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Fowler, W. T.

Publications and source records attributed to Fowler, W. T..

15 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Dynamics and control of a tumbling satellite retrieval device

The problem of capturing a satellite in an uncontrolled three-axis tumble is addressed. The proposed solution is a truss which opens and engulfs the satellite, resulting in coincident centers of mass. Torques are then applied to the truss so that it matches the tumble rates of the satellite and remains motionless in the satellite's reference frame. Equations are derived which show how to vary the mass distribution to match any set of inertia moment ratios. The physical system is shown to be controllable. An optimal control algorithm for tumble matching is then derived and a computer simulation is developed.

Neff, J. M.↗
NASA NTRS1991

Six-degree-of-freedom simulation of an astronaut detumble system

The problem of stabilizing the attitude of an untethered astronaut in a three-axis tumble is addressed. A simple six thruster detumbling system mounted on the astronaut's Portable Life Support System backpack is analyzed as a possible solution. A six-degree-of-freedom dynamical model is constructed using the Clohessy-Wiltshire equations, Euler's moment equations, and quaternions. The six thruster system produces both moments and forces when activated. However, it is shown that the thrust forces acting on the body during detumbling do not significantly affect the translational motion.

Fowler, W. T.↗
NASA NTRS1991

Minimum-fuel rescue trajectories for the Extravehicular Excursion Unit

The problem of determining minimum-fuel trajectories for rescuing astronauts or equipment which become separated from a Space Station is addressed. Using the Clohessy-Wiltshire equations of relative motion and assuming impulsive Delta-Vs, the minimum-fuel rescue problem is shown to be a parameter optimization problem. Minimum-fuel rescue trajectories are found for seventeen test cases using a recursive quadratic programming algorithm. The results are analyzed and general rules for astronaut rescue and equipment retrieval are developed.

Fowler, W. T.↗
NASA NTRS1978

Simple models for the shuttle remote manipulator system

The investigation is aimed at establishing a series of simple models which can be used to study the forces and moments which occur due to the reaction control system (RCS) jet plume firings during a deployment or retrieval of an IUS type payload. The models considered in this investigation are primarily planar in nature. In this study primary attention is given to the roles the payload play in determining the overall moments on the remote manipulator system arm.

Fowler, W. T.↗
NASA NTRS1972

Thermal protection optimization for the space shuttle.

This paper discusses optimal entry trajectories for the space shuttle that minimize the weight of an entry thermal protection system. The analysis was made using mathematical models of two types of thermal protection systems that were under consideration for the space shuttle: a metallic thermal protection system, and a reusable surface insulation thermal protection system. Optimal entries were generated using maximum orbiter nose temperature as a parameter. Thermal protection system weights were computed for both fixed and variable angles of attack using three-dimensional entry trajectories. Results indicated that variable angle-of-attack entries require less thermal protection system weight than entries at a constant angle of attack (35 deg) for both systems considered. Results also showed that 95 to 99 per cent of the thermal protection system weight requirement resulted from flight regimes in which the flow was still laminar.

Garcia, F., Jr.↗
NASA NTRS1972

Calculation of free-fall trajectories using numerical optimization methods.

An important problem in space flight is the calculation of trajectories for nonthrusting vehicles between fixed points in a given time. A new procedure based on Hamilton's principle for solving such two-point boundary-value problems is presented. It employs numerical optimization methods to perform the extremization required by Hamilton's principle. This procedure is applied to the calculation of an Earth-Moon trajectory. The results show that the initial guesses required to obtain an iteration procedure which converges are not critical and that convergence can be obtained to any predetermined degree of accuracy.

Hull, D. G.↗