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The methods employed by NASA to establish configuration control of nonmetallic materials on Apollo spacecraft are described. A five step procedure for examining contractor materials for suitability and compatibility is presented. The compatibility of the materials with the oxygen enriched environment of the spacecraft enclosures is emphasized.
Static tests were made on the compatibility of liquid fluorine with several nonmetallic materials at -3200 F and at pressures of 0 and 1500 pounds per square inch gage. The results are compared with those from previous work with gaseous fluorine at the same pressures, but at atmospheric temperature. In general, although environmental effects were not always consistent, reactivity was least with the low-temperature, low-pressure liquid fluorine. Reactivity was greatest with the warm, high-pressure gaseous fluorine. None of the liquids and greases tested was found to be entirely suitable for use in fluorine systems. Polytrifluorochloroethylene and N-43, the formula for which is (C4F9)3N, did not react with liquid fluorine at atmospheric pressure or 1500 pounds per square inch gage under static conditions, but they did react when injected into liquid fluorine at 1500 pounds per square inch gage; they also reacted with gaseous fluorine at 1500 pounds per square inch gage. While water did not react with liquid fluorine at 1500 pounds per square inch gage, it is known to react violently with fluorine under other conditions. The pipe-thread lubricant Q-Seal did not react with liquid fluorine, but did react with gaseous fluorine at 1500 pounds per square inch gage. Of the solids, ruby (Al2O3) and Teflon did not react under the test conditions. The results show that the compatibility of fluorine with nonmetals depends on the state of the fluorine and the system design.
A handbook compilation of chemical and physical property tests data obtained during qualification and receiving inspection testing of nonmetallic materials for the Viking Lander is introduced. Data cover the following materials: sealants, potting compounds, lubricants, paints and finishes, inks, films, encapsulants, elastomers, structural plastics, ablatives, adhesives, and electrical and thermal insulation. Thermochemical data showing degradation as a function of temperature, from room to 500 C, are included.
The sources of variability in the pneumatic impact test commonly used to screen nonmetallic materials for oxygen service and to rank batches or lots of particular materials were investigated together with the mechanism of ignition. Tests were conducted at the NASA/White Sands Test Facility in which the standard test chamber was replaced by an instrumented chamber to obtain information on the rates of pressurization, specimen heating, and time to ignition. Results showed that much of the variability in test data could be traced to the variability in system cleanliness and in the opening time of the high-speed valve. The prinicipal mechanism of ignition in the test is considered to be the heating of the gas initially in the test chamber by adiabatic compression; the presence of voids in the test materials may also be important.
The gaseous oxygen pneumatic impact test is used to evaluate the suitability of nonmetallic materials for use in high-pressure oxygen systems. The test was evaluated by testing the reactivity of four materials over a range of impact pressures. The evaluation also investigated the effect of valve opening time and other test variables on the frequency of reaction. The variability of the data obtained for each test material was too large for the test method to be capable of distinguishing other than gross differences in the reactivity of materials. No relation was found between this variability and changes in valve opening time and other test variables. The materials studied were found to be unacceptable for use as reference standards. Because of the high variability of the test data, it is recommended that new methods be developed for evaluating the suitability of materials for use in high-pressure oxygen systems.
On International Space Station (ISS), the Urine Processor Assembly (UPA) converts human urine and flush water into potable water. The urine is acid-pretreated primarily to control microbial growth. In recent years, the sulfuric acid (H2SO4) pretreatment was believed to be largely responsible for producing salt crystals capable of plugging filters in UPA components and significantly reducing the percentage of water recovery from urine. In 2012, ISS management decided to change the acid pretreatment for urine from sulfuric to phosphoric with the goal of eliminating or minimizing formation of salt crystals. In 2013-2014, as part of the qualification of the phosphoric acid (H3PO4) formulation, samples of 12 nonmetallic materials used in UPA components were immersed for up to one year in pretreated urine and brine solutions made with the new H3PO4 formulation. Dynamic mechanical analysis (DMA) was used to measure modulus (stiffness) of the immersed samples compared to virgin control samples. Such compatibility data obtained by DMA for the H3PO4-based solutions were compared to DMA data obtained for the H2SO4-based solutions in 2002-2003.
Specimens of 23 oxidation resistant, nonmetallic, refractory materials were systematically exposed in a high gas velocity burner to simulate a turbine engine environment. Isothermal and cyclic tests were conducted at a specimen temperature of 2200F which resulted from exposure to Mach 1 or Mach 0.5 hot gas streams. Specimen behavior was judged on the basis of failure mode, appearance, and weight change. SiC and Si3N4 exhibited the most promising behavior surviving all exposures including Mach 1 for 120 cycles (10 hr). Major failure modes identified for other materials were thermal shock, thermal fatigue, and mechanical failure due to gas loading.
Manned spacecraft nonmetallic construction materials selection criteria, testing and configuration control, considering flammability hazard
Nondestructive method uses powdered iron and eddy current probe to measure the depth/width ratio of cracks in electrically nonconductive materials. The eddy current probe measures the mass of metal in the crack after it has been filled with the powdered iron.
Elastomeric materials thermostability in simulated spacecraft environment tested to obtain ignition point values
Fibrous, cellulosic, elastomeric and plastic materials with improved flame resistant properties for space applications
The chemiluminescence from samples of polybutadiene, Viton, Teflon, Silicone, PL 731 Adhesive, and SP 296 Boron-Epoxy composite was measured at temperatures from 25 to 150 C. Excellent correlations were obtained between chemiluminescence and temperature. These correlations serve to validate accelerated aging tests (at elevated temperatures) designed to predict service life at lower temperatures. In most cases, smooth or linear correlations were obtained between chemiluminescence and physical properties of purified polymer gums, including the tensile strength, viscosity, and loss tangent. The latter is a complex function of certain polymer properties. Data were obtained with far greater ease by the chemiluminescence technique than by the conventional methods of study. The chemiluminescence from the Teflon (Halon) samples was discovered to arise from trace amounts of impurities, which were undetectable by conventional, destructive analysis of the sample.
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Thermochemical and other properties data is presented for the following types of epoxy materials: adhesives, coatings finishes, inks, electrical insulation, encapsulants, sealants, composite laminates, tapes, and thermal insulators.
In order to impose adequate contamination control requirements in the selection of Wide Field Planetary Camera (WFPC) materials and to develop a data base of potential optical degradation of the WFPC charge-couple device window, the outgassing properties of WFPC materials and the collected volatile condensed material (CVCM) effects on MgF2 transmittance were measured. Changes in the transmittance were monitored in the wavelength region from 115 nm to 300 nm for selected CVCM thicknesses up to 150 nm. The outgassing properties of reemitted CVCM were also studied.
Nonmetallic materials development - cryogenic insulation, adhesives research, and membrane diffusion theory
Planetary Protection (PP) requirements help to ensure the integrity of life-detection science conducted on solar system bodies, particularly those with liquid water. Such requirements are often met by a combination of cleaning and verification steps to reduce microbial contamination (i.e. bioburden) to an acceptable limit. There are only two cleaning methods approved by the National and Space Administration (NASA), vapor hydrogen peroxide (VHP) and heat microbial reduction (HMR), the latter of which is the most commonly employed. However, HMR can be harsh and produce its own concerns about material integrity, like aging or increasing hardness. When bioburden reduction methods cannot be employed, the project must rely on assumed NASA specification values of bioburden which can cause compliance issues with strict PP bioburden limitations. This work aimed to more accurately define the risk of contamination of a target body by providing empirical data associated with raw materials commonly used in solid rocket motors for lander missions. In this study, we pulverized nonmetallic materials using a cryogenic grinder, then analyzed the resulting substrate for microbial colony forming units (CFU). We found that many nonmetallic materials do not harbor large bioburden when compared with the NASA specification values, though a range existed depending on the material, treatment, and handling. The results from this work provide quantitative data to help reduce concerns of contamination, while also providing a foundation for follow up studies into additional sterilization methods and molecular identification of contaminating microbes.
Nonmetallic materials are used in the United States Department of Energy's Hanford Site Tank Farm waste transfer system. These materials include the inner primary hoses in the hose-in-hose transfer lines (HIHTLs), Garlock{sup R} gaskets, ethylene propylene diene monomer (EPDM) O-rings, and other nonmetallic materials. These nonmetallic materials are exposed to β and γ radiation, caustic solutions as well as high temperature and pressure stressors. How the nonmetallic components react to each of these stressors individually has been well established. However, simultaneous exposure of these stressors has not been evaluated and is of great concern to Hanford Site engineers. Florida International University's Applied Research Center engineers worked closely with key Hanford's Washington River Protection Solutions personnel to develop an experimental test plan that determines how these nonmetallic components react to various simultaneous stressor exposures. In this paper, research on the experimental testing of the hose-in-hose transfer lines used in the Hanford tank farm waste transfer system under simultaneous stressor exposures is presented. The stressor exposure experiments consisted of various combinations of simultaneous stressor exposure of caustic solution, high temperature and high pressure stressors. Research efforts focused on evaluating the aging behavior of EPDM by exposing samples of HIHTLs as well as EPDM dog bone shaped specimens to a 25% NaOH solution at (38 deg. C), operating (54 deg. C) and design temperatures (77 deg. C) for 6 months and 12 months. In addition, HIHTL and the EPDM dog-bone specimens were exposed to only hot water at 77 deg. C for a duration of one year. The mechanical and material properties of the samples were characterized and compared with those of the unexposed samples (baseline). Evaluations included burst pressure tests of the EPDM hose-in-hose transfer lines and material tensile strength test of EPDM dog-bone coupons. Both the tensile strength of the EPDM material dog bones and the burst pressure of the HIHTLs significantly decreased with the increasing temperature and increasing exposure time. When compared with the baseline samples, the burst pressure decreased by 28.75% for the sample aged at 77 deg. C after 12 months, in comparison to sample aged at 38 deg. C and 54 deg. C which had about 1.34% and 5.70% loss in burst pressures, respectively, after 12-month exposure. (authors)