Bergh associations in the near-UV A1 band (central wavelngth 2490 A), and for 130 of these stars in the far UV B1 band (central wavlength 1520 A). In addition, B-band magnitudes for 456 of the stars in approximately 30 associations, together with U- and R-band photometry for approximately 290 stars in approximately 15 associations are determined from CCD images. B-magnitudes from the catalog of Magnier et al. (1992) are given for 137 stars and R-magnitudes for 233 stars. Stellar positions are obtained from the ground based CCD images and from UIT images. Total fluxes in the UV bands are measured for 63 associations . Finding charts are presented in the NUV and FUV bands, as well as, one optical band. Tables give the images utilized in this investigation, the associations observed, with positions, total UV fluxes, extinctions estimated from color-magnitude diagrams, and stellar positions with photometry in up to five bands. UV color magnitude diagrams are presented with extinctions estimated by comparing the observed association color magnitude diagrams with colors and magnitudes of early-type stars computed from the IUE spectral atlas of Fanelli et al. (1992). Comparison with evolutionary models suggests a maximum initial mass approx. 85 solar mass. Ultraviolet extinctions within most M31 OB associations is found to follow an extinction curve similar to that of Hutchings et al. (1992). The variation in the fraction of near-UV stars also measured in the far-UV among the associations is probably caused by variations in age, extinction, and the degree of foreground contamination.

Hill, J. K.↗
NASA NTRS2015

The Application of New Optical Meteor Flux Routines to the 2014 May Camelopardalid Outburst

NASA's Meteoroid Environment Office (MEO) is charged with monitoring the meteoroid environment in near-Earth space for the protection of satellites and spacecraft. The MEO has recently established eight wide-field meteor cameras, four cameras each at two separate stations to calculate automated meteor fluxes in the millimeter size range. Each camera consists of a 17 mm focal length Schneider lens on a Watec 902H2 Ultimate CCD video camera, producing a 21.7 x 15.5 degree field of view. This configuration has a limiting meteor magnitude of about +5. One station is located at Marshall Space Flight Center in Huntsville, Alabama and the other is 31.8 kilometers away at a school in Decatur, Alabama. Both single-station and double-station fluxes are calculated every morning using data from the previous night. The flux algorithms employed here differ from others currently in use in that they do not assume a single height for all meteors observed in the common camera volume. In the MEO system, the volume is broken up into a set of height intervals, with the collecting areas determined by the position of the active shower or sporadic source radiant. The flux per height interval is calculated and summed to obtain the total meteor flux. As the mass is also computed from the photometry, a mass flux can also be calculated. First, a weather algorithm indicates if sky conditions are clear enough to calculate fluxes, at which point a limiting magnitude algorithm is employed. The limiting magnitude algorithm performs a fit of stellar magnitudes versus camera intensities. The stellar limiting magnitude is derived from this and converted to a limiting meteor magnitude for the active shower or sporadic source. The fluxes are scaled to an average limiting magnitude throughout the night and zenithal hourly rate (ZHR's) are output daily along with flux values. In addition to this process, results will be presented as applied to the 2014 May Camelopardalid outburst, using data from several different optical systems, which looked at May Camelopardalids in different size ranges.

Blaauw, Rhiannon↗