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Inspection tool detects surface contamination by measuring photoelectron emission. No vacuum chamber or controlled environment is used. Photoemission is measured under ordinary atmospheric conditions, so surfaces may easily be inspected in factories or in the field.
Application of pH-sensitive dye solution serves as test for acidic or basic contamination of critical bonding surface. Aqueous solution of 0.1 percent Direct Red No. 28 capable of indicating acid activating solution down to 10 parts per million on hardware and tooling. Dye did not cause detectable contamination of surface.
Surface contamination and degradation effect on reflectance of evaporated vacuum UV mirrors and temperature control coatings under simulated space environments
Sampling device obtains pure subsurface soil that is free of any foreign substance that may exist on the surface. It is introduced through a contaminated surface area in a closed condition, opened, and a subsurface sample collected, sealed while in the subsurface position, and then withdrawn.
A useful method for the calculation of the obscuration ratio due to particle surface contamination is described. Equations are developed for calculating the obscuration ratio for spherical particles (with diameters greater than 1 micron) and fibers for surfaces where the particle size distribution is either known to be or assumed to be of the form of a MIL-STD-1246A distribution. A simple approximation to the obscuration ratio discrete data is then derived, where the contribution from a single size interval only is treated. This derivation obtains tighter bounds on the approximation error than are provided by the usual direct approach.
Near-Angle Scatter (NAS) of the host star’s light may limit the ability of a potential Habitable Worlds Observatory (HWO) to detect and characterize an Earth-like planet around a Sun-like star via coronagraphy. NAS from each optical surface before the coronagraph’s focal plane mask produces an E-field across the dark hole that is coherent. These E-fields sum and could be as large or larger than the coronagraph mask leakage E-field. This paper assumes an error budget allocation for scatter of 20 ppt. NAS E-fields contribute to the dark hole noise floor via both shot noise and heterodyne amplification of the wavefront instability. While previous papers have developed specifications for scatter from surface scatter, this paper develops specifications for scatter from surface contamination and micrometeoroid impacts. The development process utilizes an expression that predicts scatter throughput into the dark hole based on surface BRDF. Analysis does not include scatter from coating columnar structure, edges, contamination, micrometeoroid impacts, or polarization.
A numerical procedure is presented to calculate transmittance degradation caused by contaminant films on spacecraft surfaces produced through the interaction of orbital atomic oxygen (AO) with volatile silicones and hydrocarbons from spacecraft components. In the model, contaminant accretion is dependent on the adsorption of species, depletion reactions due to gas-surface collisions, desorption, and surface reactions between AO and silicone producing SiO(x), (where x is near 2). A detailed description of the procedure used to calculate the constituents of the contaminant layer is presented, including the equations that govern the evolution of fractional coverage by specie type. As an illustrative example of film growth, calculation results using a prototype code that calculates the evolution of surface coverage by specie type is presented and discussed. An example of the transmittance degradation caused by surface interaction of AO with deposited contaminant is presented for the case of exponentially decaying contaminant flux. These examples are performed using hypothetical values for the process parameters.
A contaminant is any material or substance which is potentially undesirable or which may adversely affect any part, component, or assembly. Contamination control of SRM hardware surfaces is a serious concern, for both Thiokol and NASA, with particular concern for contaminants which may adversely affect bonding surfaces. The purpose of this study is to develop laboratory analytical techniques which will make it possible to certify the cleanliness of any designated surface, with special focus on particulates (dust, dirt, lint, etc.), oils (hydrocarbons, silicones, plasticizers, etc.), and greases (HD-2, fluorocarbon grease, etc.). The hardware surfaces of concern will include D6AC steel, aluminum alloys, anodized aluminum alloys, glass/phenolic, carbon/phenolic, NBR/asbestos-silica, and EPDM rubber.
Redesigned vacuum-probe surface sampler, consisting of wand with disposable probe and filter assembly, collects specimens of fallout and handling contamination.
X-ray photoelectron spectroscopy (XPS) has been used to study the surface composition and chemistry of Long Duration Exposure Facility (LDEF) exposed materials including silvered Teflon (Ag/FEP), Kapton, S13GLO paint, quartz crystal monitors (QCM's), carbon fiber/organic matrix composites, and carbon fiber/Al Alloy composites. In each set of samples, silicones were the major contributors to the molecular film accumulated on the LDEF exposed surfaces. All surfaces analyzed have been contaminated with Si, O, and C; most have low levels (less than 1 atom percent) of N, S, and F. Occasionally observed contaminants included Cl, Na, K, P, and various metals. Orange/brown discoloration observed near vent slots in some Ag/FEP blankets were higher in carbon, sulfur, and nitrogen relative to other contamination types. The source of contamination has not been identified, but amine/amide functionalities were detected. It is probable that this same source of contamination account for the low levels of sulfur and nitrogen observed on most LDEF exposed surfaces. XPS, which probes 50 to 100 A in depth, detected the major sample components underneath the contaminant film in every analysis. This probably indicates that the contaminant overlayer is patchy, with significant areas covered by less that 100 A of molecular film. Energy dispersive x-ray spectroscopy (EDS) of LDEF exposed surfaces during secondary electron microscopy (SEM) of the samples confirmed contamination of the surfaces with Si and O. In general, particulates were not observed to develop from the contaminant overlayer on the exposed LDEF material surfaces. However, many SiO2 submicron particles were seen on a masked edge of an Ag/FEP blanket. In some cases such as the carbon fiber/organic matrix composites, interpretation of the contamination data was hindered by the lack of good laboratory controls. Examination of laboratory controls for the carbon fiber/Al alloy composites showed that preflight contamination was the most significant factor for all the contaminants generally detected at less than 1 atom percent, or detected only occasionally (i.e., all but Si, O, and C). Flight control surfaces, including sample backsides not exposed to space radiation or atomic oxygen flux, have accumulated some contamination on flight (compared to laboratory controls), but experimentally, the LDEF exposed surface contamination levels are generally higher for the contaminants Si and O. For most materials analyzed, Si contamination levels were higher on the leading edge surfaces than on the trailing edge surfaces. This was true even for the composite samples where considerable atomic oxygen erosion of the leading edge surfaces was observed by SEM. It is probable that the return flux associated with atmospheric backscatter resulted in enhanced deposition of silicones and other contaminants on the leading edge flight surfaces relative to the trailing edge. Although the Si concentration data suggested greater on-flight deposition of contaminants on the leading edge surfaces, the XPS analyses did not conclusively show different relative total thicknesses of flight deposited contamination for leading and trailing edge surfaces. It is possible that atomic oxygen reactions on the leading edge resulted in greater volatilization of the carbon component of the deposited silicones, effectively 'thinning' the leading edge deposited overlayer. Unlike other materials, exposed polymers such as Kapton and FEP-type Teflon had very low contamination on the leading edge surfaces. SEM evidence showed that undercutting of the contaminant overlayer and damaged polymer layers occurred during atomic oxygen erosion, which would enhance loss of material from the exposed surface.
This paper describes the use of Bidirectional Scattering Distribution Functions (BSDF) to quantify surface degradation, thus providing an effective method for contamination monitoring. This approach to contamination monitoring is based on the use of witness surfaces (mirrors or glass slides) located next to the critical surfaces. Contaminant accretion can be monitored during all phases of spacecraft fabrication, assembly, and testing. The method can be applied in other areas of contamination control such as monitoring of clean room environments. The BSDF can also prove extremely useful in establishing contamination control requirements and acceptability criteria. This paper describes the apparatus adopted to perform BSDF measurements and discusses some practical aspects of data collection. The results obtained in contamination monitoring programs performed at the NASA Goddard Space Flight Center are presented. Some possible new applications of this monitoring technique are also addressed.
Descent retroburns using hydrazine thrusters will generate contaminants in their exhaust that can alter underlying samples, such as water-rich surfaces coinciding with possible life signatures or other science measurements of interest. We present an optimization technique that aims to autonomously minimize contamination during surface approach and landing for propulsive vehicles. In addition to short-range hoppers, the optimization technique is also fully applicable to traditional orbit-to-surface landers. This study addresses scenarios where surface alterations from propulsion events are counterproductive or hazardous to the mission objectives. This is of interest for landers (whether human or robotic), that may rely on pristine soils collected in the immediate vicinity of landing sites to accomplish science investigations, mining, or In Situ Resource Utilization (ISRU) surface operations. Such missions are averse to various surface-plume interactions such as thermal scoring, physical agitation, and contamination. The capability can be applied with minimal impact to the baseline concept.
Biological contamination of large-area surfaces can be determined quickly, inexpensively, and accurately with the aid of a polyester bonded cloth. Cloth is highly effective in removing microbes from a surface and releasing them for biological assay. In releasing contaminants, polyester bonded cloth was found to be superior to other commercial cleanroom cloths, including spun-bound polyamid cloths and cellulose cloths.
During that portion of Space Shuttle orbiter entry when significant aerodynamic heat transfer occurs, the flow over the vehicle is in chemical nonequilibrium. The parameter which most significantly influences the level of surface heat transfer in such a flow field is the catalytic efficiency of the surface with respect to the recombination of dissociated oxygen atoms. Significant, and instantaneous, changes were observed in the level of heat transfer at several lower surface centerline locations on STS-2 and STS-3. This phenomenon apparently resulted from a sudden change in the surface catalytic efficiency at these locations due to contamination of the surface by metallic oxides. As a result, data obtained from affected measurements cannot be considered as benchmark data with which to attempt to characterize nonequilibrium heat transfer to the orbiter's lower surface centerline.
A technique is described for the simultaneous in situ measurement of film thickness, refractive index, total normal emissivity, visible light scattering, and reflectance of contaminant films on a highly reflective liquid nitrogen-cooled, stainless steel substrate. Emissivities and scattering data were obtained for films of water, carbon dioxide, silicone oil, and a number of aromatic and aliphatic hydrocarbons as a function of film thickness between zero and 20 microns. Water had the greatest effect on emissivity, followed by silicone oil, aliphatic hydrocarbons, aromatic hydrocarbons, and carbon dioxide. Emissivity increased more rapidly with film thickness between zero and 2.5 microns, than at thickness greater than 2.5 microns. Scattering of visible light changed little below 2-microns thickness but increased rapidly with thickness beyond 2 to 3 microns. The effect of contaminant films on passive radiation coolers is discussed.
A technique is described for the simultaneous in situ measurement of film thickness, refractive index, total normal emissivity, visible-light scattering, and reflectance of contaminant films on a highly reflective liquid-nitrogen cooled, stainless steel substrate. Emissivities and scattering data are obtained for films of water, carbon dioxide, silicone oil, and a number of aromatic and aliphatic hydrocarbons as a function of film thickness between zero and 20 microns. Of the contaminants investigated, water has by far the greatest effect on emissivity, followed by silicone oil, aliphatic hydrocarbons, aromatic hydrocarbons, and carbon dioxide. The emissivity increases more rapidly with film thickness between zero and 2.5 microns than at thicknesses greater than 2.5 microns. Scattering of visible light changes very little below 2 microns thickness but increases rapidly with thickness beyond 2 to 3 microns. The effect of contaminant films on passive radiation coolers is discussed.
The SOC 400 Surface Inspection Machine/Infrared (SIMIR) is a small, ruggedized Fourier transform infrared spectrometer having dedicated diffuse reflectance optics. The SOC 400 was designed for the purpose of detecting (qualitatively and quantitatively) oil stains on the inside surface of solid rocket motor casings in the as-sandblasted and cleaned condition at levels approaching 1 mg. sq ft. The performance of this instrument is described using spectral mapping techniques.
X-ray spectrum of contaminating element reveals presence. Proposed x-ray fluorescence spectrometer used to detect thin layer of Conoco HD-2 (or equivalent) grease on D6-ac steel. Source-and-detector assembly mounted on remote manipulator with other contamination-detecting equipment and scanned across surface of specimen. Output of detector fed through coaxial cable to standard pulse-height-analyzing equipment and processed further by small computer to obtain x-ray energy spectrum.