No description available.

Steady state and transient maneuver problems for a high performance fighter aircraft with and without thrust vectoring are investigated. The steady state aspect of these studies determines control combinations with and without thrust vectoring which optimize selected level-flight point performance criteria including minimum speed, maximum instantaneous range, and maximum sustained turn rate. The transient maneuvers are initiated from straight and level flight and include a longitudinal pitch-up to a desired fuselage pointing angle and a lateral-directional transition (wind-up) to a desired steady level turn rate. For the transient maneuvers, a full six-degree-of-freedom model of the aircraft is used with three conventional aerodynamic controls, throttle control and pitch and yaw thrust vectoring control. Each of the control time histories are parameterized so as to include both the rate and range limits of the controls. A nonlinear programming algorithm is used to determine the control parameter values which yield the minimum time to execute the prescribed maneuvers. Results indicate that thrust vectoring does not significantly change the steady state behavior in the scenarios investigated. However, flight times for the transient maneuvers are found to be reduced by up to 28%. The greatest effect of thrust vectoring occurs at low Mach number. / Master of Science

The problem of maximizing the altitude of a rocket in vertical flight has been extensively analyzed by many writers since the early days of rocketry. In the beginning, solutions were obtained using the classical theory of the Calculus of Variations, and later using Optimal Control theory. For strict assumptions on the drag law and the thrust, solutions were found, even in a closed, analytic form. Nevertheless, for more realistic conditions, the problem becomes a very complex one, and the solution is far from complete. In addition to this, complexity increases if an isoperimetric constraint is added to the problem. Such a case is, for example, the problem of extremizing the rise in altitude for a given time. In the present work an attempt is made to treat the problem under the most realistic assumptions used so far, for both the system of equations and the drag model. The analysis of the problem reveals that a more complex thrust history exists than the classical sequence of full-singular-coast subarcs, for both the time-constrained case, and for the case of a drag model with a sharp rise in the transonic region. In the first case, a second full-thrust subarc is generated at the end of the singular subarc, owing to the boundedness of the thrust, while, in the second case, a full-thrust subarc appears in transition from the subsonic to the supersonic branch of the singular path. Both are new results, at least for the bounded-thrust case, and the drag law assumed, insofar as the author knows. Discussion is also provided for the limitations of such a switching structure, and it is shown that the composition of an optimal trajectory is heavily dependent on the assumed drag law. / Master of Science

A nonlinear programming technique is applied to the optimization of the thrust and lift control histories for missiles. The first problem considered is that of determining the thrust history which maximizes the range of a continuously-variable (non-pulsed) thrust rocket in horizontal lifting flight. The optimal control solution for this problem is developed. The problem is then approximated by a parameter optimization problem which is solved using a second-order, quasi-Newton method with constraint projection. The two solutions are found to compare well. This result allows confidence in the use of the nonlinear-programming technique to solve optimization problems in flight mechanics for which no analytical optimal-control solutions exist. Such a problem is to determine the thrust and lift histories which maximize the final velocity of a multiple-pulse missile. This problem is solved for both horizontal- and elevation-plane trajectories with and without final time constraints. The method is found to perform well in the solution of these optimization problems and to yield substantial improvements in performance over the nominal trajectories. / M.S.

Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Recent years have seen a decline in the rate of space exploration due to the inefficiency of chemical rockets. Therefore alternative fuel efficient propulsion methods are being sought to enable cost effective deep space exploration. The high fuel efficiency of electric thrusters enable a spacecraft to travel further, faster and cheaper than any other propulsion technology available. Thus electric propulsion has become the propulsion of choice for scientists and engineers. A typically electric thruster contains some sort of electrode to ionise the propellant. Although this is feasible for short space missions, it becomes impractical for more ambitious space missions as electrodes erode over time. The alternative is to ionise the propellant using electromagnetic fields, which eliminates lifespan issues associated with electrode based thrusters. In order to examine methods of improving the lifespan and performance of electric thrusters, this thesis aimed to study the method of microwave discharge ionisation for an electric thruster. This includes the design of an RF Ion Thruster with extraction and acceleration grids to generate thrust. A 600 W 2.45 GHz magnetron (obtained from a conventional microwave oven), coupled to circular TM010 resonant cavity, was used to ionise neutral argon gas. The process of electron cyclotron resonance (ECR) was used to ensure the efficient ionisation of a high density plasma. The thrust was achieved with a three-grid system biased at high voltages to accelerate positively charged argon ions to high exhaust velocities. Results yielded the success of the designed electromagnetic based thruster, measuring approximatively 1.78 mN of thrust with a specific impulse of Isp = 3786 seconds. The ECR process produced a high plasma density with a plasma absorption rate of approximately 77% of the total input microwave power. The final results obtained were found to match the predicted results extremely well and resembled results found in literature. This demonstrates the efficiency of the RF ion thruster that was designed in this project and the future use in space exploration activities. However, future research needs to be undertaken on a controlled feedback system that will ensure optimal operating conditions for maximum performance. In addition, the method of grid-less acceleration needs to be studied to achieve maximum thrust and specific impulse. / AFRIKAANSE OPSOMMING: In onlangse jare het ’n afname in die tempo van die verkenning van die ruimte dit te danke aan die ondoeltreffendheid van chemiese vuurpyle. Derhalwe moet alternatiewe brandstof aandrywing metodes ondersoek word, om koste-effektiewe diep ruimte-eksplorasie moontlik te maak. Die hoë brandstof-doeltreffendheid van elektriese ontbranders stel ’n ruimtetuig in staat om verder, vinniger en goedkoper te reis as enige ander aandrywing tegnologie wat tans beskikbaar is. Dus het elektriese aandrywing metodes die aandrywings keuse vir wetenskaplikes en ingenieurs geword. ’n Tipies elektriese vuurpyl/aandrywer bevat ’n vorm van elektrode om die brandstof (argon gas) te ioniseer. Alhoewel hierdie elektrode proses van ionisasie effektief is vir kort ruimte missies, word dit onprakties vir meer ambisieuse ruimte missies as gevolg van verweering van elektrodes met verloop van tyd. ’n Alternatief is om die dryfmiddel/brandstof te ioniseer deur gebruik te maak van elektromagnetiese velde. Die elekromagnetiese velde sal die lewensduur van die vuurpyl vermeerder deur die verweering van elektrodes, wat geassosieer word met tipiese elektrieses vuurpyle, te elimineer. Hierdie tesis se doelwit is om die metode van mikrogolf ontslag ionisasie vir ’n elektriese vuurpyl/aandrywer te bestudeer om ten einde die lewensduur en doeltreffendheid van elektriese vuurpyl/aandrywer te ondersoek. Dit sluit in die ontwerp van ’n radio frekewensie ioon vuurpyl/aandrywer met ’n ontginning en versnelling matriks/rooster om stukrag te genereer. ’n 2,45 GHz magnetron (verkry vanaf ’n konvensionele mikrogolfoond), gekoppel aan ’n TM010 resonante holte, was gebruik om neutrale argon gas te ioniseer. Die proses van elektron siklotron resonansie (ESR) was gebruik om die doeltreffende ionisasie van ’n hoë digtheid plasma te verseker. Die aandrywing/stukrag was behaal met ’n drie-matriks-stelsel, bevoordeel deur hoë spannings om die positief-gelaaide argon ione te versnel. Resultate opgelewer, het die sukses van die ontwerp van ’n elektromagnetiese gebaseerde vuurpyl/aandrywer met ’n benaderde meting van ongeveer 1.78 mN van stukrag/aandrywing met ’n spesifieke impuls van Isp = 3786 sekondes bewys. Die ECR proses het ’n hoë plasma digtheid geproduseer met ’n plasma opname persentasie van ongeveer 77% van die totale inset mikrogolf energie. Die finale uitslae wat verkry was, het bevind dat die voorspelde resultate baie goed inpas met resultate in beskikbare literatuur. Dit dui op die doeltreffendheid van die RF ioon vuurpyl/aandrywer wat ontwerp is in hierdie projek vir die toekomstige gebruik in ruimte eksplorasie-aktiwiteite. Toekomstige navorsing moet op ’n beheerde terugvoer sisteem onderneem word, wat optimale werktoestande verseker vir maksimum prestasie. Daarbenewens moet die metode van matriks-lose versnelling bestudeer word, om maksimum versnelling/stukrag en spesifieke impuls te verseker.