Engineering topics

See, Thomas H.

Publications and source records attributed to See, Thomas H..

32 records · Page 2

NASA NTRS1992

Dissemination and fractionation of projectile materials in the impact melts from Wabar Crater, Saudi Arabia

Results are presented from the analyses of small ballistically dispersed melt samples (occurring in the form of aerodynamically shaped spheres, dumbbells, and teardrops) from the Wabar Crater (Saudi Arabia) and of melts from the Wabar and Nejed meteorites. On the basis of the data obtained and of models for crater forming processes it is concluded that the ballistically-dispersed glasses were formed from material at shallow levels in the target zone where temperatures were higher and where intimate physical contact with the disrupting impactor was achieved. Siderophile element fractionation was completed early, while the impactor was undergoing decompression and prior to mixing with the target glasses.

Mittlefehldt, David W.↗

NASA NTRS1992

Detailed examination of LDEF's frame and the A0178 thermal blankets by the meteoroid and debris special investigations group

A responsibility of the group is to define the hypervelocity particle environment encountered by LDEF during its stay in low Earth orbit. LDEF's 6061-T6 aluminum frame and the 'Teflon silver-inconel paint' thermal blankets represent large surface areas that were widely distributed around the spacecraft. The results are reported of high resolution scans of approx. 0.36 and approx. 0.31 sq m for the intercostals and thermal blankets, respectively. The findings are in qualitative agreement with existing model predictions that suggest high differential bombardment histories for surfaces pointing into specific directions relative to the velocity vector of a non-spinning platform in LEO. The production rate for craters greater than or = 50 microns in diameter in aluminum and penetration holes greater than or = 100 microns in diameter in thin foil materials differ by more than a factor of 10 between forward and rearward facing surfaces. These are substantial differences that must be considered during the design of future long duration space platforms in LEO.

See, Thomas H.↗

NASA NTRS1992

Meteoroid and debris special investigation group; status of 3-D crater analysis from binocular imagery

During the 3 month deintegration of the LDEF, the M&D SIG generated approximately 5000 digital color stereo image pairs of impact related features from all space exposed surfaces. Currently, these images are being processed at JSC to yield more accurate feature information. Work is currently underway to determine the minimum number of data points necessary to parametrically define impact crater morphologies in order to minimize the man-hour intensive task of tie point selection. Initial attempts at deriving accurate crater depth and diameter measurements from binocular imagery were based on the assumption that the crater geometries were best defined by paraboloid. We made no assumptions regarding the crater depth/diameter ratios but instead allowed each crater to define its own coefficients by performing a least-squares fit based on user-selected tiepoints. Initial test cases resulted in larger errors than desired, so it was decided to test our basic assumptions that the crater geometries could be parametrically defined as paraboloids. The method for testing this assumption was to carefully slice test craters (experimentally produced in an appropriate aluminum alloy) vertically through the center resulting in a readily visible cross-section of the crater geometry. Initially, five separate craters were cross-sectioned in this fashion. A digital image of each cross-section was then created, and the 2-D crater geometry was then hand-digitized to create a table of XY position for each crater. A 2nd order polynomial (parabolic) was fitted to the data using a least-squares approach. The differences between the fit equation and the actual data were fairly significant, and easily large enough to account for the errors found in the 3-D fits. The differences between the curve fit and the actual data were consistent between the caters. This consistency suggested that the differences were due to the fact that a parabola did not sufficiently define the generic crater geometry. Fourth and 6th order equations were then fitted to each crater cross-section, and significantly better estimates of the crater geometry were obtained with each fit. Work is presently underway to determine the best way to make use of this new parametric crater definition.

Sapp, Clyde A.↗

NASA NTRS1992

Meteoroid and debris special investigation group data acquisition procedures

The entire LDEF spacecraft was examined by M&D SIG for impact (i.e., craters greater than or = 0.5 mm and penetrations greater than or = 0.3 mm in diameter) and related features (e.g., debris, secondaries). During the various detailed surveys conducted at NASA Kennedy, approx. 5,000 impact related features were photodocumented, and their locations measured and recorded; an additional approx. 30,000 smaller features were counted. The equipment and techniques used by the M&D SIG permitted the determination and recording of the locations and diameters of the 5,000 imaged features. A variety of experimental and LDEF structural hardware was acquired by the M&D SIG and is presently being examined and curated at NASA Johnson.

See, Thomas H.↗

NASA NTRS1992

Meteoroid, and debris special investigation group preliminary results: Size-frequency distribution and spatial density of large impact features on LDEF

All craters greater than or equal to 500 microns and penetration holes greater than or equal to 300 microns in diameter on the entire Long Duration Exposure Facility (LDEF) were documented. Summarized here are the observations on the LDEF frame, which exposed aluminum 6061-T6 in 26 specific directions relative to LDEF's velocity vector. In addition, the opportunity arose to characterize the penetration holes in the A0178 thermal blankets, which pointed in nine directions. For each of the 26 directions, LDEF provided time-area products that approach those afforded by all previous space-retrieved materials combined. The objective here is to provide a factual database pertaining to the largest collisional events on the entire LDEF spacecraft with a minimum of interpretation. This database may serve to encourage and guide more interpretative efforts and modeling attempts.

See, Thomas H.↗

NASA NTRS1992

Preliminary analysis of LDEF instrument A0187-1: Chemistry of Micrometeoroids Experiment

The Chemistry of Micrometeoroids Experiment (CME) exposed approximately 0.8 sq. m of gold on the Long Duration Exposure Facility's (LDEF's) trailing edge (location A03) and approximately 1.1 sq. m of aluminum in the forward-facing A11 location. The most significant results to date relate to the discovery of unmelted pyroxene and olivine fragments associated with natural cosmic dust impacts. The latter are sufficiently large for detailed phase studies, and they serve to demonstrate that recovery of unmelted dust fragments is a realistic prospect for further dust experiments that will employ more advanced collector media. We also discovered that man-made debris impacts occur on the LDEF's trailing edge with substantially higher frequency than expected, suggesting that orbital debris in highly elliptical orbits may have been somewhat underestimated.

Hoerz, Friedrich↗

NASA NTRS1992

Interim Report of the Meteoroid and Debris Special Investigation Group

The LDEF Meteoroid and Debris Special Investigation Group (hereafter M&D SIG) was formed to maximize the data harvest from LDEF by permitting the characterization of the meteoroid and space debris impact record of the entire satellite. Thus, our work is complementary to that of the various M&D PIs, all of whom are members of the SIG. This presentation will summarize recent results and discussions concerning five critical SIG goals: (1) Classification of impactors based upon composition of residues; (2) Small impact (microimpact) features; (3) Impact cratering and penetration data to derive projectile sizes and masses; (4) Particulate flux estimates in low-Earth orbit; (5) The LDEF Meteoroid and Debris database.

Zolensky, Michael E.↗

NASA NTRS1991

Meteoroid and orbital debris record of the Long Duration Exposure Facility

The Long Duration Exposure Facility (LDEF) was recovered in January 1990 following 5.7 years exposure of approx. 130 square meters of surface area in low-Earth orbit (250-179 miles). Kennedy Space Center acquired data are currently being reduced to yield accurate impact crater depths and diameters. Presented here is a preliminary accounting of the impact record based on the approx. 15.4 square meter surface area of LDEF's 6061-T6 aluminum frame, which was exposed in 26 different directions.

Zolensky, Mike↗

NASA NTRS1991

Preliminary results from the chemistry of micrometeoroid experiment (AO 187-1)

The purpose of experiment AO 187-1 was to expose high purity substrates of suitable cratering properties to obtain detailed crater statistics that may be converted into projectile masses and fluxes and to chemically characterize as many impactors as possible. The latter information would hopefully reveal distinct classes of natural and man-made particles in low-Earth orbit. It was found that crater that yield residues show that natural and man-made impactors may be differentiated and that diversity exists within each group. 'Chondritic' compositions dominate among natural particles, yet some craters contain unmelted fragments of minerals (Olivine and pyroxene).

Horz, Friedrich↗

NASA NTRS1991

M and D SIG progress report: Laboratory simulations of LDEF impact features

Reported here are impact simulations into pure Teflon and aluminum targets. These experiments will allow first order interpretations of impact features on the Long Duration Exposure Facility (LDEF), and they will serve as guides for dedicated experiments that employ the real LDEF blankets, both unexposed and exposed, for a refined understanding of the Long Duration Exposure Facility's collisional environment.

Horz, Friedrich↗

NASA NTRS1991

Preliminary micrometeoroid and debris effects on LDEF thermal control surfaces

Thermal control surfaces on the Long Duration Exposure Facility (LDEF) were exposed to 5.75 years of low-Earth orbit environments. Since LDEF was gravity gradient stabilized and directionally stable, the effects of each of the environments can be distinguished via changes in material responses to hypervelocity impacts. The extent of these effects are being visually and microscopically characterized using thermal control surfaces archived at Johnson Space Center in order to determine the the relationship between environment exposure and resulting ring sizes, delamination areas, and penetration diameters. The characterization of these affected areas will provide spacecraft system designers with the information they require to determine degradation of thermal control systems during satellite lifetimes.

Allbrooks, Martha K.↗

NASA NTRS1988

Formation of agglutinate-like particles in an experimental regolith

Agglutinate-like particles composed predominantly of glass were produced from a fragmental gabbro target that was repetitively impacted by Ni-alloy projectiles. The experimental glasses are much more heterogeneous in composition than their lunar counterparts, and they are dominated by incomplete mixing of melted component minerals and by plagioclase-rich compositions. Most of the particles are found to be highly enriched in feldspar and to be sustantially fractionated relative to the initial bulk target. It is suggested that fractionation trends within lunar agglutinitic glasses may be partly due to phase-specific melting.

See, Thomas H.↗

NASA NTRS1986

Apollo 16 impact-melt splashes - Petrography and major-element composition

Petrographic and major-element analyses are applied to 50 Apollo 16 impact-melt splash (IMS) samples in order to determine their origin and assess the nature of the subregolith source. The macroscopic analyses reveal that the IMSs exhibit a glassy appearance, but the textures range from holohyaline to hyalopilitic. Schlieren-rich glasses dominate the holohyaline areas, and the crystalline areas are mainly spherulitic. It is observed that most IMSs contain feldspathic monomineralic and lithic clasts and no regolithic materials. It is detected that the chemistry of most IMSs is not like the local regolith and appears to represent varied mixtures of VHA impact-melt breccias and anorthosite; the host rocks are mainly dimict breccias. It is concluded that the Cayley Formation is a polymict deposit composed of VHA impact-melt breccias and anorthosites. Tables revealing the macroscopic characteristics of the IMSs and the major-element composition of IMSs and various host rock are presented.

See, Thomas H.↗

NASA NTRS1986

Composition of the Cayley Formation at Apollo 16 as inferred from impact melt splashes

Abundances of major and trace elements and magnetic properties of 50 impact melt splashes (IMSs) from the Apollo 16 landing site are analzyed to determine the composition of their meteoritic component. MgO-Sc and Ca-Sc variation diagrams and least-squares mixing models are utilized to analyze the IMS, soil, and rock data. Consideration is given to progenitor lithologies of the IMS, the number of impact events represented by the IMS, and the heterogeneity of impact melts from single events. It is observed that the IMSs are composed of either a mixture of anorthosite and low-Sc impact melt rocks or anorthositic norite. It is determined that the surface Cayley layer is composed of TiO2, MgO, Sc, and La concentrations of 0.69, and 7.1 wt pct and 10.5 and 21.2 microg/g, respectively and 0.38 and 5.9 wt pct and 6.1 and 11.8 microg/g, respectively, for the subsurface Cayley layer. The Descartes Formation composition is estimated as TiO2, MgO, Sc, and La concentrations of 0.25, and 3.5 wt pct and 7.7 and 2.2 microg/g, respectively.

Morris, Richard V.↗