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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Simulation of a flexible spinning vehicle

Results are presented of experimental investigation of the controlled and uncontrolled dynamical behavior of a rotating or artificial gravity space station including flexible body effects. A dynamically scaled model was supported by a spherical air bearing which provided a nearly moment free environment. Reaction jet system were provided for spin-up and spin-down and for damping of wobble motion. Two single-gimbal gyros were arranged as a control moment gyro wobble damping system. Remotely controllable movable masses were provided to simulate mass shift disturbances such as arise from crew motions. An active mass balance wobble damping system which acted to minimize the wobble motions induced by crew motions was also installed. Flexible body effects were provided by a pair of inertia augmentation booms. Inertia augmentation booms are contemplated for use on rotating space stations to cause the spin axis moment of inertia to be the largest of the three moments of inertia as is necessary to assure gyroscopic stability. Test runs were made with each of the control systems with the booms locked (rigid body) and unlocked (flexible body).

Baudry, W. A.↗
NASA NTRS1972

Supplementary active stabilization of nonrigid gravity gradient satellites

The use of active control for stability augmentation of passive gravity gradient satellites is investigated. The reaction jet method of control is the main interest. Satellite nonrigidity is emphasized. The reduction in the Hamiltonian H is used as a control criteria. The velocities, relative to local vertical, of the jets along their force axes are shown to be of fundamental significance. A basic control scheme which satisfies the H reduction criteria is developed. Each jet is fired when its velocity becomes appropriately large. The jet is de-energized when velocity reaches zero. Firing constraints to preclude orbit alteration may be needed. Control is continued until H has been minimized. This control policy is investigated using impulse and rectangular pulse models of the jet outputs.

Keat, J. E.↗
NASA NTRS1973

Control of spin ambiguity during reorientation of an energy dissipating body

A quasi-rigid body initially spinning about its minor principal axis and experiencing energy dissipation will enter a tumbling mode and eventually reorient itself such that stable spin about its major principal axis is achieved. However, in this final state the body may be spinning in a positive or negative sense with respect to its major axis and aligned in a positive or negative sense with the inertially fixed angular momentum vector. This ambiguity can be controlled only through an active system. The associated dynamical formulations and simulations of uncontrolled reorientations are presented. Three control schemes are discussed and results offered for specific examples. These schemes include displacement of internal masses, spinning up of internal inertia, and reaction jets, all of which have demonstrated the ability to control spin ambiguity.

Kaplan, M. H.↗
NASA NTRS1978

Design Development of the Apollo Lunar Module

The lunar module autopilot is a first generation digital control system design. The two torque sources available for the control function of the descent stage configuration consist of 16 reaction jets and a slow, gimbaled, throttlable engine. Design history, the design requirements, criteria, constraints, and general design philosophy of the control system development are reviewed. Comparative flight test results derived from design testing are presented.

Cox, K. L.↗
NASA NTRS1979

Ground effects on USB configurations

Recent investigations of ground effects on aerodynamic characteristics have been stimulated by the interest in powered-lift STOL airplanes. The ground effects on upper-surface-blowing (USB) configurations may involve change in both the circulation forces and the jet reaction forces. In this note, a theoretical method is proposed for predicting these effects. It is shown that the predicted results agree well with available experimental data. In particular, the wing-alone method is shown to be incapable of predicting the ground effects of USB configurations.

Lan, C. E.↗
NASA NTRS1979

A theoretical investigation of ground effects on USB configurations

A formulation predicts the variation of circulation forces and jet reaction forces in ground proximity as a function of ground height. The predicted results agree well with available experimental data. It is shown that the wing-alone theory is not capable of predicting the ground effect for USB configurations.

Lan, C. E.↗
NASA NTRS1981

Silane pyrolysis in a free-space reactor

The Union Carbide process for producing silicon for photovoltaic applications proceeds via high purity silane as an intermediate. Decomposition of silane is accomplished in a freespace reactor which utilizes recirculating product hydrogen and silicon to transfer energy from a heated wall to an entering silane jet. Reaction occurs away from the wall, minimizing problems with wall deposition and contamination. A series of long duration and throughput tests has proven the feasibility of this concept. High purity powder can be produced at flows up to 4.5 kg/hr (10 lb/hr) in a 0.2 m (8 inch) diameter reactor with better than 99.99% conversion efficiency. This work is funded by DOE under JPL's Low Cost Solar Array (LSA) program.

Lay, J. R.↗
NASA NTRS1982

Magnetic suspension - The next generation in precision pointing

Today's large optical experiments, both free-flying and Shuttle-borne, are finding an increasing need for a stable pointing platform in a vibration environment. As the resolution of optical systems has improved, conventional techniques for isolation and pointing have become less attractive. This paper describes the present state of the art in magnetic suspension pointing systems. This technology combines the functions of translational isolation and precision pointing to achieve performance in the 0.01 arcsec range, in the presence of disturbances such as random noise or reaction jet firings. Ongoing technology refinements and their importance to the experiment community are also discussed. The key to these refinements is a high-resolution, vibrating quartz force sensor that will improve pointing stability.

Hamilton, B. J.↗
NASA NTRS1983

On the flight derived/aerodynamic data base performance comparisons for the NASA Space Shuttle entries during the hypersonic regime

Aerodynamic performance data from the first four Shuttle reentry flights are compared with preflight predictions covering hypersonic longitudinal mode down to Mach 2. The extraction of the flight coefficients, as measured by the spacecraft angular rates and the linear accelerations, derived from the inertial measurement unit, the best estimate trajectory, and the remotely measured atmosphere are discussed. The ground predictions were developed from 30,000 hr of wind tunnel testing. Actual flight data are presented for 80-260 kft, from Mach 2-26, comprising the dynamic pressure, the vehicle air relative attitude angles, control surface deflections, reaction jet activity, and body axis rates and accelerations. The second and fourth flights gave results which deviated from predictions between 230-260 kft. The accuracy limits of the derived atmospheric densities are considered, together with potential data base updates in the light of limitations imposed on the corrections by available flight data.

Findlay, J. T.↗
NASA NTRS1982

Computer program for prediction of capture maneuver probability for an on-off reaction controlled upper stage

A FORTRAN coded computer program which computes the capture transient of a launch vehicle upper stage at the ignition and/or separation event is presented. It is for a single degree-of-freedom on-off reaction jet attitude control system. The Monte Carlo method is used to determine the statistical value of key parameters at the outcome of the event. Aerodynamic and booster induced disturbances, vehicle and control system characteristics, and initial conditions are treated as random variables. By appropriate selection of input data pitch, yaw and roll axes can be analyzed. Transient response of a single deterministic case can be computed. The program is currently set up on a CDC CYBER 175 computer system but is compatible with ANSI FORTRAN computer language. This routine has been used over the past fifteen (15) years for the SCOUT Launch Vehicle and has been run on RECOMP III, IBM 7090, IBM 360/370, CDC6600 and CDC CYBER 175 computers with little modification.

Knauber, R. N.↗
NASA NTRS1985

Space robot simulator vehicle

A Space Robot Simulator Vehicle (SRSV) was constructed to model a free-flying robot capable of doing construction, manipulation and repair work in space. The SRSV is intended as a test bed for development of dynamic and static control methods for space robots. The vehicle is built around a two-foot-diameter air-cushion vehicle that carries batteries, power supplies, gas tanks, computer, reaction jets and radio equipment. It is fitted with one or two two-link manipulators, which may be of many possible designs, including flexible-link versions. Both the vehicle body and its first arm are nearly complete. Inverse dynamic control of the robot's manipulator has been successfully simulated using equations generated by the dynamic simulation package SDEXACT. In this mode, the position of the manipulator tip is controlled not by fixing the vehicle base through thruster operation, but by controlling the manipulator joint torques to achieve the desired tip motion, while allowing for the free motion of the vehicle base. One of the primary goals is to minimize use of the thrusters in favor of intelligent control of the manipulator. Ways to reduce the computational burden of control are described.

Cannon, R. H., Jr.↗
NASA NTRS1987

Nonlinear adaptive attitude control of spacecraft

A model reference adaptive control law is presented for large angle rotational maneuvers of spacecraft using reaction jets. It is assumed that the various parameters of the spacecraft are completely unknown, and unknown but bounded disturbance torques are acting on the spacecraft. The controller includes a dynamic system in the feedback path. Simulation results are presented to show that fast, large angle rotational maneuvers can be performed using the adaptive controller in spite of uncertainty in the system.

Singh, Sahjendra N.↗
NASA NTRS1987

On-line identification and attitude control for SCOLE

This paper documents on-line linear least-square identification and attitude control of SCOLE, a laboratory apparatus representing an offset-feed antenna attached to the Space Shuttle. Identification is done autonomously by starting a slew maneuver in pitch or roll with reaction jets and observing the time history data of associated Euler angles when the jets are quiescent. Linear least-square analysis is used to select the parameters that best fit the output of an Autoregressive (AR) model to the data. The control effectiveness of the jets is determined in a subsequent test, again using linear least squares. The parameters so derived are used to design switching lines for time-optimal attitude control. This report describes the identification and control algorithms and the experimental apparatus and procedures used. Also, experimental data are presented that reflect the performance of the identification algorithms and the attitude control system.

Montgomery, R. C.↗
NASA NTRS1989

Pulse modulated control synthesis for a flexible spacecraft

The describing function method is employed for the nonlinear control analysis and design of a flexible spacecraft equipped with pulse modulated reaction jets. The method provides a means of characterizing the pulse modulator in terms of its gain and phase for structural mode limit cycle analysis. Although the describing function method is inherently inexact and is not widely used in practice, a new way of utilizing it for practical control design problems is presented. It is shown that the approximations inherent in the method can be accounted as a modeling uncertainty for the nonlinear control robustness analysis. The pulse modulated control system of the Intelsat 5 spacecraft is used as an example to illustrate the concept and methodology developed in the paper. The nonlinear stability margins predicted by the describing function analysis are verified from nonlinear simulations.

Anthony, Tobin C.↗
NASA NTRS1989

Overview of computational control research at UT Austin

An overview of current research activities at UT Austin is presented to discuss certain technical issues in the following areas: (1) Computer-Aided Nonlinear Control Design: In this project, the describing function method is employed for the nonlinear control analysis and design of a flexible spacecraft equipped with pulse modulated reaction jets. INCA program has been enhanced to allow the numerical calculation of describing functions as well as the nonlinear limit cycle analysis capability in the frequency domain; (2) Robust Linear Quadratic Gaussian (LQG) Compensator Synthesis: Robust control design techniques and software tools are developed for flexible space structures with parameter uncertainty. In particular, an interactive, robust multivariable control design capability is being developed for INCA program; and (3) LQR-Based Autonomous Control System for the Space Station: In this project, real time implementation of LQR-based autonomous control system is investigated for the space station with time-varying inertias and with significant multibody dynamic interactions.

Bong, Wie↗
NASA NTRS1992

Minimizing spacecraft attitude disturbances in space manipulator systems

This paper presents a technique called the enhanced disturbance map to plan space manipulator motions that will result in relatively low spacecraft disturbances. This subject is of significant concern because future robotic systems used in space may encounter problems due to the dynamic disturbances imposed on their spacecraft by their manipulator motions. Although a spacecraft's attitude control reaction jets can compensate for these dynamic disturbances, jet fuel is a limited resource and excessive disturbances would limit the life of a system. The enhanced disturbance map can aid in understanding this complex problem and in the development of algorithms to reduce disturbances, including ones that use manipulator redundancy to eliminate the disturbances.

Torres, Miguel A.↗
NASA NTRS1991

Initial piloted simulation study of geared flap control for tilt-wing V/STOL aircraft

A simulation study of a representative tilt wing transport aircraft was conducted in 1990 on the Ames Vertical Motion Simulator. This simulation is in response to renewed interest in the tilt wing concept for use in future military and civil applications. For past tilt wing concepts, pitch control in hover and low-speed flight has required a tail rotor or reaction jets at the tail. Use of mono cyclic propellers or a geared flap have also been proposed as alternate methods for providing pitch control at low speed. The geared flap is a subject of this current study. This report describes the geared flap concept, the tilt wing aircraft, the simulation model, the simulation facility and experiment setup, the pilots' evaluation tasks and procedures, and the results obtained from the simulation experiment. The pilot evaluations and comments are also documented in the report appendix.

Guerrero, Lourdes M.↗
NASA NTRS1993

New Technologies for Space Avionics, 1993

The report reviews a 1993 effort that investigated issues associated with the development of requirements, with the practice of concurrent engineering and with rapid prototyping, in the development of a next-generation Reaction Jet Drive Controller. This report details lessons learned, the current status of the prototype, and suggestions for future work. The report concludes with a discussion of the vision of future avionics architectures based on the principles associated with open architectures and integrated vehicle health management.

Aibel, David W.↗