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International Review of Aerospace Engineering - December 2008 - Papers

Onboard Path Planning for Reusable Launch Vehicles Application to the Shuttle Orbiter Reentry Mission
An Optimal Linearization Approach to Spacecraft Attitude Stabilization
A Geno-fuzzy Fast Attitude Controller for Satellites Stabilized by Reaction Wheels
Rocket Performance Enhancement with Launch-assist
Flight Demonstration of Realtime Path Planning of an UAV Using Evolutionary Computation and Rule-Based Hybrid Method
Waves in Correctly Expanded Supersonic Jets
Solid Elements Based on the Explicit FEM
Optimization and Lifing Simulation Accelerates Turbomachinery Design Process
A Model for Hollow Cathode Surface Work Function Evolution
Numerical Computation for High Speed Aerodynamic Heat Transfer on the Axisymmetric Configuration

International Review of Aerospace Engineering - Papers

Onboard Path Planning for Reusable Launch Vehicles Application to the Shuttle Orbiter Reentry Mission
by V. Morio, F. Cazaurang, A. Zolghadri, P. Vernis

Abstract - This paper proposes a method for designing a model-based onboard path planning unit for reusable launch vehicles. Flatness approach is used to map the system dynamics into a lower dimension space. As a consequence, the number of optimization variables involved in the optimal control problem is reduced. In addition, nonconvex nonlinear trajectory constraints in the flat output space are inner approximated by means of superquadric shapes. Genetic algorithms are used to find a global solution both for the superquadric shapes and the associated geometric transformations tuning parameters. Finally, simulations results are presented to illustrate the proposed approach. Simulations are based on the terminal area energy management phase of the Shuttle orbiter STS-1 reentry mission.

Keywords: Trajectory planning, flatness, convexification, genetic algorithm, superquadrics.

An Optimal Linearization Approach to Spacecraft Attitude Stabilization
by K. Bousson, M. S. S. Quintiães

Abstract - Classical linearization is based on the first order Taylor approximation of a nonlinear dynamic model in the neighborhood of a given operating point. The resulting linear model approximates the original nonlinear model within relatively small variations about the operating point. Besides, the domain within which the linearized model is valid is not known precisely. The present paper deals with nonlinear spacecraft attitude stabilization using rather an approach based on optimal linearization of the nonlinear motion model. This consists in finding the best linear approximation of the nonlinear model of the spacecraft attitude motion over a given state and control domain, and then designing a linear quadratic controller to stabilize the spacecraft on the basis of the optimal linear model. The method was validated through simulation result comparisons with respect to the classical linearization concept using various scenarios including failure-free operating modes as well as modes with different levels of failure. For each case, the model that was obtained from optimal linearization enabled the controller to achieve much better stabilization performances than did the one stemming from classical linearization.

Keywords: Attitude Stabilization, Classical Linearization, Optimal Linearization, Domain Densification.

A Geno-fuzzy Fast Attitude Controller for Satellites Stabilized by Reaction Wheels
by H. M. Omar

Abstract - Fuzzy-based controller has many parameters that govern its performance which complicate the design process of this type of controllers. In this paper, a systematic procedure is proposed to design an optimal fuzzy logic controllers (FLC) for dynamical systems by the method of genetic algorithms. Then, this procedure is implemented to design a control system for three-axis satellites stabilized by reaction wheels. The parameters of FLC which include the rules and the distributions of membership functions are determined based on solving an optimization problem by minimizing a performance index. To get accurate pointing, longlife time and fast response for the satellite, the performance index includes the deviation of the satellite from its nominal position, the consumed power and the time of deviation. The simulations results show that the proposed technique was able to determine all the FLC parameters and generate a controller with a satisfactory performance.

Keywords: Fuzzy logic, genetic algorithms, satellite, attitude control.

Rocket Performance Enhancement with Launch-assist

by A. Uranga, R. B. Meinke, H. M. Gutierrez, D. R. Kirk

Abstract - This work examines performance advantages, such as gain in altitude, payload and range, which might be provided to a variety of rockets and missiles through the use of magnetically levitated launch-assist systems used as first stage prior to firing the main rocket(s). Using subsonic launch-assist speeds (Mach 0.8), it was found that rocket payloads to orbit can be increased by up to 35 percent, and dynamic pressure loads reduced compared to a conventional launch solely based on rockets. Performance improves continually with increasing launch speed. The relative importance of projectile aerodynamics was assessed through a range of drag configurations and was found to have a significant impact on performance of vehicles launched with non-zero initial speed. Optimum propulsion ignition delay times were found to exist for projectiles characterized by high launch velocity or high drag. Finally, take-off angles for a given missile and launch speed were optimized, resulting in increased range of up to 42 percent at Mach 0.8.
Copyright © 2008 Praise Worthy Prize S.r.l. - All rights reserved

Keywords: Electrodynamic Levitation Suspension, Launch-Assist, Rocket Performance.

Flight Demonstration of Realtime Path Planning of an UAV Using Evolutionary Computation and Rule-Based Hybrid Method
by S. Higashino, Y. Maruyama

Abstract - A method for path planning of an UAV while avoiding obstacles using Evolutionary Computation and rule-based hybrid method is proposed, and its effectiveness is demonstrated successfully by flights using a small UAV. Evolutionary Computation is used for the optimization of the traveling order of the waypoints which are specified for a certain mission, and for the optimization of the number and positions of the additional waypoints inserted in order to avoid obstacles. The additional waypoints are inserted following the predetermined rule so that the efficiency of the obstacle avoidance improves.

Keywords: Evolutionary Computation, Flight Testing, Path Planning, UAV.

Waves in Correctly Expanded Supersonic Jets
by E. Rathakrishnan

Abstract - This paper presents the physical reasons for the presence of waves in correctly expanded supersonic jets. Even though there is no pressure gradient at the nozzle exit, generating waves to take the exit pressure to the level of back pressure, the large space encountered by the jet makes it to relax. This relaxation positions an expansion fan at the exit of the correctly expanded nozzle. These expansion waves on reflection from the jet boundary form compression waves, thus causing the jet field to become wave dominated.

Keywords: supersonic jets, waves, expanded supersonic flow, shock-cell.

Solid Elements Based on the Explicit FEM

by L. T. Tenek

Abstract - The present article applies the Explicit FEM (finite element method) to the application of two solid elements; element ES4 and ES9. Both have 8 nodes and three degrees of freedom per node (3 global displacements) for a total of 24 degrees of freedom. Modes are applied to both elements and diagonal Modal matrices are formed. Local and global elemental matrices are also developed. All quantities are explicitly derived. Forces and central stresses are also obtained. Three dimensional effects are inherent in the elements. Computational simulations are provided.

Keywords: Solid elements, modes, modal matrices, forces/stresses, computing.

Optimization and Lifing Simulation Accelerates Turbomachinery Design Process

by J. S. Rao

Abstract - Traditionally turbomachinery bladed-disk design relied heavily on testing and this practice continues until recent times. This is because a true simulation on complex damping in the blade-disk material and friction at the interfacial slip surfaces defied blade design engineers. Moreover a simulation process to optimize the shapes of bladed disk mating profiles was not also available to minimize the local plastic strains at stress raiser locations and achieve the optimum life. This paper presents simulation methods for damping estimation and achieving optimum shapes that decreases design cycle time and eliminates testing during design phase to bring new designs faster to market. An example on weight optimization is also illustrated.

Keywords: Shape and Weight Optimization, Damping Simulation, Lifing, Design Simulation, Turbomachinery.

A Model for Hollow Cathode Surface Work Function Evolution

by M. Coletti, S. B. Gabriel

Abstract - In this paper a model to predict the evolution with time of the surface work function of an hollow cathode insert will be presented. The processes involved in BaO deposition and desorption on the surface is described and quantified using chemical data present in the literature. The model is compared with test results from the ELT NSTAR cathode. Predictions obtained from the model have been found to be qualitatively in agreement with the expectations and conservative, model predictions always overestimating the increases in work function with time. An explanation of this has been given noting that all the assumption made in the model tend to overestimate the desorption rates hence producing conservative estimate of the cathode lifetime. Possible ways to improve the model accuracy will be the development of an ignition model and the coupling of the model presented in this paper with a plasma model to take into account the effect that a change in the emission characteristics of the insert surface will produce on the cathode plasma.

Keywords: Hollow cathode, Work function, Hollow cathode lifetime, Barium oxide depletion.

Numerical Computation for High Speed Aerodynamic Heat Transfer on the Axisymmetric Configuration

by Kai-Long Hsiao

Abstract - The study provides a numerical calculation for convection coefficients and heat fluxes due to aerodynamic heating on hypersonic vehicle which are obtained analytically and computationally for protection some thermal mechatronics systems. The heat transfer through a thin, a thick wall were analyzed in the present study. Convection coefficients and heat fluxes due to aerodynamic heating on critical surfaces of hypersonic vehicle are obtained analytically. The applicability of recovery temperature for axisymmetric configuration regions is discussed. Convection coefficient for the axisymmetric configuration region is obtained directly from axisymmetric region correlation. This paper shows and application of Crank-Nicolson scheme to solve numerically transient heat conduction problem conjugate with high speed aerodynamic heating problem. The results show good agreement with a known Lumped system method solution for a thin wall. Finally, it can use to the material design for the high speed flying body.

Keywords: Aerodynamic heat transfer, Lumped system, Axisymmetric configuration.