Static Feed Water Electrolysis Subsystem Testing and Component Development

A program was carried out to develop and test advanced electrochemical cells/modules and critical electromechanical components for a static feed (alkaline electrolyte) water electrolysis oxygen generation subsystem. The accomplishments were refurbishment of a previously developed subsystem and successful demonstration for a total of 2980 hours of normal operation; achievement of sustained one-person level oxygen generation performance with state-of-the-art cell voltages averaging 1.61 V at 191 ASF for an operating temperature of 128F (equivalent to 1.51V when normalized to 180F); endurance testing and demonstration of reliable performance of the three-fluid pressure controller for 8650 hours; design and development of a fluid control assembly for this subsystem and demonstration of its performance; development and demonstration at the single cell and module levels of a unitized core composite cell that provides expanded differential pressure tolerance capability; fabrication and evaluation of a feed water electrolyte elimination five-cell module; and successful demonstration of an electrolysis module pressurization technique that can be used in place of nitrogen gas during the standby mode of operation to maintain system pressure and differential pressures

Advanced electrochemical depolarized concentrator cell development

An advanced electrochemical depolarized carbon dioxide concentrator subsystem, to collect and concentrate metabolically produced CO2 for subsequent O2 recovery in spacecraft, is discussed

Investigation of the vibration isolation of commercial jet transport pilots during turbulent air penetration

Electrohydraulic pilot seat isolation system of commercial transport pilots during turbulent air penetratio

Weak Localization Thickness Measurements of Si:P Delta-Layers

We report on our results for the characterization of Si:P delta-layers grown by low temperature molecular beam epitaxy. Our data shows that the effective thickness of a delta-layer can be obtained through a weak localization analysis of electrical transport measurements performed in perpendicular and parallel magnetic fields. An estimate of the diffusivity of phosphorous in silicon is obtained by applying this method to several samples annealed at 850 Celsius for intervals of zero to 15 minutes. With further refinements, this may prove to be the most precise method of measuring delta-layer widths developed to date, including that of Secondary Ion Mass Spectrometry analysis

Anomalous magnetoresistance peak in (110) GaAs two-dimensional holes: Evidence for Landau-level spin-index anticrossings

We measure an anomalous magnetoresistance peak within the lowest Landau level (nu = 1) minimum of a two-dimensional hole system on (110) GaAs. Self-consistent calculations of the valence band mixing show that the two lowest spin-index Landau levels anticross in a perpendicular magnetic field B consistent with where the experimental peak is measured, Bp. The temperature dependence of the anomalous peak height is interpreted as an activated behavior across this anticrossing gap. Calculations of the spin polarization in the lowest Landau levels predict a rapid switch from about -3/2 to +3/2 spin at the anticrossing. The peak position Bp is shown to be affected by the confinement electrostatics, and the utility of a tunable anticrossing position for spintronics applications is discussed.Comment: 4 pages, 4 figure

Triple redundant hydrogen sensor with in situ calibration

To meet sensing and calibration needs, an in situ calibration technique was developed. It is based on electrolytic generation of a hydrogen/air atmosphere within a hydrogen sensor. The hydrogen is generated from water vapor in the air, and being electrical in nature, the in situ calibration can be performed completely automatically in remote locations. Triply redundant sensor elements are integrated within a single, compact housing, and digital logic provides inter-sensor comparisons to warn of and identify malfunctioning sensor elements. An evaluation of this concept is presented

Scattering Mechanisms in a High Mobility Low Density Carbon-Doped (100) GaAs Two-Dimensional Hole System

We report on a systematic study of the density dependence of mobility in a low-density Carbon-doped (100) GaAs two-dimensional hole system (2DHS). At T= 50 mK, a mobility of 2.6 x 10^6 cm^2/Vs at a density p=6.2 x 10^10 cm^- was measured. This is the highest mobility reported for a 2DHS to date. Using a back-gated sample geometry, the density dependence of mobility was studied from 2.8 x 10^10 cm^-2 to 1 x 10^11 cm^-2. The mobility vs. density cannot be fit to a power law dependence of the form mu ~ p^alpha using a single exponent alpha. Our data indicate a continuous evolution of the power law with alpha ranging from ~ 0.7 at high density and increasing to ~ 1.7 at the lowest densities measured. Calculations specific to our structure indicate a crossover of the dominant scattering mechanism from uniform background impurity scattering at high density to remote ionized impurity scattering at low densities. This is the first observation of a carrier density-induced transition from background impurity dominated to remote dopant dominated transport in a single sample.Comment: 4 pages, 5 figures, prepared with LaTex2

Other Challenges in the Development of the Orbiter Environmental Control Hardware

Development of the Space Shuttle orbiter environmental control and life support system (ECLSS) included the identification and resolution of several interesting problems in several systems. Some of these problems occurred late in the program, including the flight phase. Problems and solutions related to the ammonia boiler system (ABS), smoke detector, water/hydrogen separator, and waste collector system (WCS) are addressed