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At least 253 records · Page 14

All sources NASA NTRS DOE OSTI

NASA NTRS1997

Inorganic Water Repellent Coatings for Thermal Protection Insulation on an Aerospace Vehicle

The objective of this research was two-fold: first, to identify and test inorganic water-repellent materials that would be hydrophobic even after thermal cycling to temperatures above 600 C and, second, to develop a model that would link hydrophobicity of a material to the chemical properties of its constituent atoms. Four different materials were selected for detailed experimental study, namely, boron nitride, talc, molybdenite, and pyrophyllite, all of which have a layered structure made up of ionic/covalent bonds within the layers but with van der Waals bonds between the layers. The materials tested could be considered hydrophobic for a nonporous surface but none of the observed contact angles exceeded the necessary 90 degrees required for water repellency of porous materials. Boron nitride and talc were observed to retain their water-repellency when heated in air to temperatures that did not exceed 800 C, and molybdenite was found to be retain its hydrophobicity when heated to temperatures up to 600 C. For these three materials, oxidation and decomposition were identified to be the main cause for the breakdown of water repellency after repeated thermal cycling. Pyrophyllite shows the maximum promise as a potential water-repellent inorganic material, which, when treated initially at 900 C, retained its shape and remained hydrophobic for two thermal cycles where the maximum retreatment temperature is 900 C. A model was developed for predicting materials that might exhibit hydrophobicity by linking two chemical properties, namely, that the constituent ions of the compound belong to the soft acid-base category and that the fractional ionic character of the bonds be less than about 20 percent.

Fuerstenau, D. W.↗

NASA NTRS1997

Inorganic Water Repellent Coatings for Thermal Protection Insulation on an Aerospace Vehicle

Fuerstenau, D. W.↗

NASA NTRS2007

Using Digital Radiography To Image Liquid Nitrogen in Voids

Digital radiography by use of (1) a field-portable x-ray tube that emits low-energy x rays and (2) an electronic imaging x-ray detector has been found to be an effective technique for detecting liquid nitrogen inside voids in thermal-insulation panels. The technique was conceived as a means of investigating cryopumping (including cryoingestion) as a potential cause of loss of thermal insulation foam from space-shuttle external fuel tanks. The technique could just as well be used to investigate cryopumping and cryoingestion in other settings. In images formed by use of low-energy x-rays, one can clearly distinguish between voids filled with liquid nitrogen and those filled with gaseous nitrogen or other gases. Conventional film radiography is of some value, but yields only non-real-time still images that do not show time dependences of levels of liquids in voids. In contrast, the present digital radiographic technique yields a succession of images in real time at a rate of about 10 frames per second. The digitized images can be saved for subsequent analysis to extract data on time dependencies of levels of liquids and, hence, of flow paths and rates of filling and draining. The succession of images also amounts to a real-time motion picture that can be used as a guide to adjustment of test conditions.

Cox, Dwight↗

NASA NTRS2013

Ambient Dried Aerogels

A method has been developed for creating aerogel using normal pressure and ambient temperatures. All spacecraft, satellites, and landers require the use of thermal insulation due to the extreme environments encountered in space and on extraterrestrial bodies. Ambient dried aerogels introduce the possibility of using aerogel as thermal insulation in a wide variety of instances where supercritically dried aerogels cannot be used. More specifically, thermoelectric devices can use ambient dried aerogel, where the advantages are in situ production using the cast-in ability of an aerogel. Previously, aerogels required supercritical conditions (high temperature and high pressure) to be dried. Ambient dried aerogels can be dried at room temperature and pressure. This allows many materials, such as plastics and certain metal alloys that cannot survive supercritical conditions, to be directly immersed in liquid aerogel precursor and then encapsulated in the final, dried aerogel. Additionally, the metalized Mylar films that could not survive the previous methods of making aerogels can survive the ambient drying technique, thus making multilayer insulation (MLI) materials possible. This results in lighter insulation material as well. Because this innovation does not require high-temperature or high-pressure drying, ambient dried aerogels are much less expensive to produce. The equipment needed to conduct supercritical drying costs many tens of thousands of dollars, and has associated running expenses for power, pressurized gasses, and maintenance. The ambient drying process also expands the size of the pieces of aerogel that can be made because a high-temperature, high-pressure system typically has internal dimensions of up to 30 cm in diameter and 60 cm in height. In the case of this innovation, the only limitation on the size of the aerogels produced would be in the ability of the solvent in the wet gel to escape from the gel network.

Jones, Steven M.↗

NASA NTRS2005

Aerogel Insulation Systems for Space Launch Applications

New developments in materials science in the areas of solution gelation processes and nanotechnology have led to the recent commercial production of aerogels. Concurrent with these advancements has been the development of new approaches to cryogenic thermal insulation systems. For example, thermal and physical characterizations of aerogel beads under cryogenic-vacuum conditions have been performed at the Cryogenics Test Laboratory of the NASA Kennedy Space Center. Aerogel-based insulation system demonstrations have also been conducted to improve performance for space launch applications. Subscale cryopumping experiments show the thermal insulating ability of these fully breathable nanoporous materials. For a properly executed thermal insulation system, these breathable aerogel systems are shown to not cryopump beyond the initial cooldown and thermal stabilization phase. New applications are being developed to augment the thermal protection systems of space launch vehicles, including the Space Shuttle External Tank. These applications include a cold-boundary temperature of 90 K with an ambient air environment in which both weather and flight aerodynamics are important considerations. Another application is a nitrogen-purged environment with a cold-boundary temperature of 20 K where both initial cooldown and launch ascent profiles must be considered. Experimental results and considerations for these flight system applications are discussed.

Fesmire, James E.↗

NASA NTRS1986

Ceramic-ceramic shell tile thermal protection system and method thereof

A ceramic reusable, externally applied composite thermal protection system (TPS) is proposed. The system functions by utilizing a ceramic/ceramic upper shell structure which effectively separates its primary functions as a thermal insulator and as a load carrier to transmit loads to the cold structure. The composite tile system also prevents impact damage to the atmospheric entry vehicle thermal protection system. The composite tile comprises a structurally strong upper ceramic/ceramic shell manufactured from ceramic fibers and ceramic matrix meeting the thermal and structural requirements of a tile used on a re-entry aerospace vehicle. In addition, a lightweight high temperature ceramic lower temperature base tile is used. The upper shell and lower tile are attached by means effective to withstand the extreme temperatures (3000 to 3200F) and stress conditions. The composite tile may include one or more layers of variable density rigid or flexible thermal insulation. The assembly of the overall tile is facilitated by two or more locking mechanisms on opposing sides of the overall tile assembly. The assembly may occur subsequent to the installation of the lower shell tile on the spacecraft structural skin.

Riccitiello, Salvatore R.↗

NASA NTRS1990

Apparatus for measurement of thermal conductivity of insulation systems subjected to extreme temperature differences

Advanced aerospace designs require thermal insulation systems which are consistent with cryogenic fluids, high thermal loads, and design restrictions such as weight and volume. To evaluate the thermal performance of these insulating systems, an apparatus capable of measuring thermal conductivity using extreme temperature differences (27 to 1100 K) is being developed. This system is described along with estimates of precision and accuracy in selected operating conditions. Preliminary data are presented.

Dube, W. P.↗

DOE OSTI2024

Tailoring Nanoporous Silica and Natural Straw Structural Insulation Composites

Nanoporous silica exhibits ultralow thermal conductivity as a result of its nanoscale pore size, high pore volume, and specific surface area. In this study, we report the self-assembled surfactant-templated synthesis of nanoporous silica, which is integrated with cellulose fibers derived from natural straw to manufacture high thermal insulation and mechanically robust nanocomposites. The nanocomposite shows a low thermal conductivity of 22.5 mW/(m·K), a compressive modulus of 0.93 MPa, and a hydrophobicity with a water contact angle of 125°. Moreover, we observed a marked reduction in water absorption capacity and a carbon footprint of 0.21 kg CO 2 equiv/kg. Here, this study provides a pathway toward the development of nanoporous structural insulation materials for energy-efficient building applications.

36 MATERIALS SCIENCE↗

NASA NTRS2010

Silica/Polymer and Silica/Polymer/Fiber Composite Aerogels

Aerogels that consist, variously, of neat silica/polymer alloys and silica/polymer alloy matrices reinforced with fibers have been developed as materials for flexible thermal-insulation blankets. In comparison with prior aerogel blankets, these aerogel blankets are more durable and less dusty. These blankets are also better able to resist and recover from compression . an important advantage in that maintenance of thickness is essential to maintenance of high thermal-insulation performance. These blankets are especially suitable as core materials for vacuum- insulated panels and vacuum-insulated boxes of advanced, nearly seamless design. (Inasmuch as heat leakage at seams is much greater than heat leakage elsewhere through such structures, advanced designs for high insulation performance should provide for minimization of the sizes and numbers of seams.) A silica/polymer aerogel of the present type could be characterized, somewhat more precisely, as consisting of multiply bonded, linear polymer reinforcements within a silica aerogel matrix. Thus far, several different polymethacrylates (PMAs) have been incorporated into aerogel networks to increase resistance to crushing and to improve other mechanical properties while minimally affecting thermal conductivity and density. The polymethacrylate phases are strongly linked into the silica aerogel networks in these materials. Unlike in other organic/inorganic blended aerogels, the inorganic and organic phases are chemically bonded to each other, by both covalent and hydrogen bonds. In the process for making a silica/polymer alloy aerogel, the covalent bonds are introduced by prepolymerization of the methacrylate monomer with trimethoxysilylpropylmethacrylate, which serves as a phase cross-linker in that it contains both organic and inorganic monomer functional groups and hence acts as a connector between the organic and inorganic phases. Hydrogen bonds are formed between the silanol groups of the inorganic phase and the carboxyl groups of the organic phase. The polymerization process has been adapted to create interpenetrating PMA and silica-gel networks from monomers and prevent any phase separations that could otherwise be caused by an overgrowth of either phase. Typically, the resulting PMA/silica aerogel, without or with fiber reinforcement, has a density and a thermal conductivity similar to those of pure silica aerogels. However, the PMA enhances mechanical properties. Specifically, flexural strength at rupture is increased to 102 psi (=0.7 MPa), about 50 times the flexural strength of typical pure silica aerogels. Resistance to compression is also increased: Applied pressure of 17.5 psi (=0.12 MPa) was found to reduce the thicknesses of several composite PMA/silica aerogels by only about 10 percent.

Ou, Danny↗

NASA NTRSDate not supplied

Potential of Materials to Impact Megawatt-Scale Electric Machines

High specific power density, megawatt-scale electric machines (motors and generators) are needed to enable megawatt-scale electric aircraft propulsion systems for single isle aircraft. Thermally insulating electrical insulation materials in the stator windings limits the ability to thermally manage the heat produced in these machines. Polymer-ceramic composites along with novel processing techniques offer viable options to improve the thermal conductivity of the electrical insulation system. This paper outlines current National Aeronautics and Space Administration’s Glenn Research Center efforts of developing several polymer-ceramic systems and processing techniques as they relate to electric machine insulation (including potting). There is also analysis of how these factors relate to machine performance.

electric macnhine↗

NASA NTRS1966

Insulation Materials

Cryogenic fluid insulating material, ceramic-gold reflective coating and ceramic thermal insulation

COATING↗

NASA NTRS2000

Marshall Convergent Coating Development Team: An Aerospace Success Story

The external thermal insulation systems for the Space Shuttle solid rocket boosters and the Air Force Titan IV payload fairings were in jeopardy due to EPA regulatory problems, endangering the flight status of both vehicles. The Marshall Convergent Coating (MCC-1) Development Team was formed in February 1994 to develop and implement an EPA-compliant external thermal insulation system for both systems. MCC-1 made use of a process known as Convergent Spray Technology (CST), a solventless, sprayable process that eliminated the environmentally hazardous chemicals involved with the old methods. Implemented in record time, the new insulation was so successful that it was selected for two additional flight vehicles, Boeing's Sea Launch and Delta TV. The activity also led to commercial spin-off pilot projects. The team continues today to share data between the various production sites, resolve production issues, expand the material's use, and consider potential improvements for the future.

Lester, Carl N.↗

NASA NTRS1977

Induced charging of shuttle orbiter by high electron-beam currents

Emission of high-current electron beams that was proposed for some Spacelab payloads required substantial return currents to the orbiter skin in order to neutralize the beam charge. Since the outer skin of the vehicle was covered with approximately 1200 sq m of thermal insulation which has the dielectric quality of air and an electrical conductivity that was estimated by NASA at 10 to the -9 power to 10 to the -10 power mhos/m, considerable transient charging and local potential differences were anticipated across the insulation. The theory for induced charging of spacecraft due to operation of electron guns was only developed for spherical metal vehicles and constant emission currents, which were not directly applicable to the orbiter situation. Field-aligned collection of electron return current from the ambient ionosphere at orbiter altitudes provides up to approximately 150 mA on the conducting surfaces and approximately 2.4 A on the dielectric thermal insulation. Local ionization of the neutral atmosphere by energetic electron bombardment or electrical breakdown may provide somewhat more return current.

Liemohn, H. B.↗

NASA NTRS1994

Preparation And Analysis Of Specimens Of Ablative Materials

Procedure for chemical analysis of specimens of silicone-based ablative thermal-insulation materials SLA-561 and MA25 involves acid digestion of specimens to prepare them for analysis by inductively-coupled-plasma/atomic-emission spectroscopy (ICP/AES). In comparison with atomic-absorption spectroscopy (AAS), ICP/AES is faster and more accurate than AAS. Results of analyses stored in data base, used to trace variations in concentrations of chemical elements in materials during long-term storage, and used in timely manner in investigations of failures. Acid-digestion portion of procedure applied to other thermal-insulation materials containing room-temperature-vulcanizing silicones and enables instrumental analysis of these materials.

Solomon, William C.↗

NASA NTRS1976

Investigation of the thermal control of instruments mounted in the Space Shuttle cargo bay

Results are presented for an investigation intended to examine the orbital averaged thermal response of a number of instruments, each being representative of a class of scientific instrumentation, when they are individually mounted on pallets and operated in the cargo bay of the Shuttle. The discussion covers mainly the Shuttle Orbiter thermal models, the solar viewing instrument, and the high-energy instrument. One approach to thermal insulation of smaller instruments is to provide a thermal canister insulated from the cargo bay and equipped with variable conductance heat pipes. Two approaches are proposed for larger instruments. One approach is to provide a thermal curtain across the top of the pallet which shields the pallet cavity from direct sunlight, while the second approach is to provide a fluid system to transfer heat from a specified location on an instrument to either a space viewing radiator on the pallet or instrument or the orbiter cooling system. These thermal control design concepts represent several ideas for standard reusable thermal control systems.

Bartoszek, J. T.↗

NASA NTRS1983

Conduit for high temperature transfer of molten semiconductor crystalline material

A conduit for high temperature transfer of molten semiconductor crystalline material consists of a composite structure incorporating a quartz transfer tube as the innermost member, with an outer thermally insulating layer designed to serve the dual purposes of minimizing heat losses from the quartz tube and maintaining mechanical strength and rigidity of the conduit at the elevated temperatures encountered. The composite structure ensures that the molten semiconductor material only comes in contact with a material (quartz) with which it is compatible, while the outer layer structure reinforces the quartz tube, which becomes somewhat soft at molten semiconductor temperatures. To further aid in preventing cooling of the molten semiconductor, a distributed, electric resistance heater is in contact with the surface of the quartz tube over most of its length. The quartz tube has short end portions which extend through the surface of the semiconductor melt and which are lef bare of the thermal insulation. The heater is designed to provide an increased heat input per unit area in the region adjacent these end portions.

Fiegl, George↗

NASA NTRS2003

Soft Landing of Spacecraft on Energy-Absorbing Self-Deployable Cushions

A report proposes the use of cold hibernated elastic memory (CHEM) foam structures to cushion impacts of small (1 to 50 kg) exploratory spacecraft on remote planets. Airbags, which are used on larger (800 to 1,000 kg) spacecraft have been found to (1) be too complex for smaller spacecraft; (2) provide insufficient thermal insulation between spacecraft and ground; (3) bounce on impact, thereby making it difficult to land spacecraft in precisely designated positions; and (4) be too unstable to serve as platforms for scientific observations. A CHEM foam pad according to the proposal would have a glass-transition temperature (Tg) well above ambient temperature. It would be compacted, at a temperature above Tg, to about a tenth or less of its original volume, then cooled below Tg, then installed on a spacecraft without compacting restraints. Upon entry of the spacecraft into a planetary atmosphere, the temperature would rise above Tg, causing the pad to expand to its original volume and shape. As the spacecraft decelerated and cooled, the temperature would fall below Tg, rigidifying the foam structure. The structure would absorb kinetic energy during ground impact by inelastic crushing, thus protecting the payload from damaging shocks. Thereafter, this pad would serve as a mechanically stable, thermally insulating platform for the landed spacecraft.

Sokolowski, Witold↗

NASA NTRS2004

Improved Cryostat for Cooling a Wide Panel

An improved cryostat has been developed for cooling a wide panel evenly over its surface to a temperature of -423 F (approximately equal to -253 C) by use of liquid helium. Originally, the cryostat was to be used in measuring apparent strains in wide aluminum/lithium panels as functions of temperature in order to develop data for temperature compensation of the readings of strain gauges on a tank containing liquid hydrogen. Relative to the cryostat used previously for this purpose, the improved cryostat can be prepared for a test in less time, and it loses less helium during each test. Each wide panel to be tested is instrumented with thermocouples in preparation for a test. The previous cryostat was made of two aluminum halves that, for each test, were sandwiched together and sealed around the instrumented wide panel to be tested. The panel was thus enclosed in a plenum. The cryostat and adjacent panel areas protruding from the cryostat were then coated with a thermally insulating foam. During a test, liquid helium was made to flow into the plenum through a port on the bottom. The helium vaporized and expanded, filling the plenum with cold helium gas, which eventually flowed out of the plenum through a port on the top. The nature of the flow was such that a significant portion of the helium did not come into contact with the wide panel; hence, cooling was less efficient than it might otherwise have been. After completion of each test, the foam and the cryostat were separated from the panel. The cryostat was cleaned and prepared for installation on another instrumented wide panel for the next test. It took 28 hours to install the cryostat onto the instrumented panel, apply the foam, and perform ancillary operations in preparation for a test. The volume of liquid helium consumed during each test was 750 liters. The improved cryostat (see figure) includes an upper section and a lower section, both of which include permanent housings made of a thermally insulating foam 2-in. (approximately equal to 5-cm) thick. A liquid-helium- injection manifold is attached to the inside of the top section. The bottom section includes an outlet for helium gas. The manifold contains slots that, when the cryostat is installed on the panel, are located approximately 1 in. (approximately equal to 2.5 cm) from the wide panel. The array of slots spans a substantial portion of the area of the panel. The top and bottom sections of the cryostat are sealed to the panel by use of polytetrafluoroethylene cord and aluminum tape. Liquid helium is fed into the manifold from the top. The helium leaves the manifold through the slots and thus impinges directly on the panel. Hence, all the helium entering the cryostat must come into contact with the panel before leaving the cryostat. After a test, the cryostat is removed from the panel and reinstalled onto another panel for the next test. Installation of the cryostat on an instrumented panel takes a negligible amount of time, in comparison with the 28 hours associated with the previous cryostat. The amount of liquid helium consumed during a test in the improved cryostat is 500 liters - 250 liters less than before.

Clifton, W. B.↗