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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

The Impact of Pictorial Display on Operator Learning and Performance

The effects of pictorially displayed information on human learning and performance of a simple control task were investigated. The controlled system was a harmonic oscillator and the system response was displayed to subjects as either an animated pendulum or a horizontally moving dot. Results indicated that the pendulum display did not effect performance scores but did significantly effect the learning processes of individual operators. The subjects with the pendulum display demonstrated more vertical internal models early in the experiment and the manner in which their internal models were tuned with practice showed increased variability between subjects.

Miller, R. A.↗
NASA NTRS1989

Tamper-Resistant Secure Disposal Container

Closure device for secure waste containers prevents classified papers and other proprietary articles from being withdrawn when container turned on side. Has pendulum that swings comb into closed position when container turned on side. Suspended with axis of rotation perpendicular to axes of combs. Extends through D-shaped cam ring, attached to upper comb with standoff struts. When container tilted sideways, pendulum swings along arc side of D-shaped ring. Forces cam ring aside, moving upper comb toward closed position. If container tilted forward or backward, pendulum does not interfere with comb movement. Spring catches added to combs so if actuated and close container opening, they lock in place to prevent further tampering.

Collins, Earl R., Jr.↗
NASA NTRS1990

Suspension systems for ground testing large space structures

A research program is documented for the development of improved suspension techniques for ground vibration testing of large, flexible space structures. The suspension system must support the weight of the structure and simultaneously allow simulation of the unconstrained rigid-body movement as in the space environment. Exploratory analytical and experimental studies were conducted for suspension systems designed to provide minimum vertical, horizontal, and rotational degrees of freedom. The effects of active feedback control added to the passive system were also investigated. An experimental suspension apparatus was designed, fabricated, and tested. This test apparatus included a zero spring rate mechanism (ZSRM) designed to support a range of weights from 50 to 300 lbs and provide vertical suspension mode frequencies less than 0.1 Hz. The lateral suspension consisted of a pendulum suspended from a moving cart (linear bearing) which served to increase the effective length of the pendulum. The torsion suspension concept involved dual pendulum cables attached from above to a pivoting support (bicycle wheel). A simple test structure having variable weight and stiffness characteristics was used to simulate the vibration characteristics of a large space structure. The suspension hardware for the individual degrees of freedom was analyzed and tested separately and then combined to achieve a 3 degree of freedom suspension system. Results from the exploratory studies should provide useful guidelines for the development of future suspension systems for ground vibration testing of large space structures.

Gold, Ronald R.↗
NASA NTRS1991

Impact properties of three-dimensional braided graphite/epoxy composites

An experimental study of the response and damage of three-dimensional braided graphite/epoxy composite due to sub-perforation velocity impact was carried out in this research. Simply supported square plates were impacted with an instrumented impact pendulum and also a projectile fired by a gas gun. Hemispherical nose impactors of two different diameters, 12.7 mm and 25.4 mm, were used in the pendulum tests. In addition, static flexure tests were performed. Impact damage was assessed using X-radiography, and compression after impact tests. Damages involved in impacted braided panel are matrix cracking in resin pockets, separation of fiber tows, and fiber two breakage, mostly in fiber bundle crimp areas. A quasi-isotropic laminate was impact tested with pendulum for comparison of impact tolerance between the two composite systems.

Gong, J. C.↗
NASA NTRS1990

Experimental demonstration of active vibration control for flexible structures

Active vibration control of flexible structures for future space missions is addressed. Three experiments that successfully demonstrate control of flexible structures are described. The first is the pendulum experiment. The structure is a 5-m compound pendulum and was designed as an end-to-end test bed for a linear proof mass actuator and its supporting electronics. Experimental results are shown for a maximum-entropy/optimal-projection controller designed to achieve 5 percent damping in the first two pendulum modes. The second experiment was based upon the Harris Multi-Hex prototype experiment (MHPE) apparatus. This is a large optical reflector structure comprising a seven-panel array and supporting truss which typifies a number of generic characteristics of large space systems. The third experiment involved control design and implementation for the ACES structure at NASA Marshall Space Flight Center. The authors conclude with some remarks on the lessons learned from conducting these experiments.

Phillips, Douglas J.↗
NASA NTRS1990

Computer simulation of multigrid body dynamics and control

The objective is to set up and analyze benchmark problems on multibody dynamics and to verify the predictions of two multibody computer simulation codes. TREETOPS and DISCOS have been used to run three example problems - one degree-of-freedom spring mass dashpot system, an inverted pendulum system, and a triple pendulum. To study the dynamics and control interaction, an inverted planar pendulum with an external body force and a torsional control spring was modeled as a hinge connected two-rigid body system. TREETOPS and DISCOS affected the time history simulation of this problem. System state space variables and their time derivatives from two simulation codes were compared.

Swaminadham, M.↗
NASA NTRS1961

Experimental Evaluation of Analytical Models for the Inertias and Natural Frequencies of Fuel Sloshing in Circular Cylindrical Tanks

A correlation is presented of experimental measurement and analytical prediction of free, planar oscillations of a tank of mercury hung on a pendulum. Measured frequencies are presented for the slosh mode and the pendulum-tank mode, and time-history wave forms are included for qualitative comparisons. The sloshing is represented analytically by a single pendulum or a spring-bob, and the size and location of their inertias are determined by matching forces and moments on the tank surface with linearized hydrodynamic theory for inviscid fluids. It is concluded that such analytical models are identical for small displacements in the present application (as they are in simpler applications) and that they provide excellent simulation of the stiffness and in ertia terms for fuel sloshing.

Warner, Robert W.↗
NASA NTRS2010

Thrust Stand for Vertically Oriented Electric Propulsion Performance Evaluation

A variation of a hanging pendulum thrust stand capable of measuring the performance of an electric thruster operating in the vertical orientation is presented. The vertical orientation of the thruster dictates that the thruster must be horizontally offset from the pendulum pivot arm, necessitating the use of a counterweight system to provide a neutrally-stable system. Motion of the pendulum arm is transferred through a balance mechanism to a secondary arm on which deflection is measured. A non-contact light-based transducer is used to measure displacement of the secondary beam. The members experience very little friction, rotating on twisting torsional pivots with oscillatory motion attenuated by a passive, eddy current damper. Displacement is calibrated using an in situ thrust calibration system. Thermal management and self-leveling systems are incorporated to mitigate thermal and mechanical drifts. Gravitational restoring force and torsional spring constants associated with flexure pivots provide restoring moments. An analysis of the design indicates that the thrust measurement range spans roughly four decades, with the stand capable of measuring thrust up to 12 N for a 200 kg thruster and up to approximately 800 mN for a 10 kg thruster. Data obtained from calibration tests performed using a 26.8 lbm simulated thruster indicated a resolution of 1 mN on 100 mN-level thrusts, while those tests conducted on 200 lbm thruster yielded a resolution of roughly 2.5 micro at thrust levels of 0.5 N and greater.

Moeller, Trevor↗
NASA NTRS2016

The Effects of Magnetic-Field Geometry on Longitudinal Oscillations of Solar Prominences: Cross-Sectional Area Variation for Thin Tubes

Solar prominences are subject to both field-aligned (longitudinal) and transverse oscillatory motions, as evidenced by an increasing number of observations. Large-amplitude longitudinal motions provide valuable information on the geometry of the filament channel magnetic structure that supports the cool prominence plasma against gravity. Our pendulum model, in which the restoring force is the gravity projected along the dipped field lines of the magnetic structure, best explains these oscillations. However, several factors can influence the longitudinal oscillations, potentially invalidating the pendulum model. Aims. The aim of this work is to study the influence of large-scale variations in the magnetic field strength along the field lines, i.e., variations of the cross-sectional area along the flux tubes supporting prominence threads. Methods. We studied the normal modes of several flux tube configurations, using linear perturbation analysis, to assess the influence of different geometrical parameters on the oscillation properties. Results. We found that the influence of the symmetric and asymmetric expansion factors on longitudinal oscillations is small.Conclusions. We conclude that the longitudinal oscillations are not significantly influenced by variations of the cross-section of the flux tubes, validating the pendulum model in this context.

Luna, M.↗
NASA NTRS2019

Modal Analysis of the Orion Capsule Two Parachute System

As discussed in Ref [1], it is apparent from flight tests that the system made up of two main parachutes and a capsule can undergo several distinct dynamical behaviors. The most significant and problematic of these is the pendulum mode in which the system develops a pronounced swinging motion with an amplitude of up to 24 deg. Large excursions away from vertical by the capsule could cause it to strike the ground at a large horizontal or vertical speed and jeopardize the safety of the astronauts during a crewed mission. In reference [1], Ali et al. summarized a series of efforts taken by the Capsule Parachute Assembly System (CPAS) Program to understand and mitigate the pendulum issue. The period of oscillation and location of the system's pivot point are determined from post-flight analysis. Other noticeable but benign modes include: 1) flyout (scissors) mode, where the parachutes move back and forth symmetrically with respect to the vertical axis similar to the motion of a pair of scissors; 2) maypole mode, where the two parachutes circle around the vertical axis at a nearly constant radius and period; and 3) breathing mode, in which deformation of the non-rigid canopies affects the axial acceleration of the system in an oscillatory manner. Because these modes are relatively harm- less, little effort has been devoted to analyzing them in comparison with the pendulum motion. Motions of the actual system made up of two parachutes and a capsule are extremely complicated due to nonlinearities and flexibility effects. Often it is difficult to obtain insight into the fundamental dynamics of the system by examining results from a multi-body simulation based on nonlinear equations of motion (EOMs). As a part of this study, the dynamics of each mode observed during flight is derived from first principles on an individual basis by making numerous simplifications along the way. The intent is to gain a better understanding into the behavior of the complex multi-body system by studying the reduced set of differential equations associated with each mode. This approach is analogous to the traditional modal analysis technique used to study airplane flight dynamics, in which the full nonlinear behavior of the airframe is decomposed into the phugoid and short period modes for the longitudinal dynamics and the spiral, roll-subsidence, and dutch-roll modes for the lateral dynamics. It is important to note that the study does not address the mechanisms that cause the system to transition from one mode to another, nor does it discuss motions during which two or more modes occur simultaneously.

Pei, J.↗
DOE OSTI2025

Study of the Design and Characteristics of a Modified Pulsed Plasma Thruster with Graphite and Tungsten Trigger Electrodes

The paper presents experimental results for a modified pulsed plasma thruster (PPT) with solid propellant, using a coaxial anode–cathode design. Graphite from pencil leads served as propellant, and a tungsten trigger electrode was tested to reduce carbonization effects. Experiments were performed in a vacuum chamber at 0.001 Pa, employing diagnostics such as discharge current/voltage recording, power measurement, ballistic pendulum, time-of-flight (TOF) method, and a Faraday cup. Current and voltage waveforms matched an oscillatory RLC circuit with variable plasma channel resistance. Key discharge parameters were measured, including current pulse duration/amplitude and plasma channel formation/decay dynamics. Impulse bit values, obtained with a ballistic pendulum, reached up to 8.5 μN·s. Increasing trigger capacitor capacitance reduced thrust due to unstable “pre-plasma” formation and partial pre-discharge energy loss. Using TOF and Faraday cup diagnostics, plasma front velocity, ion current amplitude, current density, and ion concentration were determined. Tungsten electrodes produced lower charged particle concentrations than graphite but offered better adhesion resistance, minimal carbonization, and stable long-term performance. The findings support optimizing trigger electrode materials and PPT operating modes to extend lifetime and stabilize thrust output.

Faraday cup↗
NASA NTRSDate not supplied

New Perspective on Slosh Dynamics in High-Gravity Regimes for Lunar Missions

Slosh dynamics particularly in high gravity regime is of high interest to the NASA Human Landing Systems program, which aims to return humans to the Moon. This paper reexamines the commonly accepted equivalence between pendulum and massspring-damper mechanical analogies, demonstrating the differences through simulations and their impact on design and analysis. This study re-derives equations of motion for these mechanical models including mass-spring-damper (MSD) and pendulum by relaxing simplifying assumptions that had been typically applied to large launch vehicles and may be violated for lunar and planetary landing applications. The newly-derived equations uncover potential modeling gaps when applying the pendulum and MSD models, and the need for additional considerations in their application. Finally, the newly-derived equations are validated using MathWorks® Simscape™ Multibody™ dynamics toolbox simulation.

Pendulum↗
NASA NTRS1966

Shock-operated valve would automatically protect fluid systems

Glandless valve shuts down high-pressure fluid systems when severe shock from an explosion or earthquake occurs. The valve uses a pendulum to support the valve closure plug in the open position. When jarred, the valve body is moved relative to the pendulum and the plug support is displaced, allowing the plug to seat and be held by spring pressure.

Branum, L. W.↗
NASA NTRS1973

Test stand for precise measurement of impulse and thrust vector of small attitude control jets

A test stand which accurately measures the impulse bit and thrust vector of reaction jet thrusters used in the attitude control system of space vehicles has been developed. It can be used to measure, in a vacuum or ambient environment, both impulse and thrust vector of reaction jet thrusters using hydrazine or inert gas propellants. The ballistic pendulum configuration was selected because of its accuracy, simplicity, and versatility. The pendulum is mounted on flexure pivots rotating about a vertical axis at the center of its mass. The test stand has the following measurement capabilities: impulse of 0.00004 to 4.4 N-sec (0.00001 to 1.0 lb-sec) with a pulse duration of 0.5 msec to 1 sec; static thrust of 0.22 to 22 N (0.05 to 5 lb) with a 5 percent resolution; and thrust angle alinement of 0.22 to 22 N (0.05 to 5 lb) thrusters with 0.01 deg accuracy.

Woodruff, J. R.↗
NASA NTRS1974

Experimental determination of the principal moments of inertia of the Helios prototype spacecraft

The moment of inertia of the Helios Spacecraft about its spin axis was determined by use of a roll-fixture using two sets of crossed flexure pivots as elastic constraints. The test procedure entailed measurement of a system oscillation period with each of a set of added moment-of-inertia increments. The tare effect of the fixture was determined by a like process and was subtracted from the gross value to yield the spacecraft roll moment of inertia to an estimated accuracy of 0.2%. Lateral moments of inertia (i.e., about each of three axes normal to the spin axis) were determined by a gravity pendulum method that makes use of the fact that any physical pendulum has a minimum period of oscillation determined by a particular distance from the axis of rotation to the system center of gravity.

Gayman, W. H.↗
NASA NTRS1975

Development of impact resistant boron/aluminum composites for turbojet engine fan blades

Composite fabrication was performed by vacuum press diffusion bonding by both the foil-filament array and preconsolidated monotape methods. The effect of matrix material, fiber diameter, matrix enhancement, fiber volume reinforcement, test temperature, angle-plying, notch, impact orientation, processing variables and fabrication methods on tensile strength and Charpy impact resistance are evaluated. Root attachment concepts, were evaluated by room and elevated temperature tensile testing, as well as by pendulum-Izod and ballistic impact testing. Composite resistance to foreign object damage was also evaluated by ballistic impacting of panels using projectiles of gelatin, RTV rubber and steel at various velocities, and impingement angles. A significant improvement in the pendulum impact resistance of B-Al composites was achieved.

Melnyk, P.↗
NASA NTRS1975

Measurement of the inertial properties of the Helios F-1 spacecraft

A gravity pendulum method of measuring lateral moments of inertia of large structures with an error of less than 1% is outlined. The method is based on the fact that in a physical pendulum with a knife-edge support the distance from the axis of rotation to the system center of gravity determines the minimal period of oscillation and is equal to the system centroidal radius of gyration. The method is applied to results of a test procedure in which the Helios F-1 spacecraft was placed in a roll fixture with crossed flexure pivots as elastic constraints and system oscillation measurements were made with each of a set of added moment-of-inertia increments. Equations of motion are derived with allowance for the effect of the finite pivot radius and an error analysis is carried out to find the criterion for maximum accuracy in determining the square of the centroidal radius of gyration. The test procedure allows all measurements to be made with the specimen in upright position.

Gayman, W. H.↗
NASA NTRS1982

Less-Costly Inertial Guidance

Two gyroscopes mounted in gimbals yield signals that allow calculation of velocity, position and altitude of an aircraft. The mass lowers center of gravity of gimbal-and-gyro assembly to below the intersection of their axes. Combination acts as a two-axis pendulum. Rate signals from the leveling gyroscope are integrated, amplified, and fed to gimbal torquers to restore pendulum to alinement with local vertical.

Merhav, S. J.↗