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Whitaker, A. F.

Publications and source records attributed to Whitaker, A. F..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2015

Tribology Experiment in Zero Gravity

A tribology experiment in zero gravity was performed during the orbital flight of Spacelab 1 to study the motion of liquid lubricants over solid surfaces. The absence of a significant gravitational force facilitates observation of such motions as controlled by interfacial and capillary forces. Two experimental configurations were used. One deals with the liquid on one solid surface, and the other with the liquid between a pair of closed spaced surfaces. Time sequence photographs of fluid motion on a solid surface yielded spreading rate data of several fluid-surface combinations. In general, a slow spreading process as governed by the tertiary junction can be distinguished from a more rapid process which is driven by surface tension controlled internal fluid pressure. Photographs were also taken through the transparent bushings of several experimental journal bearings. Morphology of incomplete fluid films and its fluctuation with time suggest the presence or absence of unsteady phenomena of the bearing-rotor system in various arrangements.

Pan, C. H. T.↗
NASA NTRS1999

Third Aerospace Environmental Technology Conference

The elimination of CFC's, Halons, TCA, other ozone depleting chemicals, and specific hazardous materials is well underway. The phaseout of these chemicals has mandated changes and new developments in aerospace materials and processes. We are beyond discovery and initiation of these new developments and are now in the implementation phase. This conference provided a forum for materials and processes engineers, scientists, and managers to describe, review, and critically assess the evolving replacement and clean propulsion technologies from the standpoint of their significance, application, impact on aerospace systems, and utilization by the research and development community. The use of these new technologies, their selection and qualification, their implementation, and the needs and plans for further developments are presented.

Whitaker, A. F.↗
NASA NTRS1997

Second Aerospace Environmental Technology Conference

The mandated elimination of CFC's, Halons, TCA, and other ozone depleting chemicals and specific hazardous materials has required changes and new developments in aerospace materials and processes. The aerospace industry has been involved for several years in providing product substitutions, redesigning entire production processes, and developing new materials that minimize or eliminate damage to the environment. These activities emphasize replacement cleaning solvents and their application verifications, compliant coatings including corrosion protection systems, and removal techniques, chemical propulsion effects on the environment, and the initiation of modifications to relevant processing and manufacturing specifications and standards.

Whitaker, A. F.↗
NASA NTRS1995

LDEF materials results for spacecraft applications: Executive summary

To address the challenges of space environmental effects, NASA designed the Long Duration Exposure Facility (LDEF) for an 18-month mission to expose thousands of samples of candidate materials that might be used on a space station or other orbital spacecraft. LDEF was launched in April 1984 and was to have been returned to Earth in 1985. Changes in mission schedules postponed retrieval until January 1990, after 69 months in orbit. Analyses of the samples recovered from LDEF have provided spacecraft designers and managers with the most extensive data base on space materials phenomena. Many LDEF samples were greatly changed by extended space exposure. Among even the most radially altered samples, NASA and its science teams are finding a wealth of surprising conclusions and tantalizing clues about the effects of space on materials. Many were discussed at the first two LDEF results conferences and subsequent professional papers. The LDEF Materials Results for Spacecraft Applications Conference was convened in Huntsville to discuss implications for spacecraft design. Already, paint and thermal blanket selections for space station and other spacecraft have been affected by LDEF data. This volume synopsizes those results.

Whitaker, A. F.↗
NASA NTRS1995

Aerospace Environmental Technology Conference: Exectutive summary

The mandated elimination of CFC's, Halons, TCA, and other ozone depleting chemicals and specific hazardous materials has required changes and new developments in aerospace materials and processes. The aerospace industry has been involved for several years in providing product substitutions, redesigning entire production processes, and developing new materials that minimize or eliminate damage to the environment. These activities emphasize replacement cleaning solvents and their application verifications, compliant coatings including corrosion protection systems, and removal techniques, chemical propulsion effects on the environment, and the initiation of modifications to relevant processing and manufacturing specifications and standards. The papers from this conference are being published in a separate volume as NASA CP-3298.

Whitaker, A. F.↗
NASA NTRS1995

Aerospace Environmental Technology Conference

The mandated elimination of CFC's, Halons, TCA, and other ozone depleting chemicals and specific hazardous materials has required changes and new developments in aerospace materials and processes. The aerospace industry has been involved for several years in providing product substitutions, redesigning entire production processes, and developing new materials that minimize or eliminate damage to the environment. These activities emphasize replacement cleaning solvents and their application verifications, compliant coatings including corrosion protection systems, and removal techniques, chemical propulsion effects on the environment, and the initiation of modifications to relevant processing and manufacturing specifications and standards. The Executive Summary of this Conference is published as NASA CP-3297.

Whitaker, A. F.↗
NASA NTRS1991

Measuring Flux Density Of Monatomic Oxygen

Improved version of catalytic-probe technique yields more accurate measurements of flux density of neutral, monatomic oxygen. Two probes measure heat of recombination on catalytic surface. Principal application of technique in experiments in which oxygen plasmas used to examine degradation of various materials by monatomic oxygen.

Carruth, M. R., Jr.↗
NASA NTRS1991

Characterization of a 5-eV neutral atomic oxygen beam facility

An experimental effort to characterize an existing 5-eV neutral atomic oxygen beam facility being developed at Princeton Plasma Physics Laboratory is described. This characterization effort includes atomic oxygen flux and flux distribution measurements using a catalytic probe, energy determination using a commercially designed quadrupole mass spectrometer (QMS), and the exposure of oxygen-sensitive materials in this beam facility. Also, comparisons were drawn between the reaction efficiencies of materials exposed in plasma ashers, and the reaction efficiencies previously estimated from space flight experiments. The results of this study show that the beam facility is capable of producing a directional beam of neutral atomic oxygen atoms with the needed flux and energy to simulate low Earth orbit (LEO) conditions for real time accelerated testing. The flux distribution in this facility is uniform to +/- 6 percent of the peak flux over a beam diameter of 6 cm.

Vaughn, J. A.↗
NASA NTRS1990

Method for determination of neutral atomic oxygen flux

A method for measuring atomic oxygen flux to a probe surface is presented which uses two probes. One is a glass probe enclosing a small ceramic resistor heater and a thermocouple for determining the ambient local temperature. Another probe has a silver tip and a thermocouple inside it. In an atomic oxygen environment, the silver probe will quickly develop a silver oxide coating which provides for atomic oxygen recombination. The use of the two probes allows a more accurate determination of the energy input into the catalytic silver oxide probe due to recombination.

Carruth, M. R., Jr.↗
NASA NTRS1989

Materials resistance to low earth orbit environmental effects

A number of flexible polymeric materials have been considered as condidates for protective coatings on Kapton film. These coatings have been tested under a variety of environments, each of which simulates one or more aspects of the low earth orbit space environment. Mass loss rates vs fluence and temperatue, optical properties, and surface characteristics under exposure to the various environments will be presented. Kinetics data on Kapton and other materials is interpreted in terms of bond strengths and relative thermodynamic stabilities of potential products. Activation energy for degradation of Kapton by oxygen atoms was determined to be 30 + or - 5 kJ/mol. Materials tested include silicones, fluorosilicones, fluorophosphazenes, fluorocarbons, and hydrocarbons.

Pippin, H. G.↗
NASA NTRS1989

Atomic oxygen resistant protective coatings for the Hubble Space Telescope solar array in low earth orbit

The Hubble Space Telescope back-up solar array (BSFR-ATOX) was designed with atomic oxygen resistant materials to replace the original high efficiency cell (HEC) array. Pending qualification of the BSFR-ATOX array, protective coatings for application to the existing HEC array were evaluated. Three polysiloxane-type coating materials, SWS V-10, DC-100, and CV-1144 were evaluated with respect to atomic oxygen resistance, outgassing, contamination potential, stability under UV irradiation, electron-proton irradiation, thermal cycling, and long-term storage after application. Atomic oxygen testing included characterization of the atomic oxygen plasma using comparison of Kapton reaction to existing flight data, residual gas analysis, and temperature measurements. Results from these tests show DC-100 as a greater contamination concern if used in the vicinity of sensitive optical surfaces, i.e., solar cell cover glasses. The SWS V-10 and CV-1144 coatings met all acceptance criteria.

Burns, H. D.↗
NASA NTRS1986

Analyses of spacecraft polymeric materials

Partial analytical characterizations are made by four different techniques of three polymeric materials used in conjunction with the Space Telescope for samples flown on mission STS-8. The polymers were Tedlar, Kapton H, and Kapton F. The surfaces of the three polymers were attacked and oxidized by atomic oxygen, and fluorine is lost from the surface of Kapton F, largely due to displacement by atomic oxygen.

Worley, S. D.↗
NASA NTRS1985

Orbital atomic oxygen effects on thermal control and optical materials - STS-8 results

The effects of exposing 23 specimens of optical and thermal control materials to space at 120 km altitude for over 40 hrs during the STS-8 mission are discussed. Ten samples of paint targeted for the Space Telescope (ST) and the Tethered Satellite were exposed, and included polyurethane, oxide, silicone, and glossy black and white samples which were scanned for alterations in the optical properties after being retrieved. Nine mirror-type materials were also investigated, along with silver specimens typical of solar cell interconnects. The oxygen flow at the orbital altitude was 3.5 x 10 to the 20th atoms/cu cm. The exposures caused no degradation of the magnesium fluoride mirror coatings, while the Kapton coating for the ST solar cell panels showed evidence of losing thickness. The Ag solar cell contacts will require coatings to extend their lifetimes. Overcoatings were also proven necessary for inhibiting degradation of painted surfaces.

Whitaker, A. F.↗
NASA NTRS1985

Protective coatings for atomic oxygen susceptible spacecraft materials - STS-41G results

Sixteen materials consisting of metallizations, silicones, and FEP Teflon were applied as protective coatings to selected spacecraft material surfaces and exposed on STS-41G to the LEO atomic oxygen environment. Evaluations of their protective effectiveness were made through assessing their mass loss/gain characteristics, maintenance of base material optical properties, and imperviousness to atomic oxygen attack. Generally, all coatings provided some degree of protection for the underlying material. In some cases the overcoat appeared to be too thin thereby providing inadequate protection.

Whitaker, A. F.↗
NASA NTRS1985

Reaction of metals in lower earth orbit during Space Shuttle flight 41-G

The effects of ambient space environment on metals were studied by exposing specimens of Cu, Ag, Au, Ni, Cr, Al, Pt, and Pd on flight 41-G (STS-17). Data obtained by ellipsometry (ELL), Rutherford backscattering (RBS), and proton-induced X-ray emission (PIXE) before and after flight are summarized. Although the effects of space environment were most pronounced for silver, there were significant changes in the surface properties of the majority of the other metals. The surface optical constants proved to be the most sensitive measure of surface changes. These changes are attributed to the interaction of the metals with atomic oxygen.

Fromhold, A. T., Jr.↗
NASA NTRS1984

LEO atomic oxygen effects on spacecraft materials: STS-5 results

Effects of low Earth orbit (LEO) atomic oxygen were measured on a variety of spacecraft materials which obtained exposure on STS-5. Material degradation dependency on temperature was found in one material. Of the five paints flown, only S13GLO was unaffected. Generally, the glossy paints became Lambertian and the diffuse coatings improved. Scanning electron microscope examinations indicated removal of urethane and epoxy paint binder materials. Reaction products were evident on the surfaces of Z302 paint and Mylar. Thin films showed thickness losses ranging from negligible loss in Teflon to considerable loss in Mylar and Kapton. Glossy films such as black Kapton and white Tedlar became diffused. Kevlar 29 rope lost tensile strength and silver solar cell interconnect material oxidized. Oxidation on the backside of an elevated specimen indicated that reflections of oxygen atoms were occurring and that reflecting surfaces, probably Kapton, were not fully accommodating the incident atoms.

Whitaker, A. F.↗
NASA NTRS1984

Tribology experiment in zero gravity

A tribology experiment in zero gravity was performed during the orbital flight of Spacelab 1 to study the motion of liquid lubricants over solid surfaces. The absence of a significant gravitational force facilitates studies of the motion of liquid lubricants over solid surfaces as controlled by interfacial and capillary forces. Observations were made of phenomena associated with the liquid on one solid surface and also with the liquid between a pair of closely spaced surfaces. Typical photographic records obtained on Spacelab 1 are described.

Pan, C. H. T.↗