06 Fakultät Luft- und Raumfahrttechnik und Geodäsie
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/7
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Item Open Access Design and analysis of vehicle and guidance concept for interplanetary return mission(2010) Afzal, Muhammad Imran; Röser, Hans-Peter (Prof. Dr. rer. nat.)Future space transportation scenarios will include Earth orbit transportation, orbit and interplanetary transfer as well as entry and re-entry. Sample return from interplanetary missions to Moon, Mars and beyond as well as ISS sample return and manned crew return vehicles from Earth orbit but also beyond, has to be established for research programs planned for the near future. Such long-term plans for the robotic or human space exploration of solar system bodies demand new and innovative concepts for the design of vehicles which can enter a planetary atmosphere and land on its surface safely. This thesis presents different vehicle concepts and new method for trajectory design, optimization and guidance of Earth capture and re-entry phase of human interplanetary return mission. The reference mission for this investigation is the Earth capture and re-entry phase of lunar return mission with crew inside. The early lunar return missions were accomplished with a so-called ‘capsule’ shaped vehicle. There are however significant disadvantages of capsule design, especially the load factor of more than 7 times of Earth gravitation, which exceeds 4.0 g’s limit of NASA’s safety standards for astronauts [40]. The report assesses the performance of 3 different configurations of re-entry vehicles. Apollo like capsule [5, 6, 7] with an L/D ratio of about 0.3, flattened bi-conic [68] with an L/D ratio of about 0.7 and winged vehicle [58] with an L/D ratio of about 2.2 are categorised as low, medium and high lifting vehicles. Flattened bi-conic and winged vehicles use aerodynamic lift to remain at certain constant altitude to get rid of excessive kinetic energy before descending to the earth surface, whereas Apollo like capsule, due to its low lift to drag ratio, can stay at constant altitude for only a short period of time and descends faster through the earth atmosphere. A comparative re-entry performance analysis is performed among three configurations for parameters like stagnation point heat flux, integral heat load, peak deceleration (g-load). A three degree of freedom trajectory simulation tool is used to simulate re-entry trajectories in a three dimensional space while treating the vehicle as a point mass. The simulation tool uses a non-linear programming (NLP) approach to find optimum trajectories as a function of a finite number of control parameters with upper and lower bounds and subjected to equality and inequality constraints. Stagnation point convective and radiative heat fluxes and integrated heat load are calculated during trajectory simulation to study the influence of vehicle and atmospheric properties on these important parameters. A predictive guidance scheme is developed and implemented for flattened bi-conic vehicle re-entering the Earth atmosphere after returning from an arbitrary lunar mission. The guidance scheme is implemented in three phases, namely hyperbolic approach phase (or the capture phase) with predicted guidance, constant altitude phase with control law, and final descend phase with predicted guidance. The core guidance algorithm is an evolution of the predictive guidance (explicit guidance) methods developed at the Institute of Space Systems (IRS), University of Stuttgart [15,16,27,28,29,32,36,37,46-50,62,65], which is a combination of onboard flight path prediction and trajectory optimization utilizing non-linear programming techniques with steering command parameterisation. The optimization program makes use of a complex optimization routine to find an optimized set of control parameters for a prescribed cost function and restrictions only once at the beginning of a mission phase, whereas the guidance program makes use of a simplified and fast routine of a Gradient Projection Algorithm (GPA) [31] in order to have less computation load onboard during the entry flight. The performance of guidance scheme is evaluated against a variety of off-nominal conditions. These off-nominal conditions include variations of atmospheric density, variations of aerodynamic and mass properties of the vehicle, and errors in initial conditions at entry interface. An extensive performance analysis of the proposed guidance scheme with the help of Monte Carlo simulations has proved its functionality and reliability.