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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 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Guidance on maneuvering flight paths for rotary wing aircraft

A synthesis procedure for on-line determination of variable speed trajectories in known winds between fixed way points is presented. The primary application is toward rotorcraft approach guidance, although the methodology can be directly applied to other types of vehicles and other problem areas. Trajectories are generated by appropriate combination of straight and turning flight segments to determine the horizontal ground track plus a vertical synthesis based on an energy rate approach. Perturbation equations and feedback laws for four-dimensional trajectory guidance are presented.

Slater, G. L.↗
NASA NTRS1988

Approach trajectory guidance for maximum concealment

An energy-management concept is examined with a view to provision of a near-optimum maneuver guidance system for military aircraft tactical operations. The data thus obtained indicate that the Quiet Short-Haul Research Aircraft, as modeled in the aircraft-specific energy-rate tables, could fly the flight paths in question. The fuel-conservative guidance system's ability to minimize pop-up flight time and carefully coordinate the aircraft's controls for this performance-oriented requirement is demonstrated.

Warner, David N., Jr.↗
NASA NTRS1988

Penetration landing guidance trajectories in the presence of windshear

Flight trajectory guidance in the presence of windshear is considered with reference to flight in a vertical plane. Both horizontal shear and the presence of a downdraft are assumed. The optimal trajectory is first determined by minimizing a performance index which is subject to touchdown constraints, under the assumption of control via angle of attack and power setting. It is shown that the coupling relation between the angle of attack and the power setting can be ignored. A guidance scheme is constructed in which the angle of attack is determined by the windshear intensity, the absolute path inclination, and the glide slope angle, while the power setting is determined by the windshear intensity and the velocity. Particular attention is given to low-altitude penetration landing.

Miele, A.↗
NASA NTRS1988

Optimal reentry guidance for aeroassisted orbit transfer vehicles

A three-state model is presented for analyzing the problem of optimal changes in heading with minimum energy loss for a hypersonic gliding vehicle. A further model order reduction to a single state model is examined using singular perturbation theory. The optimal solution for the reduced problem defines an optimal altitude profile dependent on the current energy of the vehicle. A separate boundary-layer analysis is used to account for altitude and flight path angle dynamics, and to obtain lift and bank angle control solutions. By considering alternative approximations to solve the boundary-layer problem, three guidance laws are obtained, each having a feedback form. The guidance laws are evaluated for a hypothetical vehicle, and compared to an optimal solution obtained using a multiple shooting algorithm.

Calise, Anthony J.↗
NASA NTRS1988

Controls and guidance: Aeronautics

The overall objective is to provide a validated technology base leading to the development and exploitation of new concepts, analysis and design methodologies, and flight systems for future civil and military aircraft. This will provide increased efficiency, effectiveness, reliability, and safety. The program is organized into generic elements and vehicle-specific elements. The generic elements are control theory, guidance and display concepts, and flight crucial systems. Vehicle-specific elements are generic hypersonics, subsonic transport/commuter/general aviation, rotorcraft, and fighter/attack. Research in the control theory element is directed toward the improved flight control analysis and design methodologies for highly integrated, robust flight control designs. Flight Crucial Systems research is directed toward the development of design, assessment, and validation methodologies for flight crucial systems. The generic hypersonics research concentrates on the integration of flight control, propulsion control, sensors, and displays. The Aeronautical Controls and Guidance Program involves analytical and experimental research by in-house, university, and industry personnel. Extensive use of ground-based simulation is a characteristic of the program with selected flight experiments in a variety of aircraft.

Dibattista, John D.↗
NASA NTRS1988

Controls and guidance: Space

The Space Controls and Guidance Research and Technology Program is directed toward enabling the next generation of space transportation systems, large future spacecraft, and space systems such as the Space Station to have large communication antennas and high precision segmented reflector astrophysical telescopes. The new generation of transportation vehicles has demanding requirements to provide for an order of magnitude reduction in cost as well as an increase in capability. The future orbital facilities have demanding control requirements for pointing and stabilization, momentum management, build-up and growth accomodation, and disturbance management. To address these advanced requirements, the research and development program is designed to provide the generic technology base to support the implementation of advanced guidance, navigation, and control. The area of computational controls will be stressed in order to develop cost effective, high speed, high fidelity control system simulation and analysis and synthesis tools. The trust of this work will be to develop methods and software to enable analysis and real-time hardware-in-the-loop simulation of complex spacecraft for control design certification. To address future orbital facilities requirements, an advanced technology program is underway in system identification, distributed control, integrated controls/structures design methods, and advanced sensors and actuators. Because the behavior of large, light weight per unit area deployable/assembled spacecraft is greatly influenced by the ground environment, the testing and verification activity is both ground- and space-based.

Dibattista, John D.↗
NASA NTRS1988

Optimal guidance with obstacle avoidance for nap-of-the-earth flight

The development of automatic guidance is discussed for helicopter Nap-of-the-Earth (NOE) and near-NOE flight. It deals with algorithm refinements relating to automated real-time flight path planning and to mission planning. With regard to path planning, it relates rotorcraft trajectory characteristics to the NOE computation scheme and addresses real-time computing issues and both ride quality issues and pilot-vehicle interfaces. The automated mission planning algorithm refinements include route optimization, automatic waypoint generation, interactive applications, and provisions for integrating the results into the real-time path planning software. A microcomputer based mission planning workstation was developed and is described. Further, the application of Defense Mapping Agency (DMA) digital terrain to both the mission planning workstation and to automatic guidance is both discussed and illustrated.

Pekelsma, Nicholas J.↗
NASA NTRS1988

Providing operational guidance for the development of sea breeze thunderstorms at the Kennedy Space Center - An experiment using a mesoscale numerical model

The effectiveness of a mesoscale numerical model to provide improved local forecast guidance is evaluated with respect to sea breeze convection storms at the Kennedy Space Center. The model and operational forecast guidance production are described. A case study is presented for sea breeze convection storms and lightning events on July 1, 1986. It is found that the mesoscale numerical model outperforms purely subjective predictions of sea breeze convection. The range of applications for the model are considered.

Lyons, Walter A.↗
NASA NTRS1989

A predictive guidance algorithm for Mars entry

This report presents the derivation, logic, and performance of a Mars entry guidance algorithm for the Mars Rover Sample Return Mission. This algorithm guides the Mars entry vehicle along an equilibrium glide trajectory designed to satisfy a set of equality and inequality constraints at chute deploy. An equilibrium glide assumption permits analytic prediction of terminal state conditions and eliminates the need for determining numeric state sensitivities. Trajectory deviations due to dispersions or uncertainties in Martian atmosphere, vehicle aerodynamics, or entry interface conditions are accommodated simply by predicting the compensating equilibrium glide profile and achieving this profile with the available lift control. This Mars Predictive Equilibrium Glide guidance scheme was tested on a range of vehicle configurations with a variety of aerodynamic, atmosphere, and trajectory dispersions with a high degree of success.

Tigges, M. A.↗
NASA NTRS1989

Closed loop navigation and guidance for gravity probe B orbit insertion

This paper addresses the problem of guiding the Gravity Probe B (GP-B) spacecraft from its location after initial insertion to a very precise low earth orbit. Specifically, the satellite orbit is required to be circular to within 0.001 eccentricity, polar to within 0.001 deg inclination, and aligned with the direction of the star Rigel to within 0.001 deg. Navigation data supplied by an on-board GPS receiver is used as feedback to a control algorithm designed to minimize the time to achieve the desired orbit. Translational control is provided by the proportional helium thrusters, which are used for drag-free and attitude control during the remainder of the science mission. Simulations of the guidance system are presented which give an indication of performance characteristics for several types of orbit injection errors. This research is the first reported effort to use GPS as a sensor for a closed loop space guidance system.

Axelrad, P.↗
NASA NTRS1989

Development of a tactical guidance research and evaluation system (TGRES)

The ongoing development of a tool for tactical guidance research and the analysis of airplane system performance in a tactically significant environment are described. The objective of the tool is to provide a means by which researchers can explore and exploit enhancements to high-performance airplane agility. The completed tool will include high-fidelity batch and piloted simulation capabilities, an advanced tactical guidance logic, and a user-friendly interface. While the tool is being developed for the purpose of studying fighter agility, its modularity should make it easily adaptable to the analysis of other technologies and, thus, be of interest to a number of potential users.

Goodrich, Kenneth H.↗
NASA NTRS1989

Optimal aeroassisted guidance using Loh's term approximations

This paper presents three guidance algorithms for aerocapture and/or aeroassisted orbital transfer with plane change. All three algorithms are based on the approximate solution of an optimal control problem at each guidance update. The chief assumption is that Loh's term may be modeled as a function of the independent variable only. The first two algorithms maximize exit speed for fixed exit altitude, flight path angle and heading angle. The third minimizes, in one sense, the control effort for fixed exit altitude, flight path angle, heading angle and speed. Results are presented which indicate the near optimality of the solutions generated by the first two algorithms. Results are also presented which indicate the performance of the third algorithm in a simulation with unmodeled atmospheric density disturbances.

Mceneaney, W. M.↗
NASA NTRS1989

Real-time approximate optimal guidance laws for the advanced launch system

An approach to optimal ascent guidance for a launch vehicle is developed using an expansion technique. The problem is to maximize the payload put into orbit subject to the equations of motion of a rocket over a rotating spherical earth. It is assumed that the thrust and gravitational forces dominate over the aerodynamic forces. It is shown that these forces can be separated by a small parameter epsilon, where epsilon is the ratio of the atmospheric scale height to the radius of the earth. The Hamilton-Jacobi-Bellman or dynamic programming equation is expanded in a series where the zeroth-order term (epsilon = 0) can be obtained in closed form. The zeroth-order problem is that of putting maximum payload into orbit subject to the equations of motion of a rocket in a vacuum over a flat earth. The neglected inertial and aerodynamic terms are included in higher order terms of the expansion, which are determined from the solution of first-order linear partial differential equations requiring only quadrature integrations. These quadrature integrations can be performed rapidly, so that real-time approximate optimization can be used to construct the launch guidance law.

Speyer, Jason L.↗
NASA NTRS1986

Independent Orbiter Assessment (IOA): Analysis of the guidance, navigation, and control subsystem

The results of the Independent Orbiter Assessment (IOA) of the Failure Modes and Effects Analysis (FMEA) and Critical Items List (CIL) is presented. The IOA approach features a top-down analysis of the hardware to determine failure modes, criticality, and potential critical items. To preserve independence, this analysis was accomplished without reliance upon the results contained within the NASA FMEA/CIL documentation. The independent analysis results corresponding to the Orbiter Guidance, Navigation, and Control (GNC) Subsystem hardware are documented. The function of the GNC hardware is to respond to guidance, navigation, and control software commands to effect vehicle control and to provide sensor and controller data to GNC software. Some of the GNC hardware for which failure modes analysis was performed includes: hand controllers; Rudder Pedal Transducer Assembly (RPTA); Speed Brake Thrust Controller (SBTC); Inertial Measurement Unit (IMU); Star Tracker (ST); Crew Optical Alignment Site (COAS); Air Data Transducer Assembly (ADTA); Rate Gyro Assemblies; Accelerometer Assembly (AA); Aerosurface Servo Amplifier (ASA); and Ascent Thrust Vector Control (ATVC). The IOA analysis process utilized available GNC hardware drawings, workbooks, specifications, schematics, and systems briefs for defining hardware assemblies, components, and circuits. Each hardware item was evaluated and analyzed for possible failure modes and effects. Criticality was assigned based upon the severity of the effect for each failure mode.

Trahan, W. H.↗
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 NTRS1989

Guidance analysis of the aeroglide plane change maneuver as a turning point problem

The development of guidance approximations for the atmospheric (aeroglide) portion of the minimum fuel, orbital plane change, trajectory optimization problem is described. Asymptotic methods are used to reduce the two point, boundary value, optimization problem to a turning point problem from the bank angle control. The turning point problem solution, which yields an approximate optimal control policy, is given in terms of parabolic cylinder functions, which are tabulated, and integral expressions, which must be numerically computed. Comparisons of the former, over their region of validity, with optimal control solutions show good qualitative agreement. Additional work and analysis is needed to compute the guidance approximation work.

Gracey, Christopher↗
NASA NTRS1990

Rapid near-optimal trajectory generation and guidance law development for single-stage-to-orbit airbreathing vehicles

General problems associated with on-board trajectory optimization, propulsion system cycle selection, and with the synthesis of guidance laws were addressed for an ascent to low-earth-orbit of an air-breathing single-stage-to-orbit vehicle. The NASA Generic Hypersonic Aerodynamic Model Example and the Langley Accelerator aerodynamic sets were acquired and implemented. Work related to the development of purely analytic aerodynamic models was also performed at a low level. A generic model of a multi-mode propulsion system was developed that includes turbojet, ramjet, scramjet, and rocket engine cycles. Provisions were made in the dynamic model for a component of thrust normal to the flight path. Computational results, which characterize the nonlinear sensitivity of scramjet performance to changes in vehicle angle of attack, were obtained and incorporated into the engine model. Additional trajectory constraints were introduced: maximum dynamic pressure; maximum aerodynamic heating rate per unit area; angle of attack and lift limits; and limits on acceleration both along and normal to the flight path. The remainder of the effort focused on required modifications to a previously derived algorithm when the model complexity cited above was added. In particular, analytic switching conditions were derived which, under appropriate assumptions, govern optimal transition from one propulsion mode to another for two cases: the case in which engine cycle operations can overlap, and the case in which engine cycle operations are mutually exclusive. The resulting guidance algorithm was implemented in software and exercised extensively. It was found that the approximations associated with the assumed time scale separation employed in this work are reasonable except over the Mach range from roughly 5 to 8. This phenomenon is due to the very large thrust capability of scramjets in this Mach regime when sized to meet the requirement for ascent to orbit. By accounting for flight path angle and flight path angle rate in construction of the flight path over this Mach range, the resulting algorithm provides the means for rapid near-optimal trajectory generation and propulsion cycle selection over the entire Mach range from take-off to orbit.

Calise, A. J.↗
NASA NTRS1989

Optimization and guidance of flight trajectories in the presence of windshear

Research on the optimization and guidance of flight trajectories in the presence of windshear performed in the period 1984 to 1989 is discussed. The research concerns windshear recovery systems and covers two major areas of investigation: optimal trajectories for takeoff, abort landing, and penetration landing; and guidance schemes for takeoff, abort landing, and penetration landing.

Miele, A.↗