Engineering topics

Slemp, Wayne S.

Publications and source records attributed to Slemp, Wayne S..

35 records · Page 2

NASA NTRS1991

Chemical characterization of selected LDEF polymeric materials

Chemical characterization of selected polymeric materials which received exposure on the Long Duration Exposure Facility (LDEF) is reported. The specimens examined include silvered fluorinated ethylene propylene Teflon thermal blanket material, polysulfone, epoxy, polyimide matrix resin/graphite fiber reinforced composites, and several high performance polymer films. These specimens came from numerous LDEF locations, and thus received different environmental exposures. The results to date show no significant change at the molecular level in the polymer that survived exposure. Scanning electron and scanning tunneling microscopes show resin loss and a texturing of some specimens which resulted in a change in optical properties. The potential effect of a silicon-containing molecular contamination on these materials is addressed. The possibility of continued post-exposure degradation of some polymeric films is also proposed.

Young, Philip R.↗

NASA NTRS1991

Effects of LDEF flight exposure on selected polymeric films and thermal control coatings

The characterization of polymeric films and thermal control coatings which were exposed for five years and ten months to the low-Earth environment is reported. Changes in solar absorptance, thermal emittance, and transmission are compared to laboratory control specimens. Sputter-deposited metallic coatings are shown to eliminate atomic oxygen erosion of resin matrix composite materials. The effects of long-term atomic oxygen exposure to metallized FEP Teflon film is characterized. Chemical characterization of polymeric films indicates that although surface erosion occurs, the molecular structure of the basic polymeric film has not changed significantly in response to this exposure.

Slemp, Wayne S.↗

NASA NTRS1991

Effects of LDEF flight exposure on selected polymer matrix resin composite materials

The characterization of selected graphite fiber reinforced epoxy and polysulfone matrix resin composites which received exposure to the LEO environment on the LDEF is reported. The changes in mechanical properties of ultimate tensile strength and tensile modulus for exposed flight specimens are compared to the three sets of control specimens. Marked changes in surface appearance are discussed, and resin loss is reported. The chemical characterization including IR, thermal, and selected solution property measurements showed that the molecular structure of the polymeric matrix had not changed significantly in response to this exposure.

Slemp, Wayne S.↗

NASA NTRS1991

Evaluation of thermal control coatings for use on solar dynamic radiators in low earth orbit

Thermal control coatings with high thermal emittance and low solar absorptance are needed for Space Station Freedom (SSF) solar dynamic power module radiator (SDR) surfaces for efficient heat rejection. Additionally, these coatings must be durable to low earth orbital (LEO) environmental effects of atomic oxygen, ultraviolet radiation and deep thermal cycles which occur as a result of start-up and shut-down of the solar dynamic power system. Eleven candidate coatings were characterized for their solar absorptance and emittance before and after exposure to ultraviolet (UV) radiation (200 to 400 nm), vacuum UV (VUV) radiation (100 to 200 nm) and atomic oxygen. Results indicated that the most durable and best performing coatings were white paint thermal control coatings Z-93, zinc oxide pigment in potassium silicate binder, and YB-71, zinc orthotitanate pigment in potassium silicate binder. Optical micrographs of these materials exposed to the individual environmental effects of atomic oxygen and vacuum thermal cycling showed that no surface cracking occurred.

Dever, Joyce A.↗

NASA NTRS1991

Spectrophotometer-Integrating-Sphere System for Computing Solar Absorptance

A commercially available ultraviolet, visible, near-infrared spectrophotometer was modified to utilize an 8-inch-diameter modified Edwards-type integrated sphere. Software was written so that the reflectance spectra could be used to obtain solar absorptance values of 1-inch-diameter specimens. A descriptions of the system, spectral reflectance, and software for calculation of solar absorptance from reflectance data are presented.

Witte, William G., Jr.↗

NASA NTRS1991

Evaluation of thermal control coatings for use on solar dynamic radiators in low Earth orbit

Dever, Joyce A.↗

NASA NTRS1991

Characterization of selected LDEF polymer matrix resin composite materials

The characterization of selected graphite fiber reinforced epoxy (934 and 5208) and polysulfone (P1700) matrix resin composite materials which received 5 years and 10 months of exposure to the LEO environment on the Long Duration Exposure Facility is reported. Resin loss and a decrease in mechanical performance as well as dramatic visual effects were observed. However, chemical characterization including infrared, thermal, and selected solution property measurements showed that the molecular structure of the polymeric matrix had not changed significantly in response to this exposure. The potential effect of a silicon-containing molecular contamination of these specimens is addressed.

Young, Philip R.↗

NASA NTRS1991

Evaluation of optically transparent polyetherimide films for applications in space

Several series of aromatic polyetherimide films have been synthesized and characterized with the objective of obtaining maximum optical transparency for applications in space. Incorporation of phenoxy groups into aromatic polyimides has resulted in a reduction in the color intensity of these films compared to commercial polyimide film by reducing electronic interactions between polymer chains. The resulting lightly colored to colorless polyetherimide films have been characterized by UV-visible and infrared spectroscopy before and after exposure to varying doses of UV and electron irradiation designed to simulate use as second-surface mirror thermal control coatings. After exposure to 300 equivalent solar hours UV irradiation and 1 MeV electron irradiation, the polyetherimides were 2.2 to 2.6 times more transparent than commercial polyimide film of the same thickness.

St. Clair, Anne K.↗

NASA NTRS1989

Ultraviolet radiation effects

Solar ultraviolet testing was not developed which will provide highly accelerated (20 to 50X) exposures that correlate to flight test data. Additional studies are required to develop an exposure methodology which will assure that accelerated testing can be used for qualification of materials and coatings for long duration space flight. Some conclusions are listed: Solar UV radiation is present in all orbital environments; Solar UV does not change in flux with orbital altitude; UV radiation can degrade most coatings and polymeric films; Laboratory UV simulation methodology is needed for accelerated testing to 20 UV solar constants; Simulation of extreme UV (below 200 nm) is needed to evaluate requirements for EUV in solar simulation.

Slemp, Wayne S.↗

NASA NTRS1989

Solar radiation

The effects of solar radiation in aerospace environments on aerospace systems are examined. It was concluded that most materials degrade to solar radiation. The information available on short term effects on materials provides a limited data base. Flight data on coating degradation seems to be confused by contamination. Other conclusions of data examination are listed.

Slemp, Wayne S.↗

NASA NTRS1989

Working group written presentation: Solar radiation

The members of the Solar Radiation Working Group arrived at two major solar radiation technology needs: (1) generation of a long term flight data base; and (2) development of a standardized UV testing methodology. The flight data base should include 1 to 5 year exposure of optical filters, windows, thermal control coatings, hardened coatings, polymeric films, and structural composites. The UV flux and wavelength distribution, as well as particulate radiation flux and energy, should be measured during this flight exposure. A standard testing methodology is needed to establish techniques for highly accelerated UV exposure which will correlate well with flight test data. Currently, UV can only be accelerated to about 3 solar constants and can correlate well with flight exposure data. With space missions to 30 years, acceleration rates of 30 to 100X are needed for efficient laboratory testing.

Slemp, Wayne S.↗

NASA NTRS1989

Radiation durability of polymeric matrix composites

The combined effects of thermal cycling and high-dose electron irradiation on the mechanical properties of laminated graphite/polymeric CFRPs are investigated experimentally. The test apparatus and procedures are briefly described, and the results are presented in extensive tables and graphs. It is found that electron radiation produces similar significant reductions in the glass transition temperatures of the neat resins and CFRPs. The radiation-induced degradation products tend to plasticize the matrix at high temperature but embrittle it at low temperature.

Tenney, Darrel R.↗

NASA NTRS1988

Evaluation of chromic acid anodized aluminum foil coated composite tubes for the Space Station truss structure

This paper describes the development and evaluation of chromic acid anodized (CAA) Al foil as a protective and thermal control coating for graphite/epoxy tubes designed for the Space Station truss structure. Special consideration is given to the development of solar-absorptance and thermal-emittance properties required of Al foil, the development of CAA parameters necessary to achieve these optical properties, and the atomic oxygen and UV testing of CAA Al foil. Results showed that 0.003-in CAA Al foil cocured or secondary bonded to graphite/epoxy tubes with thin epoxy film adhesive retains excellent bond strength and provides a superior protective and thermal control coating to the LEO environment. Processes were developed for CAA Al foils long enough to continuously wrap the 23-ft-long diagonal struts of the Space Station truss structure. Specifications are presented for the processes of chromic acid anodizing of Al foil and for the bonding of anodized Al foil to graphite/epoxy tubes.

Dursch, Harry W.↗

NASA NTRS1987

Colorless Polyimide Films for Thermal-Control Coatings

Series of six essentially colorless aromatic polyimide films synthesized and characterized with objective of obtaining maximum optical transparency for applications in space; optical transparency requirement for high-performance polymeric films used in second-surface mirror coatings on thermal-control systems. Films remain more transparent than commercial film after ultraviolet and electron irradiation. Increased transparency and enhanced solubility of optically transparent polyimides makes them viable candidates for use in thermal-control coatings.

St. Clair, Anne K.↗

NASA NTRS1987

Simulated space environment effects on the optical properties of poly(arylene ethers)

Results are reported from a study of the stability of poly(arylene ethers) formed in a reaction of 1,3 -bis(4-chlorobenzoyl)benzene and various bisphenols after experiencing long-term exposure to space conditions. Transparent poly(arylene ethers) films were subjected to separate electron and UV bombardments, as were polysulfone and Kapton films for comparisons. The order of exposure to the two types of radiation was reversed for two sample populations. The optical properties and glass transition temperatures of the samples were determined after irradiation. The poly(arylene ethers) films exhibited good resistance to the electron radiation but suffered severe degradation in the UV environment. The loss of optical transmissivity was proportional to the UV radiation dose.

Sykes, George F.↗

NASA NTRS1986

Assessment of space environment induced microdamage in toughened composite materials

The effects of simulated space environments on the microdamage in a series of commercially available toughened matrix composite systems was determined. Low-earth orbit (LEO) exposures were simulated by thermal cycling; geosynchronous orbit (GEO) exposures were simulated by electron irradiation plus thermal cycling. Material response was characterized by assessing the induced microcracking and its influence on chemical and mechanical property changes. All materials, including several advanced, tough thermoplastics microcracked when exposed to the simulated LEO environment except a 177 C cured single phase toughened epoxy composite. The GEO simulated environment produced microdamage in all materials. The results suggest that increased matrix toughness may not be the overriding factor leading to improved durability in the space environment.

Sykes, George F.↗

NASA NTRS1962

A Method for Measuring the Spectral Normal Emittance in Air of A Variety of Materials Having Stable Emittance Characteristics

A method and apparatus is described for the measurement of spectral normal emittance in air of a variety of materials. The system permits measurements to be performed over a wavelength region of 1.0 through 15.0 microns and over a temperature range of 600F to 1,8000F with an accuracy of 5.0 percent. The advantages of this system are described. Results obtained by this system are compared with results reported by another observer using a different technique.

COATING↗