Donald A. Jaworske

Lunar Dust on Heat Rejection System Surfaces: Problems and Prospects

Heat rejection from power systems will be necessary for human and robotic activity on the lunar surface. Functional operation of such heat rejection systems is at risk of degradation as a consequence of dust accumulation. The Apollo astronauts encountered marked degradation of performance in heat rejection systems for the lunar roving vehicle, science packages, and other components. Although ground testing of dust mitigation concepts in support of the Apollo mission identified candidate mitigation tools, the brush concept adopted by the Apollo astronauts proved essentially ineffective. A better understanding of the issues associated with the impact of lunar dust on the functional performance of heat rejection systems and its removal is needed as planning gets underway for human and robotic missions to the Moon. Renewed emphasis must also be placed on ground testing of pristine and dust‐covered heat rejection system surfaces to quantify degradation and address mitigation concepts. This paper presents a rev...

Portable infrared reflectometer for evaluating emittance

Optical methods are frequently used to evaluate the emittance of candidate spacecraft thermal control materials. One new optical method utilizes a portable infrared reflectometer capable of obtaining spectral reflectance of an opaque surface in the range of 2 to 25 microns using a Michelson-Type FTIR interferometer. This miniature interferometer collects many infrared spectra over a short period of time. It also allows the size of the instrument to be small such that spectra can be collected in the laboratory or in the field. Infrared spectra are averaged and integrated with respect to the room temperature black body spectrum to yield emittance at 300 K. Integrating with respect to other black body spectra yields emittance values at other temperatures. Absorption bands in the spectra may also be used for chemical species identification. The emittance of several samples was evaluated using this portable infrared reflectometer, an old infrared reflectometer equipped with dual rotating black body cavities, a...

Correlation of Predicted and Observed Optical Properties of Multilayer Thermal Control Coatings

Abstract Thermal control coatings on spacecraft will be increasingly important as spacecraft grow smaller and more compact. New thermal control coatings will be needed to meet the demanding requirements of next generation spacecraft. Computer programs are now available to design optical coatings, and one such program was used to design several thermal control coatings consisting of alternating layers of WO3 and SiO2. The coatings were subsequently manufactured with electron beam evaporation and characterized with both optical and thermal techniques. Optical data were collected in both the visible region of the spectrum and the infrared. Solar absorptance values were predicted in the range of 0.177–0.196 and were observed in the range of 0.155–0.228. Infrared emittance values were predicted in the range of 0.074–0.083 and were observed optically in the range 0.048–0.093 and calorimetrically in the range of 0.069–0.100.

Optical and calorimetric evaluation of Z-93-P and other thermal control coatings

Abstract The hemispherical total emissivity of two thermal control coatings, Z-93-P and black anodized aluminum, was calculated from hemispherical total reflectivity measured in the wavelength range of 2 to 40 μm. These data were compared to hemispherical total emissivity values obtained on the same samples measured in a thermal vacuum chamber with a calorimetric technique. The comparison showed close agreement in the vicinity of room temperature and above, with differing trends at lower temperatures.

Thermal modeling of a calorimetric technique for measuring the emittance of surfaces and coatings

Abstract A finite element analysis model of a transient technique used to measure the emittance of surfaces and coatings was developed and used to estimate the uncertainty in emittance. The dimensions used in the model matched the dimensions used in the design of a low temperature calorimetric vacuum emissometer being built to characterize the thermal properties of space power materials in the temperature range 173–673 K. Radiant energy from a quartz halogen lamp impinged on an aluminum sample that was coated with a thermal control coating and suspended in a liquid-nitrogen-cooled vacuum chamber by narrow gauge thermocouple wires. After removing the heat source, the temperature of the sample was monitored vs . time and the temperature-time curve was used to calculate the emittance. Factors contributing to the uncertainty in the emittance included uncertainties in time, temperature, area of the sample, heat capacity of the sample and heat loss from the uncoated back side of the sample. Heat losses from the thermocouple wires were found to be negligible. The total probable error in the emittance obtained from the low temperature calorimetric vacuum emissometer design was estimated to be less than 4% for emittance values greater than 0.5 at temperatures between 173 and 673 K.

Heat Rejection Systems Utilizing Composites and Heat Pipes: Design and Performance Testing

Polymer matrix composites offer the promise of reducing the mass and increasing the performance of future heat rejection systems. With lifetimes for heat rejection systems reaching a decade or more in a micrometeoroid environment, use of multiple heat pipes for fault tolerant design is compelling. The combination of polymer matrix composites and heat pipes is of particular interest for heat rejection systems operating on the lunar surface. A technology development effort is under way to study the performance of two radiator demonstration units manufactured with different polymer matrix composite face sheet resin and bonding adhesives, along with different titanium-water heat pipe designs. Common to the two radiator demonstration units is the use of high thermal conductivity fibers in the face sheets and high thermal conductivity graphite saddles within a light weight aluminum honeycomb core. Testing of the radiator demonstration units included thermal vacuum exposure and thermal vacuum exposure with a simulated heat pipe failure. Steady state performance data were obtained at different operating temperatures to identify heat transfer and thermal resistance characteristics. Heat pipe failure was simulated by removing the input power from an individual heat pipe in order to identify the diminished performance characteristics of the entire panel after a micrometeoroid strike. Freeze-thaw performance was also of interest. This paper presents a summary of the two radiator demonstration units manufactured to support this technology development effort along with the thermal performance characteristics obtained to date. Future work will also be discussed.

Solar Selective Coatings for High Temperature Applications

Solar selective coatings are envisioned for use on minisatellites, for applications where solar energy is to be used to power heat engines or to provide thermal energy for remote regions in the interior of the spacecraft. These coatings are designed to have the combined properties of high solar absorptance and low infrared emittance. The coatings must be durable at elevated temperatures. For thermal bus applications, the temperature during operation is likely to be near 100°C. For heat engine applications, the temperature is expected to be much greater. The objective of this work was to screen candidate solar selective coatings for their high temperature durability. Candidate solar selective coatings were composed of molecular mixtures of metal and dielectric, including: nickel and aluminum oxide, titanium and aluminum oxide, and platinum and aluminum oxide. To identify high temperature durability, the solar absorptance and infrared emittance of the candidate coatings were evaluated initially, and after heating to temperatures in the range of 400°C to 700°C. The titanium and aluminum oxide molecular mixture was found to be the most durable.

Optical Evaluation of a Refractive Secondary Concentrator

Donald A. Jaworske and Wayne A. WongGlenn Research Center, Cleveland, OhioTimothy J. SkowronskiCleveland State University, Cleveland, OhioPrepared for the34th Intersociety Energy Conversion Engineering Conferencesponsored by the Society of Automotive EngineersVancouver, British Columbia, Canada, August 1-5, 1999National Aeronautics andSpace AdministrationGlenn Research Center

MISSE-X: An ISS external platform for space environmental studies in the Post-Shuttle era

Materials International Space Station Experiment-X (MISSE-X) is a proposed International Space Station (ISS) external platform for space environmental studies designed to advance the technology readiness of materials and devices critical for future space exploration. The MISSE-X platform will expand ISS utilization by providing experimenters with unprecedented low-cost space access and return on investment (ROI). As a follow-on to the highly successful MISSE series of ISS experiments, MISSE-X will provide advances over the original MISSE configurations including incorporation of plug-and-play experiments that will minimize return mass requirements in the post-Shuttle era, improved active sensing and monitoring of the ISS external environment for better characterization of environmental effects, and expansion of the MISSE-X user community through incorporation of new, customer-desired capabilities. MISSE-X will also foster interest in science, technology, engineering, and math (STEM) in primary and secondary schools through student collaboration and participation.1,2

Design for On-Sun Evaluation of Evaporator Receivers

A heat pipe designed for operation as a solar power receiver should be optimized to accept the solar energy flux and transfer this heat into a reactor. Optical properties of the surface, thermal conductance of the receiver wall, contact resistance of the heat pipe wick, and other heat pipe wick properties ultimately define the maximum amount of power that can be extracted from the concentrated sunlight impinging on the evaporator surface. Modeling of solar power receivers utilizing optical and physical properties provides guidance to their design. On-sun testing is another important means of gathering information on performance. A test rig is being designed and built to conduct on-sun testing. The test rig is incorporating a composite strip mirror concentrator developed as part of a Small Business Innovative Research effort and delivered to NASA Glenn Research Center. In the strip concentrator numerous, lightweight composite parabolic strips of simple curvature were combined to form an array 1.5 m x 1.5 m in size. The line focus of each strip is superimposed in a central area simulating a point of focus. A test stand is currently being developed to hold the parabolic strip concentrator, track the sun, and turn the beam downward towards the ground. The hardware is intended to be sufficiently versatile to accommodate on-sun testing of several receiver concepts, including those incorporating heat pipe evaporators. Characterization devices are also being developed to evaluate the effectiveness of the solar concentrator, including a receiver designed to conduct calorimetry. This paper describes the design and the characterization devices of the on-sun test rig, and the prospect of coupling the concentrated sunlight to a heat pipe solar power receiver developed as part of another Small Business Innovative Research effort.