Space Shuttle Tail Service Mast Concept Verification

Design studies and analyses were performed to describe the loads and dynamics of the space shuttle tail service masts (TSMs). Of particular interest are the motion and interaction of the umbilical carrier plate, lanyard system, vacuum jacketed hoses, latches, links, and masthead. A development test rig was designed and fabricated to obtain experimental data. The test program is designed to (1) verify the theoretical dynamics calculations, (2) prove the soundness of design concepts, and (3) elucidate problem areas (if any) in the design of mechanisms and structural components. Design, fabrication, and initiation of TSM development testing at Kennedy Space Center are described

Design and Development of the Space Shuttle Tail Service Masts

The successful launch of a space shuttle vehicle depends on the proper operation of two tail service masts (TSMs). Reliable TSM operation is assured through a comprehensive design, development, and testing program. The results of the concept verification test (CVT) and the resulting impact on prototype TSM design are presented. The design criteria are outlined, and the proposed prototype TSM tests are described

Alcohol Fuel Cells at Optimal Temperatures

High-power-density alcohol fuel cells can relieve many of the daunting challenges facing a hydrogen energy economy. Here, such fuel cells are achieved using CsH2PO4 as the electrolyte and integrating into the anode chamber a Cu-ZnO/Al2O3 methanol steam-reforming catalyst. The temperature of operation, ~250°C, is matched both to the optimal value for fuel cell power output and for reforming. Peak power densities using methanol and ethanol were 226 and 100 mW/cm^2, respectively. The high power output (305 mW/cm^2) obtained from reformate fuel containing 1% CO demonstrates the potential of this approach with optimized reforming catalysts and also the tolerance to CO poisoning at these elevated temperatures

Solid acid proton conductors: from laboratory curiosities to fuel cell electrolytes

The compound CsH2PO4 has emerged as a viable electrolyte for intermediate temperature (200–300 °C) fuel cells. In order to settle the question of the high temperature behavior of this material, conductivity measurements were performed by two-point AC impedance spectroscopy under humidified conditions (p[H2O] = 0.4 atm). A transition to a stable, high conductivity phase was observed at 230 °C, with the conductivity rising to a value of 2.2 × 10^–2 S cm^–1 at 240 °C and the activation energy of proton transport dropping to 0.42 eV. In the absence of active humidification, dehydration of CsH2PO4 does indeed occur, but, in contradiction to some suggestions in the literature, the dehydration process is not responsible for the high conductivity at this temperature. Electrochemical characterization by galvanostatic current interrupt (GCI) methods and three-point AC impedance spectroscopy (under uniform, humidified gases) of CsH2PO4 based fuel cells, in which a composite mixture of the electrolyte, Pt supported on carbon, Pt black and carbon black served as the electrodes, showed that the overpotential for hydrogen electrooxidation was virtually immeasurable. The overpotential for oxygen electroreduction, however, was found to be on the order of 100 mV at 100 mA cm^–2. Thus, for fuel cells in which the supported electrolyte membrane was only 25 µm in thickness and in which a peak power density of 415 mW cm^–2 was achieved, the majority of the overpotential was found to be due to the slow rate of oxygen electrocatalysis. While the much faster kinetics at the anode over those at the cathode are not surprising, the result indicates that enhancing power output beyond the present levels will require improving cathode properties rather than further lowering the electrolyte thickness. In addition to the characterization of the transport and electrochemical properties of CsH2PO4, a discussion of the entropy of the superprotonic transition and the implications for proton transport is presented

Monitoring of tritium purity during long-term circulation in the KATRIN test experiment LOOPINO using laser Raman spectroscopy

The gas circulation loop LOOPINO has been set up and commissioned at Tritium Laboratory Karlsruhe (TLK) to perform Raman measurements of circulating tritium mixtures under conditions similar to the inner loop system of the neutrino-mass experiment KATRIN, which is currently under construction. A custom-made interface is used to connect the tritium containing measurement cell, located inside a glove box, with the Raman setup standing on the outside. A tritium sample (purity > 95%, 20 kPa total pressure) was circulated in LOOPINO for more than three weeks with a total throughput of 770 g of tritium. Compositional changes in the sample and the formation of tritiated and deuterated methanes CT_(4-n)X_n (X=H,D; n=0,1) were observed. Both effects are caused by hydrogen isotope exchange reactions and gas-wall interactions, due to tritium {\beta} decay. A precision of 0.1% was achieved for the monitoring of the T_2 Q_1-branch, which fulfills the requirements for the KATRIN experiment and demonstrates the feasibility of high-precision Raman measurements with tritium inside a glove box

Experimental and guided theoretical investigation of complex reaction mechanisms in a prins reaction of glyoxylic acid and isobutene

(Chemical Equation Presented) A laboratory experiment was designed for undergraduate students, in which the outcome of an easy single-step organic synthesis with well-defined conditions was not elucidated until the end of the exercise. In class, students predict and discuss the possible products using their knowledge of reaction mechanisms. In the laboratory, they learn how to carry out a reaction safely with gaseous isobutene, and to isolate and identify the two main products. The class and the laboratory components are completed in 10 h, including laboratory time of 6 to 7 h, divided in two sessions. The class-component could also be implemented independently as a theoretical exercise in a "virtual experiment" simply by presenting the methods and results to students using a guided-inquiry approach, appropriate for a standard 3 h undergraduate class. The finding that the simple reaction leads to a largely unexpected product, together with open discussions with students covering several theoretical aspects applicable to this reaction, helps to promote critical thinking and to provide an effective educational tool to better understand the process of scientific research in chemistry

A Monte Carlo Simulation Describing Melting Transition of Si-Type Structure in the Condensed Phase with BCC Lattice Model Including Many-Body Interactions

A new lattice model is proposed for Si crystallization from molten state, which is based on Monte Carlo (MC) simulation. In this model, each atom is allowed to move only on BCC lattice sites, and the potential energy of atom depends on the configuration in the 1st nearest neighbors. With the parameter that only the atoms constructing tetrahedron have lower energy than others, the 1st-order phase transition between diamond and random structures is observed, including a hysteresis behavior. On the other hand, with using a parameter set which is defined as a function of the number of the 1st nearest neighbors and the bond angles, which is determined by using genetic algorithm, the state is continuously changed with temperature

Boron-oxygen defect in Czochralski-silicon co-doped with gallium and boron

We study the boron-oxygen defect in Si co-doped with gallium and boron with the hole density 10 times higher than the boron concentration. Instead of the linear dependence of the defect density on the hole density observed in boron and phosphorus compensated silicon, we find a proportionality to the boron concentration. This indicates the participation of substitutional, rather than interstitial,boron in the defect complex. The measured defectformationrate constant is proportional to the hole density squared, which gives credit to latent defect models against defectreactions limited by the diffusion and trapping of oxygen dimers by boron atoms