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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Pyro shock simulation: Experience with the MIPS simulator

The Mechanical Impulse Pyro Shock (MIPS) Simulator at GE Astro Space Division is one version of a design that is in limited use throughout the aerospace industry, and is typically used for component shock testing at levels up to 10,000 response g's. Modifications to the force imput, table and component boundary conditions have allowed a range of test conditions to be achieved. Twelve different designs of components with weights up to 23 Kg are in the process or have completed qualification testing in the Dynamic Simulation Lab at GE in Valley Forge, Pa. A summary of the experience gained through the use of this simulator is presented as well as examples of shock experiments that can be readily simulated at the GE Astro MIPS facility.

Dwyer, Thomas J.↗
NASA NTRS2001

Fluid Physics Under a Stochastic Acceleration Field

The research summarized in this report has involved a combined theoretical and computational study of fluid flow that results from the random acceleration environment present onboard space orbiters, also known as g-jitter. We have focused on a statistical description of the observed g-jitter, on the flows that such an acceleration field can induce in a number of experimental configurations of interest, and on extending previously developed methodology to boundary layer flows. Narrow band noise has been shown to describe many of the features of acceleration data collected during space missions. The scale of baroclinically induced flows when the driving acceleration is random is not given by the Rayleigh number. Spatially uniform g-jitter induces additional hydrodynamic forces among suspended particles in incompressible fluids. Stochastic modulation of the control parameter shifts the location of the onset of an oscillatory instability. Random vibration of solid boundaries leads to separation of boundary layers. Steady streaming ahead of a modulated solid-melt interface enhances solute transport, and modifies the stability boundaries of a planar front.

Vinals, Jorge↗
NASA NTRS1994

Tolerance of Snakes to Hypergravity

Sensitivity of carotid blood flow to +Gz (head-to-tail) acceleration was studied in six species of snakes hypothesized to show varied adaptive cardiovascular responses to gravity. Blood flow in the proximal carotid artery was measured in 15 snakes before, during and following stepwise increments of +0.25Gz force produced on a 2.4 m diameter centrifuge. During centrifugation each snake was confined to a straight position within an individually- fitted acrylic tube with the head facing the center of rotation. We measured the centrifugal force at the tail of the snake in order to quantify the maximum intensity of force gradient promoting antero-posterior pooling of blood. Tolerance to increased gravity was quantified as the acceleration force at which carotid blood flow ceased. This parameter varied according to the gravitational adaptation of species defined by their ecology and behavior. At the extremes, carotid blood flow decreased in response to increasing gravity and approached zero near +1Gz in aquatic and ground-dwelling species, whereas in climbing species carotid flow was maintained at forces in excess of +2Gz. Surprisingly, tolerant (arboreal) species withstood hypergravic forces of +2 to +3 G. for periods up to 1 h without cessation of carotid blood flow or apparent loss of consciousness. Data suggest that relatively tight skin of the tolerant species provides a natural antigravity suit which is of prime importance in counteracting Gz stress on blood circulation.

Lillywhite, H. B.↗
NASA NTRS1995

Effect of microgravity and hypergravity on embryo axis alignment during postencystment embryogenesis in Artemia franciscana (Anostraca)

Cysts of brine shrimp attached with a liquid adhesive to 12-mm diameter glass coverslips in a syringe-type fluid processing apparatus were flown aboard the NASA space shuttle Discovery, flight STS-60, from 3-11 February 1994, and were allowed to undergo postencystment embryogenesis and to hatch in microgravity. The shuttle flight and the ground-based control coverslips with attached cysts were parallel to the earth's surface during incubation in salt water. Based on the position of the cyst shell crack in the attached cyst population, the ground-control nauplii emerged mostly upward. On the shuttle in microgravity, although our method of detection of orientation would not reveal emergence toward the coverslip, the ratio of the position of the cyst shell crack in the population after hatching best fit the predicted values of a random direction for nauplii emergence. Centrifugation on earth was then used to create hypergravity forces of up to 73 g during postencystment embryogenesis and hatching. The upward orientation of emerging nauplii showed a high degree of correlation (r(2) =98.8%) with a linear relationship to the log of g, with 78.2% of the total hatching upward at 1 g and 91.0% hatching upward at 73 g.

NASA Program NSCORT↗
NASA NTRS2008

High Velocity Linear Induction Launcher with Exit-Edge Compensation for Testing of Aerospace Components

Advances in ultra high speed linear induction electromagnetic launchers over the past decade have focused on magnetic compensation of the exit and entry-edge transient flux wave to produce efficient and compact linear electric machinery. The paper discusses two approaches to edge compensation in long-stator induction catapults with typical end speeds of 150 to 1,500 m/s. In classical linear induction machines, the exit-edge effect is manifest as two auxiliary traveling waves that produce a magnetic drag on the projectile and a loss of magnetic flux over the main surface of the machine. In the new design for the Stator Compensated Induction Machine (SCIM) high velocity launcher, the exit-edge effect is nulled by a dual wavelength machine or alternately the airgap flux is peaked at a location prior to the exit edge. A four (4) stage LIM catapult is presently being constructed for 180 m/s end speed operation using double-sided longitudinal flux machines. Advanced exit and entry edge compensation is being used to maximize system efficiency, and minimize stray heating of the reaction armature. Each stage will output approximately 60 kN of force and produce over 500 G s of acceleration on the armature. The advantage of this design is there is no ablation to the projectile and no sliding contacts, allowing repeated firing of the launcher without maintenance of any sort. The paper shows results of a parametric study for 500 m/s and 1,500 m/s linear induction launchers incorporating two of the latest compensation techniques for an air-core stator primary and an iron-core primary winding. Typical thrust densities for these machines are in the range of 150 kN/sq.m. to 225 kN/sq.m. and these compete favorably with permanent magnet linear synchronous machines. The operational advantages of the high speed SCIM launcher are shown by eliminating the need for pole-angle position sensors as would be required by synchronous systems. The stator power factor is also improved.

Kuznetsov, Stephen↗
NASA NTRS2016

Terrestrial Testing of the CapiBRIC, a Microgravity Optimized Brine Processor

Utilizing geometry based static phase separation exhibited in the radial vaned capillary drying tray, a system was conceived to recover water from brine. This technology has been named the Capillary BRIC; abbreviated CapiBRIC. The CapiBRIC utilizes a capillary drying tray within a drying chamber. Water is recovered from clean water vapor evaporating from the free surface leaving waste brine solids behind. A novel approach of optimizing the containment geometry to support passive capillary flow and static phase separation provides the opportunity for a low power system that is not as susceptible to fouling as membranes or other technologies employing physical barriers across the free brine surface to achieve phase separation in microgravity. Having been optimized for operation in microgravity, full-scale testing of the CapiBRIC as designed cannot be performed on the ground as the force of gravity would dominate over the capillary forces. However, subscale units relevant to full-scale design were used to characterize fill rates, containment stability, and interaction with a variable volume reservoir in the PSU Dryden Drop Tower (DDT) facility. PSU also using tested units scaled such that capillary forces dominated in a 1-g environment to characterize evaporation from a free-surface in 1-g upward, sideways and downward orientations. In order to augment the subscale testing performed by PSU, a full scale 1-g analogue of the CapiBRIC drying unit was initiated to help validate performance predictions regarding expected water recovery ratio, estimated processing time, and interface definitions for inlets, outlets, and internal processes, including vent gas composition. This paper describes the design, development and test of the terrestrial CapiBRIC prototypes.

Sargusingh, Miriam J.↗
NASA NTRS2003

Transport And Chemical Effects On Concurrent And Opposed-Flow Flame Spread At Microgravity

Flame spread over flat solid fuel beds is a useful means of understanding more complex two-phase non-premixed spreading flames, such as those that may occur due to accidents in inhabited buildings and orbiting spacecraft. The role of buoyant convection on flame spread is substantial, especially for thermally-thick fuels. With suitable assumptions, deRis showed that the spread rate (S(sub f)) is proportional to the buoyant or forced convection velocity (U) and thus suggests that S(sub f) is indeterminate at mu g (since S(sub f) = U) unless a forced flow is applied. (In contrast, for thermally thin fuels, the ideal S(sub f) is independent of U.) The conventional view, as supported by computations and space experiments, is that for quiescent g conditions, S(sub f) must be unsteady and decreasing until extinction occurs due to radiative losses. However, this view does not consider that radiative transfer to the fuel surface can enhance flame spread. In recent work we have found evidence that radiative transfer from the flame itself can lead to steady flame spread at mu g over thick fuel beds. Our current work focuses on refining these experiments and a companion modeling effort toward the goal of a space flight experiment called Radiative Enhancement Effects on Flame Spread (REEFS) planned for the International Space Station (ISS) c. 2007.

Son, Y.↗
NASA NTRS1968

Flight Test of a 40-Foot Nominal Diameter Disk-Gap-Band Parachute Deployed at a Mach Number of 2.72 and a Dynamic Pressure of 9.7 Pounds per Square Foot

A 40-foot-nominal-diameter (12.2 meter) disk-gap-band parachute was flight tested as part of the NASA Supersonic Planetary Entry Decelerator (SPED-I) Program. The test parachute was deployed from an instrumented payload by means of a deployment mortar when the payload was at an altitude of 158,500 feet (48.2 kilometers), a Mach number of 2.72, and a free-stream dynamic pressure of 9.7 pounds per foot(exp 2) (465 newtons per meter(exp 2)). Suspension line stretch occurred 0.46 second after mortar firing and the resulting snatch force loading was -8.lg. The maximum acceleration experienced by the payload due to parachute opening was -27.2g at 0.50 second after the snatch force peak for a total elapsed time from mortar firing of 0.96 second. Canopy-shape variations occurred during the higher Mach number portion of the flight test (M greater than 1.4) and the payload was subjected to large amplitude oscillatory loads. A calculated average nominal axial-force coefficient ranged from about 0.25 immediately after the first canopy opening to about 0.50 as the canopy attained a steady inflated shape. One gore of the test parachute was damaged when the deployment bag with mortar lid passed through it from behind approximately 2 seconds after deployment was initiated. Although the canopy damage caused by the deployment bag penetration had no apparent effect on the functional capability of the test parachute, it may have affected parachute performance since the average effective drag coefficient of 0.48 was 9 percent less than that of a previously tested parachute of the same configuration.

EXPERIMENTS↗
NASA NTRS1995

Changes in diaphragm muscle collagen gene expression after acute unilateral denervation

The purpose of the present study was to examine the effects of acute (3 days) unilateral diaphragm denervation (DNV) on 1) levels of alpha 1(I) and alpha 1(III) procollagen mRNA; 2) collagen concentration [hydroxyproline (HYP)]; 3) amount of the nonreducible collagen cross-link hydroxylysylpyridinoline (HP); and 4) the passive force-length relationship of the muscle. The levels of alpha 1(I) and alpha 1(III) procollagen mRNA, HYP concentration, and amount of HP were measured in muscle segments from the midcostal region of DNV and intact (INT) hemidiaphragms of adult male Fischer 344 rats (250-300 g). The in vitro passive force-length relationship of DNV and INT hemidiaphragm was determined by lengthening and shortening the diaphragm muscle segments from 85 to 115% of optimal length at a constant velocity (0.6 optimal length/s). Three days after DNV, the level of alpha 1(I) procollagen mRNA was increased over 15-fold in the DNV hemidiaphragm compared with INT (P < 0.05), whereas the level of alpha 1(III) procollagen mRNA was increased by approximately sixfold in the DNV hemidiaphragm compared with INT (P < 0.05). Collagen (HYP) concentration did not differ between groups, averaging 8.7 and 8.9 micrograms/mg dry wt for the DNV and INT hemidiaphragms, respectively. In addition, there was no difference in the amount of the mature nonreducible collagen cross-link HP between the DNV and INT hemidiaphragms (0.66 vs. 0.76 mole HP/mole collagen, respectively). The amount of passive force developed during lengthening did not differ between DNV and INT hemidiaphragms. These data indicate that acute DNV of the hemidiaphragm is associated with an increase in the mRNA level of the two principal fibrillar collagen phenotypes in skeletal muscle. However, despite extensive muscle remodeling, the passive force-length relationship of the DNV hemidiaphragm is unaffected compared with the INT muscle.

Non-NASA Center↗
NASA NTRS1982

Analysis of physical exercises and exercise protocols for space transportation system operation

A quantitative evaluation of the Thornton-Whitmore treadmill was made so that informed management decisions regarding the role of this treadmill in operational flight crew exercise programs could be made. Specific tasks to be completed were: The Thornton-Whitmore passive treadmill as an exercise device at one-g was evaluated. Hardware, harness and restraint systems for use with the Thornton-Whitmore treadmill in the laboratory and in Shuttle flights were established. The quantitative and qualitative performance of human subjects on the Thorton-Whitmore treadmill with forces in excess of one-g, was evaluated. The performance of human subjects on the Thornton-Whitmore treadmill in weightlessness (onboard Shuttle flights) was also determined.

Coleman, A. E.↗
NASA NTRS1986

Head movements in non-terrestrial force environments elicit motion sickness - Implications for the etiology of space motion sickness

Space motion sickness has become an operational concern in manned space flight. Considerable evidence exists that head movements in free fall, especially pitch movements, are provocative until adaptation occurs. The question arises whether space motion sickness is an unique nosological entity or is due to body movements in a nonterrestrial force environment, a force environment for which the body's dynamic sensory-motor adaptions to 1 G are no longer appropriate. To evaluate this issue, subjects were asked to make controlled head movements during exposure to high gravitoinertial force levels, 1.8-2.0 G, in parabolic flight maneuvers. Head movements in pitch with eyes open were most evocative of motion sickness, yaw movements with eyes covered were least provocative. This pattern is identical to that which occurs when the same types of head movements are made in the free fall phase of parabolic maneuvers. It appears that space motion sickness is the consequence of prolonged exposure to a nonterrestrial force background rather than of exposure to free fall per se.

Lackner, J. R.↗
NASA NTRS1984

The influence of gravitational body force in meteoritic chondrule and lunar glass formation

The effects of gravitational body force must be considered in the formation of extraterrestrial materials such as meteoritic chondrules and lunar glasses. Solidification experiments conducted in microgravity as well as g values greater than Earth's gravitational force have demonstrated that gravitational force can have profound and sometimes unexpected effects upon the way materials solidify and, therefore, upon their physical and mechanical properties. Solutal, thermal and sedimentation effects differ from those experienced on Earth. Because buoyancy forces are reduced, materials of different densities may remain in close proximity. The spherical morphology of chondrules and many lunar glasses may reflect the tendency for free floating liquids to form spherical droplets in a microgravity environment, a form which minimizes surface energy. Under these conditions, surface energy forces dominate gravity forces. The formation of two common chondrule textures, barred and radiating chondrules, can be explained using observations from glass science.

Budka, P. Z.↗
NASA NTRS2003

Foot-Ground Reaction Force During Resistance Exercise in Parabolic Flight

An interim Resistance Exercise Device (iRED) was designed to provide resistive exercise as a countermeasure to space flight-induced loss of muscle strength and endurance as well as decreased bone mineral density. The purpose of this project was to compare foot-ground reaction force during iRED exercise in normal gravity (l-g) versus micro gravity (O-g) achieved during parabolic flight. METHODS: Four subjects performed three exercises using the iRED (squat, heel raise, and deadlift) during I-g and O-g at a moderate intensity (60% of maximum strength during deadlift exercise). Foot-ground reaction force was measured in three axes (x,y,z) using a force plate, and the magnitude of the resultant force vector was calculated (r = ~X 2 + y2 + Z2 ). Range of motion (ROM) was measured using a linear encoder. Peak force (PkF) and total work (TW) were calculated using a customized computer program. Paired t-tests were used to test if significant differences (p.::::0.05) were observed between I-g and O-g exercise. RESULTS: PkF and TW measured in the resultant axis were significantly less in O-g for each of the exercises tested. During O-g, PkF was 42-46% and TW was 33- 37% of that measured during I-g. ROM and average time to complete each repetition were not different from I-g to O-g. CONCLUSIONS: When performing exercises in which body mass is a portion of the resistance during I-g, PkF and TW measured during resistive exercise were reduced approximately 60-70% during O-g. Thus, a resistive exercise device during O-g will be required to provided higher resistances to induce a similar training stimulus to that on Earth.

Lee, Stuart M. C.↗
NASA NTRS1977

Convection phenomena of importance for materials processing in space

The basic aspects of convection processes are delineated. It is shown that even in weak gravitational fields buoyancy can induce fluid motion. Furthermore, at reduced gravity, other nongravity forces such as surface or interfacial tensions, g jitter, thermal volume expansions, density differences due to phase changes, and magnetic and electric fields can induce fluid motions. The types of flows possible with these various driving forces are described, and criteria for determining the extent and nature of the resulting flows and heat transfer are presented. The different physical mechanisms that can occur separately and in combination are indicated, and the present state of knowledge of each of the phenomena is outlined. Specific research problems are described for many of the types of convection that are necessary to obtain greater understanding of their implications for space processing.

Ostrach, S.↗
NASA NTRS1988

Steady state micro-g environment on Space Station

In circular earth orbit, the Space Station (SS) will sense acceleration from external environmental forces due to the gravitational gradient, rotational accelerations, and atmospheric drag. This paper discusses these forces and how they will affect the SS micro-g environment. The effect of SS attitude on the micro-g profile is addressed. Sources for nonsteady state acceleration levels for which disturbance models are currently being developed are briefly considered.

Waters, L.↗
NASA NTRS1992

Dynamics of the G-excess illusion

The G-excess illusion is increasingly recognized as a cause of aviation mishaps especially when pilots perform high-speed, steeply banked turns at low altitudes. Centrifuge studies of this illusion have examined the perception of subject orientation and/or target displacement during maintained hypergravity with the subject's head held stationary. The transient illusory perceptions produced by moving the head in hypergravity are difficult to study onboard centrifuges because the high angular velocity ensures the presence of strong Coriolis cross-coupled semicircular canal effects that mask immediate transient otolith-organ effects. The present study reports perceptions following head movements in hypergravity produced by high-speed aircraft maintaining a banked attitude with low angular velocity to minimize cross-coupled effects. Methods: Fourteen subjects flew on the NASA KC-135 and were exposed to resultant gravity forces of 1.3, 1.5, and 1.8 G for 3 minute periods. On command, seated subjects made controlled head movements in roll, pitch, and yaw at 30 second intervals both in the dark and with faint targets at a distance of 5 feet. Results: head movement produced transient perception of target displacement and velocity at levels as low as 1.3 G. Reports of target velocity without appropriate corresponding displacement were common. At 1.8 G when yaw head movements were made from a face down position, 4 subjects reported oscillatory rotational target displacement with fast and slow alternating components suggestive of torsional nystagmus. Head movements evoked symptoms of nausea in most subjects, with 2 subjects and 1 observer vomiting. Conclusions: The transient percepts present conflicting signals, which introduced confusion in target and subject orientation. Repeated head movements in hypergravity generate nausea by mechanisms distinct from cross-coupled Coriolis effects.

Baylor, K. A.↗
NASA NTRS2000

Flying Qualities Evaluation of a Commuter Aircraft With an Ice Contaminated Tailplane

During the NASA/FAA (Federal Aviation Administration) Tailplane Icing Program, pilot evaluations of aircraft flying qualities were conducted with various ice shapes attached to the horizontal tailplane of the NASA Twin Otter Icing Research Aircraft. Initially, only NASA pilots conducted these evaluations, assessing the differences in longitudinal flight characteristics between the baseline or clean aircraft, and the aircraft configured with an Ice Contaminated Tailplane (ICT). Longitudinal tests included Constant Airspeed Flap Transitions, Constant Airspeed Thrust Transitions, zero-G Pushovers, Repeat Elevator Doublets, and Simulated Approach and Go-Around tasks. Later in the program, guest pilots from government and industry were invited to fly the NASA Twin Otter configured with a single full-span artificial ice shape attached to the leading edge of the horizontal tailplane. This shape represented ice formed due to a 'Failed Boot' condition, and was generated from tests in the Glenn Icing Research Tunnel on a full-scale tailplane model. Guest pilots performed longitudinal handling tests, similar to those conducted by the NASA pilots, to evaluate the ICT condition. In general, all pilots agreed that longitudinal flying qualities were degraded as flaps were lowered, and further degraded at high thrust settings. Repeat elevator doublets demonstrated reduced pitch damping effects due to ICT, which is a characteristic that results in degraded flying qualities. Pilots identified elevator control force reversals (CFR) in zero-G pushovers at a 20 deg flap setting, a characteristic that fails the FAR 25 no CFR certification requirement. However, when the same pilots used the Cooper-Harper rating scale to perform a simulated approach and go-around task at the 20 deg flap setting, they rated the airplane as having Level I and Level II flying qualities respectively. By comparison, the same task conducted at the 30 deg flap setting, resulted in Level II flying qualities for the approach portion, and Level III for the go-around portion.The results of this program indicate that safe and acceptable flying qualities with an ICT condition, can be effectively assessed by task-oriented pilot maneuvers. In addition, other maneuvers such as repeat elevator doublets provide good qualitative and quantitative assessments of pitch damping and elevator effectiveness, which are characteristics that correlate well with pilot task ratings. The results of this testing indicate that the FAR 25 zero-G pushover maneuver, which requires no CFR during its execution, may be an overly conservative pass/fail criteria for aircraft certification.

Ranaudo, Richard J.↗