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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS2004

Acoustic Modeling and Analysis for the Space Shuttle Main Propulsion System Liner Crack Investigation

Cracks were found on bellows flow liners in the liquid hydrogen feedlines of several space shuttle orbiters in 2002. An effort to characterize the fluid environment upstream of the space shuttle main engine low-pressure fuel pump was undertaken to help identify the cause of the cracks and also provide quantitative environments and loads of the region. Part of this effort was to determine the duct acoustics several inches upstream of the low-pressure fuel pump in the region of a bellows joint. A finite element model of the complicated geometry was made using three-dimensional fluid elements. The model was used to describe acoustics in the complex geometry and played an important role in the investigation. Acoustic mode shapes and natural frequencies of the liquid hydrogen in the duct and in the cavity behind the flow liner were determined. Forced response results were generated also by applying an edgetone-like forcing to the liner slots. Studies were conducted for state conditions and also conditions assuming two-phase entrapment in the backing cavity. Highly instrumented single-engine hot fire data confirms the presence of some of the predicted acoustic modes.

Casiano, Matthew J.↗
NASA NTRS1978

Non-thermal hydrogen in the Venus exosphere - The ionospheric source and the hydrogen budget

A nonthermal, or 'hot', Venus corona of H atoms has been observed by Mariners 5 and 10 and Venera 9. Of the sources investigated, reaction of H2 with ionospheric O(+) is still the strongest. It can explain the smaller densities but falls somewhat short of the largest (from Mariner 5). The subsequent recombination of OH(+), supplemented by solar-wind processes, may give an escape flux of 10 million atoms per sq cm/s. The low density of thermal H atoms on the day side has previously been attributed to either a large eddy diffusion coefficient or an escape flux tenfold greater than this. An alternative mechanism, suggested by Hartle and Mayr (1977) is supported: the hydrogen is swept to the night side by strong thermospheric winds. This process is analogous to the 'Johnson pump' for the terrestrial winter helium bulge. Large nightside bulges of H and H2 are predicted; the night/day density ratio is estimated to be as large as 100 for each.

Kumar, S.↗
NASA NTRS1991

GC/MS Gas Separator Operates At Lower Temperatures

Experiments show palladium/silver tube used to separate hydrogen carrier gas from gases being analyzed in gas-chromatography/mass-spectrometry (GC/MS) system functions satisfactorily at temperatures as low as 70 to 100 degrees C. Less power consumed, and catalytic hydrogenation of compounds being analyzed diminished. Because separation efficiency high even at lower temperatures, gas load on vacuum pump of mass spectrometer kept low, permitting use of smaller pump. These features facilitate development of relatively small, lightweight, portable GC/MS system for such uses as measuring concentrations of pollutants in field.

Sinha, Mahadeva P.↗
NASA NTRS1959

Analytical Investigation of the Effect of Turbopump Design on Gross-Weight Characteristics of a Hydrogen-Propelled Nuclear Rocket

The effect of turbopump design on rocket gross weight was investigated for a high-pressure bleed-type hydrogen-reactor long-range rocket with a fixed mission. Axial-flow, mixed-flow, and centrifugal pumps driven by single and twin turbines were considered. With an efficiency of 0.7 assumed for all pumps, the lowest rocket gross weights were obtained with an axial-flow or a mixed-flow pump driven by a single turbine of at least eight stages. All turbopump combinations could be used, however, with gross weight varying less than 8 percent for a given payload. Turbopump efficiencies have a significant effect on the ratio of gross weight to payload with the magnitude of the effect determined by the ratio of rocket structural weight to total propellant weight. One point in pump efficiency is worth 0.2 percent in gross weight for a given payload with a structural weight parameter of 0.1 and 0.6 percent with a structural weight parameter of 0.2. Turbine and pump weights are much less significant in terms of gross-to-pay weight ratio than the efficiencies of these components. One point in pump efficiency is equivalent to approximately 13 percent in pump weight, while 1 point in turbine efficiency is equivalent to about 7 percent in turbine weight.

Rohlik, Harold E.↗
NASA NTRS1992

Pathways of proton release in the bacteriorhodopsin photocycle

The pH dependencies of the rate constants in the photocycles of recombinant D96N and D115N/D96N bacteriorhodopsins were determined from time-resolved difference spectra between 70 ns and 420 ms after photoexcitation. The results were consistent with the model suggested earlier for proteins containing D96N substitution: BR hv----K----L----M1----M2----BR. Only the M2----M1 back-reaction was pH-dependent: its rate increased with increasing [H+] between pH 5 and 8. We conclude from quantitative analysis of this pH dependency that its reverse, the M1----M2 reaction, is linked to the release of a proton from a group with a pKa = 5.8. This suggests a model for wild-type bacteriorhodopsin in which at pH greater than 5.8 the transported proton is released on the extracellular side from this as yet unknown group and on the 100-microseconds time scale, but at pH less than 5.8, the proton release occurs from another residue and later in the photocycle most likely directly from D85 during the O----BR reaction. We postulate, on the other hand, that proton uptake on the cytoplasmic side will be by D96 and during the N----O reaction regardless of pH. The proton kinetics as measured with indicator dyes confirmed the unique prediction of this model: at pH greater than 6, proton release preceded proton uptake, but at pH less than 6, the release was delayed until after the uptake. The results indicated further that the overall M1----M2 reaction includes a second kinetic step in addition to proton release; this is probably the earlier postulated extracellular-to-cytoplasmic reorientation switch in the proton pump.

NASA Discipline Exobiology↗
NASA NTRS2008

Neon as a Buffer Gas for a Mercury-Ion Clock

A developmental miniature mercury-ion clock has stability comparable to that of a hydrogen-maser clock. The ion-handling components are housed in a sealed vacuum tube, wherein a getter pump is used to maintain the partial vacuum, and the evacuated tube is backfilled with mercury vapor in a buffer gas. Neon was determined to be the best choice for the buffer gas: The pressure-induced frequency pulling by neon was found to be only about two-fifths of that of helium. Furthermore, because neon diffuses through solids much more slowly than does helium, the operational lifetime of a tube backfilled with neon could be considerably longer than that of a tube backfilled with helium.

Prestage, John↗
NASA NTRS2009

Progress Toward a Compact, Highly Stable Ion Clock

There was an update on the subject of two previous NASA Tech Briefs articles: Compact, Highly Stable Ion Clock (NPO-43075), Vol. 32, No. 5 (May 2008), page 63; and Neon as a Buffer Gas for a Mercury-Ion Clock (NPO-42919), Vol. 32, No. 7 (July 2008), page 62. To recapitulate: A developmental miniature mercury-ion clock has stability comparable to that of a hydrogen-maser clock. The ion-handling components are housed in a sealed vacuum tube, wherein a getter pump maintains the partial vacuum, and the evacuated tube is backfilled with mercury vapor in a neon buffer gas. There was progress in the development of the clock, with emphasis on the design, fabrication, pump-down, and bake-out of the vacuum tube (based on established practice in the travelingwave- tube-amplifier industry) and the ability of the tube to retain a vacuum after a year of operation. Other developments include some aspects of the operation of mercury-vapor source (a small appendage oven containing HgO) so as to maintain the optimum low concentration of mercury vapor, and further efforts to miniaturize the vacuum and optical subsystems to fit within a volume of 2 L.

Prestage, John↗
NASA NTRSDate not supplied

Experimental Results of a Rapidly Cycled Temperature Swing Adsorption Pump in a Terrestrial Environment

To improve the increasing CO 2 levels on Earth, technology for carbon capture and utilization must be efficient and cost effective. One major contributor of atmospheric CO 2 is post-combustion flue gas, which can contain up to 20% CO 2 . Scrubbing this CO 2 could reduce the environmental impact of this common industrial process. In off-Earth environments, capturing and utilizing CO 2 from space resources is useful for crewed spaceflight life support. Specifically, the Bosch process, which produces water and carbon powder by reacting CO 2 and hydrogen, is a possible in-situ resource utilization (ISRU) architecture for the Moon and Mars. The Rapid Cycle Temperature Swing Adsorption (RC-TSA) pump is an innovative technology designed to capture CO 2 efficiently. The RC-TSA leverages a stacked plate geometry to cycle multiple zeolite-coated beds. The thin layers allow for rapid heat transfer of the zeolite coating, which improves performance over previously tested pump designs. The design is favorable for scalability and manufacturability, which are forward work. Initial testing of the sorption pump using a simulated flue gas environment shows favorable breakthrough capacities and reduced cycle times. Results show promise for on- and off-Earth applications, such as a Martian surface and crewed spaceflight environments.

adsorption pump↗
NASA NTRS1991

In-situ propellant rocket engines for Mars missions ascent vehicle

When contemplating the human exploration of Mars, many scenarios using various propulsion systems have been considered. One propulsion option among them is a vehicle stage with multiple, pump fed rocket engines capable of operating on propellants available on Mars. This reduces the earth launch mass requirements, resulting in economic and payload benefits. No plentiful sources of hydrogen on Mars have been identified on the surface of Mars, so most commonly used high performance liquid fuels, such as hydrogen and hydrocarbons, can be eliminated as possible in situ propellants. But 95 pct of the Martian atmosphere consists of carbon dioxide, which can be converted into carbon monoxide and oxygen. The carbon monoxide oxygen propellant combination is a candidate for a Martian in situ propellant rocket engine. The feasibility is analyzed of a pump fed engine cycle using the propellant combination of carbon monoxide and oxygen.

Roncace, Elizabeth A.↗
NASA NTRS1989

The winds of high luminosity late-type bright stars

The occurrence and characteristics of the Fe II line asymmetries were studied to determine the radial dependence of the wind velocity for each star. The dependence of the Fe II profiles on spectral type and luminosity class and thus the variation of the velocity fields with stellar type was also investigated. This allows the generality of the results reported for alpha Ori by Carpenter (1984b) to be judged. In addition, new atomic data was used along with observations of the C II (UV 0.01) multiplet to estimate N(sub e) in the stellar winds. Measures of relative Fe II fluxes can be used in a probability-of-escape model to determine the opacity and hydrogen column density versus height in the chromosphere of each star. Finally, analysis of the fluorescent Fe II lines (pumped by Ly alpha) near 2507 A will yield estimates of the intrinsic stellar Ly alpha flux that cannot be measured directly because of interstellar and circumstellar absorption. One important goal of the effort was to acquire high resolution spectra of the whole 2300 to 3200 A region of 13 luminous K and M stars as a data base that will be enormously valuable in planning observations with the Hubble Space Telescope High Resolution Spectrograph. It is also proposed to follow up the recent discovery of significant variations in the Fe II chromospheric emission line profiles from the M-giant Gamma Cru for the purpose of determining the underlying cause of the variations.

Stencel, Robert E.↗
NASA NTRS1992

Space Cryogenics Workshop, 10th, Cleveland, OH, June 18-20, 1991, Proceedings

The present workshop on cryogenics discusses the anomalous on-orbit behavior of the Cosmic Background Explorer Dewar, the SHOOT orbital operations, cooling options for Astromag, and space IR telescope facility mission and cryogenic design. Attention is given to the design of a spaceworthy adiabatic demagnetization refrigerator, the evaluation of metal hydride compressors for applications in Joule-Thomson cryocoolers, diaphragm Stirling cryocooler developments, and a computer simulation model for Stirling refrigerators. Topics addressed include low-gravity thermal stratification of liquid helium on SHOOT, a screening program to select a resin for gravity probe-B composites, a simplified generic cryostat thermal model for predicting cryogen mass and lifetime, and the effect of gas mass flux on cryogenic liquid jet breakup. Also discussed are damping criteria for thermal acoustic oscillations in slush and liquid hydrogen systems, an STS-based cryogenic fluid management experiment, and the design and testing of a cryogenic mixer pump.

Source record↗
NASA NTRS1993

Nuclear Engine System Simulation (NESS). Version 2.0: Program user's guide

This Program User's Guide discusses the Nuclear Thermal Propulsion (NTP) engine system design features and capabilities modeled in the Nuclear Engine System Simulation (NESS): Version 2.0 program (referred to as NESS throughout the remainder of this document), as well as its operation. NESS was upgraded to include many new modeling capabilities not available in the original version delivered to NASA LeRC in Dec. 1991, NESS's new features include the following: (1) an improved input format; (2) an advanced solid-core NERVA-type reactor system model (ENABLER 2); (3) a bleed-cycle engine system option; (4) an axial-turbopump design option; (5) an automated pump-out turbopump assembly sizing option; (6) an off-design gas generator engine cycle design option; (7) updated hydrogen properties; (8) an improved output format; and (9) personal computer operation capability. Sample design cases are presented in the user's guide that demonstrate many of the new features associated with this upgraded version of NESS, as well as design modeling features associated with the original version of NESS.

Pelaccio, Dennis G.↗
NASA NTRS1991

In-situ propellant rocket engines for Mars mission ascent vehicle

When comtemplating the human exploration of Mars, many scenarios using various propulsion systems have been considered. One propulsion option among them is a vehicle stage with multiple, pump fed rocket engines capable of operating on propellants available on Mars. This reduces the Earth launch mass requirements, resulting in economic and payload benefits. No plentiful sources of hydrogen on Mars have been identified on the surface of Mars, so most commonly used high performance liquid fuels, such as hydrogen and hydrocarbons, can be eliminated as possible in-situ propellants. But 95 pct. of the Martian atmosphere consists of carbon dioxide, which can be converted into carbon monoxide and oxygen. The carbon monoxide oxygen propellant conbination is a candidate for a Martian in-situ propellant rocket engine. The feasibility is analyzed of a pump fed engine cycle using the propellant combination of carbon monoxide and oxygen.

Roncace, Elizabeth A.↗
NASA NTRS1992

Orbital Transfer Vehicle Engine Technology High Velocity Ratio Diffusing Crossover

High speed, high efficiency head rise multistage pumps require continuous passage diffusing crossovers to effectively convey the pumped fluid from the exit of one impeller to the inlet of the next impeller. On Rocketdyne's Orbital Transfer Vehicle (OTV), the MK49-F, a three stage high pressure liquid hydrogen turbopump, utilizes a 6.23 velocity ratio diffusing crossover. This velocity ratio approaches the diffusion limits for stable and efficient flow over the operating conditions required by the OTV system. The design of the high velocity ratio diffusing crossover was based on advanced analytical techniques anchored by previous tests of stationary two-dimensional diffusers with steady flow. To secure the design and the analytical techniques, tests were required with the unsteady whirling characteristics produced by an impeller. A tester was designed and fabricated using a 2.85 times scale model of the MK49-F turbopumps first stage, including the inducer, impeller, and the diffusing crossover. Water and air tests were completed to evaluate the large scale turbulence, non-uniform velocity, and non-steady velocity on the pump and crossover head and efficiency. Suction performance tests from 80 percent to 124 percent of design flow were completed in water to assess these pump characteristics. Pump and diffuser performance from the water and air tests were compared with the actual MK49-F test data in liquid hydrogen.

Lariviere, Brian W.↗
NASA NTRS1988

Design optimization and testing of a pump wear ring labyrinth seal

It has been demonstrated that design optimization of labyrinth seals using the present numerical model is quite beneficial. The results shown include important, but previously unknown effects on the leakage rate, especially that of step height. Further, complete details are given of a very effective seal designed using this technique for the SSME high pressure hydrogen turbopump. Measurements using turbine flow meters revealed that the optimized configuration gives 67 percent leakage reduction over the original design. These measurements also reveal important leakage effects of the axial straining of the stator, which begins during pump start-up.

Rhode, D. L.↗
NASA NTRS1988

Characterization of a turbomolecular-pumped magnetic sector mass spectrometer

A Perkin Elmer MGA-1200, turbomolecular-pumped, magnetic sector, multiple gas analyzer mass spectrometer with modified inlet for fast response was characterized for the analysis of hydrogen, helium, oxygen and argon in nitrogen and helium background gases. This instrument was specially modified for the Vanderberg AFB SLC-6 Hydrogen Disposal Test Program, as a part of the Hydrogen Sampling System (H2S2). Linearity, precision, drift, detection limits and accuracy among other analytical parameters for each of the background gas were studied to evaluate the performance of the instrument. The result demonstrates that H2S2 mass spectrometer is a stable instrument and can be utilized for the quantitative analytical determination of hydrogen, helium, oxygen and argon in nitrogen and helium background gases.

Mehta, Narinder K.↗
NASA NTRS2007

Analyzing the Use of Gaseous Helium as a Pressurant with Cryogenic Propellants with Thermodynamic Venting System Modelling and Test Data

Cryogens are viable candidate propellants for NASA's Lunar and Mars exploration programs. To provide adequate mass flow to the system's engines and/or to prevent feed system cavitation, gaseous helium (GHe) is frequently considered as a pressurant. During low gravity operations, a Thermodynamic Venting System (TVS) is designed to maintain tank pressure during low gravity operations without propellant resettling. Therefore, a series of tests were conducted in the Multi-purpose Hydrogen Test Bed (MHTB) of Marshall Space Flight Center (MSFC) in order to evaluate the effects of GHe pressurant on pressure control performance of a TVS with liquid hydrogen (LH2) and nitrogen (LN2) as the test liquids. The TVS used in these test series consists of a recirculation pump, Joule-Thomson (J-T) expansion valve, and a parallel flow concentric tube heat exchanger combined with a longitudinal spray bar. Using a small amount of liquid extracted from the tank recirculation line, passing it through the J-T valve, and then through the heat exchanger, thermal energy is extracted from the bulk liquid and ullage thereby enabling pressure control. The LH2/GHe tests were performed at fill levels of 90%, 50%, and 25% and LN2/GHe tests were conducted at fill levels of 50% and 25%. Moreover, each test was conducted with a specified tank ullage pressure control band. A one-dimensional TVS performance program was used to analyze and correlate the test data. Predictions and comparisons with test data of ullage pressure and temperature and bulk liquid saturation pressure and temperature with test data are presented.

Hedayat, A.↗