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At least 235 records · Page 13

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NASA NTRS2013

Development of a Phasor Diagram Creator to Visualize the Piston and Displacer Forces in an Advanced Stirling Convertor

The steady-state, nearly sinusoidal behavior of the components in a free-piston Stirling engine allows for visualization of the forces in the system using phasor diagrams. Based on Newton's second law, F = ma, any phasor diagrams modeling a given component in a system should close if all of the acting forces have been considered. Since the Advanced Stirling Radioisotope Generator (ASRG), currently being developed for future NASA deep space missions, is made up of such nearly sinusoidally oscillating components, its phasor diagrams would also be expected to close. A graphical user interface (GUI) has been written in MATLAB (MathWorks), which takes user input data, passes it to Sage (Gedeon Associates), a one-dimensional thermodynamic modeling program used to model the Stirling convertor, runs Sage, and then automatically plots the phasor diagrams. Using this software tool, the effect of varying different Sage inputs on the phasor diagrams was determined. The parameters varied were piston amplitude, hot-end temperature, cold-end temperature, operating frequency, and displacer spring constant. These phasor diagrams offer useful insight into convertor operation and performance.

Saha, Dipanjan↗

NASA NTRS2015

The Safe Removal of Frozen Air from the Annulus of an LH2 Storage Tank

Large Liquid Hydrogen (LH2) storage tanks are vital infrastructure for NASA. Eventually, air may leak into the evacuated and perlite filled annular region of these tanks. Although the vacuum level is monitored in this region, the extremely cold temperature causes all but the helium and neon constituents of air to freeze. A small, often unnoticeable pressure rise is the result. As the leak persists, the quantity of frozen air increases, as does the thermal conductivity of the insulation system. Consequently, a notable increase in commodity boil-off is often the first indicator of an air leak. Severe damage can result from normal draining of the tank. The warming air will sublimate which will cause a pressure rise in the annulus. When the pressure increases above the triple point, the frozen air will begin to melt and migrate downward. Collection of liquid air on the carbon steel outer shell may chill it below its ductility range, resulting in fracture. In order to avoid a structural failure, as described above, a method for the safe removal of frozen air is needed. A thermal model of the storage tank has been created using SINDA/FLUINT modeling software. Experimental work is progressing in an attempt to characterize the thermal conductivity of a perlite/frozen nitrogen mixture. A statistical mechanics model is being developed in parallel for comparison to experimental work. The thermal model will be updated using the experimental/statistical mechanical data, and used to simulate potential removal scenarios. This paper will address methodologies and analysis techniques for evaluation of two proposed air removal methods.

cryogenic insulation↗

NASA NTRS2016

Development of a Microwave Regenerative Sorbent-Based Hydrogen Purifier

This paper describes the design and fabrication of a Microwave Regenerative Sorbent-based Hydrogen Purifier (MRSHP). This unique microwave powered technology was developed for the purification of a hydrogen stream produced by the Plasma Pyrolysis Assembly (PPA). The PPA is a hydrogen recovery (from methane) post processor for NASA's Sabatier-based carbon dioxide reduction process. Embodied in the Carbon dioxide Reduction Assembly (CRA), currently aboard the International Space Station (ISS), the Sabatier reaction employs hydrogen to catalytically recover oxygen, in the form of water, from respiratory carbon dioxide produced by the crew. This same approach is base-lined for future service in the Air Revitalization system on extended missions into deep space where resupply is not practical. Accordingly, manned exploration to Mars may only become feasible with further closure of the air loop as afforded by the greater hydrogen recovery permitted by the PPA with subsequent hydrogen purification. By utilizing the well-known high sorbate loading capacity of molecular sieve 13x, coupled with microwave dielectric heating phenomenon, MRSHP technology is employed as a regenerative filter for a contaminated hydrogen gas stream. By design, freshly regenerated molecular sieve 13x contained in the MRSHP will remove contaminants from the effluent of a 1-CM scale PPA for several hours prior to breakthrough. By reversing flow and pulling a relative vacuum the MRSHP prototype then uses 2.45 GHz microwave power, applied through a novel coaxial antenna array, to rapidly heat the sorbent bed and drive off the contaminants in a short duration vacuum/thermal contaminant desorption step. Finally, following rapid cooling via room temperature cold plates, the MRSHP is again ready to serve as a hydrogen filter.

Wheeler, Richard R., Jr.↗

NASA NTRS2016

A Synthesis of the Basal Thermal State of the Greenland Ice Sheet

Greenland's thick ice sheet insulates the bedrock below from the cold temperatures at the surface, so the bottom of the ice is often tens of degrees warmer than at the top, because the ice bottom is slowly warmed by heat coming from the Earth's depths. Knowing whether Greenland's ice lies on wet, slippery ground or is anchored to dry, frozen bedrock is essential for predicting how this ice will flow in the future. But scientists have very few direct observations of the thermal conditions beneath the ice sheet, obtained through fewer than two dozen boreholes that have reached the bottom. Our study synthesizes several independent methods to infer the Greenland Ice Sheet's basal thermal state -whether the bottom of the ice is melted or not-leading to the first map that identifies frozen and thawed areas across the whole ice sheet. This map will guide targets for future investigations of the Greenland Ice Sheet toward the most vulnerable and poorly understood regions, ultimately improving our understanding of its dynamics and contribution to future sea-level rise. It is of particular relevance to ongoing Operation IceBridge activities and future large-scale airborne missions over Greenland.

IceBridge↗

NASA NTRS2015

Vegetation Cover Change in the Upper Kings River Basin of the Sierra Nevada Detected Using Landsat Satellite Image Analysis

The Sierra Nevada of California is a region where large wildfires have been suppressed for over a century. A detailed geographic record of recent changes in vegetation cover across the Sierra Nevada remains a gap that can be filled with satellite remote sensing data. Results from Landsat image analysis over the past 25 years in the Upper Kings River basin showed that consistent, significant increases in the normalized difference vegetation index (NDVI) have not extended above 2000 m elevation, where cold temperatures presumably limit the growing season. Moreover, mean increases in NDVI since 1986 at elevations below 2000 m (which cover about half of the total basin area) have not exceeded 9%, even in the most extreme precipitation yearly comparisons. NDVI has decreased significantly at elevations above 2000 m throughout the basin in relatively wet year comparisons since the mid-1980s. These findings conflict with any assumptions that ET fluxes and river flows downstream could have been markedly altered by vegetation change over most of the Upper Kings River basin in recent decades.

normalized difference vegetation index (NDVI)↗

NASA NTRS2017

Simple Analytical Expressions for Electron Pitch Angle Diffusion Coefficients

In the present paper, we have calculated electron pitch angle diffusion coefficients due to resonant interactions with whistler mode lower band chorus (LBC), upper band chorus (UBC), and electrostatic electron cyclotron harmonic (ECH) waves. Calculations have been performed at two values of the ratio of electron plasma frequency to gyro-frequency and thirteen representative values of electron energies for the plasma sheet electrons. The numerical data of diffusion coefficients have been fitted to simple analytical expressions for each wave mode. These analytical expressions allow for simple evaluation of pitch angle diffusion coefficients for the arbitrary pitch angle, energy, the ambient magnetic field, the wave amplitude, and the ratio of plasma frequency to gyro-frequency. In the case of LBC waves, the analytical coefficients are generally within a factor of two to the numerical coefficients, except at higher pitch angles where the numerical coefficients drop to show negligible values. Likewise, also for UBC waves, the analytical coefficients are generally within a factor of two to the numerical coefficients. The analytical coefficients for ECH waves are generally in agreement with numerical coefficients. However, the analytical expressions developed for ECH waves do not reproduce sharp fluctuations, dips, and gaps, the so-called banded structure observed in the data of numerical coefficients. The effect of the shape variation on the profile of the wave spectral intensity and the effect of cold temperature on the numerical coefficients are also investigated. Applications of the analytical expressions of diffusion coefficients are discussed.

coefficients↗

NASA NTRS2018

Transient Heater Analysis for Orion Thermal Vacuum Testing

The Space Environments Complex (SEC) at NASA's Plum Brook Station is currently being prepared to perform thermal vacuum testing of the Orion spacecraft. This thermal vacuum, or T-VAC test will be run for a period of 60 days, which will be the longest such test ever conducted at SEC. The Orion Crew Module (CM) and Service Module (SM) will undergo T-VAC testing in SEC's Space Simulation Vacuum Chamber to ensure the functionality of these systems in a high vacuum environment at extremely cold temperatures. The T-VAC test setup in SEC was modeled and simulated in Thermal Desktop. The initial results from thermal analysis showed areas on the chamber floor to reach very low temperatures, which were below the minimum operating range of certain hardware located on or near the chamber floor. These hardware including elastomeric seals on the GN2 piping, bearing pads and O-rings are essential to both test and the operation of the SEC facility, and must be kept well above -20Â°F throughout the duration of the T-VAC test. Thus, further analysis was conducted to include the placement of patch heaters on the chamber floor in an effort to increase the temperature near colder areas on the floor. The results and findings from this analysis showed that using these heaters will result in a favorable temperature distribution on the chamber floor. This paper will discuss the methods used in the analysis, and the results obtained to determine the optimal configuration of these heaters on the chamber floor.

Wilhite, Jarred↗

NASA NTRS2018

Transient Heater Analysis for Orion Thermal Vacuum Testing

The Space Environments Complex (SEC) at NASA’s Plum Brook Station is currently being prepared to perform thermal vacuum testing of the Orion spacecraft. This thermal vacuum, or T-VAC test will be run for a period of 60 days, which will be the longest such test ever conducted at SEC. The Orion Crew Module (CM) and Service Module (SM) will undergo T-VAC testing in SEC’s Space Simulation Vacuum Chamber to ensure the functionality of these systems in a high vacuum environment at extremely cold temperatures. The T-VAC test setup in SEC was modeled and simulated in Thermal Desktop. The initial results from thermal analysis showed areas on the chamber floor to reach very low temperatures, which were below the minimum operating range of certain hardware located on or near the chamber floor. These hardware including elastomeric seals on the GN2 piping, bearing pads and O-rings are essential to both test and the operation of the SEC facility, and must be kept well above -20°F throughout the duration of the T-VAC test. Thus, further analysis was conducted to include the placement of patch heaters on the chamber floor in an effort to increase the temperature near colder areas on the floor. The results and findings from this analysis showed that using these heaters will result in a favorable temperature distribution on the chamber floor. This paper will discuss the methods used in the analysis, and the results obtained to determine the optimal configuration of these heaters on the chamber floor.

Wilhite, Jarred↗

NASA NTRS2016

Thermal Cycling for Development of Hybrid Fuel for a Notional Mars Ascent Vehicle

A Mars Ascent Vehicle (MAV) would be a critical part of a potential Mars sample return campaign. As currently envisioned, the MAV would launch samples from Mars into Mars orbit. Challenging requirements would be placed on a MAV as it would need to be able to survive in the harsh Martian environment which can get as cold as -120°C in the winter. At these cold temperatures, survival heating could be necessary to keep the MAV within the allowable flight temperature range. Estimates for survival heating power show that a fuel capable of operating at low temperature would significantly reduce the total required energy of the MAV. This has led to consideration of a hybrid propulsion system due to its anticipated low temperature capability. A new wax-based fuel, SP7, has been developed for a notional MAV mission. Thermal modeling of the fuel in the Mars environment was completed in order to estimate the temperature response of the fuel during Mars diurnal temperature cycling. Preliminary thermal testing was conducted to determine the max temperature range, radial gradient, and ramp rate the fuel could tolerate without cracking. The modeling and preliminary testing was used to develop a comprehensive, 100-day thermal cycling campaign. A total of 200 cycles are planned that are representative of 200 Martian diurnal cycles, roughly one-third of a Martian year. After 150 cycles, the fuel samples show no signs of cracking that would jeopardize the rocket’s performance. Though not yet complete, this testing is showing that SP7 has the potential to successfully be used on a MAV mission.

Farias, Edgardo↗

NASA NTRS2019

Overview of Thermal Design and Challenges for the Comet Astrobiology Exploration SAmple Return (CAESAR) Mission

The Comet Astrobiology Exploration SAmple Return (CAESAR) mission is one of two candidates selected by NASA in response to the New Frontiers 4 Announcement of Opportunity. If selected, CAESAR will fly to comet 67P/Churyumov-Gerasimenko (the same comet studied by ESA’s Rosetta mission) using solar electric propulsion. After some time in orbit around 67P collecting and analyzing images of 67P, a location for collecting a sample will be determined. Up to three “touch-and-go” maneuvers, similar to NASA’s OSIRIS-REx mission, can be attempted with the requirement of collecting at least 80 g of comet sample. Once the sample has been collected, it will be stored in the Sample Containment Subsystem (SCS) and the comet volatiles will be transferred into the Gas Containment System (GCS) for the return cruise back to Earth. As CAESAR approaches Earth, the Sample Return Capsule (SRC), containing the GCS and SCS will separate from the spacecraft and return back to Earth. The sample will be recovered and placed into cold storage for future studies and investigations. CAESAR presents a number of thermal challenges including significantly different power configurations and orientation constraints throughout the mission as well as a large number of mechanisms and configurations that must function at very cold temperatures. The temperature requirements for preserving the sample also present a challenge. This paper presents some of the high level thermal requirements and describes how the CAESAR thermal design was driven by these requirements.

Peabody, Hume L.↗

NASA NTRSDate not supplied

On the Importance of Laboratory Astrophysics and Astrochemistry and Interdisciplinary Research: Two Success Stories

Here we present two examples that demonstrate how cross-disciplinary research projects, where experimentalists, modelers and observers work together to answer science questions, allow expertise to be shared and misconceptions or missing key elements to be tackled by looking at the problem from different perspectives. They also show how, by working in unison, the group can accomplish more than the sum of its parts by combining results into a higher-level understanding of the chemical processes taking place. The first project is a collaborative study between experimentalists, modelers and observers to1) produce laboratory analogs of cosmic grains and planetary aerosols (Titan, Pluto...) from different gas mixtures in cold astrophysically relevant conditions (<200 K); and 2) characterize them with scanning electron microscopy and visible-to-far-infrared spectroscopy in order to assess the impact of the precursors on their growth structure and optical properties. We can then produce and study analogs that are representative of different formation stages or environments, and provide their complex refractive indices to the scientific community. We will show how, by using these experimental optical constants of more representative analogs in radiative transfer and reflectance spectra models, better interpretations of (exo)planetary atmosphere- and surface observations are possible. The second project is an interdisciplinary study of the formation of benzene clouds in the atmosphere of Saturn’s largest moon, Titan. We will show how combining Earth and Planetary Science laboratory expertise, modeling and observations has led to providing to the scientific community, for the first time, experimental vapor pressures for benzene at cold temperatures(<200K) relevant to Titan’s atmospheric conditions. These have been used in microphysical models instead of the higher temperature extrapolations used previously, allowing a better match to observations.

Ella Sciamma-o'Brien↗

NASA NTRSDate not supplied

Micro-grid for Future Planetary Surface Needs

Under the current Artemis Program, the National Aeronautics and Space Administration (NASA) will send its next set of astronauts (first woman and next man) to the Moon by 2024 and establish a sustainable presence on the lunar surface by 2028. The challenge of creating a sustained lunar surface presence is significantly different than previous efforts. Lunar surface operations will require access to continuous and highly reliable power to support mission needs, such as to support ISRU operations. Adding to this challenge, the lunar surface operations are not going to be established over a single effort, rather the system and operations will evolve and grow over time (years). The first initial loads that arrive on the lunar surface will be integrated to their own dedicated power sources. As the lunar surface operations grow, so will the demand for power and at some point these individual loads will require more power than can be generated with any single power device. This power demand drives the need for inter-connecting the loads and power devices to share power between them, resulting in a micro-grid. One of the advantages of developing a lunar surface micro-grid is that allows lunar surface operations to resemble electrical utility operations on Earth; it allows power to be generated where it is convenient and allows power to be consumed where it is convenient, rather than negotiating between generation and consumption. The micro-grid concept also provides another benefit of affording the ability to increase overall system reliability by integrating dissimilar power generation and energy storage devices together, for example modifying the power generation strategy to include both solar arrays and nuclear. Creating a lunar surface micro-grid has its advantages, however there are significant challenges associated with an evolvable micro-grid concept. The challenges include how to efficiently transmit large amounts of power (10kW+) long distances (1kW+), how to effectively integrate dissimilar power generation and energy storage devices to maximize power consumption and minimize downtime, and how to physically connect these devices together with a connector that can survive the lunar environment (dust, extreme cold temperatures) and is capable of both astronaut and robotic operation. The basic components of the micro-grid have to be designed to ensure the system is sustainable, modular, and reconfigurable. An interface to the micro-grid has to be designed that allows for additional technologies, some of which may not yet be fully designed, to easily integrate into the micro-grid concept. This presentation discusses these lunar challenges in some more depth and offers a path forward in designing an evolvable micro-grid to meet the needs of the lunar surface operations and proposes a Universal Micro-grid Interface Converter to connect these dissimilar power sources and mission loads to the micro-grid.

Jeffrey Csank↗

NASA NTRS1997

Ion-Atom Cold Collisions and Atomic Clocks

This paper is an investigation of ion-atom interactions in the cold and ultra-cold temperature regime. Some of the collisional ion-atom interactions present at room temperature are very much reduced in the low temperature regime.

Ion-Atom↗

NASA NTRS2018

Radiometric Stability in 16 years of AIRS Hyperspectral Infrared Data (SPIE OP-431-20)

With global warming at the rate of 10 mK/yr, it is important to at least characterize any trend in the AIRS data, which may impact the use of AIRS data for climate change research. We evaluated the stability of the AIRS v5 calibration for seven atmospheric window channels between 2002 and 2018 under tropical ocean clear conditions. Trends for the channels between 961, 1128 and 1231 cm-1 channels are typically +3 mK/yr; for 790 and 901 cm-1 the trend is 6 mK/yr, i.e. the observations are increasingly getting warmer than expected. The trends are day/night consistent. The trend for the 2508 and 2616 cm-1 channels is close to 10 mK/yr at night, but closer to 6 mK/yr during the day. On an absolute scale these trends are small, but not when viewed in the context of global warming at a 10 mK/yr rate. While the warming trends are consistent with increased scattering from the scan mirrors, which create an error in reading the Onboard Blackbody Calibration, the resulting changes in the gain are a factor of about five larger than observed changes in the gain. The effects of scattering due to scan mirror contamination are evident at extremely cold temperatures, but scattering does not produce the observed warming at warm temperatures. It is possible that much of the observed warming in the AIRS window channels is a geophysical effect related to the warming of the oceans, resulting in a shift in the diurnal cycle and skin effect correction. This requires more careful evaluation.

Manning, Evan M.↗

NASA NTRS2018

Radiometric Stability in 16 years of AIRS Hyperspectral Infrared Data (SPIE OP-431-20)

Manning, Evan M.↗

NASA NTRS2021

Normalization Method and Application for MODIS TEB Assessments using Earth Scene Measurements

Selected Earth targets are commonly used for satellite sensor calibration assessments (e.g. sensor stability and inter-comparisons). Moreover, typical scenes used for the calibration assessment of the thermal emissive bands (TEBs) includeDome Concordia (Dome-C), ocean, desert, and deep convective clouds (DCC). Reference data used for these calibration assessments can come from another band, another instrument, or ground measurements. The Dome-C site, covered with uniformly-distributed permanent snow, is normally used for the assessment of the TEBsat cold temperatures. Furthermore, ocean and desert measurements prove useful for scenes with higher temperatures. The DCC, one of the most consistent and coldest targets, can be used for the TEBs calibration and product stability assessments. MODIS band 31 (~ 11 m) can be used as a reference for these scenes. However, measurements over these scenes have seasonal variations, and the DCC brightness temperatures (BTs) have asymmetrical distributions. These features can introduce additional uncertainty to the stability assessments. A normalization method is applied by using an empirical model to derive reference-dependent BTs. Using the developed empirical model, measurements can be normalized to a reference BT in order to enhance the calibration assessment’s accuracy. This method is evaluated using all four scene types (i.e. ocean, desert, snow (Dome-C), and DCC) and applied to all the Terra and Aqua MODIS TEBs. Stability assessments over the instruments’ entire data records are presented and discussed. The technique can be applied in future efforts to support MODIS TEBs calibration assessments.

MODIS TEB↗

NASA NTRS2021

The Enigmatic Brown Dwarf WISEA J153429.75-104303.3 (a.k.a. "The Accident")

Continued follow-up of WISEA J153429.75−104303.3, announced in Meisner et al., has proven it to have an unusual set of properties. New imaging data from Keck/MOSFIRE and HST/WFC3 shows that this object is one of the few faint proper motion sources known withJ−ch2>8 mag, indicating a very cold temperature consistent with the latest known Y dwarfs. Despite this, it has W1−W2 and ch1−ch2 colors∼1.6 mag bluer than a typical Y dwarf. A new trigonometric parallax measurement from a combination of WISE, Spitzer, and HST astrometry confirms a nearby distance of-+16.31.21.4pc and a large transverse velocity of 207.4±15.9 km s−1. The absoluteJ,W2, and ch2 magnitudes are in line with the coldest known Y dwarfs, despite the highly discrepant W1−W2 andch1−ch2 colors. We explore possible reasons for the unique traits of this object and conclude that it is most likely an old, metal-poor brown dwarf and possibly the first Y subdwarf. Given that the object has an HST F110Wmagnitude of 24.7 mag, broadband spectroscopy and photometry from JWST are the best options for testing this hypothesis

J Davy Kirkpatrick↗

NASA NTRS2021

Europa Environmental Testing of Thermal Hardware for the Mapping Imaging Spectrometer for Europa (MISE) Instrument

The Europa Clipper spacecraft, scheduled for launch in June 2022, hosts a suite of instruments including the Mapping Imaging Spectrometer for Europa (MISE). MISE is a high-optical through-put pushbroom infrared imaging spectrometer that can collect measurements within Europa’s challenging radiation environment. It is externally mounted to the spacecraft and as a result is exposed to high radiation levels and cold temperatures. The instrument consists of a scan mirror assembly, an optical bench including a Dyson spectrometer and a telescope, and a structure that supports a cryocooler and a radiator. The cryocooler is used to actively cool the focal plane array and the spectrometer. The heat from the cryocooler is rejected through pyrolytic graphite sheet thermal straps to a honeycomb radiator. MISE will implement thermal hardware that will either not be used on other parts of the spacecraft or have a more extreme environment than the spacecraft. As a result, the MISE instrument performed numerous environmental tests on its thermal hardware. This paper discusses the results of the thermal cycling and radiation tests performed on the MISE thermal hardware including a Lockheed Martin Micro1-2 cryocooler, Pyrolytic graphite sheet thermal straps, Annealed pyrolytic graphite K-Core, Rosemount Platinum Resistance Thermometers, Tayco Kapton Thermofoil heaters, Dale Ohm resistors, and aluminum honeycomb and facesheets.

Strong, Patrick↗