Quick actuating closure and handling system

A quick activating closure and handling system, which utilizes conical sections for locking, was developed to allow quick access to the combustor internal components of the 8 ft High Temperature Tunnel. These critical components include the existing methane spraybar, a transpiration cooled nozzle and the new liquid oxygen (LOX) injection system housed within the combustor. A substantial cost savings will be realized once the mechanism is installed since it will substantially reduce the access time and increase the time available for conducting wind tunnel tests. A need exists for more frequent inspections when the wind tunnel operates at the more severe conditions generated by using LOX in the combustor. A loads analysis and a structural (finite element) analysis were conducted to verify that the new closure system is compatible with the existing pressure shell. In addition, strain gages were placed on the pressure vessel to verify how the pressure shell reacts to transient pressure loads. A scale model of the new closure system was built to verify the operation of the conical sections in the locking mechanisms

Initial Validation of Robotic Operations for In-Space Assembly of a Large Solar Electric Propulsion Transport Vehicle

Developing a capability for the assembly of large space structures has the potential to increase the capabilities and performance of future space missions and spacecraft while reducing their cost. One such application is a megawatt-class solar electric propulsion (SEP) tug, representing a critical transportation ability for the NASA lunar, Mars, and solar system exploration missions. A series of robotic assembly experiments were recently completed at Langley Research Center (LaRC) that demonstrate most of the assembly steps for the SEP tug concept. The assembly experiments used a core set of robotic capabilities: long-reach manipulation and dexterous manipulation. This paper describes cross-cutting capabilities and technologies for in-space assembly (ISA), applies the ISA approach to a SEP tug, describes the design and development of two assembly demonstration concepts, and summarizes results of two sets of assembly experiments that validate the SEP tug assembly steps

Tendon-Actuated Lightweight In-Space MANipulator (TALISMAN)

The robotic architecture of State-of-the-Art (SOA) space manipulators, represented by the Shuttle Remote Manipulator System (SRMS), inherently limits their capabilities to extend reach, reduce mass, apply force and package efficiently. TALISMAN uses a new and innovative robotic architecture that incorporates a combination of lightweight truss links, a novel hinge joint, tendon-articulation and passive tension stiffening to achieve revolutionary performance. A TALISMAN with performance similar to the SRMS has 1/10th of its mass and packages in 1/7th of its volume. The TALISMAN architecture allows its reach to be scaled over a large range; from 10 to over 300 meters. In addition, the dexterity (number of degrees-of-freedom) can be easily adjusted without significantly impacting manipulator mass because the joints are very lightweight

Deployable-erectable trade study for space station truss structures

The results of a trade study on truss structures for constructing the space station are presented. Although this study was conducted for the reference gravity gradient space station, the results are generally applicable to other configurations. The four truss approaches for constructing the space station considered in this paper were the 9 foot single fold deployable, the 15 foot erectable, the 10 foot double fold tetrahedral, and the 15 foot PACTRUSS. The primary rational for considering a 9 foot single-fold deployable truss (9 foot is the largest uncollapsed cross-section that will fit in the Shuttle cargo bay) is that of ease of initial on-orbit construction and preintegration of utility lines and subsystems. The primary rational for considering the 15 foot erectable truss is that the truss bay size will accommodate Shuttle size payloads and growth of the initial station in any dimension is a simple extension of the initial construction process. The primary rational for considering the double-fold 10 foot tetrahedral truss is that a relatively large amount of truss structure can be deployed from a single Shuttle flight to provide a large number of nodal attachments which present a pegboard for attaching a wide variety of payloads. The 15 foot double-fold PACTRUSS was developed to incorporate the best features of the erectable truss and the tetrahedral truss

Expression vectors for Neurospora crassa and expression of a bovine preprochymosin cDNA

The filamentous fungi, owing to their ability to secrete high levels of proteins, are attractive organisms for the expression and secretion of heterologous proteins of commercial and medical value. We report the construction of three expression vectors for the production of heterologous proteins in Neurospora crassa and demonstrate their utility by expression of a bovine preprochymosin cDNA and secretion of processed, enzymatically active bovine chymosin

Solitons on the edge of a two-dimensional electron system

We present a study of the excitations of the edge of a two-dimensional electron droplet in a magnetic field in terms of a contour dynamics formalism. We find that, beyond the usual linear approximation, the non-linear analysis yields soliton solutions which correspond to uniformly rotating shapes. These modes are found from a perturbative treatment of a non-linear eigenvalue problem, and as solutions to a modified Korteweg-de Vries equation resulting from a local induction approximation to the nonlocal contour dynamics. We discuss applications to the edge modes in the quantum Hall effect.Comment: 4 pages, 2 eps figures (included); to appear in Phys. Rev. Letter

Scaling Relations of Viscous Fingers in Anisotropic Hele-Shaw Cells

Viscous fingers in a channel with surface tension anisotropy are numerically studied. Scaling relations between the tip velocity v, the tip radius and the pressure gradient are investigated for two kinds of boundary conditions of pressure, when v is sufficiently large. The power-law relations for the anisotropic viscous fingers are compared with two-dimensional dendritic growth. The exponents of the power-law relations are theoretically evaluated.Comment: 5 pages, 4 figure

Nucleation and Growth of the Superconducting Phase in the Presence of a Current

We study the localized stationary solutions of the one-dimensional time-dependent Ginzburg-Landau equations in the presence of a current. These threshold perturbations separate undercritical perturbations which return to the normal phase from overcritical perturbations which lead to the superconducting phase. Careful numerical work in the small-current limit shows that the amplitude of these solutions is exponentially small in the current; we provide an approximate analysis which captures this behavior. As the current is increased toward the stall current J*, the width of these solutions diverges resulting in widely separated normal-superconducting interfaces. We map out numerically the dependence of J* on u (a parameter characterizing the material) and use asymptotic analysis to derive the behaviors for large u (J* ~ u^-1/4) and small u (J -> J_c, the critical deparing current), which agree with the numerical work in these regimes. For currents other than J* the interface moves, and in this case we study the interface velocity as a function of u and J. We find that the velocities are bounded both as J -> 0 and as J -> J_c, contrary to previous claims.Comment: 13 pages, 10 figures, Revte

Composite vortex model of the electrodynamics of high-TcT_c superconductor

We propose a phenomenological model of vortex dynamics in which the vortex is taken as a composite object made of two components: the vortex current which is massless and driven by the Lorentz force, and the vortex core which is massive and driven by the Magnus force. By combining the characteristics of the Gittleman-Rosenblum model (Phys. Rev. Lett. {\bf 16}, 734 (1966)) and Hsu's theory of vortex dynamics (Physica {\bf C 213},305 (1993)), the model provides a good description of recent far infrared measurements of the magneto-conductivity tensor of superconducting YBa$_2$Cu$_3$O$_{7-\delta }$ films from 5 cm$^{-1}$ to 200 cm$^{-1}$.Comment: LaTex file (12 pages) + 3 Postscript figures, uuencoded. More information on this paper, please check http://www.wam.umd.edu/~lihn/newmodel

Travelling waves in a drifting flux lattice

Starting from the time-dependent Ginzburg-Landau (TDGL) equations for a type II superconductor, we derive the equations of motion for the displacement field of a moving vortex lattice without inertia or pinning. We show that it is linearly stable and, surprisingly, that it supports wavelike long-wavelength excitations arising not from inertia or elasticity but from the strain-dependent mobility of the moving lattice. It should be possible to image these waves, whose speeds are a few \mu m/s, using fast scanning tunnelling microscopy.Comment: 4 pages, revtex, 2 .eps figures imbedded in paper, title shortened, minor textual change