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We use a 1-D bulk charging model to evaluate dielectric charging at cryogenic temperatures relevant to space systems using passive cooling to <100K or extended operations in permanently dark lunar craters and the lunar night.
This invention is intended for use as a load-bearing device under cryogenic temperatures and/or abrasive conditions (i.e., during missions to the Moon). The innovation consists of small-diameter, ceramic fibers that are woven or braided into devices like ropes, belts, tracks, or cables. The fibers can be formed from a variety of ceramic materials like silicon carbide, carbon, aluminosilicate, or aluminum oxide. The fiber architecture of the weave or braid is determined by both the fiber properties and the mechanical requirements of the application. A variety of weave or braid architectures is possible for this application. Thickness of load-bearing devices can be achieved by using either a 3D woven structure, or a layered, 2D structure. For the prototype device, a belt approximately 0.10 in. (0.25 cm) thick, and 3.0 in. (7.6 cm) wide was formed by layering and stitching a 2D aluminosilicate fiber weave.
The silicon substrate carrier was created so that a large-area array (in this case 62,000+ elements of a microshutter array) and a variety of discrete passive and active devices could be mounted on a single board, similar to a printed circuit board. However, the density and number of interconnects far exceeds the capabilities of printed circuit board technology. To overcome this hurdle, a method was developed to fabricate this carrier out of silicon and implement silicon integrated circuit (IC) technology. This method achieves a large number of high-density metal interconnects; a 100-percent yield over a 6-in. (approximately equal to 15-cm) diameter wafer (one unit per wafer); a rigid, thermally compatible structure (all components and operating conditions) to cryogenic temperatures; re-workability and component replaceability, if required; and the ability to precisely cut large-area holes through the substrate. A method that would employ indium bump technology along with wafer-scale integration onto a silicon carrier was also developed. By establishing a silicon-based version of a printed circuit board, the objectives could be met with one solution. The silicon substrate would be 2 mm thick to survive the environmental loads of a launch. More than 2,300 metal traces and over 1,500 individual wire bonds are required. To mate the microshutter array to the silicon substrate, more than 10,000 indium bumps are required. A window was cut in the substrate to allow the light signal to pass through the substrate and reach the microshutter array. The substrate was also the receptacle for multiple unpackaged IC die wire-bonded directly to the substrate (thus conserving space over conventionally packaged die). Unique features of this technology include the implementation of a 2-mmthick silicon wafer to withstand extreme mechanical loads (from a rocket launch); integrated polysilicon resistor heaters directly on the substrate; the precise formation of an open aperture (approximately equal to 3x3cm) without any crack propagation; implementation of IR transmission blocking techniques; and compatibility with indium bump bonding. Although designed for the microshutter arrays for the NIRSpec instrument on the James Webb Space Telescope, these substrates can be linked to microshutter applications in the photomask generation and stepper equipment used to make ICs and microelectromechanical system (MEMS) devices.
The turboelectric distributed propulsion approach for aircraft makes a contribution to all four "corners" of NASA s Subsonic Fixed Wing trade space, reducing fuel burn, noise, emissions and field length. To achieve the system performance required for the turboelectric approach, a number of advances in materials and structures must occur. These range from improved superconducting composites to structural composites for support windings in superconducting motors at cryogenic temperatures. The rationale for turboelectric distributed propulsion and the materials research and development opportunities that it may offer are outlined.
Future space missions are going to require large focal planes with many sensing arrays and hundreds of millions of pixels all read out at high data rates'' . This will place unique demands on the electrical and electronics (EE) subsystem design and it will be critically important to have high technology readiness level (TRL) EE concepts ready to support such missions. One such omission is the Joint Dark Energy Mission (JDEM) charged with making precise measurements of the expansion rate of the universe to reveal vital clues about the nature of dark energy - a hypothetical form of energy that permeates all of space and tends to increase the rate of the expansion. One of three JDEM concept studies - the Dark Energy Space Telescope (DESTINY) was conducted in 2008 at the NASA's Goddard Space Flight Center (GSFC) in Greenbelt, Maryland. This paper presents the EE subsystem framework, which evolved from the DESTINY science instrument study. It describes the main challenges and implementation concepts related to the design of an EE subsystem featuring multiple focal planes populated with dozens of large arrays and millions of pixels. The focal planes are passively cooled to cryogenic temperatures (below 140 K). The sensor mosaic is controlled by a large number of Readout Integrated Circuits and Application Specific Integrated Circuits - the ROICs/ASICs in near proximity to their sensor focal planes. The ASICs, in turn, are serviced by a set of "warm" EE subsystem boxes performing Field Programmable Gate Array (FPGA) based digital signal processing (DSP) computations of complex algorithms, such as sampling-up-the-ramp algorithm (SUTR), over large volumes of fast data streams. The SUTR boxes are supported by the Instrument Control/Command and Data Handling box (ICDH Primary and Backup boxes) for lossless data compression, command and low volume telemetry handling, power conversion and for communications with the spacecraft. The paper outlines how the JDEM DESTINY concept instrument EE subsystem can be built now, a design; which is generally U.S. Government work not protected by U.S. copyright IEEEAC paper # 1429. Version 4. Updated October 19, 2009 applicable to a wide variety of missions using large focal planes with lar ge mosaics of sensors.
One of the factors in assessing the applicability of wire or cable on the lunar surface is its flexibility under extreme cold conditions. Existing wire specifications did not address their mechanical behavior under cold, cryogenic temperature conditions. Therefore tests were performed to provide this information. To assess this characteristic 35 different insulated wire and cable pieces were cold soaked in liquid nitrogen. The segments were then subjected to bending and the force was recorded. Any failure of the insulation or jacketing was also documented for each sample tested. The bending force tests were performed at room temperature to provide a comparison to the change in force needed to bend the samples due to the low temperature conditions. The results from the bending tests were plotted and showed how various types of insulated wire and cable responded to bending under cold conditions. These results were then used to estimate the torque needed to unroll the wire under these low temperature conditions.
A modification of the design of the pulse tube in a pulse-tube cryocooler reduces axial thermal conductance while preserving radial thermal conductance. It is desirable to minimize axial thermal conductance in the pulse-tube wall to minimize leakage of heat between the warm and cold ends of the pulse tube. At the same time, it is desirable to maximize radial thermal conductance at the cold end of the pulse tube to ensure adequate thermal contact between (1) a heat exchanger in the form of a stack of copper screens inside the pulse tube at the cold end and (2) the remainder of the cold tip, which is the object to which the heat load is applied and from which heat must be removed. The modified design yields a low-heat-leak pulse tube that can be easily integrated with a cold tip. A typical pulse tube of prior design is either a thin-walled metal tube or a metal tube with a nonmetallic lining. It is desirable that the outer surface of a pulse tube be cylindrical (in contradistinction to tapered) to simplify the design of a regenerator that is also part of the cryocooler. Under some conditions, it is desirable to taper the inner surface of the pulse tube to reduce acoustic streaming. The combination of a cylindrical outer surface and a tapered inner surface can lead to unacceptably large axial conduction if the pulse tube is made entirely of metal. Making the pulse-tube wall of a nonmetallic, lowthermal- conductivity material would not solve the problem because the wall would not afford the needed thermal contact for the stack of screens in the cold end. The modified design calls for fabricating the pulse tube in two parts: a longer, nonmetallic part that is tapered on the inside and cylindrical on the outside and a shorter, metallic part that is cylindrical on both the inside and the outside. The nonmetallic part can be made from G-10 fiberglass-reinforced epoxy or other low-thermal-conductivity, cryogenically compatible material. The metallic part must have high thermal conductivity in the cryogenic temperature range and would typically be made of pure copper to satisfy this requirement. The metallic part is bonded to the nonmetallic part with epoxy. Copper screens are inserted in the metallic part to form the cold-end heat exchanger, then the assembled pulse tube is inserted in the cold tip.
Two simple position or displacement sensors based on inductance-capacitance resonant circuits have been conceived. These sensors are both powered and interrogated without use of wires and without making contact with other objects. Instead, excitation and interrogation are accomplished by means of a magnetic-field-response recorder. Both of the present position or displacement sensors consist essentially of variable rectangular parallel-plate capacitors electrically connected in series with fixed inductors. Simple inductance-capacitance circuits of the type used in these sensors are inherently robust; their basic mode of operation does not depend on maintenance of specific environmental conditions. Hence, these sensors can be used under such harsh conditions as cryogenic temperatures, high pressures, and radioactivity.
Infrared image sensors based on high density rectangular planar arrays of nano tunnel junctions have been proposed. These sensors would differ fundamentally from prior infrared sensors based, variously, on bolometry or conventional semiconductor photodetection. Infrared image sensors based on conventional semiconductor photodetection must typically be cooled to cryogenic temperatures to reduce noise to acceptably low levels. Some bolometer-type infrared sensors can be operated at room temperature, but they exhibit low detectivities and long response times, which limit their utility. The proposed infrared image sensors could be operated at room temperature without incurring excessive noise, and would exhibit high detectivities and short response times. Other advantages would include low power demand, high resolution, and tailorability of spectral response. Neither bolometers nor conventional semiconductor photodetectors, the basic detector units as proposed would partly resemble rectennas. Nanometer-scale tunnel junctions would be created by crossing of nanowires with quantum-mechanical-barrier layers in the form of thin layers of electrically insulating material between them (see figure). A microscopic dipole antenna sized and shaped to respond maximally in the infrared wavelength range that one seeks to detect would be formed integrally with the nanowires at each junction. An incident signal in that wavelength range would become coupled into the antenna and, through the antenna, to the junction. At the junction, the flow of electrons between the crossing wires would be dominated by quantum-mechanical tunneling rather than thermionic emission. Relative to thermionic emission, quantum mechanical tunneling is a fast process.
At BAM, several projects were conducted in the past years dealing with the tribological properties of friction couples at cryogenic temperature and in vacuum environment. Promising candidates for vacuum application are MoS2-filled PEEK/PTFE composites, which showed a friction coefficient as low as 0.03 in high vacuum. To complete the tribological profile of these composites, further tests were performed in ultra-high vacuum (UHV) at room temperature. In this paper, friction and stick slip behavior, as well as outgassing characteristics during the test are presented.
The space shuttle orbiter s reaction control system (RCS) is a series of small thrusters that use hypergolic fuels to orient the orbiter in space. The RCS thrusters are constructed from a special niobium-based alloy -- the C-103. This alloy retains excellent mechanical properties from cryogenic temperature all the way up to 2,500 F (1,370 C). C-103 is susceptible to rapid oxidation at elevated temperatures. The authors have developed two methods to repair damaged R512a coatings on C-103. For the first repair technique, metal foundries, semiconductor manufacturers, and many other industries have developed and routinely use coatings that can easily be painted on metal to protect it from corrosion, including oxidation, to temperatures in excess of 2,500 F (1,370 C). This first repair technique is considered somewhat temporary. The second repair technique is based on using the native coating material of the RCS nozzles. the chipped area is ground out and a "green" R512a coating is applied to the repair area. Both repair techniques can be applied for moderate protection until the permanent laser-repair technique is available to the repair area.
The problem: To design a system that automatically maintains the fluid level in a liquid nitrogen cold trap. It is frequently necessary to operate a vacuum system using one or more cold traps for a prolonged period with the cold trap liquid level maintained between set limits. Electronic devices have been subject to failure due to the effect on components of cryogenic temperatures. The solution: An automatic liquid nitrogen dispensing system that uses gas filled probes, driving Bourdon tube gauges equipped with microswitches that, through a relay, control a solenoid valve in the liquid nitrogen storage line.
Long duration missions on the Moon s equator must survive lunar nights. With 350 hr of cryogenic temperatures, lunar nights present a challenge to robotic survival. Insulation is imperfect, so it is not possible to passively contain enough heat to stay warm through the night. Components that enable mobility, environmental sensing and solar power generation must be exposed, and they leak heat. Small, lightweight rovers cannot store enough energy to warm components throughout the night without some external source of heat or power. Thermal wadis, however, can act as external heat sources to keep robots warm through the lunar night. Electrical power can also be provided to rovers during the night from batteries stored in the ground beside wadis. Buried batteries can be warmed by the wadi s heat. Results from analysis of the interaction between a rover and a wadi are presented. A detailed three-dimensional (3D) thermal model and an easily configurable two-dimensional (2D) thermal model are used for analysis.
Flexure Engineering was awarded an SBIR to research and develop technology needed to build a thermal vacuum chamber made to take laser radar metrology through a window. The XATF test is proof of concept for this, and demonstrated the need for such a chamber. XATF refers to two pieces of critical ground support equipment for NASA's JWST (James Webb Space Telescope) Integrated Science Instrument Module (ISIM), the ISIM Alignment Target Fixture (IATF) and the Master Alignment Target Fixture (MATF). These optical alignment assemblies require characterization while under cryogenic temperature. A thermal vacuum chamber equipped with a shroud cooled with gaseous and liquid nitrogen was used. An inner shroud was cooled with liquid helium to approximately 30K. The XATF assemblies were kinematically mounted and oriented inside the inner shroud such that the optical targets were visible from outside an optical window on one of the chamber ports. Laser radar and theodolite mounted outside the window took measurements of various optical targets. Two cold cycles were completed. A third cycle was aborted. Metrology was successfully taken. There were some problems with the helium system. The cryo pumps were turned off to reduce vibrations during metrology. Many new technologies and testing methods must be developed for JWST and future programs that will require precision measurements. These technologies will be applicable to other cold temperature applications, such as lunar missions and superconductors. Remote metrology technologies can also be applicable to testing in harsh environments. Facilities with remote metrology capability will be valuable.
To increase contact conductance between two mating surfaces, a conductive tape has been developed by growing dense arrays of carbon nanotubes (CNTs, graphite layers folded into cylinders) on both sides of a thermally conductive metallic foil. When the two mating surfaces are brought into contact with the conductive tape in between, the CNT arrays will adhere to the mating surface. The van der Waals force between the contacting tubes and the mating surface provides adhesion between the two mating surfaces. Even though the thermal contact conductance of a single tube-to-tube contact is small, the tremendous amount of CNTs on the surface leads to a very large overall contact conductance. Interface contact thermal resistance rises from the microroughness and the macroscopic non-planar quality of mating surfaces. When two surfaces come into contact with each other, the actual contact area may be much less than the total area of the surfaces. The real area of contact depends on the load, the surface roughness, and the elastic and inelastic properties of the surface. This issue is even more important at cryogenic temperatures, where materials become hard and brittle and vacuum is used, which prevents any gas conduction through the interstitial region. A typical approach to increase thermal contact conductance is to use thermally conducting epoxies or greases, which are not always compatible with vacuum conditions. In addition, the thermal conductivities of these compounds are often relatively low. The CNTs used in this approach can be metallic or semiconducting, depending on the folding angle and diameter. The electrical resistivity of multiwalled carbon nanotubes (MWCNTs) has been reported. MWCNTs can pass a current density and remain stable at high temperatures in air. The thermal conductivity of a MWCNT at room temperature is measured to be approximately 3,000 W/m-K, which is much larger than that of diamond. At room temperature, the thermal conductance of a 0.3 sq cm array of CNTs was measured to be as high as 10 W/K. The high thermal conductivity and the nanoscale size make CNTs ideal as thermal interface materials. The CNT-based thermal tape can be used for the thermal management of microelectronic packages and electronic systems. It also can be integrated with current device technology and packaging. The material would allow for an efficient method to manage excess heat generation without requiring any additional power. Lastly, the CNT tape can be used to enhance thermal contact conductance across two mating surfaces on some NASA missions.
The James Webb Space Telescope (JWST) is a cryogenic, 6.5 meter diameter space telescope. JWST has a unique architecture, compared to previous space telescopes, that is driven by its science requirements, ia passively cooled cryogenic design, and the need to stow the observatory for launch. JWST's large, segmented mirror meets the requirement for high angular resolution in the infrared coupled with a significant increase in collecting area compared to the Spitzer and Hubble Space telescopes in order to detect the first galaxies. JWST's unique five-layer sunshield allows the telescope and instrument module to passively cool to cryogenic temperatures. JWST will be launched on an Ariane 5, and so both its telescope optics, and the sunshield have to be stowed in order to fit the Ariane 5 fairing. Following launch the sunshield and telescope optics must be deployed, and the primary mirror phased for science operations. In this presentation we will review the design of the observatory and highlight recent progress in the construction of the JWST observatory. In particular, we address recent progress with the telescope optics, sunshield and spacecraft. We will discuss predicted observatory performance in terms of the scientific goals of JWST and address key operational considerations that might bear upon frontier science observations.
A proposed magnetometer for use in a cryogenic environment would be sensitive enough to measure a magnetic-flux density as small as a picogauss (10(exp -16) Tesla). In contrast, a typical conventional flux-gate magnetometer cannot measure a magnetic-flux density smaller that about 1 microgauss (10(exp -10) Tesla). One version of this device, for operation near the low end of the cryogenic temperature range, would include a piece of a paramagnetic material on a platform, the temperature of which would be controlled with a periodic variation. The variation in temperature would be measured by use of a conventional germanium resistance thermometer. A superconducting coil would be wound around the paramagnetic material and coupled to a superconducting quantum interference device (SQUID) magnetometer.
One of the major challenges for NASA's next-generation reusable-launch-vehicle (RLV) program is the design of a cryogenic lightweight composite fuel tank. Potential matrix resin systems need to exhibit a low coefficient of thermal expansion (CTE), good mechanical strength, and excellent barrier properties at cryogenic temperatures under load. In addition, the resin system needs to be processable by a variety of non-autoclavable techniques, such as vacuum-bag curing, resin-transfer molding (RTM), vacuum-assisted resin-transfer molding (VaRTM), resin-film infusion (RFI), pultrusion, and advanced tow placement (ATP). To meet these requirements, the Advanced Materials and Processing Branch (AMPB) at NASA Langley Research Center developed a new family of wholly aromatic liquid-crystal oligomers that can be processed and thermally cross-linked while maintaining their liquid-crystal order. All the monomers were polymerized in the presence of a cross-linkable unit by use of an environmentally benign melt-condensation technique. This method does not require hazardous solvents, and the only side product is acetic acid. The final product can be obtained as a powder or granulate and has an infinite shelf life. The obtained oligomers melt into a nematic phase and do not exhibit isotropization temperatures greater than the temperatures of decomposition (Ti > T(sub dec)). Three aromatic formulations were designed and tested and included esters, ester-amides, and ester-imides. One of the major advantages of this invention, named LaRC-LCR or Langley Research Center-Liquid Crystal Resin, is the ability to control a variety of resin characteristics, such as melting temperature, viscosity, and the cross-link density of the final part. Depending on the formulation, oligomers can be prepared with melt viscosities in the range of 10-10,000 poise (100 rad/s), which can easily be melt-processed using a variety of composite-processing techniques. This capability provides NASA with custom-made matrix resins that meet the required processing conditions for the fabrication of textile composites. Once the resin is in place, the temperature is raised to 375 C and the oligomers are cross-linked into a high-glass-transition-temperature (Tg) nematic network without releasing volatiles. The mechanical properties of the fully crosslinked, composite articles are comparable to typical composites based on commercially available epoxy resins.