A feasibility study of a hypersonic real-gas facility

A four month feasibility study of a hypersonic real-gas free flight test facility for NASA Langley Research Center (LARC) was performed. The feasibility of using a high-energy electromagnetic launcher (EML) to accelerate complex models (lifting and nonlifting) in the hypersonic, real-gas facility was examined. Issues addressed include: design and performance of the accelerator; design and performance of the power supply; design and operation of the sabot and payload during acceleration and separation; effects of high current, magnetic fields, temperature, and stress on the sabot and payload; and survivability of payload instrumentation during acceleration, flight, and soft catch

Homopolar generator power supply system

A high-energy, high-current homopolar generator pulsed power supply system that is compact and field portable. The power supply system includes a hompolar generator (HPG), an auxiliary supply and drive system, both mounted on a skid frame, and a control system coupled to the HPG and drive system. The homopolar generator has a split rotor with insulation between the halves and a recess in the periphery. A stator ring and field coil, for producing a magnetic field through which the rotor halves make two simultaneous voltage-generating passes, are disposed within the recess in the rotor. Air-actuated brush mechanisms inside and outside the recess contact surfaces of the rotor and collect discharge current. The auxiliary supply and drive system includes a motoring system comprising hydraulic motors for driving the HPG to speed, a bearing lubrication system, a generator for energizing the field coil, and a brush actuator air supply system, all of which are driven by a prime mover. The control system comprises a logic controller for executing a prescribed sequence of steps including turning on the prime mover, initiating motoring of the HPG, energizing the field coil, and initiating the discharge of electrical current.Board of Regents, University of Texas Syste

Reinforced composite flywheels and shafts

The maximum safe operating speed or flywheels and shafts made of low tensile strength material is often determined by the speed at which radial tensile stress exceeds a radial tensile stress limit for the material. Circumferentially wound fiber composite material, for example, has a relatively low tensile strength along the radial direction perpendicular to the fibers. To increase the maximum safe operating speed, it is therefore desirable to form a fiber composite flywheel or shaft with radial compressive prestress. Such a prestressed flywheel or shaft has an outer annulus and an inner cylinder disposed in the outer annulus, and an annular layer of solidified bonding agent within an annular region between the outer annulus and the inner cylinder, wherein the outer annulus and the inner cylinder include substantial radial prestress induced by the bonding agent. The rim portion of a flywheel, for example, is formed from an outer ring (the annulus) and an inner ring (the cylinder, which is hollow in this case). Large, thick flywheels preferably have multiple cylindrical sections joined by such layers of bonding agent, and a plurality of the cylindrical sections each including an outer layer of relatively stiff fiber-composite material, and an inner layer of relatively compliant fiber-composite material within an integral matrix material.Board of Regents, University of Texas Syste

Effect of Temperature on Wear Rate of Homopolar Pulse Consolidated Electrical Brush

Binderless copper-graphite composite electrical brushes are being developed using a high-energy, high-rate pulse sintering technique by the Center for Electromechanics at The University of Texas at Austin (CEM-UT). Experiments were done to investigate temperature's effect on the homopolar pulse consolidated (HPC) brush wear rate for an apparent brush current density of 180 A cm−2, a brush downforce of 44.5 N, and rotor surface sliding speeds of 10 m s−1 and 40 m s−1. At a sliding speed of 10 m s−1, it was found that brush wear rate dropped steeply as the brush bulk temperature increased from 80 °C to 103 °C. Other than this unusual wear finding in this particular sliding speed and temperature range, test results indicated that brush wear rate generally increased with increasing brush bulk temperature. At a sliding speed of 40 m s−1, it was found that brush wear rate suddenly increased by several times as the brush bulk temperature approached 149 °C. In the case of 10 m s−1 sliding speed, no stepwise rise in brush wear rate was observed even as the brush bulk temperature reached 156 °C.Center for Electromechanic

NIRCam: Development and Testing of the JWST Near-Infrared Camera

The Near Infrared Camera (NIRCam) is one of the four science instruments of the James Webb Space Telescope (JWST). Its high sensitivity, high spatial resolution images over the 0.6 - 5 microns wavelength region will be essential for making significant findings in many science areas as well as for aligning the JWST primary mirror segments and telescope. The NIRCam engineering test unit was recently assembled and has undergone successful cryogenic testing. The NIRCam collimator and camera optics and their mountings are also progressing, with a brass-board system demonstrating relatively low wavefront error across a wide field of view. The flight model?s long-wavelength Si grisms have been fabricated, and its coronagraph masks are now being made. Both the short (0.6 - 2.3 microns) and long (2.4 - 5.0 microns) wavelength flight detectors show good performance and are undergoing final assembly and testing. The flight model subsystems should all be completed later this year through early 2011, and NIRCam will be cryogenically tested in the first half of 2011 before delivery to the JWST integrated science instrument module (ISIM)

A homogenization study of the effects of cycling on the electronic conductivity of commercial lithium-ion battery cathodes

State-of-the-art image acquisition, image analysis, and modern homogenization theory are used to study the effects of cycling on commercial lithium-ion battery cathodes’ ability to conduct electronic current. This framework allows for a rigorous computation of an effective, or macroscale, electronic conductivity given an arbitrarily complicated three-dimensional microstructure comprised of three different material phases, i.e., active material, binder (polymer mixed with conductive carbon black), and electrolyte. The approach explicitly takes into account the geometry and is thus a vast improvement over the commonly used Bruggeman approximation. We apply our framework to two different types of lithium-ion battery cathodes before and after cycling. This leads us to predict an appreciable decrease in the effective electronic conductivity as a direct result of cycling. In addition, we present an ad-hoc “neighbor counting” methodology which meaningfully quantifies the effect of binder detaching from the surface of the active material due to the internal mechanical stresses experienced under operating conditions, thereby supporting the results of the homogenization calculations

Spin states of asteroids in the Eos collisional family

Eos family was created during a catastrophic impact about 1.3 Gyr ago. Rotation states of individual family members contain information about the history of the whole population. We aim to increase the number of asteroid shape models and rotation states within the Eos collision family, as well as to revise previously published shape models from the literature. Such results can be used to constrain theoretical collisional and evolution models of the family, or to estimate other physical parameters by a thermophysical modeling of the thermal infrared data. We use all available disk-integrated optical data (i.e., classical dense-in-time photometry obtained from public databases and through a large collaboration network as well as sparse-in-time individual measurements from a few sky surveys) as input for the convex inversion method, and derive 3D shape models of asteroids together with their rotation periods and orientations of rotation axes. We present updated shape models for 15 asteroids and new shape model determinations for 16 asteroids. Together with the already published models from the publicly available DAMIT database, we compiled a sample of 56 Eos family members with known shape models that we used in our analysis of physical properties within the family. Rotation states of asteroids smaller than ~20 km are heavily influenced by the YORP effect, whilst the large objects more or less retained their rotation state properties since the family creation. Moreover, we also present a shape model and bulk density of asteroid (423) Diotima, an interloper in the Eos family, based on the disk-resolved data obtained by the Near InfraRed Camera (Nirc2) mounted on the W.M. Keck II telescope.Comment: Accepted for publication in ICARUS Special Issue - Asteroids: Origin, Evolution & Characterizatio

High performance electromagnetic railgun launcher

A railgun operates at high pressure (up to 350 MPa) without structural damage and is readily disassembled for inspection, maintenance and component testing. A rail assembly is pressed into a hoop-wound epoxy fiberglass containment tube and clamped within a steel compression frame. The geometry of the rail assembly permits rail movement without insulator intrusion and achieves bore sealing during rail movement at maximum pressure. The rail assembly also has replaceable insulator inserts which are isolated from rail re-bound shock. Fused quartz insulator inserts provide the best results. A flash tube is provided at the gun muzzle to suppress precursor discharge and commutate precursor current back to the armature. To realize increased velocity without sacrificing in-bore projectile stability, a cut-corner projectile is used having a L/D ratio as small as 0.65 which reduces the mass by about 11%.Board of Regents, University of Texas Syste

Observation of anomalous spin-state segregation in a trapped ultra-cold vapor

We observe counter-intuitive spin segregation in an inhomogeneous sample of ultra-cold, non-condensed Rubidium atoms in a magnetic trap. We use spatially selective microwave spectroscopy to verify a model that accounts for the differential forces on two internal spin states. In any simple understanding of the cloud dynamics, the forces are far too small to account for the dramatic transient spin polarizations observed. The underlying mechanism remains to be elucidated.Comment: 5 pages, 3 figure

Internal state conversion in ultracold gases

We consider an ultracold gas of (non-condensed) bosons or fermions with two internal states, and study the effect of a gradient of the transition frequency between these states. When a $\pi/2$ RF pulse is applied to the sample, exchange effects during collisions transfer the atoms into internal states which depend on the direction of their velocity. This results, after a short time, in a spatial separation between the two states. A kinetic equation is solved analytically and numerically; the results agree well with the recent observations of Lewandowski et al.Comment: Accepted version, to appear in PR