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At least 685 records · Page 38

All sources NASA NTRS DOE OSTI

DOE OSTI2021

Accelerated reliability tests of n + and p + poly-Si passivated contacts

We report on the stability of encapsulated, low-pressure chemical vapor-deposited phosphorus (n + poly-Si) doped and boron (p + poly-Si) doped poly-Si/SiO x passivated contacts by exposing the samples to three different accelerated tests: damp heat test, thermal cycling and ultraviolet exposure, adhering closely to the IEC 61215 standard. Outdoor testing was also performed by exposing the samples in the outdoor testing field at the National Renewable Energy Laboratory, and preliminary data accumulated for 1000 h from February to April of 2021 is reported. We studied non-metallized, thermally-metallized, and screen-printed n + and p + poly-Si by monitoring the effective minority carrier lifetime at the implied maximum power point using a Sinton lifetime tester, and recorded photoluminescence images before and after the exposure. Furthermore, the samples were found to be stable under all test conditions, which is encouraging for incorporation of these contacts in next-generation industrial silicon solar cells.

14 SOLAR ENERGY↗

DOE OSTI2021

Charge collection in h -BN neutron detectors at elevated temperatures

Many of the neutron detector applications are in the environments with harsh conditions such as high temperatures. We report here the measurements of charge collection parameters of hexagonal boron nitride (h-BN) detectors at elevated temperatures, including the electron mobility-lifetime product (μτ) and surface recombination field (s/μ). It was found that μτ is increased, while s/μ is decreased as temperature increases. The temperature dependence of the surface recombination field (s/μ) revealed that electrons trapped in the surface states tend to thermally activate to the bulk region at higher temperatures with an activation energy of about 0.22 eV, leading to a reduction in the density of the charged surface states at elevated temperatures. Consequently, the charge collection efficiency is enhanced at elevated temperatures due to a reduced surface recombination field and increased electron mobility-lifetime product. The results suggested that h-BN neutron detectors are favorable for high temperature operation.

47 OTHER INSTRUMENTATION↗

NASA NTRS2009

Evaluation of Advanced COTS Passive Devices for Extreme Temperature Operation

Electronic sensors and circuits are often exposed to extreme temperatures in many of NASA deep space and planetary surface exploration missions. Electronics capable of operation in harsh environments would be beneficial as they simplify overall system design, relax thermal management constraints, and meet operational requirements. For example, cryogenic operation of electronic parts will improve reliability, increase energy density, and extend the operational lifetimes of space-based electronic systems. Similarly, electronic parts that are able to withstand and operate efficiently in high temperature environments will negate the need for thermal control elements and their associated structures, thereby reducing system size and weight, enhancing its reliability, improving its efficiency, and reducing cost. Passive devices play a critical role in the design of almost all electronic circuitry. To address the needs of systems for extreme temperature operation, some of the advanced and most recently introduced commercial-off-the-shelf (COTS) passive devices, which included resistors and capacitors, were examined for operation under a wide temperature regime. The types of resistors investigated included high temperature precision film, general purpose metal oxide, and wirewound.

Patterson, Richard↗

DOE OSTI2021

Light Management in Bifacial Photovoltaics with Spectrally Selective Mirrors

Spectrally-selective mirrors that simultaneously provide above-bandgap anti-reflection and sub-bandgap light rejection are tested for their ability to provide passive cooling to partially sub-bandgap transparent bifacial photovoltaics. The optical and thermal benefits of both idealized and real, low-complexity spectrally-selective mirrors on single-axis tracking, bifacial PERC arrays under realistic conditions are tested via rigorous finite element simulations. Four- and six-layer mirror designs increased carrier generation beyond what traditional antireflection coatings can provide without the associated cell heating. Here, idealized mirrors were found to provide up to 2.4 °C of cooling when included on both air/glass interfaces of the bifacial module.

14 SOLAR ENERGY↗

DOE OSTI2025

Where to cool off: a geospatial framework for placement of cooling centers

Indoor cooling is essential to reduce heat stress and increase passive survivability during heatwaves. Although air conditioning (AC) is recommended for maintaining indoor thermal comfort, low- and medium-income households in the U.S. often do not own an AC and/or limit AC usage to reduce energy consumption and associated costs, thereby risking their health and safety. With the frequency and intensity of heatwaves increasing, cooling centers are considered an appropriate alternative to indoor cooling and a possible mitigation strategy to prevent adverse health impacts of heat exposure. However, these centers are limited in numbers and not always accessible. This requires (i) developing a geospatial framework using physical and social factors for optimal siting of cooling centers to meet future needs and (ii) ranking of existing and potential cooling centers (schools, libraries, religious institutions) based on their accessibility among vulnerable populations and proximity to healthcare facilities. We developed and deployed a geospatial framework based on the Multi-criteria Decision Analysis approach in five U.S. cities (Los Angeles (LA), Phoenix, Austin, Atlanta, Miami) to evaluate the effectiveness of the framework in ranking cooling centers based on accessibility and population coverage. The results revealed that (i) access to cooling centers varies across cities and 32.2–50.7% of centers are within walking distance of the most vulnerable populations, (ii) vulnerable populations exposed to Urban Heat Island (UHI) effects are more likely to experience energy burden, and (iii) about 21.2–49.4% of population with high energy burden have access to these centers. Considering that more cooling centers are needed to assist energy burdened households alleviate heat exposure impacts, the framework developed herein could be adapted to incorporate other factors (e.g. health impacts, policies) to assess site suitability of existing shelters, identify potential sites for new cooling centers, and geo-target communities where energy efficient emerging technologies could be deployed to reduce heat stress.

58 GEOSCIENCES↗

NASA NTRS1988

SP-100 flight qualification testing assessment

The SP-100 is a compact space power system driven by a nuclear reactor that provides 100 kWe to the user at 200 VDC. The thermal energy generated by the nuclear reactor is converted into electrical energy by passive thermoelectric devices. Various options for tailoring the MIL-STD-1540B guidelines to the SP-100 nuclear power system are discussed. This study aids in selecting the appropriate qualification test program based on the cost, schedule, and test effectiveness of the various options.

Jeanmougin, Nanette M.↗

NASA NTRS1988

A high power spacecraft thermal management system

This paper describes the design and test results of an ammonia hybrid capillary pumped loop thermal control system. As a hytbrid, the system can operate as either a passive, capillary pumped loop, or, as a mechanically pumped system. The system is comprised of an evaporator section, a condenser section, 10 meters of liquid and vapor transport lines, a mechanical pump, and a reservoir. In the evaporator section, four capillary pumps are each integrated into three cold plates. The mechanical pump is installed in the liquid line and is in series with the capillary pumps. Testing has demonstrated that in the capillary pumped mode, the HPSTM can acquire and transport a total heat load of between 120 W and 24 kW, with a maximum heat flux density of 4.3 W/sq cm in the evaporator section. In the mechanically pumped configuration, a heat acquisition potential of 50 kW (9 W/sq cm heat flux density) has been demonstrated. The hybrid system still retains the proven capillary capabilities of temperature control, heat load sharing and fluid flow control between evaporator plates, rapid power cycling, and pressure priming recovery of deprimed evaporators.

Ku, J.↗

NASA NTRS2000

The Low Temperature Microgravity Physics Experiments Project

The Low Temperature Microgravity Physics Facility (LTMPF) is being developed by NASA to provide long duration low temperature and microgravity environment on the International Space Station (ISS) for performing fundamental physics investigations. Currently, six experiments have been selected for flight definition studies. More will be selected in a two-year cycle, through NASA Research Announcement. This program is managed under the Low Temperature Microgravity Physics Experiments Project Office at the Jet Propulsion Laboratory. The facility is being designed to launch and returned to earth on a variety of vehicles including the HII-A and the space shuttle. On orbit, the facility will be connected to the Exposed Facility on the Japanese Experiment Module, Kibo. Features of the facility include a cryostat capable of maintaining super-fluid helium at a temperature of 1.4 K for 5 months, resistance thermometer bridges, multi-stage thermal isolation system, thermometers capable of pico-Kelvin resolution, DC SQUID magnetometers, passive vibration isolation, and magnetic shields with a shielding factor of 80dB. The electronics and software architecture incorporates two VME buses run using the VxWorks operating system. Technically challenging areas in the design effort include the following: 1) A long cryogen life that survives several launch and test cycles without the need to replace support straps for the helium tank. 2) The minimization of heat generation in the sample stage caused by launch vibration 3) The design of compact and lightweight DC SQUID electronics. 4) The minimization of RF interference for the measurement of heat at pico-Watt level. 5) Light weighting of the magnetic shields. 6) Implementation of a modular and flexible electronics and software architecture. The first launch is scheduled for mid-2003, on an H-IIA Rocket Transfer Vehicle, out of the Tanegashima Space Center of Japan. Two identical facilities will be built. While one facility is onboard the ISS, the other is re-integrated on the ground with new experiments. When the cryogen of the facility in space are exhausted, it will be swapped with the other facility with the new experiment. A total of 20 science missions are envisioned over the next 20 years.

Holmes, Warren↗

NASA NTRS2006

Thrust Stand for Electric Propulsion Performance Evaluation

An electric propulsion thrust stand capable of supporting testing of thrusters having a total mass of up to 125 kg and producing thrust levels between 100 microN to 1 N has been developed and tested. The design features a conventional hanging pendulum arm attached to a balance mechanism that converts horizontal deflections produced by the operating thruster into amplified vertical motion of a secondary arm. The level of amplification is changed through adjustment of the location of one of the pivot points linking the system. Response of the system depends on the relative magnitudes of the restoring moments applied by the displaced thruster mass and the twisting torsional pivots connecting the members of the balance mechanism. Displacement is measured using a non-contact, optical linear gap displacement transducer and balance oscillatory motion is attenuated using a passive, eddy-current damper. The thrust stand employs an automated leveling and thermal control system. Pools of liquid gallium are used to deliver power to the thruster without using solid wire connections, which can exert undesirable time-varying forces on the balance. These systems serve to eliminate sources of zero-drift that can occur as the stand thermally or mechanically shifts during the course of an experiment. An in-situ calibration rig allows for steady-state calibration before, during and after thruster operation. Thrust measurements were carried out on a cylindrical Hall thruster that produces mN-level thrust. The measurements were very repeatable, producing results that compare favorably with previously published performance data, but with considerably smaller uncertainty.

Polzin, Kurt A.↗

DOE OSTI2020

Terrestrial radiative cooling: Using the cold universe as a renewable and sustainable energy source

Photonic materials designed at wavelength scales have enabled a range of emerging energy technologies, from solid-state lighting to efficient photovoltaics that have transformed global energy landscapes. Daytime passive radiative cooling materials shed heat from the ground to the cold universe by taking advantage of the terrestrial thermal radiation that is as large as the renewable solar energy. Newly developed photonic materials permit subambient cooling under direct sunshine, and their applications are expanding rapidly enabled by scalable manufacturing. We review here the recent advancement of daytime subambient radiative cooling materials, which allow energy-efficient cooling and are paving the way toward technologies that harvest the coldness from the universe as a new renewable energy source.

Science & Technology - Other Topics↗

NASA NTRS1974

Space tug thermal control

It was determined that space tug will require the capability to perform its mission within a broad range of thermal environments with currently planned mission durations of up to seven days, so an investigation was conducted to define a thermal design for the forward and intertank compartments and fuel cell heat rejection system that satisfies tug requirements for low inclination geosynchronous deploy and retrieve missions. Passive concepts were demonstrated analytically for both the forward and intertank compartments, and a worst case external heating environment was determined for use during the study. The thermal control system specifications and designs which resulted from the research are shown.

Source record↗

DOE OSTI2022

HI-STORM Overpack and MPC-32 Thermal-Hydraulic Model with MOOSE Framework

Nuclear power is a significant source of electricity in the United States, but the average age of nuclear power plants is around 40 years old. The safe management of the spent nuclear fuel (SNF) is a key aspect of the back-end of the nuclear fuel cycle. Spent fuel dry storage systems are becoming a popular and effective solution in this area, given the absence of a final disposal system. The spent fuel cask system (dry cask method) provides a feasible solution to maintain spent fuel for 60 years before final disposal. Dry cask storage has many characteristics that make it attractive. It fulfills the safety requirements of the Nuclear Regulatory Commission (NRC) while providing modularity and flexibility to contractors. The HI-STORM overpack and MPC-32 canister are the main parts of the HI-STORM 100 dry cask storage system. These components remove heat from the system using natural circulation, requiring no human intervention. This is the characteristic that provides passive heat removal and low maintenance features in dry cask storage systems. To develop a thermal model for a dry cask storage system, the physics behind the system should be defined clearly. There are two natural circulation loops in the system; circulation of helium cools down the nuclear assemblies in the MPC, while circulation of air cools down the walls of the MPC. This work aims to develop a thermal model of the MPC-32 canister and HI-STORM overpack using the Multiphysics Object-Oriented Simulation Environment (MOOSE). MOOSE is an open-source framework developed by Idaho National Laboratory (INL) for multiscale, multiphysics simulations. In this study, we will investigate and demonstrate the thermal-hydraulics modeling capabilities of the MOOSE framework, including natural circulation, heat transfer, and porous flow.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2022

Development of a MOOSE thermal model of the MPC-32 canister and HI-STORM overpack

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

NASA NTRS2017

Design and Fabrication of a Composite Morphing Radiator Panel Using High Conductivity Fibers

Upcoming crewed space missions will involve large internal and external heat loads and require advanced thermal control systems to maintain a desired internal environment temperature. Radiators with at least 12:1 turndown ratios (the ratio between the maximum and minimum heat rejection rates) will be needed. However, current technologies are only able to achieve turndown ratios of approximately 3:1. A morphing radiator capable of altering shape could significantly increase turndown capabilities. Shape memory alloys offer qualities that may be well suited for this endeavor; their temperature-dependent phase changes could offer radiators the ability to passively control heat rejection. In 2015, a morphing radiator prototype was constructed and tested in a thermal vacuum environment, where it successfully demonstrated the morphing behavior and variable heat rejection. Newer composite prototypes have since been designed and manufactured using two distinct types of SMA materials. These models underwent temperature cycling tests in a thermal vacuum chamber and a series of fatigue tests to characterize the lifespan of these designs. The focus of this paper is to present the design approach and testing of the morphing composite facesheet. The discussion includes: an overall description of the project background, definition of performance requirements, composite materials selection, use of analytic and numerical design tools, facesheet fabrication, and finally fatigue testing with accompanying results.

Wescott, Matthew T.↗

NASA NTRS2018

Working Fluid Trade Study for a Two-Phase Mechanically Pumped Loop Thermal Control System

NASA Jet Propulsion Laboratory is investigating a two-phase mechanically pumped fluid loop (MPFL) technology for spacecraft thermal control for future planetary space science mission concepts. The two-phase technology combines the potential of single-phase MPFL and the passive two-phase heat pipe systems. Previous two-phase MPFL studies at JPL have identified an evaporator system with a separated flow architecture as providing a robust light mass thermal control system with very high spatial and temporal thermal stability required by the science instruments on these missions. These studies have further identified the thermophysical properties of the working fluid to be key to the performance of a two-phase fluid loop. This paper describes the methodology used in the selection of the working fluids for optimizing the performance of the two-phase MPFL. A high level model was developed that includes the constraints and boundaries driven by the system components. The performance of fluids from the REFPROP database are investigated and rated for this system. The working fluid attributes such as cost, hazardous properties, and heritage were taken into account in this selection. A typical spacecraft dissipating 1000 W and a fluid loop consisting of an evaporator, accumulator, radiator, and associated tubing components is used as an example in this study.

Daimaru, Takuro↗

NASA NTRS2010

MISSE 6 Polymer Film Tensile Experiment

The Polymer Film Tensile Experiment (PFTE) was flown as part of Materials International Space Station Experiment 6 (MISSE 6). The purpose of the experiment was to expose a variety of polymer films to the low Earth orbital environment under both relaxed and tension conditions. The polymers selected are those commonly used for spacecraft thermal control and those under consideration for use in spacecraft applications such as sunshields, solar sails, and inflatable and deployable structures. The dog-bone shaped samples of polymers that were flown were exposed on both the side of the MISSE 6 Passive Experiment Container (PEC) that was facing into the ram direction (receiving atomic oxygen, ultraviolet (UV) radiation, ionizing radiation, and thermal cycling) and the wake facing side (which was supposed to have experienced predominantly the same environmental effects except for atomic oxygen which was present due to reorientation of the International Space Station). A few of the tensile samples were coated with vapor deposited aluminum on the back and wired to determine the point in the flight when the tensile sample broke as recorded by a change in voltage that was stored on battery powered data loggers for post flight retrieval and analysis. The data returned on the data loggers was not usable. However, post retrieval observation and analysis of the samples was performed. This paper describes the preliminary analysis and observations of the polymers exposed on the MISSE 6 PFTE.

Miller, Sharon K. R.↗

NASA NTRS1991

Structural design of the Large Deployable Reflector (LDR)

An integrated Large Deployable Reflector (LDR) analysis model was developed to enable studies of system responses to the mechanical and thermal disturbances anticipated during on-orbit operations. Functional requirements of the major subsystems of the LDR are investigated, design trades are conducted, and design options are proposed. System mass and inertia properties are computed in order to estimate environmental disturbances, and in the sizing of control system hardware. Scaled system characteristics are derived for use in evaluating launch capabilities and achievable orbits. It is concluded that a completely passive 20-m primary appears feasible for the LDR from the standpoint of both mechanical vibration and thermal distortions.

Satter, Celeste M.↗

NASA NTRS2010

James Webb Space Telescope Integrated Science Instrument Module Thermal Balance/Thermal Vacuum Test Configuration and Test Planning at NASA's Goddard Space Flight Center

The James Webb Space Telescope (JWST) is the next of the great observatories , scheduled to be launched in 2014. Three of the four science instruments are passively cooled to their operational temperature range of 36K to 40K, and the fourth instrument is actively cooled to its operational temperature of approximately 6K. Thermal-vacuum testing of the flight science instruments at the Integrated Science Instrument Module (ISIM) element level will take place within a newly constructed shroud cooled by gaseous helium inside Goddard Space Flight Center s (GSFC) Space Environment Simulator (SES). The test enclosure surrounding the instruments during the integrated ISIM-level thermal balance testing is complex, and is designed to simulate as closely as possible the in-flight conductive and radiative thermal environment around the ISIM. Thermal control and measurement of parasitic sources of heat leak into the test volume is critical, as the dissipation plus known parasitics in the flight ISIM is approximately 454 mW, and additional parasitics attributed to the flight enclosure itself are nearly equal to this, resulting in the energy balance of the inflight ISIM being less than 1.0 W. Sources of test-induced parasitics must be carefully controlled and measured, and the ability to thermally control the test environment is critical to enable accurate thermal balance testing and thermal model correlation. This paper describes the test configuration and plans for the ISIM-level thermal vacuum/thermal balance testing at GSFC.

Glazer, Stuart↗