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At least 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

The vehicle design evaluation program - A computer-aided design procedure for transport aircraft

The vehicle design evaluation program is described. This program is a computer-aided design procedure that provides a vehicle synthesis capability for vehicle sizing, external load analysis, structural analysis, and cost evaluation. The vehicle sizing subprogram provides geometry, weight, and balance data for aircraft using JP, hydrogen, or methane fuels. The structural synthesis subprogram uses a multistation analysis for aerodynamic surfaces and fuselages to develop theoretical weights and geometric dimensions. The parts definition subprogram uses the geometric data from the structural analysis and develops the predicted fabrication dimensions, parts material raw stock buy requirements, and predicted actual weights. The cost analysis subprogram uses detail part data in conjunction with standard hours, realization factors, labor rates, and material data to develop the manufacturing costs. The program is used to evaluate overall design effects on subsonic commercial type aircraft due to parameter variations.

Oman, B. H.↗
NASA NTRS2019

Aerodynamic Characterization and Improved Testing Methods for the Space Launch System Liftoff and Transition Environment

Low-speed wind tunnel testing for the liftoff and transition environment of the Space Launch System (SLS) was recently completed in the NASA Langley Research Center 14- by 22-Foot Subsonic Tunnel using 1.75%-scale models of three SLS vehicle configurations. During the liftoff testing, the primary objective was to evaluate the aerodynamic forces and moments on the SLS launch vehicles, as the vehicle, launch tower, and mobile launch platform were subjected to ground winds from all directions at varying heights for the vehicle off the launch pad. Additionally, aerodynamic forces and moments were acquired for all three SLS vehicles during the transition phase from liftoff to ascent that covered a wide range of angles of attack and angles of side slip. Details of the experimental setup including improved testing methods and a stiffer sting-balance system based on lessons learned from previous test entries are presented. Also, a new force measurement technique was applied during the test where two subminiature six-component load cells were installed in each Solid Rocket Booster (SRB) to acquire forces and moments for each SRB separately from the full vehicle forces and moments measured by the main strain gauge balance. Finally, sample results from the experiment are presented including improved overall data coverage, evaluation of the new SRB data, and smoke flow visualization photos.

Chan, David T.↗
NASA NTRS2010

Orion Flight Performance Design Trades

A significant portion of the Orion pre-PDR design effort has focused on balancing mass with performance. High level performance metrics include abort success rates, lunar surface coverage, landing accuracy and touchdown loads. These metrics may be converted to parameters that affect mass, such as ballast for stabilizing the abort vehicle, propellant to achieve increased lunar coverage or extended missions, or ballast to increase the lift-to-drag ratio to improve entry and landing performance. The Orion Flight Dynamics team was tasked to perform analyses to evaluate many of these trades. These analyses not only provide insight into the physics of each particular trade but, in aggregate, they illustrate the processes used by Orion to balance performance and mass margins, and thereby make design decisions. Lessons learned can be gleaned from a review of these studies which will be useful to other spacecraft system designers. These lessons fall into several categories, including: appropriate application of Monte Carlo analysis in design trades, managing margin in a highly mass-constrained environment, and the use of requirements to balance margin between subsystems and components. This paper provides a review of some of the trades and analyses conducted by the Flight Dynamics team, as well as systems engineering lessons learned.

Jackson, Mark C.↗
NASA NTRS2004

Design of a Wideband 900 GHz Balanced Frequency Tripler for Radioastronomy

We report on the design of a fix-tuned split-block waveguide balanced frequency tripler working nominally at 900GHz. It uses a GaAs Schottky planar diode pair in a balanced configuration. The circuit will be fabricated with JPL membrane technology in order to minimize dielectric loading. The multiplier is bias-less to dramatically ease the mounting and the operating procedure. At room temperature, the expected output power is 50- 130 (micro)W in the band 800-970 GHz when the tripler is pumped with 4mW. By modifying the waveguide input and output matching circuit, the multiplier can be tuned to operate at lower frequencies.

Schottky diode multipliers↗
NASA NTRS2004

Design of a Wideband 6-Anode Frequency Tripler at 300 GHz with Optimum Balance

We report on the design methodology of a fix-tuned split-block waveguide balanced frequency tripler working nominally at 300 GHz. It features six GaAs Schottky planar diodes in a balanced configuration. The circuit will be fabricated with JPL membrane technology in order to minimize dielectric loading and insure an accurate and uniform thickness of the substrate. The multiplier power handling is limited by the breakdown voltage of the diodes that depends on the doping level of the active layer. With six diodes, the current choice for the doping level leads to medium power handling capabilities of about 50 mW. Increasing the number of diodes to eight would be an option but would lead to increased difficulties in design and fabrication.

Schottky diode multipliers↗
NASA NTRS2012

Pressure Dome for High-Pressure Electrolyzer

A high-strength, low-weight pressure vessel dome was designed specifically to house a high-pressure [2,000 psi (approx. = 13.8 MPa)] electrolyzer. In operation, the dome is filled with an inert gas pressurized to roughly 100 psi (approx. = 690 kPa) above the high, balanced pressure product oxygen and hydrogen gas streams. The inert gas acts to reduce the clamping load on electrolyzer stack tie bolts since the dome pressure acting axially inward helps offset the outward axial forces from the stack gas pressure. Likewise, radial and circumferential stresses on electrolyzer frames are minimized. Because the dome is operated at a higher pressure than the electrolyzer product gas, any external electrolyzer leak prevents oxygen or hydrogen from leaking into the dome. Instead the affected stack gas stream pressure rises detectably, thereby enabling a system shutdown. All electrical and fluid connections to the stack are made inside the pressure dome and require special plumbing and electrical dome interfaces for this to be accomplished. Further benefits of the dome are that it can act as a containment shield in the unlikely event of a catastrophic failure. Studies indicate that, for a given active area (and hence, cell ID), frame outside diameter must become ever larger to support stresses at higher operating pressures. This can lead to a large footprint and increased costs associated with thicker and/or larger diameter end-plates, tie-rods, and the frames themselves. One solution is to employ rings that fit snugly around the frame. This complicates stack assembly and is sometimes difficult to achieve in practice, as its success is strongly dependent on frame and ring tolerances, gas pressure, and operating temperature. A pressure dome permits an otherwise low-pressure stack to operate at higher pressures without growing the electrolyzer hardware. The pressure dome consists of two machined segments. An O-ring is placed in an O-ring groove in the flange of the bottom segment and is trapped by the flange on the top dome segment when these components are bolted together with high-strength bolts. The pressure dome has several unique features. It is made (to ASME Pressure Vessel guidelines) in a high-strength aluminum alloy with the strength of stainless steel and the weight benefits of aluminum. The flange of the upper dome portion contains specially machined flats for mounting the dome, and other flats dedicated to the special feedthroughs for electrical connections. A pressure dome can be increased in length to house larger stacks (more cells) of the same diameter with the simple addition of a cylindrical segment. To aid in dome assembly, two stainless steel rings are employed. One is used beneath the heads of the high-strength bolts in lieu of individual hardened washers, and another is used instead of individual nuts. Like electrolyzers could be operated at low or high pressures simply by operating the electrolyzer outside or inside a pressurized dome.

Norman, Timothy↗
NASA NTRS2013

An Approximate Solution and Master Curves for Buckling of Symmetrically Laminated Composite Cylinders

Nondimensional linear-bifurcation buckling equations for balanced, symmetrically laminated cylinders with negligible shell-wall anisotropies and subjected to uniform axial compression loads are presented. These equations are solved exactly for the practical case of simply supported ends. Nondimensional quantities are used to characterize the buckling behavior that consist of a stiffness-weighted length-to-radius parameter, a stiffness-weighted shell-thinness parameter, a shell-wall nonhomogeneity parameter, two orthotropy parameters, and a nondimensional buckling load. Ranges for the nondimensional parameters are established that encompass a wide range of laminated-wall constructions and numerous generic plots of nondimensional buckling load versus a stiffness-weighted length-to-radius ratio are presented for various combinations of the other parameters. These plots are expected to include many practical cases of interest to designers. Additionally, these plots show how the parameter values affect the distribution and size of the festoons forming each response curve and how they affect the attenuation of each response curve to the corresponding solution for an infinitely long cylinder. To aid in preliminary design studies, approximate formulas for the nondimensional buckling load are derived, and validated against the corresponding exact solution, that give the attenuated buckling response of an infinitely long cylinder in terms of the nondimensional parameters presented herein. A relatively small number of "master curves" are identified that give a nondimensional measure of the buckling load of an infinitely long cylinder as a function of the orthotropy and wall inhomogeneity parameters. These curves reduce greatly the complexity of the design-variable space as compared to representations that use dimensional quantities as design variables. As a result of their inherent simplicity, these master curves are anticipated to be useful in the ongoing development of buckling-design technology.

Nemeth, Michael P.↗
NASA NTRS1999

Forced and Moment Measurements with Pressure-Sensitive Paint

The potential of pressure-sensitive paint (PSP) to provide aerodynamic loads measurements has been a driving force behind the development of this measurement technique. To demonstrate the suitability of PSP for this purpose, it is necessary to show that PSP-derived pressures can be accurately integrated over the model surface. This cannot be done simply by demonstrating the accuracy of PSP as compared to pressure taps. PSP errors due to misregistration or temperature sensitivity may be high near model edges, where they will have a strong effect on moment measurements, but where pressure taps are rarely installed. A more suitable technique is to compare integrated PSP data over the entire model surface with balance and/or CFD results. This paper presents results from three experiments in which integrated PSP data is compared with balance and/or CFD data. This allows the usefulness of PSP for force and moment measurements, and by implication for loads measurements, to be assessed.

Bell, James H.↗
NASA NTRS2016

Development of a Protocol to Test Proprioceptive Utilization as a Predictor for Sensorimotor Adaptability

Astronauts returning from space flight show significant inter-subject variations in their abilities to readapt to a gravitational environment because of their innate sensory weighting. The ability to predict the manner and degree to which each individual astronaut will be affected would improve the effectiveness of countermeasure training programs designed to enhance sensorimotor adaptability. We hypothesize participant's ability to utilize individual sensory information (vision, proprioception and vestibular) influences adaptation in sensorimotor performance after space flight. The goal of this study is to develop a reliable protocol to test proprioceptive utilization in a functional postural control task. Subjects "stand" in a supine position while strapped to a backpack frame holding a friction-free device using air-bearings that allow the subject to move freely in the frontal plane, similar to when in upright standing. The frame is attached to a pneumatic cylinder, which can provide different levels of a gravity-like force that the subject must balance against to remain "upright". The supine posture with eyes closed ensures reduced vestibular and visual contribution to postural control suggesting somatosensory and/or non-otolith vestibular inputs will provide relevant information for maintaining balance control in this task. This setup is called the gravity bed. Fourteen healthy subjects carried out three trials each with eyes open alternated with eyes closed, "standing" on their dominant leg in the gravity bed environment while loaded with 60 percent of their body weight. Subjects were instructed to: "use your sense of sway about the ankle and pressure changes under the foot to maintain balance." Maximum length of a trial was 45 seconds. A force plate underneath the foot recorded forces and moments during the trial and an inertial measurement unit (IMU) attached on the backpack's frame near the center of mass of the subject recorded upper body postural responses. Series of linear and non-linear analyses were carried out on several force plate and IMU data including stabilogram diffusion analysis on the center of pressure (COP) to find a subset of parameters that were sensitive to detect differences in postural performance between eyes open and closed conditions. Results revealed that seven parameters (root mean square (RMS) of medio-lateral (ML) COP, range of ML COP, RMS of roll moment, range of trunk roll, minimum time-to-boundary (TTB), integrated TTB, and critical mean square planar displacement (delta r (sup 2) (sub c)) were significantly different between eyes open and closed conditions. We will present data to show the efficacy of using performance in single leg stance with eyes closed on the gravity bed to assess individuals' ability to utilize proprioceptive information in a functional postural control task to predict re-adaptation for sensorimotor and functional performance.

Goel, R.↗
NASA NTRS1989

Wind tunnel balance

A flow-through balance is provided which includes a non-metric portion and a metric portion which form a fluid-conducting passage in fluid communication with an internal bore in the sting. The non-metric and metric portions of the balance are integrally connected together by a plurality of flexure beams such that the non-metric portion, the metric portion and the flexure beams form a one-piece construction which eliminates mechanical hysteresis between the non-metric and the metric portion. The system includes structures for preventing the effects of temperature, pressure and pressurized fluid from producing asymmetric loads on the flexure beams. A temperature sensor and a pressure sensor are located within the fluid-conducting passage of the balance. The system includes a longitudinal bellows member connected at two ends to one of the non-metric portion and the metric portion and at an intermediate portion thereof to the other of (1) and (2). A plurality of strain gages are mounted on the flexure beams to measure strain forces on the flexure beams. The flexure beams are disposed so as to enable symmetric forces on the flexure beams to cancel out so that only asymmetric forces are measured as deviations by the strain gages.

Horne, Warren L.↗
NASA NTRS1985

Use of optimum stiffness tailoring to improve the compressive strength of composite plates with holes

A structural optimization procedure is used to tailor the cross-sectional stiffness distribution of compression-loaded composite plates with holes. Minimum mass designs are obtained for plates with cross sections consisting of two different balanced symmetric laminates with 0 deg, + or - 45 deg and 90 deg plies. The plate interior region contains the hole and is designed from a softer material system with a higher failure strain than the plate exterior region. All-graphite-epoxy plates and hybrid graphite/glass-epoxy plates were studied. Other designs with different percentages of 0 deg and + or 45 deg plies in the exterior laminate are compared with the optimum designs. Designs with uniform cross-sectional stiffnesses also are compared with the tailored cross-sectional stiffness designs. Specimens of each design were tested to verify the analytical predictions. The results show that cross-sectional stiffness tailoring can increase the compressive strength and decrease the mass of compression-loaded laminated plates with holes.

Haftka, R. T.↗
NASA NTRS1997

Estrogen regulates the rate of bone turnover but bone balance in ovariectomized rats is modulated by prevailing mechanical strain

Estrogen deficiency induced bone loss is associated with increased bone turnover in rats and humans. The respective roles of increased bone turnover and altered balance between bone formation and bone resorption in mediating estrogen deficiency-induced cancellous bone loss was investigated in ovariectomized rats. Ovariectomy resulted in increased bone turnover in the distal femur. However, cancellous bone was preferentially lost in the metaphysis, a site that normally experiences low strain energy. No bone loss was observed in the epiphysis, a site experiencing higher strain energy. The role of mechanical strain in maintaining bone balance was investigated by altering the strain history. Mechanical strain was increased and decreased in long bones of ovariectomized rats by treadmill exercise and functional unloading, respectively. Functional unloading was achieved during orbital spaceflight and following unilateral sciatic neurotomy. Increasing mechanical loading reduced bone loss in the metaphysis. In contrast, decreasing loading accentuated bone loss in the metaphysis and resulted in bone loss in the epiphysis. Finally, administration of estrogen to ovariectomized rats reduced bone loss in the unloaded and prevented loss in the loaded limb following unilateral sciatic neurotomy in part by reducing indices of bone turnover. These results suggest that estrogen regulates the rate of bone turnover, but the overall balance between bone formation and bone resorption is influenced by prevailing levels of mechanical strain.

STS-62 Shuttle Project↗
NASA NTRSDate not supplied

Evaluation of a Traditional Regression Model Term Selection Process for Balance Calibration Data Sets

Key elements of a traditional regression model term selection process for the analysis of wind tunnel strain-gage balance calibration data are discussed. The traditional process is sometimes applied when regression models of the gage outputs are needed and an analyst does not have access to a term selection algorithm. In principle, the traditional process identifies supported regression model terms of a gage output by combining an analyst's subject- matter knowledge with a visual examination of selected plots of the calibration loads. Twelve empirical rules are listed that may be used to select regression model terms. Data from the manual calibration of a force balance is used to illustrate the application of the traditional term selection process. The data example shows that the traditional process can become very complex. Its successful application highly depends on an analyst's experience and skills. Therefore, it is suggested to replace the traditional term selection process with an automated term selection algorithm. Then, objective metrics are systematically applied during the term selection that make the identification of the regression model more repeatable and less dependent on an analyst's personal skills.

strain-gage balance↗
NASA NTRS1989

Liquid Angular-Momentum Compensator

Report discusses use of fluid-loop reaction ring as part of system orienting spacecraft. Proposed device imparts angular rotation to spacecraft by reacting against liquid contained in loop. Pump, or pumps, provide impetus to both spacecraft and fluid. Hydraulic accumulators and valves added to control flow. Technique offers better control than attitude-control thrusters. Several advantages in applications otherwise requiring large, rigid reaction wheel: Fluid loop need occupy only peripheral circulation path; does not necessarily require motor sized for maximum torque; does not require difficult-to-make bearings specified to withstand high launch-acceleration loads, provide high stiffness, operate smoothly, and exert minimal fractional torque. Unlike reaction wheel, fluid loop not balanced dynamically.

Iskenderian, Theodore C.↗
NASA NTRS1991

A drag measurement technique for free piston shock tunnels

A new technique is described for measuring drag with 100-microsecond rise time on a nonlifting model in a free piston shock tunnel. The technique involves interpretation of the stress waves propagating within the model and its support. A finite element representation and spectral methods are used to obtain a mean square optimal estimate of the time history of the aerodynamic loading. Thus, drag is measured instantaneously and the previous restriction caused by the mechanical time constant of balances is overcome. The effectiveness of the balance is demonstrated by measuring the drag on cones with 5 and 15 deg semi-vertex angles in nominally Mach 5.6 flow with stagnation enthalpies from 2.6 to 33 MJ/kg.

Sanderson, S. R.↗
NASA NTRS1993

Research on Earth's rotation and the effect of atmospheric pressure on vertical deformation and sea level variability

The work done under NASA grant NAG5-485 included modelling the deformation of the earth caused by variations in atmospheric pressure. The amount of deformation near coasts is sensitive to the nature of the oceanic response to the pressure. The PSMSL (Permanent Service for Mean Sea Level) data suggest the response is inverted barometer at periods greater than a couple months. Green's functions were constructed to describe the perturbation of the geoid caused by atmospheric and oceanic loading and by the accompanying load-induced deformation. It was found that perturbation of up to 2 cm are possible. Ice mass balance data was used for continental glaciers to look at the glacial contributions to time-dependent changes in polar motion, the lod, the earth's gravitational field, the position of the earth's center-of-mass, and global sea level. It was found that there can be lateral, non-hydrostatic structure inside the fluid core caused by gravitational forcing from the mantle, from the inner core, or from topography at the core/mantle or inner core/outer core boundaries. The nutational and tidal response of a non-hydrostatic earth with a solid inner core was modeled. Monthly, global tide gauge data from PSMSL was used to look at the 18.6-year ocean tide, the 14-month pole tide, the oceanic response to pressure, the linear trend and inter-annual variability in the earth's gravity field, the global sea level rise, and the effects of post glacial rebound. The effects of mantle anelasticity on nutations, earth tides, and tidal variation in the lod was modeled. Results of this model can be used with Crustal Dynamics observations to look at the anelastic dissipation and dispersion at tidal periods. The effects of surface topography on various components of crustal deformation was also modeled, and numerical models were developed of post glacial rebound.

Wahr, John↗
NASA NTRS1949

Investigation in Simulated Vertical Descent of the Characteristics of a Cargo-Dropping Device having Extensible Rotating Blades

The characteristics of a cargo-dropping device having extensible rotating blades as load-carrying surfaces have been studied in simulated vertical descent in the Langley 20-foot free-spinning tunnel. The investigation included tests to determine the variation in vertical sinking speed with load. A study of the blade characteristics and of the test results indicated a method of dynamically balancing the blades to permit proper functioning of the device.

Stone, Ralph W., Jr.↗
NASA NTRS2005

EOSDIS Petabyte Archives: Tenth Anniversary

One of the world s largest scientific data systems, NASA'S Earth Observing System Data and Information System (EOSDIS) has stored over three petabytes of earth science data in a geographically distributed mass storage system. Design for this system began in the early 1990s and included a presentation of the design of the mass storage system at this conference in 1995. Many changes have occurred in the ten years since that presentation, much of it performed while the system was operational. In its first operational year (2000), the EOSDIS system had increased NASA's collection of earth science data holdings eight-fold. Today, EOSDIS collects over 7,000 gigabytes of data per week, almost 60 times more than the Hubble Space Telescope. This load represents major challenges for ingest into the mass storage system, as well as for timely and balanced data distribution out of the mass storage system. This paper discusses the evolution of the EOSDIS focusing primarily on the mass storage system component of the archive. We present the lessons that were learned over the years and some directions that we are taking for the future.

Behnke, Jeanne↗