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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 163 records · Page 9

All sources NASA NTRS DOE OSTI

NASA NTRS1982

Liquid helium management for Gravity Probe-B

The Gravity Probe-B (GP-B) experiment will be degraded if accelerations at a proof mass become larger than one ten billionth g. This makes necessary the management of the configuration and dynamical behavior of the large amount of liquid helium present in the GP-B spacecraft dewar. Three approaches to the solution of this problem are discussed. It is concluded that the most promising technique involves the use of baffles into which the liquid helium can be forced during a relatively high spacecraft rotation period, and in which the liquid helium will be held by capillary forces during the operational period when the rotation rate is much lower. Some likely baffle configurations are suggested.

Schafer, C. F.↗

NASA NTRS1996

Compensating For Friction In A Rotation-Testing Turntable

Proposed turntable for testing heavy equipment in rotation driven by two motors. One operates under actuator commands from position-control subsystem; rotates turntable to commanded angular positions according to specifications for test. Other operates under actuator commands from friction-compensating control subsystem; cancels effect of frictional torque in and on turntable, so equipment tested as though in nearly frictionless environment. Conceived for testing angular-positioning systems for spacecraft solar arrays weighing several tons; equally useful for effectively frictionless rotational testing of heavy terrestrial equipment.

Sullender, Craig C.↗

NASA NTRS2009

Windage Power Loss in Gas Foil Bearings and the Rotor-Stator Clearance of High Speed Generators Operating in High Pressure Environments

Closed Brayton Cycle (CBC) and Closed Supercritical Cycle (CSC) engines are prime candidates to convert heat from a reactor into electric power for robotic space exploration and habitation. These engine concepts incorporate a permanent magnet starter/generator mounted on the engine shaft along with the requisite turbomachinery. Successful completion of the long-duration missions currently anticipated for these engines will require designs that adequately address all losses within the machine. The preliminary thermal management concept for these engine types is to use the cycle working fluid to provide the required cooling. In addition to providing cooling, the working fluid will also serve as the bearing lubricant. Additional requirements, due to the unique application of these microturbines, are zero contamination of the working fluid and entirely maintenance-free operation for many years. Losses in the gas foil bearings and within the rotor-stator gap of the generator become increasingly important as both rotational speed and mean operating pressure are increased. This paper presents the results of an experimental study, which obtained direct torque measurements on gas foil bearings and generator rotor-stator gaps. Test conditions for these measurements included rotational speeds up to 42,000 revolutions per minute, pressures up to 45 atmospheres, and test gases of nitrogen, helium, and carbon dioxide. These conditions provided a maximum test Taylor number of nearly one million. The results show an exponential rise in power loss as mean operating density is increased for both the gas foil bearing and generator windage. These typical "secondary" losses can become larger than the total system output power if conventional design paradigms are followed. A nondimensional analysis is presented to extend the experimental results into the CSC range for the generator windage.

Bruckner, Robert J.↗

NASA NTRS1986

Multidisciplinary capability for analysis of the dynamics and control of flexible space structures

The paper describes a computerized data distribution capability, IMAT, in place at the NASA Langley Research Center for the multidisciplinary analysis of the dynamics and control of large flexible space structures. The paper includes results obtained in using IMAT to investigate the influence of the structural response of the space station framework on the control of a 300kw class, solar-dynamic-powered, dual-keel space station during an orbital reboost maneuver. The method of control, using an unfiltered proportional-plus-differential control law, led to a stable control system even with local flexible response measured at the control sensor location included as a part of the control error signal. The flexible response at the outboard solar dynamic system sun-line axis was close to the maximum rotation allowed for efficient operation; thus, active local control of each solar dynamic system may be necessary to limit sun-line axis rotations effectively during a reboost maneuver.

Cooper, P. A.↗

NASA NTRS1982

Clutchless multiple drive source for output shaft

A first shaft is connected to a source of rotational power and has a gear fixedly mounted on the shaft. A second gear is fixedly mounted on a gear shaft that is parallel to the first shaft. A third gear, also fixedly mounted on gear shaft, meshes with a fourth gear fixedly mounted on the output shaft. The first input shaft and output shaft are rotatably mounted through a housing that is itself rotatable with respect to a support. Both shafts are coaxial and in end-to-end relationship. A second input shaft is connected to a second source of rotational power. A fifth gear, fixedly mounted on second input shaft, meshes with a sixth gear, which is fixedly mounted on rotatable housing and in coaxial relationship with first input shaft. In operation, the first drive source and gear train provide rotational power in a first direction to drive the output shaft in a given direction of rotation. The second source of rotational power may be operated either to decrease the rate of rotation imparted to the output shaft by the first source of rotational power, or to increase that rate of rotation, depending on which direction the housing is rotated by the second source of rotational power.

Webster, L. D.↗

NASA NTRS1997

Molecular Dynamics Simulations of Laser Powered Carbon Nanotube Gears

Dynamics of laser powered carbon nanotube gears is investigated by molecular dynamics simulations with Brenner's hydrocarbon potential. We find that when the frequency of the laser electric field is much less than the intrinsic frequency of the carbon nanotube, the tube exhibits an oscillatory pendulam behavior. However, a unidirectional rotation of the gear with oscillating frequency is observed under conditions of resonance between the laser field and intrinsic gear frequencies. The operating conditions for stable rotations of the nanotube gears, powered by laser electric fields are explored, in these simulations.

Srivastava, Deepak↗

NASA NTRS1993

High-temperature, high-pressure oxygen metering valve

A control valve includes a body defining a central cavity arranged between a fluid inlet and outwardly-diverging first and second fluid outlets respectively disposed in a common transverse plane. A valve member is arranged in the cavity for rotation between first and second operating positions where a transverse fluid passage through the valve member alternatively communicates the fluid inlet with one or the other of the fluid outlets. To minimize fluid turbulence when the valve member is rotated to an alternate operating position, the fluid passage has a convergent entrance for maintaining the passage in permanent communication with the fluid inlet as well as an oblong exit opening with spaced side walls for enabling the exit opening to temporarily span the first and second fluid outlets as the valve member is turned between its respective operating positions.

Christianson, Rollin C.↗

NASA NTRS1991

Bidirectional drive and brake mechanism

A space transport vehicle is disclosed as including a body which is arranged to be movably mounted on an elongated guide member disposed in outer space and driven therealong. A drive wheel is mounted on a drive shaft and arranged to be positioned in rolling engagement with the elongated guide carrying the vehicle. A brake member is arranged on the drive shaft for movement into and out of engagement with an adjacent surface of the drive wheel. An actuator is mounted on the body to be manually moved back and forth between spaced positions in an arc of movement. A ratchet-and-pawl mechanism is arranged to operate upon movements of the actuator in one direction between first and second positions for coupling the actuator to the drive wheel to incrementally rotate the wheel in one rotational direction and to operate upon movements of the actuator in the opposite direction for uncoupling the actuator from the wheel. The brake member is threadedly coupled to the drive shaft in order that the brake member will be operated only when the actuator is moved on beyond its first and second positions for shifting the brake member along the drive shaft and into frictional engagement with the adjacent surface on the drive wheel.

Swan, Scott A.↗

NASA NTRS1996

Dynamic Modeling of Starting Aerodynamics and Stage Matching in an Axi-Centrifugal Compressor

A DYNamic Turbine Engine Compressor Code (DYNTECC) has been modified to model speed transients from 0-100% of compressor design speed. The impetus for this enhancement was to investigate stage matching and stalling behavior during a start sequence as compared to rotating stall events above ground idle. The model can simulate speed and throttle excursions simultaneously as well as time varying bleed flow schedules. Results of a start simulation are presented and compared to experimental data obtained from an axi-centrifugal turboshaft engine and companion compressor rig. Stage by stage comparisons reveal the front stages to be operating in or near rotating stall through most of the start sequence. The model matches the starting operating line quite well in the forward stages with deviations appearing in the rearward stages near the start bleed. Overall, the performance of the model is very promising and adds significantly to the dynamic simulation capabilities of DYNTECC.

Wilkes, Kevin↗

NASA NTRS1984

Sintered plug flow modulation of a vapor-liquid phase separator for a helium II vessel

Presented is a system for modulation of a superfluid (helium II) flow in a vapor-liquid phase separator, for use in cryogenic storage tanks in future space missions. The system consists of a semicircular mechanically operated shutter, downstream of the separator plug, rotated at 0.1 rpm to control the operational surface area of the separator. The mass flow rate was varied from 10 to 22 mg/s. Pressure gradients across the plug are also discussed.

Frederking, T. H. K.↗

NASA NTRS2001

Optimized suspension culture: the rotating-wall vessel

Suspension culture remains a popular modality, which manipulates mechanical culture conditions to maintain the specialized features of cultured cells. The rotating-wall vessel is a suspension culture vessel optimized to produce laminar flow and minimize the mechanical stresses on cell aggregates in culture. This review summarizes the engineering principles, which allow optimal suspension culture conditions to be established, and the boundary conditions, which limit this process. We suggest that to minimize mechanical damage and optimize differentiation of cultured cells, suspension culture should be performed in a solid-body rotation Couette-flow, zero-headspace culture vessel such as the rotating-wall vessel. This provides fluid dynamic operating principles characterized by 1) solid body rotation about a horizontal axis, characterized by colocalization of cells and aggregates of different sedimentation rates, optimally reduced fluid shear and turbulence, and three-dimensional spatial freedom; and 2) oxygenation by diffusion. Optimization of suspension culture is achieved by applying three tradeoffs. First, terminal velocity should be minimized by choosing microcarrier beads and culture media as close in density as possible. Next, rotation in the rotating-wall vessel induces both Coriolis and centrifugal forces, directly dependent on terminal velocity and minimized as terminal velocity is minimized. Last, mass transport of nutrients to a cell in suspension culture depends on both terminal velocity and diffusion of nutrients. In the transduction of mechanical culture conditions into cellular effects, several lines of evidence support a role for multiple molecular mechanisms. These include effects of shear stress, changes in cell cycle and cell death pathways, and upstream regulation of secondary messengers such as protein kinase C. The discipline of suspension culture needs a systematic analysis of the relationship between mechanical culture conditions and biological effects, emphasizing cellular processes important for the industrial production of biological pharmaceuticals and devices.

Non-NASA Center↗

NASA NTRS2005

Towards Rocket Engine Components with Increased Strength and Robust Operating Characteristics

High-energy rotating machines, powering liquid propellant rocket engines, are subject to various sources of high and low cycle fatigue generated by unsteady flow phenomena. Given the tremendous need for reliability in a sustainable space exploration program, a fundamental change in the design methodology for engine components is required for both launch and space based systems. A design optimization system based on neural-networks has been applied and demonstrated in the redesign of the Space Shuttle Main Engine (SSME) Low Pressure Oxidizer Turbo Pump (LPOTP) turbine nozzle. One objective of the redesign effort was to increase airfoil thickness and thus increase its strength while at the same time detuning the vane natural frequency modes from the vortex shedding frequency. The second objective was to reduce the vortex shedding amplitude. The third objective was to maintain this low shedding amplitude even in the presence of large manufacturing tolerances. All of these objectives were achieved without generating any detrimental effects on the downstream flow through the turbine, and without introducing any penalty in performance. The airfoil redesign and preliminary assessment was performed in the Exploration Technology Directorate at NASA ARC. Boeing/Rocketdyne and NASA MSFC independently performed final CFD assessments of the design. Four different CFD codes were used in this process. They include WIL DCA T/CORSAIR (NASA), FLUENT (commercial), TIDAL (Boeing Rocketdyne) and, a new family (AardvarWPhantom) of CFD analysis codes developed at NASA MSFC employing LOX fluid properties and a Generalized Equation Set formulation. Extensive aerodynamic performance analysis and stress analysis carried out at Boeing Rocketdyne and NASA MSFC indicate that the redesign objectives have been fully met. The paper presents the results of the assessment analysis and discusses the future potential of robust optimal design for rocket engine components.

Marcu, Bogdan↗

NASA NTRS1993

Gravity sensitivity of a resistojet water vaporizer

A laboratory model of a water vaporizer for resistojet applications was designed, fabricated, and steady and transient characteristics were measured. Vaporizer operation was not impacted by rotation about a horizontal axis normal to its own. The vaporizer was operated under low and high accelerations aboard a jet aircraft for periods up to 25 s at flow rates ranging from 159(10)(exp -6) to 230(10)(exp -6) kg/s. Slight changes in inlet and outlet pressures and some heat exchanger temperatures were observed during the low-gravity tests. However, the results of these tests indicated probable compatibility of the vaporizer design tested with a low-gravity environment.

Morren, W. Earl↗

NASA NTRS1993

Gravity sensitivity of a resistojet water vaporizer

Morren, W. E.↗

NASA NTRS2015

Progress of a Cross-Correlation Based Optical Strain Measurement Technique for Detecting Radial Growth on a Rotating Disk

The modern turbine engine operates in a harsh environment at high speeds and is repeatedly exposed to combined high mechanical and thermal loads. The cumulative effects of these external forces lead to high stresses and strains on the engine components, such as the rotating turbine disks, which may eventually lead to a catastrophic failure if left undetected. The operating environment makes it difficult to use conventional strain gauges, therefore, non-contact strain measurement techniques is of interest to NASA and the turbine engine community. This presentation describes one such approach; the use of cross correlation analysis to measure strain experienced by the engine turbine disk with the goal of assessing potential faults and damage.

cross-correlation↗

NASA NTRS1969

Rotating space station stabilization criteria for artificial gravity

Operational and structural design criteria for artificial gravity stabilization of rotating space station

Larson, C. A.↗

NASA NTRS1988

Mechanical pumps for superfluid helium transfer in space

Two alternate mechanical pump concepts have been identified for the transfer of superfluid helium in space. Both pumps provide flow at sufficient head and have operating characteristics suitable for the Space Infrared Telescope Facility (SIRTF) refill mission. One pump operates at a relatively low speed and utilizes mechanical roller bearings, while the other operates at a higher rotational speed using either electromagnetic or tilting pad gas-dynamic bearings. The use of gas bearings requires transfer of normal helium so that the gas pressure within the pump casing is high enough to operate the bearings. The operating characteristics of both pumps are predicted, the dimensions are estimated and major technology issues are identified. The major issues for each pump design are cavitation performance and bearing development. Roller bearings require quantified reliability for operation in space while electromagnetic bearings require basic development as well as a complex control system. The low speed pump has significantly poorer hydraulic efficiency than the high speed pump.

Izenson, M. G.↗

NASA NTRS1980

Testing EKG electrodes on-line

Simple test instrument allows electrocardiograph operator to check individual electrodes while they are attached to subject. Simply by rotating switch and observing meter, operator verifies that each electrode is not short-circuited or open-circuited and does not present excessive contact resistance at its interface with skin. Instrument also makes it convenient to check electrode cables that are subject to frequent bending and wear, such as cables used on patients who are exercising.

Crosier, W. G.↗