The kinetics of molecular transport of contaminant species is highly dependent on the distribution of desorption activation energies. Accurate measurements of these kinetics are essential to improving confidence in molecular transport modeling and setting appropriate beginning of life (BOL) cleanliness requirements. We present results that combine laboratory experiments with computer simulations to determine the distribution of effective activation energies for outgassing species from a urethane paint system and non-volatile residue (NVR) collected from an ISO Class 5 cleanroom contamination monitoring plate. Outgassing from samples of primer overcoated with urethane paint were analyzed with the temperature controlled quartz crystal microbalance thermogravimetric analysis (QTGA) technique during the final stages of vacuum baking; cleanroom NVR was also analyzed via QTGA. A computer model was developed to simulate the QTGA results. Data from the experimental QTGA were compared to the simulated QTGA to obtain a distribution of desorption activation energies for contaminant species. The interior of the Ozone Mapping and Profiler Suite (OMPS) science instrument is primed and painted with polyurethane/epoxy material. The distribution of activation energies derived in this study was incorporated in the molecular transport model of the OMPS science instrument, on the Suomi National Polar-Orbiting Partnership Satellite, yielding results that are consistent with the on-orbit optical performance data.
The air present in every spacecraft will vent during launch, so spacecraft hardware must be designed sufficiently to withstand the resulting pressure differences that develop as the external pressure decreases from that at sea level to negligible levels in about 2 minutes. Pressure differentials can be significant, especially for honeycomb panels within which air must travel through many small perforations in honeycomb cell walls to reach vent ports, and cases have been reported of honeycomb panels exploding during launch. Thus, work has been conducted at Ball Aerospace to not only model air venting from honeycomb panels, but also develop techniques to simplify the simulations. Predictions have compared well with pressure differences measured in a test panel during depressurization tests. The results provide confidence in the ability to predict pressure differences in honeycomb panels of any shape and cell size.
A molecular transport model for the Europa UV Spectrograph instrument has been developed to predict optical throughput over the course of the mission lifetime. At beginning of life, internal surfaces will be covered with a thin layer of non-volatile residue (NVR); after launch, contaminants from the electronics components will diffuse out of their parent materials, adding to the overall contaminant environment. The transport of these contaminants, and accumulation onto optical elements, is dependent on geometry, temperature, transport kinetics, and contamination process control during instrument build. Quantitative thermogravimetric analysis (QTGA) was used to estimate the distribution of activation energies for desorption of contaminant from electronics, and that of NVR. An assessment of the effectiveness of different lengths and frequencies of decontamination cycles was performed, and a 12-hour decontamination sequence was effective at removing accumulated contaminant. We found that the combined effects of temperature and view factors resulted in the curious result that whether the telescope aperture door was open or closed had insignificant effect on optics cleanliness. Allowing the door to be closed through much of mission life, in turn, protects the spectrograph from being contaminated by thruster plumes or contaminant from the spacecraft environment. Finally, a parametric analysis of the effect of activation energy distribution was performed. If a lower energy distribution, characteristic of electronics outgassing was used for NVR transport, the throughput margin would be reduced significantly, but the coverage would still be below that at beginning of life.
On October 28, 2011, the Suomi National Polar-orbiting Partnership (Suomi NPP) satellite launched at Vandenberg Air Force base aboard a United Launch Alliance Delta II rocket. Included among the five instruments was the Ozone Mapping and Profiler Suite (OMPS), an advanced suite of three hyperspectral instruments built by Ball Aerospace and Technologies Corporation (BATC) for the NASA Goddard Space Flight Center. Molecular transport modeling is used to predict optical throughput changes due to contaminant accumulation to ensure performance margin to End Of Life. The OMPS Nadir Profiler, operating at the lowest wavelengths of 250 – 310 nm, is most sensitive to contaminant accumulation. Geometry, thermal profile and material properties must be accurately modeled in order to have confidence in the results, yet it is well known that the complex chemistry and process dependent variability of aerospace materials presents a substantial challenge to the modeler. Assumptions about the absorption coefficients, desorption and diffusion kinetics of outgassing species from polymeric materials dramatically affect the model predictions, yet it is rare indeed that on-mission data is analyzed at a later date as a means to compare with modeling results. Optical throughput measurements for the Ozone and Mapping Profiler Suite on the Suomi NPP Satellite indicate that optical throughput degradation between day 145 and day 858 is less than 0.5%. We will show how assumptions about outgassing rates and desorption energies, in particular, dramatically affect the modeled optical throughput and what assumptions represent the on-orbit data.
Tenacious adhesion of dust to surfaces in the vacuum environment of space is a significant obstacle to exploration and scientific discovery on the Moon, Mars and asteroids. Mitigating particle adhesion is also costly and difficult during semiconductor or optics processing on earth. Over the last eight years at Ball Aerospace and Technologies Corp (BATC), we have demonstrated the effectiveness of an ion beam process that dramatically reduces the adhesion of lunar simulant dust to quartz, glass, Kapton, Teflon and silicon surfaces in dry, ambient, and vacuum environments. Treated silvercoated Teflon coupons performed well in a space-simulated environment at NASA Glenn Research Center. Surface roughening on an Ångstrom-level scale was found to correlate well with reduced adhesion, as did contact angle hysteresis. The large difference in advancing and receding contact angles reflects topological and/or chemical heterogeneity. Differences in contact charging are not believed to be major players in dust adhesion reduction. The physical basis of the dust mitigating properties of these modified surfaces is believed to be substantially due to nanometer scale differences between treated and virgin surfaces. Lastly, because this process does not add material, unlike a lotus-like coating or the work function matching coating, nor does it require power like the electrodynamic screen, it is particularly attractive for optical or thermal control materials that cannot tolerate coatings or where power is not available.
Historical experience and previously published papers have shown that contamination sampling techniques influence the
cleanliness results of spaceflight hardware. Programs rely on this data to show that derived or contractual requirements
are met at delivery. Particle sampling using tape lifts and rinses was performed on the James Webb Space Telescope
(JWST) Primary Mirror Segment Assemblies (PMSAs) hardware. Sampling was performed on identical hardware with
both sampling techniques. The hardware was sampled at comparable stages of assembly which provided hardware with
similar levels of particulate contamination. Results from the two sampling techniques are compared. In one technique,
sampling was performed by rinsing (with a hand-squeeze bottle with low pressure) followed by a tape lift; the other
technique used a tape lift only. The relationship of particle size distribution, types of particles, level of particle
contamination, and particle removal rate by sampling technique are examined. Comparison of the particle sampling
results provides a basis for interpreting results depending on sampling techniques. Improving the contamination
engineer’s ability to interpret results is particularly useful when hardware configuration or surface finish dictate which
sampling technique can be used. When one can choose the sampling technique, the results of this study can provide
guidance on which technique is more appropriate depending on the circumstances. Results show that tape lifts remove
more particles than low pressure rinses; furthermore that tape lift only is better than the combined operation of a rinse
closely followed by a tape lift. Results also indicate that further work should be performed on different surface finishes,
rinsing techniques, and particulate contamination levels.
We have developed surface chemical modification processes which when applied to a variety of surfaces renders the
surfaces resistant to particulate contamination. Chemically modified surfaces are shown to shed particles at a
dramatically higher level as compared to native surfaces. This is demonstrated on a variety of surfaces that include
optics, polymers, metals and silicon. The adhesive force between lunar stimulant particles (JSC-1AF) and black
Kapton is measured to decrease by 95% when the black Kapton surface is chemically modified. The chemical
modification process is demonstrated to not change the surface roughness of a smooth silicon wafer while decreasing
particle affinity. The optical properties of chemically modified surfaces are reported. The surface modification
process is robust and stable to aggressive cleaning. The particle shedding properties of chemically modified surfaces
are retained after simulated extraterrestrial vacuum ultra-violet light exposure and temperature excursions to 140°C.
This technology has the potential to provide a robust passive particle mitigation solution for optics, mechanical
systems and particle sensitive applications.