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Thompson, Z.

Publications and source records attributed to Thompson, Z..

11 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Influence of hot isostatic pressing on the performance of aluminum alloy fabricated by ultrasonic additive manufacturing

Ultrasonic additive manufacturing (UAM) is a solid-state manufacturing technique employing principles of ultrasonic welding coupled with mechanized tape layering to fabricate fully functional parts. However, UAM-fabricated parts often exhibit a reduction in strength when loaded normal to the welding interfaces (Z-direction). Here, the effect of hot isostatic pressing (HIP) on UAM builds of aluminum alloy was explored. Tensile testing and microstructure characterization were conducted; it was established that HIP eliminated the brittle Z-direction fracture and improved the strength and ductility of the Z-direction specimens. HIP eliminated voids and produced recrystallized structure; however, welding interfaces survived the HIP treatment.

36 MATERIALS SCIENCE↗
NASA NTRS1974

Optimum propellant usage for reaction jet systems of space vehicles

The on-off type control for reaction jet systems is proven to be the optimal fuel scheme. However, due to the nonlinear characteristics of this type control, no direct method of solution is known for this optimal process being applied to the attitude control of space vehicles. This paper will discuss the optimization of fuel usage for an attitude control of space vehicles. A computation technique is developed for the calculation of optimal control law. The method of calculus of variations is applied to the estimation of the changes of performance index as well as terminal constraints. Thus an algorithm is obtained by the steepest descent method. A numerical example is given in the paper.

Liu, T. C.↗
NASA NTRS1974

Autonomous target relative navigation

The present work outlines eight candidate navigation systems for autonomous target relative navigation near a comet, asteroid, or planet. An analytic model is developed for each system, showing how the solution of the relative state vector is obtained from measurement data.

Brock, H. I.↗
NASA NTRS1974

A method for compensating on-off relay control systems

A method is proposed for adjusting the characteristics of an on-off relay or contactor servomechanism to make it behave as a positive hysteresis relay intended to stabilize a control system. In this method, the nonlinear portion of the system, instead of the linear portion, is shaped by adding a positive hysteresis circuit to the system. A servomotor system using a typical relay for position control is studied as an application of the proposed method. It is shown that since the synthesis is mainly to improve the nonlinear characteristics of the on-off relay, the method will not affect the characteristics of other elements in the system, which is indispensable to the control of space vehicles.

Thompson, Z.↗
NASA NTRS1974

Unmanned docking

An algorithm is developed which effects unmanned docking of two space vehicles. The docking is controlled by an onboard computer and sensor. Control laws are expressed in two phase-plane trajectories such that modest computer load results. Simulation reveals time-fuel trades and effects of orbit, noise, etc.

Pace, M.↗
NASA NTRS1973

Identification of comet nucleus from comet coma.

The study of comets is of important scientific value as part of the exploration of the solar system. This paper proposes a method, called 'stationary target identification,' to detect the nucleus within the coma. The method makes use of the fact that the coma is ever expanding about the nucleus. Therefore, when a radar beam is used for detection, the coma particles will produce a return signal that is Doppler shifted. The effects of the spatial extent of the coma and Doppler bandwidth of the coma returns upon the required data processing are considered. Also different methods of implementation are considered.-

Brock, H. I.↗
NASA NTRS1973

Optimal control of a variable spin speed CMG system for space vehicles

Many future NASA programs require very high accurate pointing stability. These pointing requirements are well beyond anything attempted to date. This paper suggests a control system which has the capability of meeting these requirements. An optimal control law for the suggested system is specified. However, since no direct method of solution is known for this complicated system, a computation technique using successive approximations is used to develop the required solution. The method of calculus of variations is applied for estimating the changes of index of performance as well as those constraints of inequality of state variables and terminal conditions. Thus, an algorithm is obtained by the steepest descent method and/or conjugate gradient method. Numerical examples are given to show the optimal controls.

Liu, T. C.↗
NASA NTRS1972

Actuator participation in a bending mode identification system

A hydraulic actuator designed for a thrust vector control system used as a shaker for a vehicle to determine the bending mode frequencies is described. The actuator is used as the prime mover and the frequency sensor for the flexible vehicle in a test tower. Advantages in using the actuator piston position with respect to a commanded position to obtain the bending mode frequencies are shown.

Thompson, Z.↗
NASA NTRS1972

Optimum switching boundaries for space vehicle control.

Description of a new scheme using parabolic switching boundaries as opposed to the current method of linear switching to improve the fuel consumption of manned orbital space vehicles. Fuel consumption during error recovery and limit cycle phases are both considered.

Brock, H. I.↗
NASA NTRS1972

Digital controller for high pressure rocket engine.

Description of a general approach for the design of an adaptive digital control system for liquid bipropellant rocket engines. The technique employs linearized transfer functions derived from perturbations of an engine simulation. The linear models serve as a basis on which to develop candidate closed-loop control laws quickly and economically.

Thompson, Z.↗