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Home>Products>Journal and Reviews>I.RE.AS.E.>Latest issue International Review of Aerospace Engineering - December 2008 - Papers
International Review of Aerospace Engineering - Papers
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. Copyright © 2008 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Trajectory planning, flatness, convexification, genetic algorithm, superquadrics.
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. Copyright © 2008 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Attitude Stabilization, Classical Linearization, Optimal Linearization, Domain Densification.
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. Copyright © 2008 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Fuzzy logic, genetic algorithms, satellite, attitude control.
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.
Keywords: Electrodynamic Levitation Suspension, Launch-Assist, Rocket Performance.
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. Copyright © 2008 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Evolutionary Computation, Flight Testing, Path Planning, UAV.
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. Copyright © 2008 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: supersonic jets, waves, expanded supersonic flow, shock-cell.
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