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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 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
NASA NTRS2007

Mechanical Analog Approach to Parameter Estimation of Lateral Spacecraft Fuel Slosh

The nutation (wobble) of a spinning spacecraft in the presence of energy dissipation is a well-known problem in dynamics and is of particular concern for space missions. Even with modern computing systems, CFD type simulations are not fast enough to allow for large scale Monte Carlo analyses of spacecraft and launch vehicle dynamic behavior with slosh included. Simplified mechanical analogs for the slosh are preferred during the initial stages of design to reduce computational time and effort to evaluate the Nutation Time Constant (NTC). Analytic determination of the slosh analog parameters has met with mixed success and is made even more difficult by the introduction of propellant management devices such as elastomeric diaphragms. By subjecting full-sized fuel tanks with actual flight fuel loads to motion similar to that experienced in flight and measuring the forces experienced by the tanks, these parameters can be determined experimentally. Currently, the identification of the model parameters is a laborious trial-and-error process in which the hand-derived equations of motion for the mechanical analog are evaluated and their results compared with the experimental results. Of particular interest is the effect of diaphragms and bladders on the slosh dynamics and how best to model these devices. An experimental set-up is designed and built to include a diaphragm in the simulated spacecraft fuel tank subjected to lateral slosh. This research paper focuses on the parameter estimation of a SimMechanics model of the simulated spacecraft propellant tank with and without diaphragms using lateral fuel slosh experiments. Automating the parameter identification process will save time and thus allow earlier identification of potential vehicle problems.

Chatman, Yadira↗
NASA NTRS1992

Closed form solutions of constrained trajectories - Application in optimal ascent of aerospace plane

The present consideration of the flight trajectory of hypersonic aerospace vehicles subject to a class of path constraints notes the constrained dynamics to constitute a natural two-timescale system, so that problems of trajectory optimization and guidance can be dramatically simplified by means of the asymptotic analytical solutions thus obtained. An illustrative application in ascent trajectory optimization for an aerospace vehicle is presented.

Lu, Ping↗
NASA NTRS1975

Sustained small oscillations in nonlinear control systems

Some results of bifurcation theory were used to study the existence of small-amplitude periodic behavior in launch vehicle dynamics, assuming that nonlinearity exists as a cubic term in the rudder response. The analysis follows closely Sattinger's (1973) approach to the theory of periodic bifurcations. The conditions under which a bifurcating branch of orbitally stable periodic solutions will exist are determined. It is shown that in more complicated cases, the conditions under which the system matrix has a pair of simple purely imaginary eigenvalues can be determined with the aid of linear stability techniques.

George, J. H.↗
NASA NTRS1974

A wind-tunnel investigation of a B-52 model flutter suppression system

Flutter modeling techniques have been successfully extended to the difficult case of the active suppression of flutter. The demonstration was conducted in a transonic dynamics tunnel using a 1/30 scale, elastic, dynamic model of a Boeing B-52 control configured vehicle. The results from the study show that with the flutter suppression system operating there is a substantial increase in the damping associated with the critical flutter mode. The results also show good correlation between the damping characteristics of the model and the aircraft.

Redd, L. T.↗
NASA NTRS1994

Hypersonic vehicle model and control law development using H(infinity) and micron synthesis

The control system design for a Single Stage To Orbit (SSTO) air breathing vehicle will be central to a successful mission because a precise ascent trajectory will preserve narrow payload margins. The air breathing propulsion system requires the vehicle to fly roughly halfway around the Earth through atmospheric turbulence. The turbulence, the high sensitivity of the propulsion system to inlet flow conditions, the relatively large uncertainty of the parameters characterizing the vehicle, and continuous acceleration make the problem especially challenging. Adequate stability margins must be provided without sacrificing payload mass since payload margins are critical. Therefore, a multivariable control theory capable of explicitly including both uncertainty and performance is needed. The H(infinity) controller in general provides good robustness but can result in conservative solutions for practical problems involving structured uncertainty. Structured singular value mu framework for analysis and synthesis is potentially much less conservative and hence more appropriate for problems with tight margins. An SSTO control system requires: highly accurate tracking of velocity and altitude commands while limiting angle-of-attack oscillations, minimized control power usage, and a stabilized vehicle when atmospheric turbulence and system uncertainty are present. The controller designs using H(infinity) and mu-synthesis procedures were compared. An integrated flight/propulsion dynamic mathematical model of a conical accelerator vehicle was linearized as the vehicle accelerated through Mach 8. Vehicle acceleration through the selected flight condition gives rise to parametric variation that was modeled as a structured uncertainty. The mu-analysis approach was used in the frequency domain to conduct controller analysis and was confirmed by time history plots. Results demonstrate the inherent advantages of the mu framework for this class of problems.

Gregory, Irene M.↗
NASA NTRS1989

Guidance, steering, load relief and control of an asymmetric launch vehicle

A new guidance, steering, and control concept is described and evaluated for the Third Phase of an asymmetrical configuration of the Advanced Launch System (ALS). The study also includes the consideration of trajectory shaping issues and trajectory design as well as the development of angular rate, angular acceleration, angle of attack, and dynamic pressure estimators. The Third Phase guidance, steering and control system is based on controlling the acceleration-direction of the vehicle after an initial launch maneuver. Unlike traditional concepts, the alignment of the estimated and commanded acceleration-directions is unimpaired by an add-on load relief. Instead, the acceleration-direction steering-control system features a control override that limits the product of estimated dynamic pressure and estimated angle of attack. When this product is not being limited, control is based exclusively on the commanded acceleration-direction without load relief. During limiting, control is based on nulling the error between the limited angle of attack and the estimated angle of attack. This limiting feature provides full freedom to the acceleration-direction steering and control to shape the trajectory within the limit, and also gives full priority to the limiting of angle of attack when necessary. The flight software concepts were analyzed on the basis of their effects on pitch plane motion.

Boelitz, Frederick W.↗
NASA NTRS1972

Large-deformation modal coordinates for nonrigid vehicle dynamics

The derivation of minimum-dimension sets of discrete-coordinate and hybrid-coordinate equations of motion of a system consisting of an arbitrary number of hinge-connected rigid bodies assembled in tree topology is presented. These equations are useful for the simulation of dynamical systems that can be idealized as tree-like arrangements of substructures, with each substructure consisting of either a rigid body or a collection of elastically interconnected rigid bodies restricted to small relative rotations at each connection. Thus, some of the substructures represent elastic bodies subjected to small strains or local deformations, but possibly large gross deformations, in the hybrid formulation, distributed coordinates referred to herein as large-deformation modal coordinates, are used for the deformations of these substructures. The equations are in a form suitable for incorporation into one or more computer programs to be used as multipurpose tools in the simulation of spacecraft and other complex electromechanical systems.

Likins, P. W.↗
NASA NTRS1995

System Identification of Damped Truss-Like Space Structures

A spacecraft payload flown on a launch vehicle experiences dynamic loads. The dynamic loads are caused by various phenomena ranging from the start-up of the launch vehicle engine to wind gusts. A spacecraft payload should be designed to meet launch vehicle dynamic loads. One of the major steps taken towards determining the dynamic loads is to correlate the finite element model of the spacecraft with the test results of a modal survey test. A test-verified finite element model of the spacecraft should possess the same spatial properties (stiffness, mass, and damping) and modal properties (frequencies and mode shapes) as the test hardware representing the spacecraft. The test-verified and correlated finite element model of the spacecraft is then coupled with the finite element model of the launch vehicle for analysis of loads and stress. Modal survey testing, verification of a finite element model, and modification of the finite element model to match the modal survey test results can easily be accomplished if the spacecraft structure is simple. However, this is rarely the case. A simple structure here is defined as a structure where the influence of nonlinearity between force and displacement (uncertainty in a test, for example, with errors in input and output), and the influence of damping (structural, coulomb, and viscous) are not pronounced. The objective of this study is to develop system identification and correlation methods with the focus on the structural systems that possess nonproportional damping. Two approaches to correct the nonproportional damping matrix of a truss structure were studied, and have been implemented on truss-like structures such as the National Aeronautics and Space Administration's space station truss. The results of this study showed nearly 100 percent improvement of the correlated eigensystem over the analytical eigensystem. The first method showed excellent results with up to three modes used in the system identification process. The second method could handle more modes, but required more computer usage time, and the results were less accurate than those of the first method.

Armand, Sasan↗
NASA NTRS2023

Space Launch System Unsteady Forces Developed from Unsteady-Pressure-Sensitive-Paint–Based Corcos Model Parameters

During atmospheric ascent, launch vehicles (LVs) experience large dynamic loads at transonic conditions where aerodynamic buffet is most critical. To estimate buffet loads, coupled loads analyses typically utilize suitable forcing functions, called buffet forcing functions (BFFs). One of the key buffet environment contributors is the turbulent boundary layer (TBL) on the LV outer skin. The TBL-induced fluctuating pressures can be estimated using the widely-accepted Corcos model. In the context of transonic buffet, the performance of this model is not well established, partly because of lack of data. To fill this gap, NASA recently acquired extremely high-spatial-density data for the Space Launch System (SLS) vehicle, using the unsteady pressure sensitive paint (uPSP) optical measurement technique. A methodology is developed for validation of the Corcos model using these unique data, with a focus on the LV-design application. The model hypotheses are verified and the model parameters are empirically tuned. For selected panels on the vehicle, BFF coherence factors are derived based on the Corcos model and the associated panel BFFs are compared to uPSP data. It is shown that the modeled BFFs are in agreement with direct integration of uPSP data, except for regions where pressure fluctuations are spatially nonuniform. In those regions, the Corcos-based BFFs exhibit inherent limitations of BFF estimation methods that rely on discrete pressure measurements.

buffet↗
DOE OSTI2020

The Mertens Unrolled Network (MU-Net): A High Dynamic Range Fusion Neural Network for Through the Windshield Driver Recognition

Face recognition of vehicle occupants through windshields in unconstrained environments poses a number of unique challenges ranging from glare, poor illumination, driver pose and motion blur. In this paper, we further develop the hardware and software components of a custom vehicle imaging system to better overcome these challenges. After the build out of a physical prototype system that performs High Dynamic Range (HDR) imaging, we collect a small dataset of through-windshield image captures of known drivers. We then reformulate the classical Mertens-Kautz-Van Reeth HDR fusion algorithm as a pre-initialized neural network, which we name the Mertens Unrolled Network (MU-Net), for the purpose of fine-tuning the HDR output of through-windshield images. Reconstructed faces from this novel HDR method are then evaluated and compared against other traditional and experimental HDR methods in a pre-trained state-of-the-art (SOTA) facial recognition pipeline, verifying the efficacy of our approach.

Ruby, Max↗
NASA NTRS2001

The Analysis and Modeling of the Deployment of NASA's X-38 Parafoil

NASA is currently working on developing the X-38 Crew Return Vehicle for the Internati6nal Space Station (ISS). The aerodynamics of the X-38 and its enormous 7500 square ft parafoil are extremeJy complicated and must be understood and modeled accurately before the vehicle is actually used for human space flight. A large amount of analysis has been performed on the steady state regions of the flight profile when the parafoil is already open. However, the deployment region of the flight profile has not been analyzed in much depth and is a particularly complicated dynamic flight period. During deployment, the X-38 system has its parafoil open up to its full area in five stages over a period of 20-30 seconds. The vehicle transitions from angles of attack around 90 deg to 0 deg in about two seconds and is extremely dynamic. This paper will detail the analysis work done to generate accurate flight profile characteristics of the deployment from flight data from vehicle test drops. Additionally, a computer simulation tool for steady state flight was modified to analyze and model the parafoil deployment. Eventually, a computer model was produced that generated accurate representations of the parafoil deployment dynamics for the vehicle test drops to date.

Ranier, Chris↗
NASA NTRSDate not supplied

Dynamic Vehicle Assessment for Intelligent Contingency Management of Urban Air Mobility Vehicles

New algorithms will be required to ensure passenger and bystander safety during the expected era of autonomous urban air mobility (UAM) aircraft. This paper examines an approach for assessing the vehicle capability to fly itself and to complete a mission safely. The concepts combine elements of system identification, adaptive control, flight dynamics, envelope predictions, and handling qualities, as well as human pilot intuition. The approach is applied to a simulation of a generic distributed electric propulsion urban air mobility-type aircraft, which was developed under the NASA Transformational Tools and Technologies (TTT) project, Autonomous Systems / Intelligent Contingency Management subproject.

flight envelope↗
NASA NTRSDate not supplied

Dynamic Vehicle Assessment for Intelligent Contingency Management for Urban Air Mobility Vehicles

New algorithms will be required to ensure passenger and bystander safety during the expected era of autonomous urban air mobility (UAM) aircraft. This paper examines an approach for assessing the vehicle capability to fly itself and to complete a mission safely. The concepts combine elements of system identification, adaptive control, flight dynamics, envelope predictions, and handling qualities, as well as human pilot intuition. The approach is applied to a simulation of a generic distributed electric propulsion urban air mobility-type aircraft, which was developed under the NASA Transformational Tools and Technologies (TTT) project, Autonomous Systems / Intelligent Contingency Management subproject.

flight envelope prediction↗
NASA NTRS1992

NASP - A status report

The current status of the NASP program, a joint DoD-NASA effort in advancing the technologies needed for the X-30 research flight vehicle is described. The X-30 single stage to orbit (SSTO) vehicle utilizes an air-breathing primary propulsion system and takes off and lands horizontally on a conventional runaway. The technologies under development include high specific strength, high temperature capable materials and structures, ramjet/scramjet propulsion systems, hypersonic aerodynamics and computational fluid dynamics, and cryogenics. A concept for a follow-on NASP-derived operational vehicle and its potential use as a space transportation vehicle are also discussed.

Thomas, John P., Jr.↗
NASA NTRS1990

Lunar articulated remote transportation system

A first generation lunar transportation vehicle was designed for use on the surface of the Moon between the years 2010 and 2020. Attention is focussed on specific design details on all components of the Lunar Articulated Remote Transportation System (Lunar ARTS). The Lunar ARTS will be a three cart, six-wheeled articulated vehicle. It's purpose will be for the transportation of astronauts and/or materials for excavation purposes at a short distance from the base (37.5 kilometers). The power system includes fuel cells for both the primary system and the back-up system. The vehicle has the option of being operated in a manned or unmanned mode. The unmanned mode includes stereo imaging with signal processing for navigation. For manned missions the display console is a digital readout displayed on the inside of the asronaut's helmet. A microprocessor is also on board the vehicle. Other components of the vehicle include: a double wishbone/flexible hemispherical wheel suspension; chassis; a steering system; motors; seat restraints, heat rejection systems; solar flare protection; dust protection; and meteoroid protection. A one-quarter scale dynamic model was built to study the dynamic behavior of the vehicle. The dynamic model closely captures the mechanical and electrical details of the total design.

Beech, Geoffrey↗
NASA NTRS1997

NASA X-34 Technology in Motion

The X-34 technology development program is a joint industry/government project to develop, test, and operate a small, fully-reusable hypersonic flight vehicle. The objective is to demonstrate key technologies and operating concepts applicable to future reusable launch vehicles. Integrated in the vehicle are various systems to assure successful completion of mission objectives, including the Main Propulsion System (MPS). NASA-Marshall Space Flight Center (MSFC) is responsible for developing the X-34's MPS including the design and complete build package for the propulsion system components. The X-34 will be powered by the Fastrac Engine, which is currently in design and development at NASA-MSFC. Fastrac is a single-stage main engine, which burns a mixture of liquid oxygen (LOX) and kerosene(RP-1). The interface between the MPS and Fastrac engine are critical for proper system operation and technologies applicable to future reusable launch vehicles. Deneb's IGRIP software package with the Dynamic analysis option provided a key tool for conducting studies critical to this interface as well as a mechanism to drive the design of the LOX and RP-1 feedlines. Kinematic models were created for the Fastrac Engine and the feedlines for various design concepts. Based on the kinematic simulation within Envision, design and joint limits were verified and system interference controlled. It was also critical to the program to evaluate the effect of dynamic loads visually, providing a verification tool for dynamic analysis and in some cases uncovering areas that had not been considered. Deneb's software put the X-34 technology in motion and has been a key factor in facilitating the strenuous design schedule.

Beech, Geoffrey↗