This paper presents an overview of International Space Station (ISS) on-orbit environments exposure flight experiments. International teams are flying, or preparing to fly, externally mounted materials exposure trays and sensor packages. The samples in these trays are exposed to a combination of induced molecular contamination, ultraviolet radiation, atomic oxygen, ionizing radiation, micrometeoroids and orbital debris. Exposed materials samples are analyzed upon return. Typical analyses performed on these samples include optical property measurements, X-ray photo spectroscopy (XPS) depth profiles, scanning electron microscope (SEM) surface morphology and materials properties measurements. The objective of these studies is to characterize the long-term effects of the natural and induced environments on spacecraft materials. Ongoing flight experiments include the U.S. Materials International Space Station Experiment (MISSE) program, the Japanese Micro-Particles Capturer and Space Environment Exposure Device (SM/MPAC&SEED) experiment, the Russian SKK and Kromka experiments from RSC-Energia, and the Komplast flight experiment. Flight experiments being prepared for flight, or in development stage, include the Japanese Space Environment Data Acquisition Attached Payload (SEDA-AP), the Russian BKDO monitoring package from RSC-Energia, and the European Materials Exposure and Degradation Experiment (MEDET). Results from these ISS flight experiments will be crucial to extending the performance and life of long-duration space systems such as Space Station, Space Transportation System, and other missions for Moon and Mars exploration.

The GOES-8 Imager and Sounder radiant coolers have lost some of its ability to dissipate heat over time. This is shown by the temperature increase over time of the vacuum cooler housings that are cooled with optical solar reflector (OSR) radiators. Contamination has a significant, well-documented effect on the solar absorptance of OSRs. This evaluation attempts to discern how much molecular contamination has collected on the Imager and Sounder radiant coolers by analyzing the increase in temperature of the vacuum cooler housing. In the first part, temperature change is transformed into solar absorptance units by a method devised by ITT. The second part transforms the solar absorptance gain into a molecular film thickness and correlates the film thickness to the number of days after radiant cooler cover deployment.

The Midcourse Space Experiment (MSX) spacecraft has now been in orbit for over 8 years. The Total Pressure Sensor (TPS) has continually made measurements of the ambient and spacecraft induced environment since launch on April 24, 1996. The environment surrounding the satellite continues to be very dynamic. The magnitude of the solar induced pressure peaks has not decayed with time as would be expected. Even sole consideration of measured pressure versus duration of solar illumination does not illustrate long term decay. The TPS has continued to measure pressure variations of more than 2 orders of magnitude as the sun illuminates the blankets surrounding the instrument. The multi-layer thermal blankets appear to represent a large virtual source of water. The measured pressure is highly dependent upon the solar angle and the shadowing of surfaces by other structures. We will focus our attention on the results from an identical set of experiments conducted each year in July.

We present the results of a laboratory test to determine the effects of bulk-deposited DC-704 silicone-oil contaminant film on the transmittance properties of an anti-reflective (AR) coated fused-silica optical substrate. Testing and optical measurements were performed in vacuum in the Boeing Contamination Effects Test Facility (CETF). The test and measurement procedures are described herein. Measurement results are presented showing the change in transmittance characteristics as a function of contaminant deposit thickness and vacuum-ultraviolet (VUV) exposure levels. The results show an initial degradation in the transmittance of the contaminated sample. This is followed by a partial recovery in transmittance as the sample is exposed to additional VUV radiation. The results also show a loss of transmittance in the ultraviolet portion of the spectrum and an increase in transmittance in the infrared portion of the spectrum. Thin-film interference analysis indicates that some of the observed transmittance results can be successfully modeled, but only if the contaminant film is assumed to have the complex index of refraction of SiO₂ rather than DC-704 silicone oil. Post-test Scanning Electron Microscope (SEM) scans of the test sample indicate the formation of contaminant islands and the presence of a thin uniform contaminant film on the sample.

Molecular contamination of ultraviolet (UV) optics has been well characterized at wavelengths longer than 120 nm, and some tests have been done at very short wavelengths (10 nm). Characterization of molecular contamination effects at intermediate wavelengths is scarce. This paper draws a parallel between organic light filters and molecular contaminants, considering the contaminant as an extra organic film on an existing filter. This allows the analyst to use Henke light absorptance analysis to characterize extreme ultraviolet (EUV) light attenuation. This technique shows that peak light attenuation occurs near 73 nm (17 eV), rather than the previously assumed 121.6 nm, due to the preferential ejection of 2s electrons in carbon near 17 eV.

The advantages of backside irradiation and controlling the polarization and angle of incidence of laser beams used to conventionally clean surfaces have been described previously. This paper considers beams internally incident upon the surface of a transparent substrate at angles of incidence beyond the critical angle for total internal reflection. Attenuated total internal reflection provides an efficient means for both finding and removing absorbing contaminants. Beams may enter the substrate through an edge or a coupling prism. Erbium laser pulses were used to remove water from several dielectric and semiconductor materials. In some cases the water was explosively removed, with no sign of damage to the substrate. A 2.94 μm laser should be especially effective whenever water is present, either naturally from adsorption or capillary condensation or when added for steam laser cleaning. Unabsorbed light can be efficiently routed to clean adjacent areas through multiple total internal reflections. Thus some of the scanning is done at the speed of light. Theory indicates that ATR laser cleaning is effective for very small particles that cannot be removed by shock laser cleaning. This paper will describe attenuated total internal reflection laser cleaning and compare it to conventional laser cleaning techniques.

Novel light scattering properties of molecular films in a “droplet” configuration are presented and discussed. The illuminated films are shown to disappear when viewed at particular angles. The phenomenon is discussed in the context of Germer’s analysis of out-of-plane scattering from particles and surface micro-roughness.

Particle-induced light scatter reduces sensitivity and degrades performance of optical systems. Though particles are generally considered to be the primary source responsible for stray radiation, there is evidence that molecular contaminants also induce light scatter. The primary objective for this research effort has been to increase our understanding of molecular contaminant film growth and its implications for light scatter. Herein, our new molecular film deposition and imaging facility is described. In-situ imaging data, acquired from non-uniform films of contaminant analogues, has revealed that even small quantities (less than 100 angstrom mass equivalent) of molecular contamination can produce scattered light. These data suggest that small amounts of molecular contamination have the potential to significantly impact the performance of scatter sensitive optical systems.

This paper describes the characterization of a thermally conductive, electrically insulating aromatic silicone film adhesive used in a flexible heat sink assembly that is part of an optical telescope aboard the planned New Horizons mission to Pluto and the Kuiper Belt. This application requires high thermal conductivity, high electrical resistance, low-temperature flexibility, resistance to creep, and very low outgassing. Post-cure conditioning in thermal vacuum was shown to drastically reduce the total mass loss (TML) and collected volatile condensable material (CVCM) in standard ASTM outgassing tests. Thermal vacuum treatment also affected activation energy and diffusion rate of the adhesive as determined by multi-rate and isothermal thermogravimetric analysis. Dynamic mechanical testing was performed to compare stiffness of the adhesive under representative loads at cryogenic temperatures to its stiffness at ambient temperature. The material was shown to remain relatively flexible at the minimum operating temperature for this mission. Test data also indicate the adhesive is resistant to creep at sub-ambient temperatures.

This paper provides a review and discussion of current and future efforts associated with the NASA’s Space Environments and Effects (SEE) Program. An update of the Satellite Contamination and Materials Outgassing Knowledgebase is also presented. Recent additions to the Knowledgebase are discussed.

Gaseous contamination on an optical surface causes a degradation of the transmissivity and reflectivity of an optical surface, an increase light scattering and a deterioration of optical characteristics.In optical sensors installed in earth observation satellites, the extraction of physical quantities must be reliable, and deterioration of the optical system due to gas adsorption is a leading factor which reduces the reliability of sensor output data derived from acquired data.We developed a measurement system to quantitatively evaluate the transmissivity decrease of optical surfaces due to gas adsorption in the visible and near- infrared regions where the optical sensors used for earth observation have many observation bands.In this system, a gas having known components was adsorbed on a glass material installed in a container under vacuum, and the spectral transmittance before and after adsorption was measured. The gas adsorption amount on the sample glass material was controlled by controlling the gas injection pressure and sample surface temperature.The gas injection pressure can be controlled from atmospheric pressure to 4x10^-4Pa, and the temperature can be controlled from -140°C to +125°C to a precision of 0.02K. As this instrument can control the injection pressure of the adsorption gas and the sample glass material temperature when installed in the measurement optical path, the transmissivity can be measured while continually varying the gas pressure and sample temperature. The transmissivity change due to gas adsorption can be measured within a wavelength range of 250 to 2500nm to a precision of 0.15%.

This paper examines outgassing kinetics in the air and purging flow environments, as well as including a comparison to full outgassing in vacuum. The experimental data and models reported in the literature on the material outgassing in those environments are examined and summarized. The models are used to examine evaporation of water and DC 200 silicone fluid and outgassing of representative spacecraft materials in the normal air, purging flow and vacuum environments. The models can be used to estimate the outgassing rates of materials under various conditions in those environments, by knowing the outgassing rate in one of those environments. The implication of study results to spacecraft contamination control is also addressed.

Standards are an important component of national and international trade. We depend upon standards to assure that manufactured parts will work together, wherever they are made, and that we speak the same technical language, no matter what language we speak. Understanding is important in order to know when to take exceptions to or tailor the standard to fit the job. Standards that are used in contamination control have increased in numbers over the years as more industries have had to improve their manufacturing processes to enhance reliability or yields of products. Some older standards have been revised to include new technologies, and many new standards have been developed. Some of the new standards were written for specific industries while others apply to many industries. Many government standards have been replaced with standards from nongovernmental standards organizations. This trend has been encouraged by U.S. law that requires the government to use commercial standards where possible. This paper reviews some of the more important standards for the aerospace industry, such as IEST-STD-CC1246 and ISO 14644-1, that have been published in recent years. Benefits, usage, and problems with some standards will be discussed. Some standards are referenced, and websites of some standards organizations are listed.

The molecular and liquid droplet thruster-induced contamination is studied numerically for a 130 N ISS bipropellant thruster using Navier-Stokes and DSMC flow solvers and a Lagrangian particle tracking. The molecular sources contributing to the inorganic components of the plume backflow contaminant are estimated, and a qualitative characterization of the liquid droplet contribution to the organic part of contaminant is conducted. The total calculated mass flux of the molecular contaminant in the backflow region compares very well with the experimental measurement on-board of Mir space station. The computations show that approximately 20 to 30 per cent of the droplets formed at the break up of the unburned propellant film at the exit can contribute to the organic part of the backflow contaminant.

Based upon our previous study, the outgassing and deposition phenomena under thermal vacuum conditions can be expressed by empirically based mathematical models for each material. Herein, we compared several time-dependent outgassing models and temperature-dependent sticking models with the data obtained from ASTM E1559 tests. This study suggests that the Volatile Condensable Materials (VCMs) on a receiver at wide-range temperature can be simulated in consideration of re-evaporation effect of deposited species. On the other hand, we found that temperature-dependent outgassing models were necessary to predict actual molecular contamination environments considering the on-orbit thermal cycles. This paper describes evaluation results of temperature-dependent outgassing models and deposition models where deposited species are taken into consideration by using the test data of Outgassing Rate Measurement Apparatus in accordance with ASTM E1559. In these isothermal tests, operating temperatures of four QCMs were set <90 K, 213 K, 263 K and 298 K. The effusion cell temperature was 323 K, 373 K and 423 K for each test. Furthermore, we discussed validity and issues of the mathematical models in order to predict on-orbit molecular contamination deposition.

Silicones and polyolefins are versatile polymeric materials that are often used for spacecraft applications but can produce considerable amounts of non-volatile residue (NVR) contamination. Outgassing properties of a commercial off-the-shelf (COTS) polyolefin tubing and GE RTV615 silicone potting, both of which are known to outgas at high levels, were characterized using ASTM E595 testing and infrared (IR) absorption spectroscopy. The total mass loss (TML) values for the polyolefin tubing varied between 1.8 and 2.5%, while the collected volatile condensable material (CVCM) was between 0.7 and 1.2%. The silicone potting had somewhat lower outgassing levels, with TML values between 1.0 and 1.7% and CVCM ranging from 0.7 to 1.3%. IR analysis of the outgassed residue indicates the materials produce NVR contamination through different mechanisms. The polyolefin tubing, which was composed of a hydrocarbon co-polymer mixed with additives, disproportionately outgassed low-weight molecular compounds containing ester functional groups. In contrast, RTV615 outgassing appeared to proceed through the release of shorter chain silicone polymers or oligomers. Combining outgassing test data with the chemical characterization of NVR residue provides a better understanding of contamination processes and will contribute to the development of more efficient mitigation strategies.

This paper describes the use of an automated optical inspection system to determine the percent area coverage of particle matter on surfaces for determination of surface cleanliness in accordance with IEST-STD-CC1246 (formerly MIL-STD-1246). This system consists of an optical microscope, motor-driven X-Y stage, digital camera, and software and can be used to scan surfaces for particles with selected features; an example will be given of a scan for glass beads on Gel-Pak surfaces used to tape-lift spacecraft structure prior to shipment to a propulsion system supplier who prohibits glass beads from entering their facility.

We present comparisons of the optical, surface, and physical properties of morphologically variant black materials used to suppress reflected and scattered stray light. The black materials in this study include: carbon aerogel, black appliqués, and anodized surfaces. Each material utilizes a different geometry and material properties to absorb incident radiation. The optical measurements in this paper cover the ultraviolet to the infrared spectral regions and include: Bi-directional Reflectance Distribution Function (BRDF), Directional Hemispherical Reflectance (DHR) as a function of incidence angle and incident polarization state, and infrared reflectance microscopy. In addition, the surface and constituent properties of the black materials are measured by scanning electron microscopy (SEM), stylus profilometry, and energy dispersive spectroscopy (EDS). Finally, we present optical constant estimates for two of the black materials studied.

A Mueller matrix imaging polarimeter is used to acquire polarization-sensitive images of seven different manmade samples in multiple scattering geometries. Successive Mueller matrix images of a sample with changing incidence and scatter angles are used to develop a Mueller matrix bidirectional reflectance distribution function for the sample in one plane of measurement. The Mueller matrix bidirectional reflectance distribution functions are compared, and patterns are noted. The most significant data for the scattering samples measured occurs along the diagonal of the respective Mueller matrices, indicating significant depolarization effects. Reduced depolarization data in the form of the average degree of polarization (of exiting light) for each sample is examined as a function of changing scattering geometry. Five of seven manmade samples exhibit an inverted Gaussian profile of depolarization with changing scattering geometry, the shape of which may prove useful for measuring sample properties (e.g. roughness) and for classifying or categorizing samples in a remote sensing scheme. Depolarization differences for each sample in response to changing incident polarization states are also examined, and a new metric, the degree of polarization surface, has been developed to visualize all such data simultaneously.

Some of Morpho butterflies are well known with its brilliant metallic blue wings. The blue luster is produced from the butterfly's scale that is composed of almost transparent cuticle protein. The origin of the coloration is then not pigment but rather microscopic structure. The principle of this phenomenon has long been referred to as grating or multilayer that can also explain its high reflectivity. However, its optical characteristics on the scattered wavelength cannot be explained by grating or multilayer. The mystery of the lack of multi-coloration (it appears blue from wide angle) remained unnoticed for many years. This mysterious feature has recently been explained with a peculiar optical structure that includes discrete multilayers. This model is based on both of the order and disorder structures: it is not their simple medium but their delicate combination. However, a theoretical hypothesis needs a proof by experiments and we tried to fabricate the optical film by controlling the parameters. A simple fabrication process including a conventional lithography technique in the semiconductor industry was used from viewpoint of application. The result showed that the optical scattering property was basically reproduced and affected by the structure of 100-300 nanometer scales in agreement with the anticipation. A wide variety of applications are relevant to such artificial structural color.

We have investigated several methods to reduce reflectance and scattering levels from a selected group of highly absorbing materials. Each material has vastly different morphologies but similar reflectance and scattering levels. The highly absorbing materials considered in this study include: fibrous black appliques, carbon aerogels, Martin Black, and Enhanced Martin Black. Our investigation reveals that for the fibrous appliques, the fiber area density and length are the dominant factors in determining their absorption properties. For the porous materials that utilize cavities to absorb and trap incident radiation, our results indicate that the cavity geometry and surface pore density are the dominant factors in determining the effectiveness of a porous applique in absorbing light. With regards to the carbon aerogels, the aerogel porosity has the largest impact on its absorption levels. Finally, in order to reduce the reflectance properties of the anodized surfaces requires modifying the surface structure and dye characteristics.

This paper presents a theoretical study of diffraction driven instrumental stray light present in the coronagraph optical system. The externally occulted solar coronagraph is emphasized. Basic design rules are provided for future coronagraph designs. Physical insight of the occulting efficiency for multiple-disk occulters is discussed. The relationships among the internal occulter, external occulter, and Lyot stop is addressed in detail. A new approach is proposed to further reduce the inner Field Of View (FOV) cutoff without sacrificing the outer FOV.

One retrieval technique of ozone profiles using scattered light from the limb of the atmosphere utilizes measurements made high in the atmosphere as a reference. While this procedure relaxes the radiometric accuracy required, it accentuates the need for stray light characterization. In addition, when the entire limb (all altitudes of interest) is imaged simultaneously, as done by the Limb Ozone Retrieval Experiment (LORE) with a linear diode array, the stray light must be characterized for the reference altitude to within 1.0e-04 of the maximum signal in the field of regard (typically at the lowest altitudes). For this system this further translates into the need to know the spatial point-spread function over 5-6 orders of magnitude. We demonstrate the use of pre-flight laboratory instrument characterization, in flight observations and radiative transfer modeling to characterize the stray light of LORE during STS107.

Rigorous finite-difference time-domain electromagnetic simulation is used to simulate the scattering from proto-typical pupil mask cross-section geometries and to quantify the differences from the normally assumed ideal on-off behavior. Shaped pupil plane masks are a promising technology for the TPF coronagraph mission. However the stringent requirements placed on the optics require that the detailed behavior of the edge-effects of these masks be examined carefully. End-to-end optical system simulation is essential and an important aspect is the polarization and cross-section dependent edge-effects which are the subject of this paper. Pupil plane masks are similar in many respects to photomasks used in the integrated circuit industry. Simulation capabilities such as the FDTD simulator, TEMPEST, developed for analyzing polarization and intensity imbalance effects in nonplanar phase-shifting photomasks, offer a leg-up in analyzing coronagraph masks. However, the accuracy in magnitude and phase required for modeling a chronograph system is extremely demanding and previously inconsequential errors may be of the same order of magnitude as the physical phenomena under study. In this paper, effects of thick masks, finite conductivity metals, and various cross-section geometries on the transmission of pupil-plane masks are illustrated. Undercutting the edge shape of Cr masks improves the effective opening width to within λ/5 of the actual opening but TE and TM polarizations require opposite compensations. The deviation from ideal is examined at the reference plane of the mask opening. Numerical errors in TEMPEST, such as numerical dispersion, perfectly matched layer reflections, and source haze are also discussed along with techniques for mitigating their impacts.

The Optical Navigation Camera (ONC) is a technical demonstration slated to fly on NASA’s Mars Reconnaissance Orbiter in 2005. Conventional navigation methods have reduced accuracy in the days immediately preceding Mars orbit insertion. The resulting uncertainty in spacecraft location limits rover landing sites to relatively safe areas, away from interesting features that may harbor clues to past life on the planet. The ONC will provide accurate navigation on approach for future missions by measuring the locations of the satellites of Mars relative to background stars. Because Mars will be a bright extended object just outside the camera’s field of view, stray light control at small angles is essential. The ONC optomechanical design was analyzed by stray light experts and appropriate baffles were implemented. However, stray light testing revealed significantly higher levels of light than expected at the most critical angles. The primary error source proved to be the interface between ground glass surfaces (and the paint that had been applied to them) and the polished surfaces of the lenses. This paper will describe troubleshooting and correction of the problem, as well as other lessons learned that affected stray light performance.

In this work, we present a study of Fresnel diffraction of periodic structures in an optical system of two apertures. This system of two apertures was used successfully for measuring color in textile samples solving the problems of illumination and directionality that present current commercial equipments. However, the system is sensible to the spatial frequency of the periodic sample’s area enclosed in its optical field of view. The study of Fresnel diffraction allows us to establish criteria for geometrical parameters of measurements in order to assure invariance in angular rotations and spatial positions. In this work, we use the theory of partial coherence to calculate the diffraction through two continuous apertures. In the calculation process, we use the concept of point-spread function of the system for partial coherence, in this way we avoid complicated statistical processes commonly used in the partial coherence theory.

Radiation pyrometers are widely used in industries and laboratories for non-contact temperature measurement of objects. In the case of very accurate pyrometry, the measurements are affected by two effects, namely, the size-of-source effect (SSE) and the distance to the source effect (DE). The lack of accuracy in the measurements due to the SSE is associated to variations in the size of the object for a fixed measuring distance, whereas for the DE is associated to variations of the measuring distance for a fixed size of the object. In this work we present a numerical method that can be used for the calculation of corrections for both effects. In this case the method is applied to a lensless double aperture pyrometer. The method is based on the theory of partial coherence for the calculation of the energy transport through the pyrometer. The corrections can be made for sources of any size and shape and for any distance. In this case we consider sources of circular shape given our black body radiators. We present experimental results that confirm our numerical calculations.

A formation flying interferometer suffers a unique stray light problem: it is the only space astronomical instrument which looks at starlight in the presence of a bright object (the sunlit collector spacecraft) which is intentionally placed in the field of view. The combiner instrument is a collection of astronomical telescopes looking at stellar targets relayed by the collectors; but other parts of the collector spacecraft can scatter or emit substantial fluxes. Screening the glare while collecting the starlight is the challenge. The TPF formation-flying interferometer is especially vulnerable because the planets it seeks are so faint. We present a preliminary estimate of stray light from various sources appearing in the interferometer science detector. We assumed a pinhole field stop would be employed, but that two mirrors preceding that pinhole in the combiner optical system would scatter off-axis light into the pinhole. Sources include scattering of direct sunlight and thermal emission, both from the multi-layer thermal shades which permit passive cooling of the instruments to about 40K. We find that the estimated stray light fluxes are of order 10⁴ times the planet flux. We conclude that the optics at the combiner entrance must be blocked from any direct view of the thermal shades.