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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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Vector-matrix differential equation for second order sensitivity coefficients applied to trajectory optimization, modeling and compensation and guidance and control
Minimum fuel takeoff and landing paths for VTOL aircraft with constraints on state and control, determining optimal trajectories
Optimal trajectory and control approximate solution by asymptotic expansion, considering Mayer variational problem solution
Closed form expressions for linear and higher order corrections to multiimpulse approximations of space flight trajectory optimization solutions, using bang-bang thrust control
Atmospheric ascent optimal trajectories for medium to high lift drag ratio space shuttle type rocket vehicles
Optimized trajectories and spacecraft for solar- electric missions to asteroids, using chemical booster for injection
Space shuttle transition trajectory optimization for cruising flight entry, considering longitudinal control, pitchup instability and angle of attack
Perturbation theory for fuel space trajectory optimization
Using FORMAC system to solve optimal control problem of behavior of higher space derivatives of optimal value function along optimal trajectory
Computer program for transfer orbit trajectory optimization based on Lagrange multipliers, Newton-Raphson method, and power series
Weierstrass condition for optimality in coplanar elliptic orbit transfer involving velocity impulse control variables, discussing switching relations at corner of optimal trajectory
Analytical models are presented for optimal trajectories and reentry guidance of the space shuttle orbiter. Major emphasis is placed on the development of a "footprint', which refers to a set of reachable destination positions attainable by the shuttle at a specified terminal altitude. An unconstrained reentry footprint was calculated for a shuttle vehicle which enters the earth's atmosphere at 93 km initial altitude after a deboost from a near earth orbit. The method of computation is briefly described, and graphs are presented which illustrate the footprint and the variation of state and control variables along it. The effects of constraints and of variations in initial state upon the footprint are discussed.
Research on planetary atmospheres, trajectory optimization, wave propagation, solid state physics, radiation shielding, and spacecraft antennas
A space vehicle in an orbit around a spherical planet is considered. It is proposed to bring the vehicle, by a series of orbital maneuvers, into a final orbit. It is sought to minimize the total characteristic velocity for the maneuver. Since for a high-thrust propulsion system the characteristic velocity provides a direct measure of the fuel consumption, the optimal trajectory considered yields the minimum fuel expenditure. It is assumed that the planet is surrounded by a spherical atmosphere.
Selected missions using solar electric propulsion and conventional propulsion systems were studied. The accomplishment of the tasks required extensive modification of the trajectory optimization computer program HILTOP. In addition to adding new program features, HILTOP was completely restructured to reduce execution time. The specific mission studies reported on are the direct and Venus swingby missions to the comet Encke and solar electric propulsion missions to Encke and to a distance of 0.25 AU from the sun.
Study of the horizontal guidance of aircraft in and near the terminal area. The problem of guiding an aircraft in minimum time from an arbitrary point to the outer marker is formulated as a nonlinear optimal control problem, and the control law solution is obtained by the application of the maximum principle. It is found that for some initial states the problem is singular. Furthermore, the extremal controls for this problem are not unique. Consequently, the optimal controls must be obtained on the basis of the value of the performance index. The control law is implemented in the form of a digital computer program which computes the optimal trajectory for arbitrary initial conditions.
Consideration of the problem of optimal ascent from an initial circular planetary orbit to some specified final energy level by a spacecraft equipped with a low-thrust engine. Optimal is defined as minimum time. An accurate small parameter perturbation solution is presented, and the optimal trajectory is analyzed and compared with a tangential thrust trajectory.
A centerline heating approximation is proposed in which only three basic equations need be solved. The heat rates correlate well with those obtained by more complex procedures. The approximation is readily adaptable to existing trajectory optimization programs to provide realistic surface temperature constraint capability with little increase in computer storage capacity and computer time. It is based on an analysis of heat-rate data computed for altitudes from 36,000 to 122,000 m, velocities from 600 to 7900 m/sec, and angles of attack from 0 to 60 degrees.