Engineering topics

Gregory, John C.

Publications and source records attributed to Gregory, John C..

48 records · Page 3

NASA NTRS1991

The interactions of atmospheric cosmogenic radionuclides with spacecraft surfaces

The discovery of the cosmogenic radionuclide Be-7 on the front surface of the Long Duration Exposure Facility (LDEF) has opened new opportunities to study several unexplored regions of space science. The experiments have shown that the Be-7 found was concentrated in a thin surface layer of spacecraft material. The only reasonable source of the isotope is the atmosphere through which the spacecraft passed. It is expected that the uptake of Be in such circumstances will depend on the chemical form of the Be and the chemical nature of the substrate. It was found that the observed concentration of Be-7 does differ between metal surfaces and organic surfaces such as PTFE (Teflon). It is noted however, that (1) organic surfaces are etched by the atomic oxygen found under these orbital conditions, and (2) the relative velocity of the species is 8 km/s relative to the surface and the interaction chemistry and physics may differ from the norm. Be-7 is formed by disintegration of O and N nuclei under cosmic ray proton bombardment. Many other isotopes are produced by cosmic ray reactions, and some of these are suited to measurement by the extremely sensitive methods of accelerator mass spectrometry.

Gregory, John C.↗

NASA NTRS1991

Chemical analysis of metal and polymer surfaces on the front and rear LDEF

The University of Alabama in Huntsville experiment AO114 contained 128 solid surface samples, half of which were exposed on the front and half on the rear of the Long Duration Exposure Facility (LDEF). Each sample is being subject to a battery of analysis methods. In poster form, details of the x-ray photoelectron spectra, Auger electron spectra, Fourier Transform Infrared and ATR infrared spectra, high resolution profilometry, and scanning electron microscope imagery will be presented from a selection of metal and non-metal surfaces.

Christi, L.↗

NASA NTRS1991

Interactions of atomic oxygen with material surfaces in low Earth orbit: Preliminary results from experiment A0114

The University of Alabama at Huntsville atomic oxygen experiment consisted of two trays of 64 one inch diameter solid samples. One tray was placed on the leading edge and one on the trailing edge of the spacecraft. Half of each sample was covered to provide a control. Thus it was intended that the effects of atomic oxygen and solar ultraviolet radiation on the surface properties of each material could be distinguised from each other and from the effects of aging. Sixteen of the samples were placed on a thermally isolated plate of highly polished aluminum, while the main plate was coated with the thermal control coating S13-GLO. Though the experiment was entirely passive, it was hoped that the effects of thermal activation might be observed, if present. The plates were expected to stabilize at temperatures differing by 20 to 30 C. The experiment also carried a device to measure the spacecraft altitude and several oxygen atom reflectometers which have not been analyzed to date. The samples included thin films of metals Os, Ir, Pt, Ni, W, Mo, and Al coated onto fused silica optical flats; metal carbides (WC, SiC), solid carbons of various types, eight polymers and some other coatings of various types.

Gregory, John C.↗

NASA NTRS1991

A measurement of the energy spectra of cosmic rays from 20 to 1000 GeV per amu

A group collaboration was made in the development of the Bristol University Gas Spectrometer number 4 (BUGS 4). The BUGS 4 detector is designed to measure the charge spectrum for species between oxygen and the iron peak as a function of energy per nucleon, between 20 and 1000 GeV/amu. It is particularly concerned with energies above 50 GeV/amu. The high energy component is considerably less affected by propagation through the interstellar medium than the lower energy component and is expected to approach the original charge spectrum of the source more closely. This information allows one to unravel the effects of cosmic ray production, acceleration, and propagation. The detector is described in total detail. The method of estimating the charge and energy of a cosmic ray depends on the energy of the particle. Calculations and experiments lead to the expectation of a nearly constant charge resolution of about 0.2 charge units over the whole energy range except 4.5 less than gamma less than 20. In this band, the experiment is insensitive to energy. A balloon flight is planned in 1993.

Gregory, John C.↗

NASA NTRS1991

Partial analysis of LDEF experiment A-0114

During the contract period, work concentrated on four main components. Data from the UAH silver pin hole camera was analyzed for determination of the mean Long Duration Exposure Facility (LDEF) satellite attitude and stability in orbit, to include pitch and yaw. Chemical testing performed on the AO-114 hot plate determined the form and locus of absorption of cosmogenic beryllium-7. Reaction rates of atomic oxygen with Kapton and other polymeric solids integrated over the whole LDEF orbital lifetime were analyzed. These rates were compared with the JSC estimated values for Space Station exposures. Metal and polymer films exposed on A0114 (C-9 and C-3 plates) were also analyzed.

Gregory, John C.↗

NASA NTRS1989

Gamma radiation background measurements from Spacelab 2

A Nuclear Radiation Monitor incorporating a NaI(Tl) scintillation detector was flown as part of the verification flight instrumentation on the Spacelab 2 mission, July 29 to August 6, 1985. Gamma-ray spectra were measured with better than 20 s resolution throughout most of the mission in the energy range 0.1 to 30 MeV. Knowledge of the decay characteristics and the geomagnetic dependence of the counting rates enable measurement of the various components of the Spacelab gamma-ray background: prompt secondary radiation, earth albedo, and delayed induced radioactivity. The status of the data analysis and present relevant examples of typical background behavior are covered.

Paciesas, William S.↗

NASA NTRS1988

Auger and ESCA analysis

X-ray photoelectron spectroscopy (XPS or ESCA) and Auger electron spectroscopy (AES) techniques are discussed. The XPS instrument is a Perkin-Elmer 5400 system which provides both elemental and chemical state information without restriction on the type of material that can be analyzed. The AES instrument is a Kratos Analytical XSAM 800 system. AES uses a beam of high energy electrons as a surface probe. Following electronic rearrangements within excited atoms by this probe, Auger electrons characteristic of each element present are emitted from the sample. Specific examples of analytic techniques and results are presented.

Gregory, John C.↗

NASA NTRS1988

Gamma radiation background measurements from Spacelab 2

A Nuclear Radiation Monitor incorporating a NaI(Tl) scintillation detector was flown as part of the verification flight instrumentation on the Spacelab 2 mission, July 29 to August 6, 1985. Gamma-ray spectra were measured with better than 20 s resolution throughout most of the mission in the energy range 0.1 to 30 MeV. Knowledge of the decay characteristics and the geomagnetic dependence of the counting rates enable measurement of the various components of the Spacelab gamma-ray background: prompt secondary radiation, Earth albedo, and delayed induced radioactivity. The status of the data analysis and present relevant examples of typical background behavior are covered.

Paciesas, William S.↗

NASA NTRS1987

Materials preparation and longevity in hyperthermal atomic oxygen

Flight hardware fabrication, the design and fabrication of an atom beam source, construction of a surface science laboratory, and progress in research on processes and mechanisms of interaction of hyperthermal atoms at solid surfaces are discussed.

Bareiss, Lyle E.↗

NASA NTRS1987

Cosmic ray detectors

Work on the MSFC emulsion laboratory microscopes in which mechanical modifications previously made were verified is reviewed, as is a design study of a large area hybrid electronic/emulsion chamber balloon flight detector system. This design is built upon the experience obtained with the highly successful MSFC/UAH hybrid instrument flown by the JACEE consortium. The design included overall system design and specification, design and fabrication of a prototype large light diffusion for Cerenkov charge detector or scintillator, design of a multiwire proportional counter array and design of the gondola or flight support system.

Gregory, John C.↗

NASA NTRS1986

Free molecule drag and lift deduced from Shuttle flight experiment

A gas surface interaction experiment was flown on the STS-8 flight of the Space Shuttle in which atomic oxygen was allowed to reflect off a glassy carbon surface. The spatial distribution of the reflected molecules was recorded showing a lobe between the specular and normal directions. Using the Nocilla treatment of the reflected molecules, the speed ratio of the reflected molecules and the angle of the drifting velocity with respect to the surface were determined. This information is used to determine the drag coefficient of a sphere and the drag and lift coefficients of a flat plate.

Karr, Gerald R.↗

NASA NTRS1986

A measurement of the angular distribution of 5 eV atomic oxygen scattered off a solid surface in earth orbit

The angular distribution of 5 eV atomic oxygen scattered off a polished vitreous carbon surface was measured on a recent Space Shuttle flight. The experimental apparatus was of novel design, completely passive, and used thin silver films as the recording device for oxygen atoms. Most of the incident oxygen was contained in the reflected beam and remained in an active form and probably still atoms. Allowance was made for 12 percent loss of incident atoms which are converted to CO at the carbon surface. The scattered distribution which is wide lobular, peaking 15 deg in the forward direction, shows almost but not quite full accommodation.

Gregory, John C.↗