Stephanie A. Wise

Displacement properties of RAINBOW and THUNDER piezoelectric actuators

Abstract The electromechanical displacement properties of two recently developed piezoelectric actuators, referred to as RAINBOW and THUNDER, have been measured and compared. The actuators evaluated in this investigation are fabricated from 2.54 cm diameter PZT-5H and PZT-5A piezoelectric ceramic disks and are produced with the same total device thicknesses and ceramic-to-metal thickness ratios. For the compositions tested, the RAINBOW devices are found to exhibit 10–25% greater free-displacement properties than comparable THUNDER devices. This finding indicates that larger internal stresses are developed during the RAINBOW process, which lead to enhanced amplification of axial displacement.

Design and Development of an Optical Path Difference Scan Mechanism for Fourier Transform Spectrometers Using High Displacement RAINBOW Actuators

A new piezoelectric drive mechanism has been developed for optical translation in space-based spectrometer systems. The mechanism utilizes a stack of RAINBOW high displacement piezoelectric actuators to move optical components weighing less than 250 grams through a one centimeter travel. The mechanism uses the direct motion of the piezoelectric devices, stacked such that the displacement of the individual RAINBOW actuators is additive. A prototype device has been built which utilizes 21 RAINBOWs to accomplish the necessary travel. The mechanism weighs approximately 0.6 kilograms and uses less than 2 Watts of power at a scanning frequency of 0.5 Hertz, significantly less power than that required by state-of-the-art motor systems.

High Tc leads for remote sensing applications

Abstract Several NASA programmes designed to monitor the earths atmosphere from space utilize infrared detectors which operate at or below 4.2 K for optimum performance. At present, the detectors are maintained at cryogenic temperatures by a stored volume of liquid helium. These detectors must be electrically linked to amplification electronics and data storage instruments maintained at 80 K. The electrical connections over the temperature gradient account for ≈20% of the total heat load on the Dewar for some systems, accelerating the boil-off of liquid helium cryogen and reducing the operational lifetime of the space-borne instruments. The recent discovery of high temperature superconductors has provided an opportunity to develop electrically conductive, thermally insulating links to bridge this thermal gradient. This paper describes the modelling of the thermal transport properties of thick film, high T c electrical bridges across a 4.2–80 K temperature gradient and the impact of such devices on a space-borne remote sensing system.

Design and testing of the MIDAS spaceflight instrument

Several applications of high temperature superconductor technology have been identified for the National Aeronautics and Space Administrations (NASA) aerospace systems. However, validation of critical superconductive properties in the space environment is necessary before this technology can be inserted into satellite systems. Researchers at NASAs Langley Research Center have designed the Materials In Devices As Superconductors (MIDAS) experiment to evaluate the electrical characteristics of high temperature superconductive materials during extended spaceflight. The MIDAS experiment will evaluate four superconductive test circuits over a temperature range of 300 to 75 K. The MIDAS test circuit is produced by thick film printing and combines both superconductive and conventional electronics into a single, active microelectronics package designed to operate at cryogenic temperatures. All electrical measurements are performed directly on the test circuit, eliminating the need for intricate wiring and reducing thermal losses. This paper describes the design, fabrication, and testing of the primary subsystems of the MIDAS instrument.<<ETX>>

High-Tc thermal bridges for space-borne cryogenic infrared detectors

Abstract Several space-borne infrared detectors require cryogenic temperatures for successful operation. As a result, mission durations are substantially limited due to cryogen evaporation. The electrical leads connecting the detectors to the amplification electronics comprise a significant portion of the heat load on the dewar (i.e., 20% for some systems). Currently, manganin wires are used for these connections, due to the alloys low thermal conductivity at cryogenic temperatures. However, replacement of these leads within high Tc materials would result in a substantial reduction in thermal loss, translating into approximately 10–15% enhancement in mission lifetime. The potential for using the high-Tc materials as thermal bridges to replace the manganin connections is currently under investigation at NASA-LaRC.

Nonaqueous slip casting of YBa2Cu3O7−x ceramics

Abstract A ceramic casting process based on the fundamentals of slip casting has been developed to form high Tc superconductive ceramics. In this process, YBa 2 Cu 3 O 7−x powders ( μ m) dispersed in acetone are cast into foundry molds prepared by a lost wax process. After casting, the mold is peeled away from the superconductor, yielding a ceramic monolith in the shape of the mold. This work describes the casting process, as well as the result of a preliminary investigation into the use of magnetic fields to orient the YBa 2 Cu 3 O 7−x grains during the forming process.

Optimization of YBa/sub 2/Cu/sub 3/O/sub 7-x/ thick films on yttria stabilized zirconia substrates

This report describes the optimization of the firing process used in the production of YBa/sub 2/Cu/sub 3/O/sub 7-x/ thick films screen printed on yttria-stabilized zirconia substrates. The highest critical current density (J/sub c/) values were obtained by employing a double layer printing technique in which a single superconductive layer was printed onto a zirconia substrate and fired, followed by the subsequent deposition and firing of second superconductive layer. Using this procedure, thick film superconductors with a superconductive transition temperature (T/sub c/) of 85 K and a J/sub c/ of 130 A/cm/sup 2/ were obtained by sintering the printed films at 950/spl deg/C for 90 minutes, followed by a six hour oxygen annealing treatment at 600/spl deg/C. Specimens sintered for comparable periods of time at 940 and 960/spl deg/C did not exhibit superconductive behavior above 77 K due to either incomplete microstructural development or thermal decomposition of the superconductive phase respectively.<<ETX>>

Effects of process variables on the properties of YBa/sub 2/Cu/sub 3/O/sub 7-x/ ceramics formed by investment casting

An investment casting process has been developed to produce net-shape, superconducting ceramics. In this work, a factorial experiment was performed to determine the critical process parameters for producing cast YBa/sub 2/Cu/sub 3/O/sub 7/ ceramics with optimum properties. An analysis of variance procedure indicated that the key variables in casting superconductive ceramics are the particle size distribution and sintering temperature. Additionally, the interactions between the sintering temperature and the other process parameters (e.g. particle size distribution and the use of silver dopants) were also found to influence the density, porosity, and critical current density of the fired ceramics.<<ETX>>

Environmental Testing of High Tc Superconductive Thermal Isolators for Space-Borne Cryogenic Detector Systems

Thick films of superconductive material on low thermal conductivity substrates (e.g., yttria-stabilized zirconia and fused silica) are considered as a replacement for the existing electrical connections between the detector array and data acquisition and storage electronics in the cryogenic detector systems being developed by NASA. The paper describes some of the design constraints on the superconducting device and presents results of a preliminary analysis of the effects of vibration, gamma irradiation, and long-term exposure to high vacuum and liquid nitrogen encountered in operating such a device in space.

Environmental considerations for application of high Tc superconductors in space

Abstract High temperature superconductive materials can have significant impact in several space-based applications due to the improved electrical, magnetic, or thermal properties of the superconductive devices over existing components. However, for high temperature superconductors to be successfully applied in space-borne systems, several environmental considerations associated with spaceflight must first be addressed. The environmental factors encountered during spaceflight missions will be discussed, and a review of studies addressing the effects of these factors on the performance of the superconductive devices will be provided.