Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “TRAJECTORIES”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

SARS-CoV2 Protein-Ligand Simulation Dataset: Layer 3 (Raw Temperature Replica Exchange Molecular Dynamics Trajectories)

Raw temperature replica-exchange molecular dyanmics trajectories of 23 different SARS CoV-2 Systems including S Protein ACE2-receptor binding-domain, MPro, PLPro, NSP3 ADRP (X-domain/macrodomain/phosphatase), NSP15 (endoribonuclease), NSP9, NSP10, NSP16, and N-protein N-terminus. Systems were prepared with charmm-gui and simulated using the GROMACS simulation software suite. Non-demuxed, i.e. discontinuous/constant temperature window, trajectories are provided in compressed GROMACS xtc and full trr formats. This data supplements the data releases DOI: 10.13139/OLCF/160650 'SARS-CoV2 Protein-Ligand Simulation Dataset: Layer 1 (Simulation Initial Conditions and Parameters)' and DOI: 10.13139/OLCF/1657844 'SARS-CoV2 Protein-Ligand Simulation Dataset: Layer 2 (Extracted Protein Coordinate Trajectories)'

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Trajectory Optimization via Unsupervised Probabilistic Learning On Manifolds

This report investigates the use of unsupervised probabilistic learning techniques for the analysis of hypersonic trajectories. The algorithm first extracts the intrinsic structure in the data via a diffusion map approach. Using the diffusion coordinates on the graph of training samples, the probabilistic framework augments the original data with samples that are statistically consistent with the original set. The augmented samples are then used to construct conditional statistics that are ultimately assembled in a path-planing algorithm. In this framework the controls are determined stage by stage during the flight to adapt to changing mission objectives in real-time. A 3DOF model was employed to generate optimal hypersonic trajectories that comprise the training datasets. The diffusion map algorithm identfied that data resides on manifolds of much lower dimensionality compared to the high-dimensional state space that describes each trajectory. In addition to the path-planing worflow we also propose an algorithm that utilizes the diffusion map coordinates along the manifold to label and possibly remove outlier samples from the training data. This algorithm can be used to both identify edge cases for further analysis as well as to remove them from the training set to create a more robust set of samples to be used for the path-planing process.

42 ENGINEERING↗
DOE OSTI2023

Stochastic Framework for Optimal Control of Planetary Reentry Trajectories Under Multilevel Uncertainties

We present a novel stochastic optimal control framework that accounts for various types of uncertainties, with application to reentry trajectory planning. The formulation of the optimal trajectory control problem is presented in the context of an indirect method where a functional objective associated with the terminal vehicle speed is to be minimized. Uncertain input parameters in the optimal trajectory control model, including aerodynamic parameters and initial and terminal conditions, are modeled as aleatory random variables, while the statistical parameters of these aleatory distributions are themselves random variables. The parametric and model uncertainties are simultaneously propagated through an extended polynomial chaos expansion (EPCE) formalism. Several metrics are described to evaluate response statistics and presented as insightful tools for robust decision making. Specifically, the response probability density function (PDF) reflecting influence of both epistemic and aleatory uncertainties is obtained. By sampling over the random variables representing model error, an ensemble of response PDFs is generated and the associated failure probability is estimated as a random variable with its own polynomial chaos expansion. Besides, the sensitivity index functions of response PDF with respect to the statistical parameters are evaluated. Coupling parametric and model uncertainties within the EPCE framework leads to a robust and efficient paradigm for multilevel uncertainty propagation and PDF characterization in general optimal control problems.

Engineering↗
NASA NTRS1970

Overlapped conic simulation of three-body trajectories

Trajectory computation technique for three-body motion is based on analytical derivation and empirical validation of pseudostate theory. Application of technique yields ''overlapped conic'' trajectories with error magnitudes only 20 percent as great as those of patched conic trajectories.

Wilson, S. W., Jr.↗
NASA NTRS1971

Lander Trajectory Reconstruction computer program

The Lander Trajectory Reconstruction (LTR) computer program is a tool for analysis of the planetary entry trajectory and atmosphere reconstruction process for a lander or probe. The program can be divided into two parts: (1) the data generator and (2) the reconstructor. The data generator provides the real environment in which the lander or probe is presumed to find itself. The reconstructor reconstructs the entry trajectory and atmosphere using sensor data generated by the data generator and a Kalman-Schmidt consider filter. A wide variety of vehicle and environmental parameters may be either solved-for or considered in the filter process.

Adams, G. L.↗
NASA NTRS1972

Optimal cruise trajectories for supersonic airplanes

Equations are derived for maximizing range for specified initial and final values of mass and altitude. Constant-velocity flight is assumed, and normal acceleration is neglected. The problem is solved by using the maximum principle. Optimal trajectories are obtained and uniqueness is demonstrated. Results are obtained for a supersonic airplane. Curves are presented which can be used to obtain the optimal trajectory and maximum range for a range of initial and final mass and altitude. The optimal range is compared to the range obtained by using the standard cruise trajectory profile (consisting of a Bereguet cruise plus maximum- and minimum-thrust connecting segments) and to the range obtained at constant-altitude cruise.

Teren, F.↗
NASA NTRS1972

Numerical analysis of the asymptotic two-point boundary value solution for N-body trajectories.

Previously published asymptotic solutions for lunar and interplanetary trajectories have been modified and combined to formulate a general analytical boundary value solution applicable to a broad class of trajectory problems. In addition, the earlier first-order solutions have been extended to second-order to determine if improved accuracy is possible. Comparisons between the asymptotic solution and numerical integration for several lunar and interplanetary trajectories show that the asymptotic solution is generally quite accurate. Also, since no iterations are required, a solution to the boundary value problem is obtained in a fraction of the time required for numerically integrated solutions.

Lancaster, J. E.↗
NASA NTRS1972

A study of numerical methods for computing reentry trajectories for shuttle-type space vehicles

The reuseable exterior insulation system (REI) is studied to determine the optimal reentry trajectory for a space shuttle, which minimizes the heat input to the fuselage. The REI is composed of titanium, covered by a surface insulation material. The method of perturbation functions was used to generate the trajectories, and proved to be an effective technique for generating families of solutions, once an initial trajectory has been obtained.

Source record↗
NASA NTRS1972

Apollo/Saturn 5 postflight lunar impact trajectory - AS-511 S-4B/IU

The postflight trajectory is presented for the Apollo/Saturn V AS-511 spent S-IVB/IU stage from CSM separation to lunar impact. The lunar impact coordinates and conditions are included. Some combinations of small S-IVB/IU stage related forces are hypothesized to account for a significant angular momentum increase and small translational perturbations. Trajectory dependent parameters in geocentric and selenocentric inertial coordinates (PACSS4, reference epoch at mean nearest Besselian year) module separation to lunar impact. Data relating to the tracking residuals (observed minus model calculated (O-C)) are also given for the best-estimate trajectory.

Source record↗
NASA NTRS1973

An analysis of atmospheric entry trajectories for manned and unmanned missions to the planet Venus

A unified atmospheric density model is presented for the planet Venus, and this model is compatible with Russian and American data obtained during the 1967 Venus launch opportunity. Trajectory characteristics involved in atmospheric entry are discussed with reference to roll-control modulation and entry corridor. Subsequent to a trajectory-oriented discussion of potential Venus mission characteristics, a parametric analysis of manned and unmanned vehicle entry trajectories into the Venusian atmosphere is presented. A sensitivity analysis with reference to atmospheric density deviations is included to show the dependence of corridor depth on the atmospheric density profile.

Craig, M. K.↗
NASA NTRS1972

The effects of trajectory characteristics on scientific objectives for major planetary orbiters.

Outline of specific solutions in the areas of attitude control, interplanetary trajectory parameters, and orbital configurations of major planetary spacecraft. It is shown that inertia wheel supplementation to a three-axis, stabilized attitude control system will substantially reduce propellant weight and attitude jet firings, especially when considering three-year orbital lifetimes as well as interplanetary trip times of several years. Eight interplanetary trajectory parameters including the earth injection energy and the declination of the launch asymptote are shown for a 1980 earth launch mission to Jupiter. The effects of the interplanetary trajectory parameters on the deboost velocities and resulting orbits about Jupiter are summarized. Orbital mode and science interfaces are defined, and a celestial mechanics experiment independent of earth tracking is briefly outlined.

Paul, C. K.↗
NASA NTRS1974

Effects of selected trajectory parameters on weight trends in the shuttle thermal protection system

An empirical heating model, thermal protection system unit weight correlation, and trajectory analysis were used to develop a computation procedure for studying the sensitivity of thermal protection system weights to variations in pertinent trajectory parameters. The analytical techniques used in developing this computer program are described. Application of the analysis to a Space Shuttle Orbiter configuration was performed to demonstrate gross thermal protection system weight trends with selected entry trajectory parameters.

Curry, D. M.↗
NASA NTRS1974

Performance capability of laser-powered launch vehicles using vertical ascent trajectories

The use of a ground-based high-power laser source to power a vertically launched rocket vehicle is investigated. By using a vertical ascent trajectory, only a single laser source is required. The vertical ascent mode is not applicable to earth orbit destinations but is applicable to missions beyond earth escape. Performance and trajectory characteristics are examined for vertical trajectories to earth escape and solar escape (which may be of interest in the future for radioactive waste disposal). Specific impulse values from 2000 to 5000 seconds are considered. With these values, a single-stage vehicle can deliver payloads to earth escape and beyond, but extremely high power sources (gigawatts) are required.

Spurlock, O. F.↗
NASA NTRS1974

Erosion in radial inflow turbines. Volume 3: Trajectories of erosive particles in radial inflow turbines

The theoretical trajectories that erosive particles follow in the gas flow fields of a typical radial inflow turbine were investigated. A discussion of the theoretical trajectories that the particles follow in the scroll, in the nozzles, in the vortex between the nozzles and the rotor, and in the rotor passages is included. The results are presented in terms of the characteristic length, a similarity parameter which relates the particles that follow the same trajectory in equivalent flow fields. For Vol, 1, see N74-19395.

Clevenger, W. B., Jr.↗
NASA NTRS1974

Program manual for HILTOP, a heliocentric interplanetary low thrust trajectory optimization program. Part 1: User's guide

A performance-analysis computer program, that was developed explicitly to generate optimum electric propulsion trajectory data for missions of interest in the exploration of the solar system is presented. The program was primarily designed to evaluate the performance capabilities of electric propulsion systems, and in the simulation of a wide variety of interplanetary missions. A numerical integration of the two-body, three-dimensional equations of motion and the Euler-Lagrange equations was used in the program. Transversality conditions which permit the rapid generation of converged maximum-payload trajectory data, and the optimization of numerous other performance indices for which no transversality conditions exist are included. The ability to simulate constrained optimum solutions, including trajectories having specified propulsion time and constant thrust cone angle, is also in the program. The program was designed to handle multiple-target missions with various types of encounters, such as rendezvous, stopover, orbital capture, and flyby. Performance requirements for a variety of launch vehicles can be determined.

Mann, F. I.↗
NASA NTRS1974

Program manual for ASTOP, an Arbitrary space trajectory optimization program

The ASTOP program (an Arbitrary Space Trajectory Optimization Program) designed to generate optimum low-thrust trajectories in an N-body field while satisfying selected hardware and operational constraints is presented. The trajectory is divided into a number of segments or arcs over which the control is held constant. This constant control over each arc is optimized using a parameter optimization scheme based on gradient techniques. A modified Encke formulation of the equations of motion is employed. The program provides a wide range of constraint, end conditions, and performance index options. The basic approach is conducive to future expansion of features such as the incorporation of new constraints and the addition of new end conditions.

Horsewood, J. L.↗
NASA NTRS1975

Trajectory design of a solar electric propulsion Encke slow flyby mission

A slow flyby of the periodic comet, Encke, prior to its perihelion passage in 1980 has been shown to be a feasible mission for a solar electric propulsion spacecraft using a moderate power level of around 15 kw. The mission is accomplished in slightly less than two years with a planned miss distance and flyby speed of 1000 km and 4 km/s respectively. The results of a performance tradeoff study are presented together with a description of the nominal trajectory. The trajectories used in these mission studies were calculated using an updated model of the 30 cm mercury bombardment thruster's performance. The trajectory simulations include optimum staging of operating thrusters as a function of input power level constraints and limits on the variation of thruster specific impulse and efficiency as a function of thruster input power.

Sauer, C. G., Jr.↗
NASA NTRS1975

Preliminary Entry Trajectory for 1st Orbital Flight Test (OFT). Space Shuttle Engineering and Operations Support, Engineering Systems Analysis

A preliminary trajectory from entry interface to terminal area energy management interface for the first orbital flight test is presented based on information in the Strawman master flight test assignments document Reference A. The enclosed point-mass trajectory may be utilized for preliminary purposes, meeting the requirements of this document. The trajectory was derived utilizing the January 1975 analytic drag control guidance, the latest thermal protection subsystem model information from NASA ES and December 1974 Aerodynamics for a mid center-of-gravity location.

Frohme, K. R.↗