This thesis aims at investigating numerical methods through which the accuracy in landing of a Mars entry-descent-landing (EDL) vehicle can be improved. The methods investigated include the collocation method and model predictive control (MPC). The primary control variable utilized in this study is the bank angle of the spacecraft, which is the angle between the lift vector and the vertical direction. Modulating this vector affects the equations of system of equations and the seven state variables, namely altitude, velocity, latitude, longitude, flight path angle, heading angle and total time taken. An optimizer is implemented which utilizes the collocation method, through which the optimal bank angle is found at every discretized state along the trajectory which are equally separated through a definite timestep, which is a function of the end time state. A 3-sigma wind disturbance model is introduced to the system, as a function of the altitude, which introduces uncertainties to the system, resulting in a final state deviating from the targeted location. The trajectory is split into two parts, for better control of the vehicle during the end stages of flight. The MPC aims at reducing the end state deviation, through the implementation of a predictor-corrector algorithm that propagates the trajectory for a certain number of timesteps, followed by running the optimizer from the current disturbed state to the desired target location. At the end of this analysis, a new set of optimal bank angle are found, which account for the wind disturbances and navigates the EDL vehicle to the desired location. / M.S. / Landing on Mars has always been a process of following a set of predetermined instructions by the spacecraft, in order to reach a calculated landing target. This work aims to take the first steps towards autonomy in maneuvering the spacecraft, and finding a method by which the vehicle navigates itself towards the target. This work determines the optimal control scheme a Mars reentry vehicle must have through the atmosphere to reach the target location, and employs method through which the uncertainty in the final landing location is mitigated. A model predictive controller is employed which corrects the disturbed trajectory of the vehicle at certain timesteps, through which the previously calculated optimal control is changed so as to account for the disturbances. The control is achieved by means of changing the bank angle of the spacecraft, which in turn affects the lift and drag experienced by the vehicle. Through this work, a method has been demonstrated which reduces the uncertainty in final landing location, even with wind disturbances present.

The 2012 Decadal Survey has stated that there is a critical role for a Venus In-situ Explore (VISE) missions to a variety of important sites, specifically the Tessera terrain. This work aims to answer the Decadal Survey's call by developing a new comprehensive Entry, Descent, Landing, and Locomotion (EDLL) vehicle for in-situ exploration of Venus, especially in the Tessera regions. TANDEM, the Tension Adjustable Network for Deploying Entry Membrane, is a new planetary probe concept in which all of EDLL is achieved by a single multifunctional tensegrity structure. The concept uses same fundamental concept as the ADEPT (Adaptable Deployable Entry and Placement Technology) deployable heat shield but replaces the standard internal structure with the structure from the tensegrity-actuated rover to provide a combined aeroshell and rover design. The tensegrity system implemented by TANDEM reduces the mass of the overall system while enabling surface locomotion and mitigating risk associated with landing in the rough terrain of Venus's Tessera regions, which is otherwise nearly inaccessible to surface missions. TANDEM was compared to other state-of-the-art lander designs for an in-situ mission to Venus. It was shown that TANDEM provides the same scientific experimentation capabilities that were proposed for the VITaL mission, with a combined mass reduction for the aeroshell and lander of 52% (1445 kg), while eliminating the identified risks associated with entry loads and very rough terrain. Additionally, TANDEM provides locomotion when on the surface as well as a host of other maneuvers during entry and descent, which was not present in the VITaL design. Based on its unique multifunctional infrastructure and excellent crashworthiness for impact on rough surfaces, TANDEM presents a robust system to address some of the Decadal Survey's most pressing questions about Venus. / Ph. D. / NASA has proposed the possibility of performing a robotic mission to Venus in this upcoming decade. This could be NASA’s first attempt to design a robot that is capable of landing on the surface of our solar systems hottest planet. Venus presents a great exploration opportunity, as it is our closest planetary neighbor. Venus is similar to Earth in both size and location in the solar system, yet it is profoundly different in many other aspects regarding habitability. There is a significant scientific interest in exploring the mysteries of the greenhouse gases and runaway climate change present in the Venusian atmosphere. Understanding Venus’ atmosphere will help us to increase our knowledge of Earth’s atmosphere. Exploring the difference in these two planets will greatly further our intuition of other planetary systems and will aid in our search for life in the universe. Yet, exploring Venus presents a number of severe engineering challenges: the extreme temperature and pressure at the planet's surface, the highly corrosive atmosphere, and lack of terrain resolution caused by the dense permanent cloud layer. In order to address these engineering challenges, a new ultra-lightweight planetary probe has been invented. TANDEM, the Tension Adjustable Network for Deploying Entry Membrane, is unique in its design as it has combined all of the subsystems in needs to safely land on the surface into a single lightweight, multifunctional structure. This enables the design to be nearly 1.5 metric tons lighter than the same mission that was proposed in 2010 using the current state-of-the-art technologies. Based on this and other unique capabilities that are provided, TANDEM presents a robust system to address some of NASA’s most pressing questions about Venus.

Submitted by Emanuel Varela Cardoso (emanuel.varela@ufcg.edu.br) on 2018-09-06T19:24:24Z No. of bitstreams: 1 RODOLFO DE ANDRADE MARINHO SILVA – DISSERTAÇÃO (PPGCC) 2018.pdf: 798016 bytes, checksum: 4dfd41c1185e692e1c3b8a11f541a6a6 (MD5) / Made available in DSpace on 2018-09-06T19:24:24Z (GMT). No. of bitstreams: 1 RODOLFO DE ANDRADE MARINHO SILVA – DISSERTAÇÃO (PPGCC) 2018.pdf: 798016 bytes, checksum: 4dfd41c1185e692e1c3b8a11f541a6a6 (MD5) Previous issue date: 2018-03-01 / No decorrer das últimas décadas, uma quantidade de dados de usuários cada vez maior vem sendo enviada para ambientes não controlados pelos mesmos. Em alguns casos esses dados são enviados com o objetivo de tornar esses dados públicos, mas na grande maioria das vezes há a necessidade de manter esses dados seguros e privados, ou autorizar o seu acesso apenas em usos bem específicos. Considerando o caso onde os dados devem ser mantidos privados, entidades devem tomar cuidados especiais para manter a segurança e privacidade de tais dados tanto durante a transmissão quanto durante o armazenamento e processamento dos mesmos. Com esse objetivo, vários esforços vêm sendo feitos, inclusive o desenvolvimento de componentes de hardware que provêem ambientes de execução confiável,TEEs, como o Intel Software Guard Extensions(SGX). O uso dessa tecnologia, porém, pode ser feito de forma incorreta ou ineficiente, devido a cuidados não observados durante o desenvolvimento de aplicações. O trabalho apresentado nessa dissertação aborda os principais desafios enfrentados no desenvolvimento de aplicações que façam uso deSGX, e propõe boas práticas e um conjunto de ferramentas (DynSGX) que ajudam a fazer melhor uso das capacidades da tecnologia. Tais desafios incluem, mas não são limitados a, particionamento de aplicações de acordo com o modelo de programação do SGX, colocação de aplicações em ambientes de computação na nuvem, e, sobretudo, gerência de memória. Os estudos apresentados neste trabalho apontam que o mal uso da tecnologia pode acarretar em uma perda de performance considerável se comparado com implementações que levam em conta as boas práticas propostas. O conjunto de ferramentas proposto neste trabalho também mostrou possibilitar a proteção de código de aplicações em ambientes de computação na nuvem, com uma sobrecarga desprezível em comparação com o modelo de programação padrão de SGX. / During the last few decades, an increasing amount of user data have been sent to environments not controlled by data owners. In some cases these data are sent with the objective to turn them public, but in the vast majority of times, these data need to be kept safe and private, or to be allowed access only in very specific use cases. Considering the case where data need to be kept private, entities must take specific measures to maintain the data security and privacy while transmitting, storing and processing them. With this objective many efforts have been made, including the specification of hardware components that provide a trusted execution environment (TEEs), like the Intel Software Guard Extensions (SGX). The use of this technology , though, can be made in incorrect or ineffective ways, due to not taking some considerations into account during the development of applications. In this work, we approach the main challenges faced in the development of applications that use SGX, and propose good practices and a toolset (DynSGX) that help making better use of the capabilities of this technology. Such challenges include, but are not limited to, application partitioning, application colocation in cloud computing environments, and memory management. The studies presented in this work show that the bad use of this technology can result in a considerable performance loss when compared to implementations that take into account the good practices proposed. The toolset proposed in this work also showed to enable protecting application code in cloud computing environments, having a negligible performance overhead when compared to the regular SGX programming model.

La thèse porte sur les problèmes posés par la conception et la réalisation de la partie logicielle des systèmes de traduction automatisée (TAO) hétérogènes, intégrant des systèmes de TA multiples et/ou à composants hétérogènes, ainsi qu'une partie THAM (traduction humaine aidée par la machine), reposant sur des mémoires de traductions. Ces systèmes se développent à côté des systèmes de TA homogènes et de THAM, et les supplanteront peut-être à moyen terme. Leurs différents composants de TA seront construits par des équipes différentes, distribuées autour de la planète, avec des méthodes algorithmiques et des outils différents (langages spécialisés ou LSPL), ainsi que des ressources et composants linguiciels différents (dictionnaires et corpus de divers types, grammaires et transducteurs basés sur des règles), à l'aide d'EDL (environnements de développement linguiciel) eux aussi différents. Les contributions de la thèse concernent en particulier : • l'amélioration des « méta-EDL de TAO », permettant d'effectuer une transition incrémentale entre les EDL natifs des systèmes de TA utilisés pour construire un systèmes de TAO à composants hétérogènes, et un futur EDL intégrateur universel, dans lequel on pourra « rapatrier » la compilation et l'exécution des LSPL ; • la conception et la réalisation d'une base lexicale partageant un même pivot lexical, PIVAX, réalisée au-dessus de la plate-forme Jibiki (G. Sérasset, GETALP) ; • la réingénierie de langages spécialisés « externes » (non supportés par l'EDL Ariane-G5), avec application aux « systèmes-Q » (A. Colmerauer, 1967), qui servit de base pendant 15 ans au système de TA TAUM-météo destiné aux bulletins météorologiques canadiens ; • la conception et la réalisation d'un « moniteur » adapté à la partie « production » d'un système de TAO hétérogène, EMEU_w.1.0, qui a été développé et utilisé dans le cadre d'un projet de grande ampleur.

<p>Aerocapture has been envisioned as a potential orbit insertion technique for planetary destinations with an atmosphere. Despite not being flight proven technique, many studies found in the literature and recent mission proposals have employed aerocapture into their respective mission designs. The potential varying levels of trajectory dispersions experienced during atmospheric flight at each destination drives the need for robust and fuel-efficient guidance and control solutions. Existing guidance algorithms have relied on tracking precomputed reference trajectories, which are computed using significant simplifications to the flight mechanics, are not generally designed to be fuel-efficient, and require tedious performance gain tuning. When simulated with higher levels of uncertainty, the existing algorithms have been shown to produce large orbit insertion errors. Furthermore, existing flight control methodologies have been limited in scope to bank angle modulation. While some studies have introduced new methodologies, such as drag modulation and direct force control, they haven’t been tested at the same level of rigor as the existing methods. Advances in on-board computational power are allowing for modern guidance and control solutions, in the form of numerical predictor-corrector algorithms, to be realized. This dissertation presents an aerocapture guidance architecture based on a numerical predictor-corrector algorithm. Optimal control theory is utilized to formulate and numerically obtain fuel-minimizing flight control laws for lifting and ballistic vehicles. The unified control laws are integrated into a common guidance algorithm. The architecture is utilized to conduct Monte Carlo simulation studies of Discovery-class and SmallSat-class aerocapture missions at various planetary destinations.</p>

The focus of this thesis has been to determine the usable voltage range of carbon-based supercapacitors (SC). Supercapacitors are a relatively new type of capacitors with a vast increase in capacitance compared to capacitors which utilize a dielectric as charge separator. A SC consists of two electrodes and an electrolyte separating the electrodes. The charges are stored by electrostatic forces in the interface between the electrode and the electrolyte, forming the so called electrochemical double-layer (EDL). With porous electrodes the effective surface area of the interfacial zone can be made very large, giving SCs a large storage capacity. The limiting factors of a SC is the decomposition potential of the electrolyte and the decomposition of the electrodes. For commercially manufactured SCs the electrolyte is usually an organic solvent, which has a decomposition potential of up to 2.7-2.8 V. Compared to aqueous electrolytes with a thermodynamic limit of 1.23 V. The drawback of using non-aqueous electrolytes is that they are not environmentally friendly, and they increase the production cost. It is claimed that the voltage range can be up to 1.9 V using aqueous electrolytes. Some researchers have focused on aqueous electrolytes for these reasons. In this thesis two different electrolytes were tested to determine if the voltage range could be extended. The experiments were conducted using a three electrode cell and performing cyclic voltammogram measurements (CV). The carbon electrodes were made of  two different sources of grahite, battery graphite or exfoliated graphite, and nano fibrilated cellulose was added to increase the mechanical stability. The results show that the oxidation potential of the carbon electrode was the positive limit. A usable potential of about 1 V was shown. However, when cycling the electrodes to potentials below the decomposition limit, for hydrogen evolution, interesting effects were seen. A decrease in reaction kinetics, indicating a type of conditioning of the electrode was observed. An increase in charge storage capacitance was also observed when comparing the initial measurements with the final, probably corresponding to an increase in porosity. / KEPS projekt Sundsvall Mitt Universitet

Investigations performed in order to understand the electronic and optoelectronic properties of field effect transistors based on few layers of 2D Copper Indium Selenide (CuIn7Se11) are reported. In general, field effect transistors (FETs), electric double layer field effect transistors (EDL-FETs), and photodetectors are crucial part of several electronics based applications such as tele-communication, bio-sensing, and opto-electronic industry. After the discovery of graphene, several 2D semiconductor materials like TMDs (MoS2, WS2, and MoSe2 etc.), group III-VI materials (InSe, GaSe, and SnS2 etc.) are being studied rigorously in order to develop them as components in next generation FETs. Traditionally, thin films of ternary system of Copper Indium Selenide have been extensively studied and used in optoelectronics industry as photoactive component in solar cells. Thus, it is expected that atomically thin 2D layered structure of Copper Indium Selenide can have optical properties that could potentially be more advantageous than its thin film counterpart and could find use for developing next generation nano devices with utility in opto/nano electronics. Field effect transistors were fabricated using few-layers of CuIn7Se11 flakes, which were mechanically exfoliated from bulk crystals grown using chemical vapor transport technique. Our FET transport characterization measurements indicate n-type behavior with electron field effect mobility µFE ≈ 36 cm^2 V^-1 s^-1 at room temperature when Silicon dioxide (SiO2) is used as a back gate. We found that in such back gated field effect transistor an on/off ratio of ~ 10^4 and a subthreshold swing ≈ 1 V/dec can be obtained. Our investigations further indicate that Electronic performance of these materials can be increased significantly when gated from top using an ionic liquid electrolyte [1-Butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF6)]. We found that electron field effect mobility µFE can be increased from ~ 3 cm^2 V^-1 s^-1 in SiO2 back gated device to ~ 18 cm^2 V^-1 s^-1 in top gated electrolyte devices. Similarly, subthreshold swing can be improved from ~ 30 V/dec to 0.2 V/dec and on/off ratio can be increased from 10^2 to 10^3 by using an electrolyte as a top gate. These FETs were also tested as phototransistors. Our photo-response characterization indicate photo-responsivity ~ 32 A/W with external quantum efficiency exceeding 10^3 % when excited with a 658 nm wavelength laser at room temperature. Our phototransistor also exhibit response times ~ tens of µs with specific detectivity (D*) values reaching ~ 10^12 Jones. The CuIn7Se11 phototransistor properties can be further tuned & enhanced by applying a back gate voltage along with increased source drain bias. For example, photo-responsivity can gain substantial improvement up to ~ 320 A/W upon application of a gate voltage (Vg = 30 V) and/or increased source-drain bias. The photo-responsivity exhibited by these photo detectors are at least an order of magnitude better than commercially available conventional Si based photo detectors coupled with response times that are orders of magnitude better than several other family of layered materials investigated so far. Further photocurrent generation mechanisms, effect of traps is discussed in detail.

The current limits of supersonic parachute technology may constrain the ability to safely land future robotic assets on the surface of Mars. This constraint has led to a renewed interest in supersonic inflatable aerodynamic decelerator (IAD) technology, which offers performance advantages over the DGB parachute. Two supersonic IAD designs of interest include the isotensoid and tension cone, named for their respective formative structural theories. Although these concepts have been the subject of various tests and analyses in the 1960s, 1970s, and 2000s, significant work remains to advance supersonic IADs to a technology readiness level that will enable their use on future flight missions. In particular, a review of the literature revealed a deficiency in adequate aerodynamic and aeroelastic data for these two IAD configurations at transonic and subsonic speeds. The first portion of this research amended this deficiency by testing flexible IAD articles at relevant transonic and subsonic conditions. The data obtained from these tests showed that the tension cone has superior drag performance with respect to the isotensoid, but that the isotensoid may demonstrate more favorable aeroelastic qualities than the tension cone. Additionally, despite the best efforts in test article design, there remains ambiguity regarding the accuracy of the observed subscale behavior for flight scale IADs. Due to the expense and complexity of large-scale testing, computational fluid-structure interaction (FSI) analyses will play an increasingly significant role in qualifying flight scale IADs for mission readiness. The second portion of this research involved the verification and validation of finite element analysis (FEA) and computational fluid dynamic (CFD) codes for use within an FSI framework. These verification and validation exercises lend credence to subsequent coupled FSI analyses involving more complex geometries and models. The third portion of this research used this FSI framework to predict the static aeroelastic response of a tension cone IAD in supersonic flow. Computational models were constructed to mimic the wind tunnel test articles and flow conditions. Converged FSI responses computed for the tension cone agreed reasonably well with wind tunnel data when orthotropic material models were used and indicated that current material models may require unrealistic input parameters in order to recover realistic deformations. These FSI analyses are among the first results published that present an extensive comparison between FSI computational models and wind tunnel data for a supersonic IAD.

Supersonic deceleration has been identified as a critical deficiency in extending heritage technologies to the high-mass systems required to achieve long-term exploration goals at Mars. Supersonic retropropulsion (SRP), or the use of retropropulsive thrust while an entry vehicle is traveling at supersonic conditions, is an approach addressing this deficiency. The focus of this dissertation is aerodynamic and performance evaluation of SRP as a decelerator technology for high-mass Mars entry systems. This evaluation was completed through a detailed SRP performance analysis, establishment of the relationship between vehicle performance and the aerodynamic-propulsive interaction, and an assessment of the required fidelity and computational cost in simulating SRP flowfields, with emphasis on the effort required in conceptual design. Trajectory optimization, high-fidelity computational aerodynamic analysis, and analytical modeling of the SRP aerodynamic-propulsive interaction were used to define the fidelity and effort required to evaluate individual SRP concepts across multiple mission scales.

No description available.