<p dir="ltr"> As part of humanity's constant effort to explore and expand, the race to establish a cislunar economy is afoot. The Cryobubbles experiment seeks to advance the state of the art in long-term cryogenic propellant management, a field that is an integral part of exploring the next great frontier. The Cryobubbles experiment was created to understand an unexpected bubble formation phenomenon during a tank-pressure control strategy test of NASA's Zero Boil-off Tank (ZBOT) on the International Space Station. A few hypotheses about the causes of bubble formation were developed, and thanks to a NASA flight opportunities grant, the Cryobubbles experiment was designed and manufactured with a \$95,000 budget to test these hypotheses on a parabolic flight.</p><p dir="ltr"> This master's thesis explains the importance of understanding the causes of bubble formation and the thermodynamic operating point chosen to replicate ZBOT conditions. The operation of the experiment and the design of technologies developed to make these operations work are also discussed. Some notable technologies include an insulation sizing algorithm created to maintain the experiment operating point, cryogenically rated viewports that allow for high-quality video recording of the experiment, and copper coils sized to allow for the safe use of noncryogenic equipment in a cryogenic test setup. All of these designs were constrained by a budget, a fast-approaching flight test deadline, and safety considerations.</p><p dir="ltr"> At the time of this writing, the experiment has been fully designed, manufactured, and assembled. The next step is to conduct testing.</p>

La thèse porte sur l'étude d'un système de contrôle de la pression au sein de réservoirs d’ergols cryogéniques (dihydrogène ou dioxygène) dans le cadre de missions spatiales de longue durée. Ce système de contrôle doit permettre d’éviter la perte excessive d’ergols associée à un contrôle basique de la pression consistant en l’évacuation directe d’une fraction du fluide. Le système alternatif étudié, dit de contrôle thermodynamique, repose sur la réinjection d’un spray sous-refroidi permettant d’abaisser température et pression dans un réservoir soumis à une chauffe (en pratique, le rayonnement solaire). Nous avons analysé les performances de ce système en développant en parallèle un banc d'essai adapté aux conditions du laboratoire, et un modèle théorique de type 0D, à base de bilans globaux, de l’effet du spray sous-refroidi sur les caractéristiques thermodynamiques de l’enceinte. La confrontation des mesures et des calculs a permis de valider l’outil de modélisation théorique. Les caractéristiques du système réel (ensemble des circuits d'injection et de refroidissement) ont ensuite été introduites dans le modèle théorique afin de quantifier de façon réaliste les gains offerts par le système de contrôle thermodynamique, i.e. en prenant en compte la pénalité en masse associée à ces circuits. Des solutions optimales de contrôle de la pression au sein de réservoirs d’ergols cryogéniques lors de missions spatiales de longue durée ont pu alors être proposées. / This PHD thesis deals with the study of a pressure control system inside a cryogenic propellant tank for long duration space missions. This system must be able to reduce propellant losses induced by direct venting, which is the simplest pressure control system. The alternative system which has been studied, called Thermodynamic Vent System (TVS), is based on reinjecting subcooled spray to make the pressure and temperature decrease in a heated tank. The system performance has been analysed developing simultaneously an experimental setup, adapted to laboratory environment, and a theoretical 0D-modelling of subcooled spray impact on tank's thermodynamic characteristics. Facing experimental and theoretical results has permitted to validate the 0D-modelling tool. Inputing the real system characteristics in theoretical modelling has enabled to assess the effective gains of thermodynamic vent system. Finally, optimal solutions to control pressure inside a cryogenic propellant tank for long duration space missions have been proposed.