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ItemEvaluation of Deployable Aerosurface Systems for Mars Entry(Georgia Institute of Technology, 2012-12-14) Cruz-Ayoroa, Juan G.One of the challenges presented by the exploration of Mars is the entry, descent and landing (EDL) of payloads to the surface. Current robotic missions to Mars are reaching the limist of existing Viking heritage EDL technologies. A number of EDL technology improvements can be made to extend the capabilities beyond the current landed mass limits, including increasing the entry vehicle hypersonic drag and lift capability. Technologies being currently studied include inflatable aerodynamic decelerators, which are designed to increase vehicle drag. Many of these concepts center on axisymmetric designs, which provide high drag but relatively low lift and are most easily integrated to blunt entry vehicles. However, due to packaging density and launch vehicle fairing constraints, it is likely that future missions will require the use of slender bodies. This study investigates three deployable concepts designed to provide better integration into a slender vehicle while augmenting its performance by increasing its hypersonic drag. The deployable aerosurfaces are applied to a 5 meter diameter slender vehicle for a robotic mission at Mars with entry masses ranging from 10 to 60t. A multidisciplinary design optimization framework is used to estimate the landed mass capability of each system. Results show that the deployable concepts can significantly improve payload mass capability by reducing the terminal propulsion propellant required. Initial feasibility studies show that the concepts are hypersonically statically stable and comply with mechanical and thermal material capabilities
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ItemImplementation of a Mesomechanical Material Model for IAD Fabrics within LS-DYNA(Georgia Institute of Technology, 2012-12-14) Hill, JeremyThe implementation and evaluation of a high fidelity material model for dry fabrics is the main objective of this paper. Inflatable Aerodynamic Decelerators (IADs) and other air inflated structures quite often utilize woven fabrics due to their lightweight and high loading carrying capabilities. Design optimization of these inflated structures relies on a detailed understanding of the woven fabric mechanics. Woven fabrics are composite orthotropic materials that respond differently under load from traditional solid mechanics. While low fidelity fabric materials usually assume a continuous medium, a higher fidelity model needs to account for the reorientation of yarns and weave geometry. An existing mesomechanical material model within the LS-DYNAÒ commercial non-linear finite element software package is utilized. In this paper, experimental stress-strain data for Kevlar 129 samples are validated against numerical simulations of models with matching geometry and loading conditions.
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ItemDynamic Stability Analysis of Blunt Body Entry Vehicles Through the Use of a Time-Lagged Aftbody Pitching Moment(Georgia Institute of Technology, 2012-10-05) Kazemba, ColeThis analysis defines an analytic model for the pitching motion of blunt bodies during atmospheric entry. The proposed model is independent of the pitch damping sum term which is present in the standard equations of motion, instead using the principle of a time-lagged aftbody moment as the forcing function for oscillation divergence. Four parameters, all with intuitive physical relevance, are introduced to fully define the aftbody moment and the associated time delay. It is shown that the dynamic oscillation responses typical to blunt bodies can be produced using hysteresis of the aftbody moment alone. The approach used in this investigation is shown to be useful in understanding the governing physical mechanisms for blunt body dynamic stability and in guiding vehicle and mission design requirements. A case study using simulated ballistic range test data is conducted. From this, parameter identification is carried out through the use of a least squares optimizing routine. Results show good agreement with the limited existing literature for the parameters identified. The model parameters were found to be accurate for a wide array of initial conditions and can be identified with a reasonable number of ballistic range shots and computational effort.
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ItemGuided Entry Performance of Low Ballistic Coefficient Vehicles at Mars(Georgia Institute of Technology, 2012-05-21) Meginnis, Ian M.Current Mars entry, descent, and landing technology is near its performance limit and is generally unable to land payloads on the surface that exceed approximately 1 metric ton. One option for increasing landed payload mass capability is decreasing the entry vehicle’s hypersonic ballistic coefficient. A lower ballistic coefficient vehicle decelerates higher in the atmosphere, providing additional timeline and altitude margin necessary for landing more massive payloads. This study analyzed the guided entry performance of several low ballistic coefficient vehicle concepts at Mars. A terminal point controller guidance algorithm, based on the Apollo Final Phase algorithm, was used to provide precision targeting capability. Terminal accuracy, peak deceleration, peak heat rate, and integrated heat load were assessed and compared to a traditional Mars entry vehicle concept to determine the effects of lowering the vehicle ballistic coefficient on entry performance. Results indicate that, while terminal accuracy degrades slightly with decreasing ballistic coefficient, the terminal accuracy and other performance metrics remain within reasonable bounds for ballistic coefficients as low as 1 kg/m2 . As such, this investigation demonstrates that from a performance standpoint, guided entry vehicles with low ballistic coefficients (large diameters) may be feasible at Mars. Additionally, flight performance may be improved through the use of guidance schemes designed specifically for low ballistic coefficient vehicles, as well as novel terminal descent systems designed around low ballistic coefficient trajectories