abstract: In-situ exploration of planetary bodies such as Mars or the Moon have provided geologists and planetary scientists a detailed understanding of how these bodies formed and evolved. In-situ exploration has aided in the quest for water and life-supporting chemicals. In-situ exploration of Mars carried out by large SUV-sized rovers that travel long distance, carry sophisticated onboard laboratories to perform soil analysis and sample collection. But their large size and mobility method prevents them from accessing or exploring extreme environments, particularly caves, canyons, cliffs and craters. This work presents sub- 2 kg ball robots that can roll and hop in low gravity environments. These robots are low-cost enabling for one or more to be deployed in the field. These small robots can be deployed from a larger rover or lander and complement their capabilities by performing scouting and identifying potential targets of interest. Their small size and ball shape allow them to tumble freely, preventing them from getting stuck. Hopping enables the robot to overcome obstacles larger than the size of the robot. The proposed ball-robot design consists of a spherical core with two hemispherical shells with grouser which act as wheels for small movements. These robots have two cameras for stereovision which can be used for localization. Inertial Measurement Unit (IMU) and wheel encoder are used for dead reckoning. Communication is performed using Zigbee radio. This enables communication between a robot and a lander/rover or for inter-robot communication. The robots have been designed to have a payload with a 300 gram capacity. These may include chemical analysis sensors, spectrometers and other small sensors. The performance of the robot has been evaluated in a laboratory environment using Low-gravity Offset and Motion Assistance Simulation System (LOMASS). An evaluation was done to understand the effect of grouser height and grouser separation angle on the performance of the robot in different terrains. The experiments show with higher grouser height and optimal separation angle the power requirement increases but an increase in average robot speed and traction is also observed. The robot was observed to perform hops of approximately 20 cm in simulated lunar condition. Based on theoretical calculations, the robot would be able to perform 208 hops with single charge and will operate for 35 minutes. The study will be extended to operate multiple robots in a network to perform exploration. Their small size and cost makes it possible to deploy dozens in a region of interest. Multiple ball robots can cooperatively perform unique in-situ science measurements and analyze a larger surface area than a single robot alone on a planet surface. / Dissertation/Thesis / Masters Thesis Mechanical Engineering 2016

Two topics relating to low gravity fluid behavior in satellite propellant tanks are considered. In the first, static case, the problem of liquid trapping is examined. Satellite propellant tank end caps optimized for weight are generally shallower and more oblate than hemispherical end caps of the same radius. However, these shallower end caps pose an interesting challenge for propellant management. In the absence of vanes, it is possible for liquid propellant to be trapped in the tank and become unusable. Understanding of how propellant tends to distribute itself in the bare, vaneless tank can be used to drive vane design to counteract these tendencies and ensure propellant remains where desired. The first section of this thesis aims to demonstrate methods that can be used to identify when, how, and why liquid trapping occurs in a given tank geometry. A fluid statics code called Surface Evolver is used to calculate possible fluid configurations for different propellant volumes, contact angles, and end cap designs. The specific case of a cylindrical tank with 2:1 ellipsoidal end caps is studied extensively for ranges of fill fractions and contact angles to illustrate the methods used. Results are computed for each possible propellant configuration: a spherical liquid-gas interface, an asymmetric liquid-gas interface, and a liquid ring. Analytical solutions are found and compared against Surface Evolver results for the spherical liquid-gas interface and liquid ring, showing excellent agreement. Results are also found for other aspect ratio ellipsoidal end caps, superellipsoidal end caps, and torispherical end caps. Each non-hemispherical dome design is found to be able to trap liquid away from the axis of the tank regardless of contact angle. The second part of this thesis, focusing on the dynamic case, details the development of an experimental payload designed to fly on Virgin Galactic’s SpaceShipTwo. This experiment is designed to obtain data on sloshing behavior of liquids in microgravity in response to rotation. The payload contains eight scaled down propellant tanks that are rotated while in microgravity, and the resulting slosh is recorded by video cameras inside the payload. The video will be analyzed after the experiment to extract data on damping rates and potentially positional data of the liquid-gas interface. The impact of constraints on the design of the overall experiment are discussed. The purpose of each component in the experiment is explained and justified relative to the design constraints. The remaining work that must be completed before flight on SpaceShipTwo is reviewed, highlighting the most significant unknowns.<br>

L'étude du comportement d'un fluide proche de son point critique et soumis à des vibrations ou une variation rapide de gravité/acceleration est un sujet extrêmement intéressant. Les phénomènes physiques impliqués sont d'un grand intérêt non seulement pour la physique fondamentale mais aussi pour l'industrie spatiale. Dans cette thèse, trois problèmes sont principalement trait&s: (i) Etude de l'interaction de vibrations harmoniques avec une couche limite thermique dans un fluide supercritique en absence de gravité, (ii) Etude de l'interaction de vibrations avec une interface liquide/vapeur d'un fluide sous−critique sous plusieurs niveaux de gravité (les instabilités de Faraday et d'onde gelée, l'équilibre dynamique d'une interface) et (iii) Etude du phénomène de geyser à l'intérieur d'un réservoir partiellement rempli d'oxygène lorsqu'il est soumis à une variation rapide de la gravité (ou accélération). La thèse comporte une partie expérimentale et une partie numérique. Des expériences ont été réalisées sur les installations HYLDE et OLGA du CEA Grenoble utilisant respectivement les fluides H2 et O2 dans la zone sous−critique. Des simulations numériques sont réalisées pour étudier la stabilité d'une couche limite thermique et la dynamique d'une interface fluide soumise à une variation rapide de la gravité en utilisant des codes numériques basées sur le méthode volumes finis utilisant les algorithmes SIMPLER et VOF−PLIC respectivement. Plusieurs résultats intéressants ont été obtenus. Différents phénomènes ont été étudiés et quantifiés, comme l'instabilité de Faraday et l'instabilité d'onde gelée dans le domaine sous−critique et l'instabilité parametrique et l'instabilité Rayleigh−vibrationnelle dans le domaine supercritique. Les expériences ont permis de bien comprendre les raisons de la transition de l'instabilité de Faraday vers une structuration en bandes verticales très près du point critique. Les expériences et les simulations numériques sur le phénomène de geyser ont aidé à développer des corrélations empiriques pour les vitesses de la bulle et du geyser en prenant en compte les effets des parois. / The behavior of a near-critical fluid subjected to vibration or a rapid variation of acceleration is an extremely interesting topic of research. The resulting physical phenomena are of great interest in view of the fundamental physics involved and have great relevance to the space industry. The thesis addresses mainly three problems: (i) study of the interaction of harmonic vibration with a thermal boundary layer of a supercritical fluid under the absence of gravity, (ii) study of the inter- action of vibration with the liquid−vapor interface of a near−critical fluid under various gravity levels (Faraday and frozen wave instabili- ties, dynamic equilibrium of the interface) (iii) study of the geysering phenomenon inside a reservoir partially filled with a liquid when it is subjected to a rapid variation of gravity. Experiments are conducted onboard the zero−g installations HYLDE and OLGA developed by CEA Grenoble using H2 and O2 as the work- ing fluids. Numerical simulations are carried out using finite volume codes based on SIMPLER (for the problem involving the supercriti- cal fluid) and VOF−PLIC (for the interface dynamics problem under rapid variation of gravity). New and interesting results have been obtained. Various phenom- ena like the Faraday instability and the frozen wave instability in the sub−critical region and the parametric instability and the Rayleigh−vibrational instability in the supercritical region have been quantified. The experiments have successfully explained the reason behind the transition of the Faraday instability into vertical band pattern very close to the critical point. Experiments and numerical simulation of the geysering phenomenon have helped to evolve empir- ical correlations for the bubble rise and geyser edge velocities taking into account the effect of walls on these velocities.

Les challenges posés par les missions d’exploration du système solaire sont très différents de ceux de la Station Spatiale Internationale, puisque les distances sont beaucoup plus importantes, limitant la possibilité de ravitaillements réguliers. Les systèmes support-vie basés sur des plantes supérieures et des micro-organismes, comme le projet de l’Agence Spatiale Européenne (ESA) MELiSSA (Micro Ecological Life Support System Alternative) permettront aux équipages d’être autonomes en termes de production de nourriture, revitalisation de l’air et de recyclage d’eau, tout en fermant les cycles de l’eau, de l’oxygène, de l’azote et du carbone, pendant les missions longue durée, et deviendront donc essentiels.La croissance et le développement des plantes et autres organismes biologiques sont fortement influencés par les conditions environnementales (par exemple la gravité, la pression, la température, l’humidité relative, les pressions partielles en O2 et CO2). Pour prédire la croissance des plantes dans ces conditions non-standard, il est crucial de développer des modèles de croissance mécanistiques, permettant une étude multi-échelle des différents phénomènes, ainsi que d’acquérir une compréhension approfondie de tous les processus impliqués dans le développement des plantes en environnement de gravité réduite et d’identifier les lacunes de connaissance.En particulier, les échanges gazeux à la surface de la feuille sont altérés en gravité réduite, ce qui pourrait diminuer la croissance des plantes dans l’espace. Ainsi, nous avons étudié les relations complexes entre convection forcée, niveau de gravité et production de biomasse et avons trouvé que l’inclusion de la gravité comme paramètre dans les modèles d’échanges gazeux des plantes nécessite une description précise des transferts de matière et d’énergie dans la couche limite. Nous avons ajouté un bilan d’énergie au bilan de masse du modèle de croissance de plante déjà existant et cela a ajouté des variations temporelles sur la température de surface des feuilles.Cette variable peut être mesurée à l’aide de caméras infra-rouges et nous avons réalisé une expérience en vol parabolique et cela nous a permis de valider des modèles de transferts gazeux locaux en 0g et 2g, sans ventilation.Enfin, le transport de sève, la croissance racinaire et la sénescence des feuilles doivent être étudiés en conditions de gravité réduite. Cela permettrait de lier notre modèle d’échanges gazeux à la morphologie des plantes et aux allocations de ressources dans une plante et ainsi arriver à un modèle mécanistique complet de la croissance des plantes en environnement de gravité réduite. / Challenges triggered by human space exploration of the solar system are different from those of the International Space Station because distances and time frames are of a different scale, preventing frequent resupplies. Bioregenerative life-support systems based on higher plants and microorganisms, such as the ESA Micro-Ecological Life Support System Alternative (MELiSSA) project will enable crews to be autonomous in food production, air revitalization, and water recycling, while closing cycles for water, oxygen, nitrogen, and carbon, during long-duration missions and will thus become necessary.The growth and development of higher plants and other biological organisms are strongly influenced by environmental conditions (e.g. gravity, pressure, temperature, relative humidity, partial pressure of O2 or CO2). To predict plant growth in these non-standard conditions, it is crucial to develop mechanistic models of plant growth, enabling multi-scale study of different phenomena, as well as gaining thorough understanding on all processes involved in plant development in low gravity environment and identifying knowledge gaps.Especially gas exchanges at the leaf surface are altered in reduced gravity, which could reduce plant growth in space. Thus, we studied the intricate relationships between forced convection, gravity levels and biomass production and found that the inclusion of gravity as a parameter in plant gas exchanges models requires accurate mass and heat transfer descriptions in the boundary layer. We introduced an energy coupling to the already existing mass balance model of plant growth and this introduced time-dependent variations of the leaf surface temperature.This variable can be measured using infra-red cameras and we implemented a parabolic flight experiment, which enabled us to validate local gas transfer models in 0g and 2g without ventilation.Finally, sap transport needs to be studied in reduced gravity environments, along with root absorption and leaf senescence. This would enable to link our gas exchanges model to plant morphology and resources allocations, and achieve a complete mechanistic model of plant growth in low gravity environments.