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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

A new approach to the design of time varying control systems with application to the space shuttle booster

A general approach toward the analysis and design of closed loop control for slowly time-varying linear systems was investigated. The approach is by the method of generalized multiple scales, in which slow and fast dynamics are systematically separated by employing different clocks which measure time at varying rates. The clocks, which are necessarily nonlinear functions of time, so that the system dynamics are asymptotically invariant with respect to the new time scale. A transfer function relating the output to the input for general linear slowly time-varying systems is developed and represents the actual system under certain conditions. The clock functions are shown to satisfy an algebraic characteristic equation and can be determined in general in terms of the coefficients.

Ramnath, R. V.↗
NASA NTRS1975

Space shuttle Solid Rocket Booster (SRB) separation

The system is described which is used to separate the solid rocket boosters from the space shuttle after they have expended most of their propellant and their thrust is near burnout. The dynamics of the separation are simulated in a computer program so that the separation system can be analyzed. The assumptions and ground rules used in analyzing this system are explained and the method of analysis is delineated. The capability of the separation system is presented together with data which may be used to aid in the design of the external tank and solid rocket booster interface. The results of a parameter study to determine the sensitivity of the separation to the initial state of the space shuttle are also presented.

Tomlin, D. D.↗
NASA NTRS1980

SPS attitude control and stationkeeping: Requirements and tradeoffs

The dominant control requirements of solar power satellites change appreciably relative to small contemporary spacecraft. Trade studies and analyses illustrated preferred control approaches. It was found that the geosynchronous equatorial orbit is preferred over the alternative orbits considered, that the solar pressure orbit perturbation dominates stationkeeping propulsion requirements and that a combined AC and SK system using ion electric propulsion can satisfy the attitude control requirements. It was also found that control system/structural dynamic interaction stability can be obtained through frequency separation with reasonable structural dynamic requirements and simplify spacecraft design.

Oglevie, R. E.↗
NASA NTRS1974

Analysis of dynamic stall using unsteady boundary-layer theory

The unsteady turbulent boundary layer and potential flow about a pitching airfoil are analyzed using numerical methods to determine the effect of pitch rate on the delay in forward movement of the rear flow reversal point. An explicit finite difference scheme is used to integrate the unsteady boundary layer equations, which are coupled at each instant of time to a fully unsteady and nonlinear potential flow analysis. A substantial delay in forward movement of the reversal point is demonstrated with increasing pitch rate, and it is shown that the delay results partly from the alleviation of the gradients in the potential flow, and partly from the effects of unsteadiness in the boundary layer itself. The predicted delay in flow-reversal onset, and its variation with pitch rate, are shown to be in reasonable agreement with experimental data relating to the delay in dynamic stall. From the comparisons it can be concluded (a) that the effects of time-dependence are sufficient to explain the failure of the boundary layer to separate during the dynamic overshoot, and (b) that there may be some link between forward movement of the reversal point and dynamic stall.

Scruggs, R. M.↗
NASA NTRS1973

A new approach to the design of time-varying control systems with application to the Space Shuttle Boost

A general approach to the analysis and design of closed-loop control for slowly time-varying linear systems is presented. The approach uses the method of generalized multiple scales in which slow and fast dynamics are systematically separated by employing different 'clocks' which measure time at varying rates. The clocks, which are necessarily nonlinear functions of time, are chosen in such a manner that the system dynamics are asymptotically invariant with respect to the new time scale. A transfer function relating the output to the input for general linear slowly time-varying systems is developed and represents the actual system under certain conditions. The clock function is shown to satisfy an algebraic characteristic equation and can be determined in terms of the coefficients. The approach can be viewed as an extension of time-invariant linear feedback control theory.

Ramanth, R. V.↗
NASA NTRS2011

Analysis of Separation Corridors for Visiting Vehicles from the International Space Station

The International Space Station (ISS) is a very dynamic vehicle with many operational constraints that affect its performance, operations, and vehicle lifetime. Most constraints are designed to alleviate various safety concerns that are a result of dynamic activities between the ISS and various Visiting Vehicles (VVs). One such constraint that has been in place for Russian Vehicle (RV) operations is the limitation placed on Solar Array (SA) positioning in order to prevent collisions during separation and subsequent relative motion of VVs. An unintended consequence of the SA constraint has been the impacts to the operational flexibility of the ISS resulting from the reduced power generation capability as well as from a reduction in the operational lifetime of various SA components. The purpose of this paper is to discuss the technique and the analysis that were applied in order to relax the SA constraints for RV undockings, thereby improving both the ISS operational flexibility and extending its lifetime for many years to come. This analysis focused on the effects of the dynamic motion that occur both prior to and following RV separations. The analysis involved a parametric approach in the conservative application of various initial conditions and assumptions. These included the use of the worst case minimum and maximum vehicle configurations, worst case initial attitudes and attitude rates, and the worst case docking port separation dynamics. Separations were calculated for multiple ISS docking ports, at varied deviations from the nominal undocking attitudes and included the use of two separate attitude control schemes: continuous free-drift and a post separation attitude hold. The analysis required numerical propagation of both the separation motion and the vehicle attitudes using 3-degree-of-freedom (DOF) relative motion equations coupled with rigid body rotational dynamics to generate a large set of separation trajectories.

Zaczek, Mariusz P.↗
NASA NTRS1972

Experiments on the dynamic stability of the space shuttle

Some dynamic stability experiments on the space shuttle using a half-model oscillatory technique are discussed. Resulting information from the experiments is presented and includes: (1) dynamic pitching characteristics of both the orbiter and the booster alone as well as of the two models mated into a single launch configuration; (2) the static and dynamic interference effects during an abort separation maneuver; and (3) the dynamic plume interference effect.

Orlik-Rueckermann, K. J.↗
NASA NTRS1974

Pre-mare cratering and early solar system history

An evaluation of the application of the high extra-lunar flux in pre-mare times to more general problems of early solar system history is attempted by combining the results of dynamic studies with lunar chronological data. Dynamical studies permit separate evaluation of the possible sources for both the normal flux during the first 600 m.y. years of lunar history as well as the peak which apparently occurred 4.0 b.y. ago. Dynamical studies have been carried out in order to determine the extent to which a heliocentric flux could be confined to the Moon (and Earth). A Monte Carlo method has been used to calculate the relative impact rates of planet-crossing bodies with the moon and the terrestrial planets. It is concluded that the time-variation of the flux on these planets is closely related to that on the moon.

Wetherill, G. W.↗
NASA NTRS1991

Aerodynamics of powered missile separation from a wing

A 3D dynamic 'chimera' algorithm that solves the thin-layer Navier-Stokes equations over multiple moving bodies was modified to numerically simulate the aerodynamics, missile dynamics, and missile plume of a finless missile separating from a wing in transonic flow. A powered missile separation case was considered to examine the influence of the missile and plume on the wing. The wing and missile is at a two degree angle of attack. The computational results show the details of the flow field.

Shanks, S. P.↗
NASA NTRS1993

Aerodynamics of powered missile separation from F/A-18 aircraft

A 3D dynamic 'chimera' algorithm that solves the thin-layer Navier-Stokes equations over multiple moving bodies was modified to numerically simulate the aerodynamics, missile dynamics, and missile plume interactions of a missile separating from a generic wing and from an F/A-18 aircraft in transonic flow. The missile is mounted below the wing for missile separation from the wing and on the F/A-18 fuselage at the engine inlet side for missile separation from aircraft. Static and powered missile separation cases are considered to examine the influence of the missile and plume on the wing and F/A-18 fuselage and engine inlet. The aircraft and missile are at two degrees angle of attack, Reynolds number of 10 million, freestream Mach number of 1.05 and plume Mach number of 3.0. The computational results show the details of the flow field.

Ahmad, J. U.↗
NASA NTRS2015

Nonequilibrium Supersonic Freestream Studied Using Coherent Anti-Stokes Raman Spectroscopy

Measurements were conducted at the University of Virginia Supersonic Combustion Facility of the flow in a constant-area duct downstream of a Mach 2 nozzle. The airflow was heated to approximately 1200 K in the facility heater upstream of the nozzle. Dual-pump coherent anti-Stokes Raman spectroscopy was used to measure the rotational and vibrational temperatures of N2 and O2 at two planes in the duct. The expectation was that the vibrational temperature would be in equilibrium, because most scramjet facilities are vitiated air facilities and are in vibrational equilibrium. However, with a flow of clean air, the vibrational temperature of N2 along a streamline remains approximately constant between the measurement plane and the facility heater, the vibrational temperature of O2 in the duct is about 1000 K, and the rotational temperature is consistent with the isentropic flow. The measurements of N2 vibrational temperature enabled cross-stream nonuniformities in the temperature exiting the facility heater to be documented. The measurements are in agreement with computational fluid dynamics models employing separate lumped vibrational and translational/rotational temperatures. Measurements and computations are also reported for a few percent steam addition to the air. The effect of the steam is to bring the flow to thermal equilibrium, also in agreement with the computational fluid dynamics.

Cutler, Andrew D.↗
NASA NTRS1973

Dynamic effects of shock-induced flow separation.

Shock-induced flow separation is the flow mechanism usually responsible for what the structural dynamicist terms 'buffet.' The shock-induced flow separation affects the aeroelastic response via two different mechanisms: (1) the flow separation generates fluctuating pressures, i.e., a forcing function that is independent of the motion of the aerodynamic surface, e.g., an aircraft wing, and (2) the flow separation affects the motion-dependent forces and can in some cases generate negative aerodynamic damping. A simple analysis is presented which, using static experimental data as an input, can predict these two buffet-components for a wing in high Mach number subsonic flow.

Ericsson, L. E.↗
NASA NTRS1976

Dynamic control of SRB thrust tailoff for separation

The use of the difference in chamber pressure between solid rocket booster engines as a controlling signal to the flight control system during booster thrust tailoff was examined. In addition, the control capability of the Generalized Attitude Control System (GACS) was compared to that of the baseline. Results indicate that the difference in chamber pressure signal provided essentially no improvement. However, the GACS is considerably better than the baseline in controlling during tailoff disturbances.

Webb, W. W.↗
NASA NTRS1989

Direct method for solution of three-dimensional unsteady incompressible Navier-Stokes equations

A three-dimensional, unsteady analysis for the velocity-vorticity formulation of the Navier-Stokes (NS) equations is described. This formulation highlights the natural separation of the spin dynamics of a fluid particle from its translational kinematics. This separation is exploited to produce a single pass direct inversion of the full unsteady NS operator without the need to iterate either the future wall vorticity or the nonlinear vorticity convection terms. The method has uniform second-order accuracy in time and space. As an example, it is applied to the problem of the three-dimensional flow within a shear-driven cubical box. Results are obtained for Re = 100, 400, and 1000 using a preliminary (25, 25, 25) mesh.

Osswald, G. A.↗
NASA NTRS1993

Finite-Element Analysis Of Geared Rotors

Rotor and gear dynamics, previously treated separately, combined in one model. Geared-rotor model developed to consider coupling of torsional vibrations of gears with lateral as well as torsional vibrations of shafts. Geared-rotor system includes motor connected to one of two shafts via coupling, load at far end of other shaft, and pair of gears that couple shafts. Used in parametric studies on effects of compliances of bearings on dynamics of geared-rotor systems.

Kahraman, Ahmet↗
NASA NTRSDate not supplied

Methodology and Development of SLS Liftoff Loads

The methodologies and development of the loads experienced during liftoff of the NASA SLS Block I vehicle will be presented in this paper. The liftoff loads analysis traditionally captures the dynamics of vehicle/pad separation after engine/booster ignition coupled with other launch day environments like wind, overpressure, and engine side loads. Additionally, the liftoff analysis includes an on-pad engine shutdown prior to booster ignition. The SLS liftoff analysis is performed using a Monte Carlo analysis and this paper will explore the Monte Carlo process and the statistical approach to calculating the limit loads.

SLS↗
NASA NTRSDate not supplied

Methodology and Development of SLS Liftoff Loads

The methodologies and development of the loads experienced during liftoff of the NASA SLS Block I vehicle will be presented in this paper. The liftoff loads analysis traditionally captures the dynamics of vehicle/pad separation after engine/booster ignition coupled with other launch day environments like wind, overpressure, and engine side loads. Additionally, the liftoff analysis includes an on-pad engine shutdown prior to booster ignition. The SLS liftoff analysis is performed using a Monte Carlo analysis and this paper will explore the Monte Carlo process and the statistical approach to calculating the limit loads.

SLS↗