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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 559 records · Page 31

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NASA NTRS1989

Coma and tail trajectory design for the CRAF mission

The design of the trajectory for the proposed Comet Rendezvous Asteroid Flyby (CRAF) mission to study comet coma and tail development is examined. A two part trajectory is planned for the CRAF mission to study comet Kopff. It is proposed that, during the 213 day perihelion phase of the trajectory, CRAF should perform multiple petallike flybys at 50-5000 km from the comet's nucleus. Nine days after the perihelion, the spacecraft would transition into the comet tail in the antisun direction to a maximum distance of 50,000 km. The objectives of these two phases of exploration are discussed.

Ionasescu, Rodica↗

NASA NTRS1990

Minimum fuel trajectories for a low-thrust power-limited mission to the moon and to Lagrange points L4 and L5

Minimum fuel trajectories from a low earth parking orbit to Lagrange points L4 or L5 and to the moon are obtained for a low-thrust limited-power spacecraft, with thrust acceleration levels of the order of 0.001 G. The procedure to find a trajectory to the libration point starts from an analytical description of a slightly elliptical spiral, given by Breakwell and Rauch. The earth moon trajectory is found by matching an earth spiral to a moon spiral on the sphere of influence. Earth oblateness effect is considered.

Breakwell, John V.↗

NASA NTRS1990

Minimum fuel trajectory for the aerospace-plane

An overall trajectory for a single-stage-to-orbit vehicle with an initial weight of 234 tons is calculated, and four different propulsion models including turbojet, ramjet, scramjet, and rocket are considered. First, the atmospheric flight in the thicker atmosphere is discussed with emphasis on trajectory optimization, optimization problem, aerodynamic problem, propulsion model, and initial conditions. The performance of turbojet and ramjet-scramjet engines is analyzed; and then the flight to orbit is assessed from the optimization point of view. It is shown that roll modulation saves little during the trajectory, and the combined application of airbreathing propulsion and aerodynamic lift is suggested.

Breakwell, John V.↗

NASA NTRS1990

Iso-chemical potential trajectories in the P-T plane for He II

Trajectories of constant chemical potential in the P-T plane serve as an integral formulation of London's equation. The trajectories are useful for analysis and synthesis of fountain effect pump performance. A family of trajectories is generated from available numerical codes.

Maytal, B.↗

NASA NTRS1991

Plotting Orbital Trajectories For Maneuvers

Interactive Orbital Trajectory Planning Tool (EIVAN) computer program is forward-looking interactive orbit-trajectory-plotting software tool for use with proximity operations (operations occurring within 1-km sphere of space station) and other maneuvers. Developed to plot resulting trajectories, to provide better comprehension of effects of orbital mechanics, and to help user develop heuristics for planning missions on orbit. Program runs with Microsoft's Excel for execution on MacIntosh computer running MacIntosh OS.

Brody, Adam R.↗

NASA NTRS1990

Optimization and guidance of flight trajectories for the national aerospace plane

The research on optimal trajectories for the National Aerospace Plane (NASP) performed by the Aero-Astronautics Group of Rice University from June 22, 1989 to December 31, 1990 is summarized. The aerospace plane is assumed to be controlled via the angle of attack and the power setting. The time history of the controls is optimized simultaneously with the switch times from one powerplant to another and the final time. The intent is to arrive at NASP guidance trajectories exhibiting many of the desirable characteristics of NASP optimal trajectories.

Miele, Angelo↗

NASA NTRS1990

Trajectory optimization for real-time guidance. I - Time-varying LQR on a parallel processor

A key algorithmic element of a real-time trajectory optimization hardware/software implementation, the quadratic program (QP) solver element, is presented. The purpose of the effort is to make nonlinear trajectory optimization fast enough to provide real-time commands during guidance of a vehicle such as an aeromaneuvering orbiter. Many methods of nonlinear programming require the solution of a QP at each iteration. In the trajectory optimization case the QP has a special dynamic programming structure, a LQR-like structure. QP algorithm speed is increased by taking advantage of this special structure and by parallel implementation.

Psiaki, Mark L.↗

NASA NTRS1991

PEM-West trajectory climatology and photochemical model sensitivity study prepared using retrospective meteorological data

Trajectory and photochemical model calculations based on retrospective meteorological data for the operations areas of the NASA Pacific Exploratory Mission (PEM)-West mission are summarized. The trajectory climatology discussed here is intended to provide guidance for flight planning and initial data interpretation during the field phase of the expedition by indicating the most probable path air parcels are likely to take to reach various points in the area. The photochemical model calculations which are discussed indicate the sensitivity of the chemical environment to various initial chemical concentrations and to conditions along the trajectory. In the post-expedition analysis these calculations will be used to provide a climatological context for the meteorological conditions which are encountered in the field.

Merrill, John T.↗

NASA NTRS1992

Trajectory optimization for the National Aerospace Plane

The primary objective of this research is to develop an efficient and robust trajectory optimization tool for the optimal ascent problem of the National Aerospace Plane (NASP). This report is organized in the following order to summarize the complete work: Section two states the formulation and models of the trajectory optimization problem. An inverse dynamics approach to the problem is introduced in Section three. Optimal trajectories corresponding to various conditions and performance parameters are presented in Section four. A midcourse nonlinear feedback controller is developed in Section five. Section six demonstrates the performance of the inverse dynamics approach and midcourse controller during disturbances. Section seven discusses rocket assisted ascent which may be beneficial when orbital altitude is high. Finally, Section eight recommends areas of future research.

Lu, Ping↗

NASA NTRS1991

Trajectory optimization and guidance for a hypersonic vehicle

The optimal ascent problem for a hypersonic vehicle is formulated as an inverse dynamic problem. This formulation is essential in solving the trajectory optimization problem via the nonlinear programming approach. Both minimum-fuel and minimax type of performance indices are considered. The results reveal important features of the optimal trajectory and controls, and they are subsequently used to construct a nonlinear feedback midcourse control law. This control law not only greatly simplifies the difficult constrained optimization problem and yields improved solutions, but is also suitable for onboard implementation. Finally, off-nominal trajectory guidance is addressed using combination of feedback compensation and onboard generation of control through the inverse dynamics approach.

Lu, Ping↗

NASA NTRS1992

Parallel solver for trajectory optimization search directions

A key algorithmic element of a real-time trajectory optimization hardware/software implementation is presented, the search step solver. This is one piece of an algorithm whose overall goal is to make nonlinear trajectory optimization fast enough to provide real-time commands during guidance of a vehicle such as an aeromaneuvering orbiter or the National Aerospace Plane. Many methods of nonlinear programming require the solution of a quadratic program (QP) at each iteration to determine the search step. In the trajectory optimization case, the QP has a special dynamic programming structure. The algorithm exploits this special structure with a divide- and conquer type of parallel implementation. The algorithm solves a (p.N)-stage problem on N processors in O(p + log2 N) operations. The algorithm yields a factor of 8 speed-up over the fastest known serial algorithm when solving a 1024-stage test problem on 32 processors.

Psiaki, M. L.↗

NASA NTRS1992

Galileo trajectory design

The trajectory design of the Galileo spacecraft is examined. The Galileo spacecraft was launched on a six-year long trip to Jupiter in October 1989. A new Venus-Earth-Earth-Gravity Assist (VEEGA) trajectory mode is being used for the transfer to Jupiter and involves two phasing orbits around the sun and gravity-assist flybys with Venus. The aggregate delta V acquired from these flybys is 18.3 km/s. The interplanetary trajectory includes a close flyby of asteroid 951-Gaspra in October 1991 and a possible flyby of 243-Ida in August 1993. After arrival at Jupiter in December 1995, the previously released Galileo atmospheric probe will relay data to earth via the Galileo Orbiter. The orbital phase of the mission will involve 10 orbits of Jupiter over a 22 month period. In this phase the Orbiter will use repeated gravity-assisted flybys of Europa, Ganymede and Callisto during which Jupiter, its magnetosphere and the Galilean satellites will be investigated. The mission is scheduled to end in October 1997.

D'Amario, Louis A.↗

NASA NTRS1992

Canonical transformations for space trajectory optimization

Canonical transformations are developed between the Cartesian coordinates, equinoctial elements, trajectory variables, and orbital elements for coplanar space trajectory optimization problems. The canonical transformations permit the state and adjoint or their solution, transversality conditions, the optimal control, and integrals of the motion, to be transformed between any of the common sets of coordinates for planar space trajectory optimization problems. Variations on the canonical transformations shown are straightforward to develop given the group properties of the canonical transformations.

Haissig, Christine M.↗

NASA NTRS1992

Transfer trajectory design for the SOHO libration-point mission

It is shown that transfer trajectories to the halo orbit exist throughout the year, with a one week closure of the launch window each month because of unfavorable lunar perturbations that cannot be corrected in the case of transfer trajectory insertion errors. The launch window for transfers to large-amplitude Lissajous orbits is virtually the same as that for transfers to the baseline halo orbit. Details of these trajectories are described and questions about groundstation coverage are discussed.

Dunham, D. W.↗

NASA NTRS1992

An inverse dynamics approach to trajectory optimization for an aerospace plane

An inverse dynamics approach for trajectory optimization is proposed. This technique can be useful in many difficult trajectory optimization and control problems. The application of the approach is exemplified by ascent trajectory optimization for an aerospace plane. Both minimum-fuel and minimax types of performance indices are considered. When rocket augmentation is available for ascent, it is shown that accurate orbital insertion can be achieved through the inverse control of the rocket in the presence of disturbances.

Lu, Ping↗

NASA NTRS1992

Interplanetary Program to Optimize Simulated Trajectories (IPOST). Volume 1: User's guide

IPOST is intended to support many analysis phases, from early interplanetary feasibility studies through spacecraft development and operations. The IPOST output provides information for sizing and understanding mission impacts related to propulsion, guidance, communications, sensor/actuators, payload, and other dynamic and geometric environments. IPOST models three degree of freedom trajectory events, such as launch/ascent, orbital coast, propulsive maneuvering (impulsive and finite burn), gravity assist, and atmospheric entry. Trajectory propagation is performed using a choice of Cowell, Encke, Multiconic, Onestep, or Conic methods. The user identifies a desired sequence fo trajectory events, and selects which parameters are independent (controls) and dependent (targets), as well as other constraints and the coat function. Targeting and optimization is performed using the Stanford NPSOL algorithm. IPOST structure allows sub-problems within a master optimization problem to aid in the general constrained parameter optimization solution. An alternate optimization method uses implicit simulation and collocation techniques.

Hong, P. E.↗

NASA NTRS1992

Analytical solutions to constrained hypersonic flight trajectories

The flight trajectory of aerospace vehicles subject to a class of path constraints is considered. The constrained dynamics is shown to be a natural two-time-scale system. Asymptotic analytical solutions are obtained. Problems of trajectory optimization and guidance can be dramatically simplified with these solutions. Applications in trajectory design for an aerospace plane strongly support the theoretical development.

Lu, Ping↗

NASA NTRS1991

Manned space flight - The effects of Shuttle perturbations on orbital trajectory

Orbit determination and trajectory prediction for the National Space Transportation System program is complicated by trajectory perturbations that are unique to the Shuttle. Orbital energy changes are seen during extended hold periods as well as during unmodeled attitude maneuvers. While a portion of these changes are due to dynamical mismodeling, the majority of the changes are due to dynamics that are unique to the Shuttle. The ability to take these previously unmodeled effects into account will allow a more accurate preflight and real-time prediction of the orbital trajectory to support payload requirements. This paper deals with the determination of the databases used to determine preflight and real-time energy growth and the results of using the databases to accurately predict energy growth for future flights.

Barrett, Charles P.↗