Engineering topics

Hughes, David W.

Publications and source records attributed to Hughes, David W..

16 records

NASA NTRS2014

A Statistical Treatment of Bioassay Pour Fractions

The binomial probability distribution is used to treat the statistics of a microbiological sample that is split into two parts, with only one part evaluated for spore count. One wishes to estimate the total number of spores in the sample based on the counts obtained from the part that is evaluated (pour fraction). Formally, the binomial distribution is recharacterized as a function of the observed counts (successes), with the total number (trials) an unknown. The pour fraction is the probability of success per spore (trial). This distribution must be renormalized in terms of the total number. Finally, the new renormalized distribution is integrated and mathematically inverted to yield the maximum estimate of the total number as a function of a desired level of confidence ( P(<n)=LOC ). Selected results of the indicated numerical calculations are presented. For LOC=0.5, or the likely value, the estimates differ little from the usual calculation: the number of spores counted divided by the pour fraction. The extension to recovery efficiency corrections is also presented. Now the product of recovery efficiency and pour fraction may be small enough that the likely value may be much larger than the usual calculation: the number of spores divided by that product. The use of this analysis would not be limited to microbiological data.

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NASA NTRS2014

MAVEN Contamination Venting and Outgassing Analysis

Mars Atmosphere and Volatile EvolutioN (MAVEN) is the first mission to focus its study on the Mars upper atmosphere. MAVEN will study the evolution of the Mars atmosphere and climate, by examining the conduit through which the atmosphere has to pass as it is lost to the upper atmosphere. An analysis was performed for the MAVEN mission to address two distinct concerns. The first goal of the analysis was to perform an outgassing study to determine where species outgassed from spacecraft materials would redistribute to and how much of the released material might accumulate on sensitive surfaces. The second portion of the analysis serves to predict what effect, if any, Mars atmospheric gases trapped within the spacecraft could have on instrument measurements when re-released through vents. The re-release of atmospheric gases is of interest to this mission because vented gases from a higher pressure spacecraft interior could bias instrument measurements of the Mars atmosphere depending on the flow rates and directions.

Petro, Elaine M.↗

NASA NTRS2012

Particle-Surface Interaction Model and Method of Determining Particle-Surface Interactions

A method and model of predicting particle-surface interactions with a surface, such as the surface of a spacecraft. The method includes the steps of: determining a trajectory path of a plurality of moving particles; predicting whether any of the moving particles will intersect a surface; predicting whether any of the particles will be captured by the surface and/or; predicting a reflected trajectory and velocity of particles reflected from the surface.

Hughes, David W.↗

NASA NTRS2009

Algorithm for Computing Particle/Surface Interactions

An algorithm has been devised for predicting the behaviors of sparsely spatially distributed particles impinging on a solid surface in a rarefied atmosphere. Under the stated conditions, prior particle-transport models in which (1) dense distributions of particles are treated as continuum fluids; or (2) sparse distributions of particles are considered to be suspended in and to diffuse through fluid streams are not valid.

Hughes, David W.↗

NASA NTRS2008

Extra Terrestrial Environmental Chamber Design

A vacuum chamber designed to simulate the dusty environment on the Moon or Mars has been built for Goddard Space Flight Center. The path from concept to delivery is reviewed, with lessons learned and pitfalls highlighted along the way.

Hughes, David W.↗

NASA NTRS2007

Hardware Outgassing Certification

This course will provide students with the understanding necessary to calculate certification requirements for and interpret the data from hardware undergoing vacuum bakeout. The fundamental physics that driv e hardware outgassing and contaminant deposition will be explained, a nd data reduction techniques will be applied to examples.

Hughes, David W.↗

NASA NTRS2006

QTGA Analysis with Concurrent Deposition

Analysis of outgassed species behavior is often performed using QCM thermogravimetric analysis (QTGA). Prior methods are suited to laboratory testing of materials samples where the source of contaminant can be removed from the system. An approach suitable presented for use during hardware bakeout and outgassing certification is presented. An iterative process is shown to fit surface activation energies and the arrival flux for multiple species.

Hughes, David W.↗

NASA NTRS1999

Innovative Contamination Certification of Multi-Mission Flight Hardware

Maintaining contamination certification of multi-mission flight hardware is an innovative approach to controlling mission costs. Methods for assessing ground induced degradation between missions have been employed by the Hubble Space Telescope (HST) Project for the multi-mission (servicing) hardware. By maintaining the cleanliness of the hardware between missions, and by controlling the materials added to the hardware during modification and refurbishment both project funding for contamination recertification and schedule have been significantly reduced. These methods will be discussed and HST hardware data will be presented.

Hansen, Patricia A.↗

NASA NTRS1998

Innovative Contamination Certification of Multi-Mission Flight Hardware

Hansen, Patricia A.↗

NASA NTRS1998

Innovative Contamination Certification of Multi-Mission Flight Hardware

Hansen, Patricia A.↗

NASA NTRS1994

Hubble Space Telescope servicing mission scientific instrument protective enclosure design requirements and contamination controls

The Scientific Instrument Protective Enclosures were designed for the Hubble Space Telescope Servicing Missions to provide a beginning environment to a Scientific Instrument during ground and on orbit activities. The Scientific Instruments required very stringent surface cleanliness and molecular outgassing levels to maintain ultraviolet performance. Data from the First Servicing Mission verified that both the Scientific Instruments and Scientific Instrument Protective Enclosures met surface cleanliness level requirements during ground and on-orbit activities.

Hansen, Patricia A.↗

NASA NTRS1994

Clean assembly and integration techniques for the Hubble Space Telescope High Fidelity Mechanical Simulator

A mechanical simulator of the Hubble Space Telescope (HST) Aft Shroud was built to perform verification testing of the Servicing Mission Scientific Instruments (SI's) and to provide a facility for astronaut training. All assembly, integration, and test activities occurred under the guidance of a contamination control plan, and all work was reviewed by a contamination engineer prior to implementation. An integrated approach was followed in which materials selection, manufacturing, assembly, subsystem integration, and end product use were considered and controlled to ensure that the use of the High Fidelity Mechanical Simulator (HFMS) as a verification tool would not contaminate mission critical hardware. Surfaces were cleaned throughout manufacturing, assembly, and integration, and reverification was performed following major activities. Direct surface sampling was the preferred method of verification, but access and material constraints led to the use of indirect methods as well. Although surface geometries and coatings often made contamination verification difficult, final contamination sampling and monitoring demonstrated the ability to maintain a class M5.5 environment with surface levels less than 400B inside the HFMS.

Hughes, David W.↗

NASA NTRS1992

CCD imaging of the inner coma jets of comet P/Halley

We analyze the inner coma section of a CCD image of comet P/Halley taken at 1807 UT on 13 March 1986 using a C2 filter (wavelength 5000 to 5200A, half maximum) with the 3.8 m Anglo Australian Telescope at Siding Springs, Australia. Atmospheric turbulence leads to a spreading of the image detail and this produces a blander image of the inner coma region with a slower radial decrease of brightness in comparison to the unaffected image. We remove this smearing by utilizing the point spread function of a star on the same CCD image. Jets were then revealed by removing the average background. Analysis of the jet structure enabled us to estimate the lower limit of the parent molecule velocity. This is found to be 0.3 km s(exp -1).

Boswell, James↗

NASA NTRS1992

The spatial distribution of large cometary meteoroids in the inner solar system

A model of the spatial density distribution of large (m greater than 10(exp -3) g) cometary meteoroids in the inner solar system is obtained assuming that they have orbits closely associated with that of their parent comet. Distributions of the orbital parameters of the Taurid, Quadrantid and Perseid meteoroid streams are used in developing the model.

Mcbride, Neil↗

NASA NTRS1990

Buoyancy-driven instabilities and the nonlinear breakup of a sheared magnetic layer

Motivated by problems concerning the storage and subsequent escape of the solar magnetic field, a study has been made of how a magnetic layer embedded in a convectively stable atmosphere evolves due to axisymmetric instabilities driven by magnetic buoyancy. The initial equilibrium consists of a toroidal field sheared by a weaker poloidal component. The linear stability problem is investigated for both ideal and resistive MHD, and the nonlinear evolution is followed by numerical integration of the equations of motion. In all cases, the instability is greatly affected by the distribution and strength of the poloidal field. In particular, both the horizontal and vertical scales of the motions are controlled by the location of the surface on which the poloidal field vanishes: the resonant surface. In the nonlinear regime, a resonant surface close to the interface between the magnetized and field-free fluid leads to the localization of the instability, so that only a fraction of the magnetic region is disrupted by the motions. By contrast, a deeply seated resonant surface leads to the complete disruption of the layer and to the formation of large, helical magnetic fragments whose identity is preserved for the entire simulation.

Cattaneo, Fausto↗

NASA NTRS1990

A new twist to the solar cycle

Recent numerical simulations of magnetic buoyancy instabilities suggest a new mechanism for the variation with the solar cycle in the scale and structure of surface magnetic flux. The nonlinear evolution of a predominantly toroidal field is found to depend crucially on the distribution of the weaker poloidal ingredient. For certain field configurations large, helical magnetic fragments are produced; for others the escaping field is small-scale and untwisted. We propose that the observed structural variations in flux may be accounted for by small changes in the twist of a deep-seated field. The large fragments will appear at the surface as active regions, which dominate at solar maximum, while the small-scale field will emerge as ephemeral regions which constitute practically all of the flux at solar minimum.

Cattaneo, Fausto↗