Engineering topics

Miller, Edgar R.

Publications and source records attributed to Miller, Edgar R..

8 records

NASA NTRS1995

Trend analysis of in-situ spectral reflectance data from the Thermal Control Surfaces Experiment (TCSE)

The Thermal Control Surfaces Experiment (TCSE) on the LDEF was a comprehensive experiment that combined in-space measurements with extensive pre- and post-flight analyses of thermal control surfaces to determine the effects of exposure to the low earth orbit (LEO) space environment. The TCSE is the first space experiment to directly measure in-situ total hemispherical reflectance of thermal control surfaces in the same way they are routinely measured in the laboratory. In-space optical measurements performed by the TCSE provide the unique opportunity for trend analysis of the performance of materials in the space environment. Such trend analysis of flight data offers the potential to develop an empirical life time prediction model for several thermal control surfaces. For material research, trend analysis of the TCSE flight data, particularly the spectral data, can provide insight into the damage mechanisms of space exposure. Trend analysis for the TCSE samples has been limited to those materials that were not significantly eroded by the atomic oxygen (AO) environment. The performance of several materials on the LDEF mission was dominated by AO effects. Trend analysis was performed on both the detailed spectral reflectance measurements (in-space, pre-flight, and post-flight) and on the integrated solar absorptance. Results of this analysis for the five selected TCSE materials are presented along with the spectral flight data. Possible degradation and effects mechanisms will be discussed to better understand and predict the behavior of these materials in the LEO space environment.

Wilkes, Donald R.↗

NASA NTRS1995

Whisker/Cone growth on the thermal control surfaces experiment no. S0069

An unusual surface 'growth' was found during scanning electron microscope (SEM) investigations of the Thermal Control Surface Experiment (TCSE) S0069 front thermal cover. This 'growth' is similar to the cone type whisker growth phenomena as studied by G. K. Wehner beginning in the 1960's. Extensive analysis has identified the most probable composition of the whiskers to be a silicate type glass. Sources of the growth material are outgassing products from the experiment and orbital atomic oxygen, which occurs naturally at the orbital altitudes of the LDEF mission in the form of neutral atomic oxygen. The highly ordered symmetry and directionality of the whiskers are attributed to the long term (5.8 year) stable flight orientation of the LDEF.

Zwiener, James M.↗

NASA NTRS1993

The performance of thermal control coatings on LDEF and implications to future spacecraft

The stability of thermal control coatings over the lifetime of a satellite or space platform is crucial to the success of the mission. With the increasing size, complexity, and duration of future missions, the stability of these materials becomes even more important. The Long Duration Exposure Facility (LDEF) offered an excellent testbed to study the stability and interaction of thermal control coatings in the low-Earth orbit (LEO) space environment. Several experiments on LDEF exposed thermal control coatings to the space environment. This paper provides an overview of the different materials flown and their stability during the extended LDEF mission. The exposure conditions, exposure environment, and measurements of materials properties (both in-space and postflight) are described. The relevance of the results and the implications to the design and operation of future space vehicles are also discussed.

Wilkes, Donald R.↗

NASA NTRS1993

The continuing materials analysis of the thermal control surfaces experiment (S0069)

The long term effects of the natural and induced space environment on spacecraft surfaces are critically important to future spacecraft - including Space Station Freedom. The damaging constituents of this environment include thermal vacuum, solar ultraviolet radiation, atomic oxygen, particulate radiation, and the spacecraft induced environment. The behavior of materials and coatings in the space environment continues to be a limiting technology for spacecraft and experiments. The Thermal Control Surfaces Experiment (TCSE) was flown on the National Aeronautics and Space Administration (NASA) Long Duration Exposure Facility (LDEF) to study these environmental effects on surfaces-particularly on thermal control surfaces. The TCSE was a comprehensive experiment that combined in-space measurements with extensive pre- and post-flight analyses of thermal control surfaces to determine the effects of exposure to the low Earth orbit space environment. The TCSE is the first space experiment to directly measure the total hemispherical reflectance of thermal control surfaces in the same way they are routinely measured in the laboratory. The trend analyses of selected coatings performed as part of the continuing post-flight analysis of the TCSE are described. A brief description of the TCSE and its mission on LDEF are presented. There are several publications available that describe the TCSE, it's mission on LDEF, and initial results in greater detail. These are listed in the TCSE Bibliography.

Wilkes, Donald R.↗

NASA NTRS1992

Fluorescence of thermal control coatings on S0069 and A0114

Many of the thermal control surfaces exposed to the space environment during the 5.8 year LDEF mission experienced changes in fluorescence. All of the thermal control coatings flown on LDEF experiments S0069 and A0114 were characterized for fluorescence under ambient conditions. Some of the black coatings, having protective overcoats, appear bright yellow under ultraviolet exposure. Urethane based coatings exhibited emission spectra shifts toward longer wavelengths in the visible range. Zinc oxide pigment based coatings experienced a quenching of fluorescence, while zinc orthotitanate pigment based and other ceramic type coatings had no measurable fluorescence.

Zwiener, James M.↗

NASA NTRS1992

Thermal Control Surfaces Experiment (TCSE) materials analysis

Materials on the Thermal Control Surfaces Experiment (TCSE) underwent changes in their properties during the 5.8 years of exposure to the combined space environment. The analysis of these materials is continuing and current results are discussed. Some materials were significantly degraded such as silver Teflon, S13GLO, and Z302; while others such as Z93 and YB71 were stable. Time dependent flight data is provided, along with preflight and postflight measurements. Results are compared with other experiments, demonstrating the atomic oxygen (AO) ram effect. Atomic oxygen texturing of silver Teflon varies with incident angle. Even indirect exposure to atomic oxygen appears to be involved with surface texturing on the interior of the TCSE. Localized contamination occurred at discrete locations both inside and on exterior surfaces. Most of the visible deposits were the result of the classical photo-enhanced contamination deposition. The synergism of combined space environmental effects is demonstrated by the specific localization of contamination caused by photo-enhanced deposition versus AO removal. Optical degradation measurements of these contaminated areas, utilizing a new portable reflectometer, are presented.

Wilkes, Donald R.↗

NASA NTRS1992

Flouorescence measurements of the thermal control coatings on LDEF experiments S0069 and A0114

Strong fluorescence emissions were observed, during post flight ultraviolet light inspection of experiments S0069 and A0114, from some of the surfaces exposed to the space environment. Subsequent wavelength measurements of the fluorescence emission characteristics, indicated large changes occurred between controls and exposed materials. Black urethane based coatings, especially ones having a silicone atomic oxygen protective overcoat, appear bright yellow under ultraviolet exposure. Measurements showed that the urethane based coatings had their emission spectra shifted into the visible wavelength range. In contrast, zinc oxide pigment type coatings showed a different effect, which was a quenching or reduction of their fluorescence versus exposure time. Silver Teflon bonded to aluminum with acrylic adhesive also showed a slight measurable fluorescence, which was found to originate in the acrylic adhesive.

Zwiener, James M.↗

NASA NTRS1992

Unusual materials effects observed on the thermal control surfaces experiment (S0069)

A number of unusual effects were observed on the Thermal Control Surfaces Experiment (TCSE) test samples, front cover, and structural components. These effects include atomic oxygen (AO) texturing of the exposed surface of the silver Teflon (Ag/FEP) thermal control material, 'brownish' discoloration of the Ag/FEP material, changes in fluorescence of thermal control paint samples, and meteoroid/debris impact effects on silver Teflon.

Zwiener, James M.↗