Thesis (M.S.)--University of Michigan, 1990.

Thesis (M.S.)--University of Michigan, 1990.

Thesis--School of Advanced Airpower Studies, Maxwell Air Force Base, Ala., 1992-93. / Title from title screen (viewed Oct. 21, 2003). "August 1994." Includes bibliographical references.

<div>Mission designs have been focused on using proven orbital maneuvers (i.e., propulsive maneuvers and gravity-assist) to deliver spacecraft to planetary destinations. Aeroassist maneuvers, despite their potential benefits, have not been given serious considerations due to the perceived risk and complexity. As entry technologies mature, aeroassist maneuvers need to be considered more extensively. Currently, there is no tool available that can perform rapid preliminary mission designs using aeroassist maneuvers. In this dissertation, integrated design methodologies for aerocapture and aerogravity-assist are developed, which can be readily converted to design tools that enable rapid mission concept formulations. </div><div> </div><div>The aerocapture design methodology is used to develop extensive design rules and relations for aerocapture missions to Titan, Venus, and Uranus, considering a wide range of vehicle parameters and interplanetary trajectories. These design rules and relations are intended as a convenient resource for mission designers and system engineers to evaluate the feasibility of aerocapture (e.g., effects of V-infinity on aerocapture missions) and the relevant design requirements, such as choices for vehicle characteristics and TPS materials. In addition, potentials for inclination change for Titan aerocapture are also quantified, presenting additional benefits of using aerocapture. Given the unusual orientation of Uranus, the changes in inclination and shift of line of apsides are also quantified for Uranus aerocapture. </div><div> </div><div>A novel design methodology is developed for Saturn system missions using nontraditional aerogravity-assist maneuvers at Titan. Compared with the existing literature, the novel methodology explores a comprehensive design space by integrating design considerations for interplanetary trajectories, atmospheric trajectories, arrival geometries at Titan, and vehicle designs. The methodology enables preliminary design trades and allows the mission designer to assess the feasibility of Titan aerogravity-assist and quickly develop requirements for trajectory designs and vehicle designs. The methodology also identifies potential Saturn and Titan arrival conditions. Results for an example Enceladus mission and Saturn system mission are presented, showing that a Saturn arrival V-infinity of 7 km/s renders Titan aerogravity-assist feasible for an Enceladus mission, while using the current entry technology. </div><div> </div><div>Bank modulation and drag modulation have been considered separately for aeroassist vehicles in the literature. The investigation combines bank modulation and drag modulation to improve the control authorities for aeroassist vehicles and such improvements are quantified using numerical simulations for a wide range of vehicle design configurations. The results show the potential of using a low-L/D vehicle for aerocapture at Uranus using combined bank and drag modulation. </div><div><br></div>

Thesis (M.S. in Mechanical Engineering)--Naval Postgraduate School, March 2003. / Thesis advisor(s): Fotis A. Papoulias. Includes bibliographical references (p. 61). Also available online.

Thesis (M.A.)--Naval Postgraduate School, 1996. / Includes abstract. "June 1996." DTIC report no.: ADA312719. Includes bibliographical references (p. 99-103). Full text available online from DTIC.

Most spacecraft are designed to be maneuvered to achieve pointing goals. This is generally accomplished by designing a three-axis control system. This work explores new maneuver strategies when only two control inputs are available: (i) sequential single-axis maneuvers and (ii) three-dimensional (3D) coupled maneuvers. The sequential single-axis maneuver strategies are established for torque, time, and fuel minimization applications. The resulting control laws are more complicated than the equivalent results for three-axis control because of the highly nonlinear control switch-times. Classical control approaches lead to optimal, but discontinuous control profiles. This problem is overcome by introducing a torque-rate penalty for the torque minimization case. Alternative approaches are also considered for achieving smooth continuous control profiles by introducing a cubic polynomial multiplicative control switch smoother for the time and fuel minimization cases. Numerical and analytical results are presented to compare optimal maneuver strategies for both nominal and failed actuator cases. The 3D maneuver strategy introduces a homotopy algorithm to achieve optimal nonlinear maneuvers minimizing the torque. Two cases are considered: (i) one of the three-axis control actuators fails and (ii) two control actuators fail among four control actuators. The solution strategy first solves the case when all three actuators are available. Then, the failed actuator case is recovered by introducing a homotopy embedding parameter, ε, into the nonlinear dynamics equation. By sweeping ε, a sequence of neighboring optimal control problems is solved that starts with the original maneuver problem and arrives at the solution for the under-actuated case. As ε approaches 1, the designated actuator no longer provides control inputs to the spacecraft, effectively modeling the failed actuator condition. This problem is complex for two reasons: (i) the governing equations are nonlinear and (ii) ε fundamentally alters the spacecraft’s controllability. Davidenko’s method is introduced for developing an ordinary differential equation for the costate variable as a function of ε. For each value of ε, the costate initial conditions are iteratively adjusted so that the terminal boundary conditions for the 3D maneuver are achieved. Optimal control applications are presented for both rest-to-rest and motion-to-rest cases that demonstrate the effectiveness of the proposed algorithm.

To improve the recoverability and survivability of aircraft after damage, a better understanding of the flight dynamics and the structural loads is needed. However, damage can introduce asymmetries that complicate the modeling. An extended vortex lattice code is used to model the quasi-steady aerodynamic forces. The vortex lattice method provides the force distribution which is not available elsewhere. Snapshots from the vortex lattice model are used to generate a reduced order model (ROM). This ROM contains non-linear terms to account for non-linearities that the damage can introduce. The ROM is coupled with equations of motion which are able to account for instantaneous shifts in the center of gravity caused by the damage. This methodology is applied to the generic transport model (GTM) with the loss of a portion of the port wing tip. This model is used to examine the effects of the damage on the aircraft's trim and the stability of that trim. This model is also used to calculate the aerodynamic, inertial, and propulsive loads on the wing as the aircraft is maneuvering. / Master of Science

Syftet med denna uppsats var att undersöka hur manliga mellanchefer handlade, i sin strävan att förena arbetsliv och familjeliv. Två tidskrävande delar av männens liv, som båda ställer krav, och påverkar dem, i deras möjlighet till handlande. Metoden vi valt är kvalitativ och vi genomförde intervjuer med fem mellanchefer, i Stockholmsområdet. De fick under intervjun berätta om sitt liv som pappa och chef. Vi såg att samhällets normer, och företagens policys, påverkade männen i deras handlande. För att bemöta de krav som dessa yttre faktorer ställde på dem skapade de strategier. Vi såg att de hade olika många strategier att ta till, beroende på vilka krav de ställdes inför. Hur många strategier de kunde välja mellan påverkades av deras handlingsutrymme. Vi såg också att i vissa situationer agerade männen lika när de ställdes inför liknande problem, oberoende av varandra. Vi fann även stöd för att männen, i större utsträckning än sina fruar, fick betalt för det arbete de utfört. / The purpose of this study was to investigate how male middle managers acted, in their efforts to balance work and family life. These two, time-consuming, parts of men's lives, both demand and influence them, in their ability to act. The method we have chosen is qualitative and we conducted interviews with five middle managers, in the Stockholm area. During the interview they got to talk about their roles as fathers and managers. We saw that social norms and business policies affected the men in their actions. To meet the requirements that these external factors put on them, they created strategies. We saw that they had a different number of approaches to choose from, depending on the demands they faced. How many strategies they could choose from were affected by their room for maneuver. We also saw that in some situations, when they were faced with similar problems, the men acted similarly, independently. We also found support for the fact that the men, to a greater extent than their wives, got paid for the work they did.

Orientador: Rodolpho Vilhena de Moraes / Banca: Othon Cabo Winter / Banca: Claudia Celeste Celestino / Resumo: No presente trabalho é abordada a manobra orbital Terra-Lua - Terra com o objetivo de um menor consumo de combustível. Inicialmente o satélite executa uma órbita em torno da Terra. Em um certo instante um impulso é efetuado para efetuar uma manobra não con-focal em que o satélite é transferido para uma órbita de transferência geocêntrica até um ponto da esfera de influência da Lua. A partir deste ponto o satélite é transferido para uma órbita hiperbólica em torno da Lua, e, no perilúnio desta órbita um novo impulso é dado transferindo o satélite para uma órbita lunar. A seguir é efetuada a manobra de volta em que o satélite é transferido para a órbitra geocêntrica de transferência, e no pericentro desta o satélite é transferido para a sua órbita inicial em torno da Terra. O caso não coplanar e a influência das perturbações devidas ao achatamento da Terra e a atração gravitacional da Lua também são analisados. / Abstract: In the present work an Earth-Moon-Earth orbital maneuver is studied with the purpose of minimum fuel consumption. Initially it is considered an artificial satellite orbiting around the Earth. In a certain instant an impulse is effected to effect a not cofocal maneuver where the satellite is transferred to an orbit of geocentric transference until a point of the sphere of influence of the Moon. From this point the satellite is transferred to a hyperbolic orbit around the Moon, and, in the perilúnio of this orbit a new impulse is given transferring the satellite to a lunar orbit. To follow the maneuver is effected in return where the satellite is transferred to geocentric orbit of transference, and in pericentro of this the satellite is transferred to its initial orbit around the Earth. The non-coplanar case and the influence of the disturbances due to the flattening of the Earth and the gravitational attraction of the Moon also are analyzed. / Mestre