Thermal control surfaces experiment flight system performance

The Thermal Control Surfaces Experiment (TCSE) is the most complex system, other than the LDEF, retrieved after long term space exposure. The TCSE is a microcosm of complex electro-optical payloads being developed and flow by NASA and the DoD including SDI. The objective of TCSE was to determine the effects of the near-Earth orbital environment and the LDEF induced environment on spacecraft thermal control surfaces. The TCSE was a comprehensive experiment that combined in-space measurements with extensive post flight analyses of thermal control surfaces to determine the effects of exposure to the low earth orbit space environment. The TCSE was the first space experiment to measure the optical properties of thermal control surfaces the way they are routinely measured in a lab. The performance of the TCSE confirms that low cost, complex experiment packages can be developed that perform well in space

Micrometeoroid/space debris effects on materials

The Long Duration Exposure Facility (LDEF) micrometeoroid/space debris impact data has been reduced in terms that are convenient for evaluating the overall quantitative effect on material properties. Impact crater flux has been evaluated as a function of angle from velocity vector and as a function of crater size. This data is combined with spall data from flight and ground testing to calculate effective solar absorption and emittance values versus time. Results indicate that the surface damage from micrometeoroid/space debris does not significantly affect the overall surface optical thermal physical properties. Of course the local damage around impact craters radically alter optical properties. Damage to composites and solar cells on an overall basis was minimal

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

The Passive Optical Sample Assembly (POSA): I Experiment: First Flight Results and Conclusions

The Passive Optical Sample Assembly-I (POSA-I), part of the Mir Environmental Effects Payload (MEEP), was designed to study the combined effects of contamination, atomic oxygen, ultraviolet radiation, vacuum, thermal cycling, and other constituents of the space environment on spacecraft materials. The MEEP program is a Phase 1 International Space Station Risk Mitigation Experiment. SSP 30258 "Thermal Control Architectural Control Document", section 3.1.2 requires that International Space Station (ISS) external materials meet performance requirements when exposed to the external environment as defined in SSP 30426, "Space Station External Contamination Control Requirements." Contamination control documents call for less than 3 x 10(exp -7) gm/sq cm/yr of molecular contamination on a surface at 300 K at the Prime Measurement Points during quiescent periods and less than 1 x 10(exp-6) gm/sq cm/yr during non-quiescent periods. Assuming a density of 1.0 g/cu cm for the contaminant, this is roughly equivalent to 30-100 A per year. A previous Mir flight experiment (Guillaumon et al. 1991) measured 321-716 A per year. Were this to happen on ISS, the radiators would reach end-of-life properties much sooner than the planned 10 years. Therefore, POSA was proposed to expose ISS-baselined materials (such as Z93 white thermal control paint and chromic acid anodized aluminum) to the Mir environment and determine not only the level of contamination from an orbiting, active space station but also the effect of contamination on thermal optical properties. POSA-I consisted of nearly 400 samples of various candidate materials for ISS. Paint samples flown included Z-93 and YB-71 white thermal control paints and a new inorganic bright yellow paint htat can be utilized for astronaut visual aids

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

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

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

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

Changes in chemical and optical properties of thin film metal mirrors on LDEF

Thin films of the metals Cu, Ni, Pt, Au, Sn, Mo, and W deposited on fused silica flats were exposed at ambient temperature on the leading and trailing faces of the LDEF. Reflectances of these films were measured from 250 to 2500 nm and compared with controls. The exposed films were subjected to the LDEF external environment including atomic oxygen, molecular contamination, and solar ultraviolet. Major changes in optical and infrared reflectance were seen for Cu, Mo, Ni, and W films on the leading face of LDEF and are attributed to partial conversion of metal to metal oxide. Smaller changes in optical properties are seen on all films and are probably caused by thin contaminant films deposited on top of the metal. The optical measurements are correlated with film thickness measurements, x-ray photoelectron spectroscopy, optical calculations, and, in the case of Cu, with x-ray diffraction measurements. In a few cases, comparisons with results from a similar UAH experiment on STS-8 have been drawn

Thermal Control Materials on MISSE-6 with Comparison to Earlier Flight Data

This slide presentation reviews the results of exposing thermal control materials as studied during Materials International Space Station Experiment-6 (MISSE-6). It discusses the location of the materials, and the type of environmental exposure. It then reviews the effect on the various types of coatings, showing the results with graphs and photos of the samples after the experimental exposure to the low earth orbital environment for comparison with the control sample and with earlier flights