Picosatellites are defined as satellites with a mass between 0.1 and 1kg (Miniaturized satellite). Picosatellites are typically designed to work together or function in formations (Miniaturized satellite). A specific type of Picosatellite known as CubeSats were introduced in 1999 and since then have increased in popularity so that there are now over 80 CubeSat programs around the world. CubeSats are defined as cubic units 10cm on each side and no more than 1kg in mass. CubeSats are required to conform to the CubeSat Standard created by California Polytechnic State University and Stanford University and be compatible with Cal Poly’s P-POD deployment system (Toorian, 2005). Some CubeSat uses include earth imaging, communications projects and various scientific experiments. CubeSats currently require attitude control and in the future, may require, maintaining a specific orbit, or changing orbit. With this ability many new activities may be possible for CubeSats. These activities could include rendezvous, vehicle inspection, formation flying and de-orbiting. For these activities to be possible, a high performance propulsion system is required. The goal of this thesis is to design and test an affordable, safe, and effective micro-propulsion system for CubeSats.

Propellants based on hydroxylammonium nitrate (HAN) have shown promise as a hydrazine replacement because of their comparably low toxicity, low vapor pressure, high specific impulse and high density. Herein, the recent history of advanced monopropellant research is explored, and new experimental techniques are presented to investigate the combustion behavior of a potential hydrazine replacement propellant. Nitromethane, a widely available monopropellant with a recent resurgence in research, is utilized in the current study as a proof of concept for the newly designed equipment and as a step towards investigating more-advanced, HAN-based monopropellants. A strand bomb facility capable of supporting testing at up to 340 atm was employed, and experiments were performed between 28 atm and 130 atm. Burning rate data for nitromethane are calculated from experiments and a power correlation is established as r(mm/s) = 0.33[P(MPa)]^1.02. A comparison with available literature reveals this correlation to be very much in agreement to other studies of nitromethane. Other physical characteristics of nitromethane combustion are presented. Updates to the facility and new methods to examine the combustion of liquid propellant are described in detail. Special focus is given to procedures and safety information.

Propulsive capabilities on a CubeSat are the next step in advancement in the Aerospace Industry. This is no longer a quest that is being sought by just university programs, but a challenge that is being taken on by all of the industry due to the low-cost missions that can be accomplished. At this time, all of the proposed micro-thruster systems still require some form of development or testing before being flight-ready. Stellar Exploration, Inc. is developing a monopropellant micropropulsion system designed specifically for CubeSat application. The addition of a thruster to a CubeSat would expand the possibilities of what CubeSat missions are capable of achieving. The development of these miniature systems comes with many challenges. One of the largest challenges that a hot thruster faces is the ability to complete burns for the specified mission without transferring excessive heat into the propulsion tank. Due to the close proximity of the thruster to the tank, thermal standoff options are necessary to help alleviate the heat going through the system, especially while in a thermally extreme environment. This thesis examines the heat transfer that occurs within a CubeSat with an operating hydrazine monopropellant thruster. Thermal analysis of the system revealed that having a solid stainless steel barrier between the thruster and tank led to increasing temperatures greater than 400K in the propellant tank while in an environment exposed to the sun. This creates a large amount of risk for the CubeSat and its mission. The use of a thermal insulating material or a hollow barrier for the standoff decreased the risk of using this system. This creates a standoff where the heat of the propellant reaction does not reach the propellant in the tank. Therefore, the maximum temperature that the tank reaches is equivalent to the temperature of the external environment while in extreme conditions. These results create the confidence that the thermal standoffs will function as intended to protect the spacecraft and its payload during flight.

Increasing interest in the development of nontoxic monopropellants for the replacement of hydrazine and its derivatives stems from the desire for safer and thus more cost-effective alternatives. Ionic liquid monopropellants based on the hydroxylammonium nitrate and ammonium dinitramide ionic oxidizer salts have received the majority of attention over the last two decades and present a promising alternative with higher performance and more attractive handling qualities than hydrazine. These monopropellants are employed using catalytic methods which lead to their decomposition and ignition. However, the development of compatible catalysts remains a limiting step in the technological readiness of these alternative monopropellants. Due to their ionic nature, the development of ionic liquid monopropellants has led to many investigations on the utilization of electrolysis to achieve combustion. Separately, there has been a longtime interest in the use of gelled propellants for enhanced handling and operating safety. Atomization and combustion inefficiencies associated with gels have continued to limit their use. Monopropellants composed of gel polymer electrolytes present a unique opportunity which combines the safety features of gelled propellants as well as the ionic conductivity seen in ionic liquids, allowing them to decompose and ignite electrolytically. In this research, a family of electrically controlled monopropellants that utilize electrolysis in this fashion was developed from a gel polymer electrolyte. Their fundamental properties, including those pertaining to rheology, conductivity, thermal stability, and combustion, are explored as the composition of the oxidizer salt is varied. / Master of Science / Current advancements in rocket propulsion include interests in developing alternative green propellants for use in spacecraft propulsion systems with the hope of replacing current options which may be toxic to handle and present a serious safety hazard. Alternative propellants are generally thought of as not requiring special safety equipment or protocols in their handling, thereby reducing costs. Several promising options belonging to a category of propellants known as ionic liquids have made significant progress in development since the 1990s and have the potential to be used alongside a novel electrical combustion method known as electrolysis. Gelled propellants are another possible alternative which have been researched for their appealing safety qualities for some time. While not researched for their use as rocket propellants until very recently, gel polymer electrolytes have received interest in this application due to their composition which includes a polymer, commonly used as rocket fuel, and an oxidizer salt. Due to their inherent electrical conductivity, their potential to use electrolysis in a similar manner to ionic liquids to achieve combustion is of interest. The research detailed in this thesis was completed to characterize fundamental material and combustion properties of a gel polymer electrolyte propellant as its oxidizer constituents are varied.

Nitrous oxide (N2O) is an inexpensive and readily available non-toxic rocket motor oxidizer. It is the most commonly used oxidizer for hybrid bipropellant rocket systems, and several bipropellant liquid rocket designs have also used nitrous oxide. In liquid form, N2O is highly stable, but in vapor form it has the potential to decompose exothermically, releasing up to 1865 Joules per gram of vapor as it dissociates into nitrogen and oxygen. Consequently, it has long been considered as a potential "green" replacement for existing highly toxic and dangerous monopropellants. This project investigates the feasibility of using the nitrous oxide decomposition reaction as a monopropellant energy source for igniting liquid bipropellant and hybrid rockets that already use nitrous oxide as the primary oxidizer. Because nitrous oxide is such a stable propellant, the energy barrier to dissociation is quite high; normal thermal decomposition of the vapor phase does not occur until temperatures are above 800 C. The use of a ruthenium catalyst decreases the activation energy for this reaction to allow rapid decomposition below 400 C. This research investigates the design for a prototype device that channels the energy of dissociation to ignite a laboratory scale hybrid rocket motor.

<p>  </p> <p>Monolithic catalyst beds have been used extensively in other industries and are gaining interest for space propulsion applications. Additive manufacturing of monolithic supports allows for catalyst beds with a wider range of geometries than could be produced using conventional methods, potentially allowing for higher performance monoliths that can compete with conventional packed beds in performance. Achieving these gains requires a consistent, even, and well-adhering washcoating procedure for the additively manufactured supports, one which works well on varied geometry and on support materials that can be readily printed. I conducted an extensive development process on improving methods of surface preparation and coating for high temperature ceramic monoliths that resulted in improvements in the state of the art. The materials and methods used are appropriate for rocket grade hydrogen peroxide, hydrazine, or other monopropellants with similar operating temperatures. Using existing published coating methods resulted in uneven coating distribution and poor adhesion. I demonstrate that this was due to the substrate surface morphology producing a hydrophobic effect. Surface morphology plays a significant role in coating coverage and adhesion and differences in initial support surfaces likely account for much of the variation in results seen across the literature. I present a method of controlled thermochemical surface etching using pure sodium hydroxide at 420°C that can reliably produce a roughened hydrophilic surface from a variety of starting morphologies. I also present several modifications to the primer formulation that improve evenness of coverage, the most significant of which is the inclusion of a surfactant at a concentration of 1 g per 36 g water. The surface treatment and coating formulation improvements combine well and produce an even coating with strong adhesion to the substrate. I also conducted preliminary work on the investigation of novel geometric designs for monolithic catalyst beds, and on the reactivity of different transition metal oxide catalysts for rocket grade hydrogen peroxide decomposition. </p>

<p dir="ltr">This work studies the kinetics of nitrous oxide decomposition over alumina-based catalysts, specifically at the high temperatures and high nitrous oxide (N2O) concentrations that would be experienced in catalyst beds for monopropellant rocket thruster applications. High- and low- order models are developed to understand the interaction between reaction kinetics and mass transfer in monolith catalyst tubes. However, nitrous oxide decomposition is not observed on monolith catalyst tubes on account of their lower geometric surface area leading to a majority of the gas not coming into contact with the catalyst surface. Pellet-bed catalysts are studied for the remainder of this work, starting from experiments with a constant-volume batch reactor. The batch experiments demonstrate N2O decomposition over catalyst pellets, and a one-dimensional, time-varying model is developed to quantify the reaction rate based on measured temperature and pressure rise from experimental data. The reaction rates predicted by the model are significantly lower than predicted in the literature for the same catalysts. The inaccuracy is attributed to the fact that the model cannot capture N2O decomposition occurring during the first few seconds of filling the batch tube. Additionally, the simplified temperature distribution applied in the model may not be accurate, and obtaining a higher fidelity temperature distribution experimentally would require more advanced diagnostics.</p><p dir="ltr">The final experiment is a conventional flow-through pellet bed reactor which uses infrared spectroscopy to measure the concentration of nitrous oxide in the decomposed gas mixture. The analysis method incorporates uncertainties from infrared measurements and other sources, and initial activity results of a cobalt oxide-on-alumina catalyst are consistent with the literature. Results from additional testing indicate that manganese oxide catalysts are more active than nickel oxide or cobalt oxide catalysts. At weight loadings of ~10%, results indicate that the Arrhenius pre-exponential constant is roughly an order or magnitude greater for manganese oxide catalysts than cobalt or nickel oxide catalysts. The results also indicate hysteresis in catalytic activity of all oxides. Surface area and x-ray diffraction measurements do not reveal any permanent change in the surface area or crystal structure of these catalysts. The findings lead to the conclusion that the temperature and surrounding environment of the catalyst (either nitrous oxide or nitrogen during system purges) cause short-lived changes to the crystal structure of the active phase, leading to the observed hysteresis.</p>

Aiming at applications in space exploration as well as for monitoring natural hazards, this thesis focuses on understanding and overcoming the challenges of extending the applicability of microsystems to temperatures above 600°C as well as chemically harsh environments. Alumina and zirconia high-temperature co-fired ceramics (HTCC) with platinum as the conductor material, have in this thesis, been used to manufacture a wide range of high-temperature tolerant miniaturized sensors and actuators, including pressure and flow sensors, valves, a combustor, and liquid monopropellant microthrusters. Interfacing for high temperatures is challenging. One solution is to transfer the signal wirelessly. Here, therefor, wireless pressure sensors have been developed and characterized up to 1000°C. It is usually unwanted that material properties change with temperature, but by using smart designs, such changes can be exploited to sense physical properties as in the gas flow sensor presented, where the temperature-dependent electrical conductivity of zirconia has been utilized. In the same manner, various properties of platinum have been exploited to make temperature sensors, heaters and catalytic beds. By in-situ electroplating metals after sintering, even more capabilities were added, since many metals that do not tolerate HTCC processing can be added for additional functionality. An electroplated copper layer that was oxidized and used as an oxygen source in an alumina combustor intended for burning organic samples prior to sample analysis in a lab on a chip system, and a silver layer used as a catalyst in order to decompose hydrogen peroxide in a microthuster for spacecraft attitude control, are both examples that have been explored here. Ceramics are both high-temperature tolerant and chemically resistant, making them suitable for both thrusters and combustors. The corresponding applications benefit from miniaturization of them in terms of decreased mass, power consumption, integration potential, and reduced sample waste. Integrating many functions using as few materials as possible, is important when it comes to microsystems for harsh environments. This thesis has shown the high potential of co-fired ceramics in manufacturing microsystems for aggressive environments. However, interfacing is yet a major challenge to overcome.