This work was motivated by questions raised from multifrequency microwave interferometer measurements taken in a cylindrical plasma on the Variable Specific Impulse Magnetoplasma Rocket (VASIMR) project. Standard data analysis based on a thin beam model neglecting refraction yields inconsistent electron densities and density profiles for different frequencies. This work focuses on the development of a model for the wave propagation through cylindrical plasmas when the plasma radius is on the order of the beam waist. For the calculations presented a Gaussian beam profile and plasma spatial profile were assumed. Both refraction by density gradients and finite beam sizes are found to play important roles and explain polychromatic differences in the electron densities and profiles. Calculations for the new model are compared to a thin beam model not accounting for refraction and experimental data from VASIMR.

General uncertainty analysis was used to evaluate the performance of a Rocket-Based Combined Cycle (RBCC) engine system. To estimate the uncertainties of test results, uncertainties of basic measurements such as temperature, pressure, mass flow rate, and thrust were determined. The desired test results of interest included specific impulse and characteristic velocity. Various possible test facilities were reviewed to obtain background information and example test run conditions. Based on the test run conditions, five methods of determining specific impulse were evaluated. Also, theoretical and actual characteristic velocities were analyzed to evaluate C* efficiency. Initially, general uncertainty analyses were completed relative to 1% accuracy for each measured variable. Then, cases were run using more realistic uncertainty estimates. The relative contributions of the different variables? uncertainties to the overall uncertainty of the selected performance parameters were also calculated. This process helps to identify the critical measurements from an uncertainty standpoint and can be a significant guide in the cost effective use of resources to reduce the test uncertainty.

Hybrid rocket motors have become of great international interest during the last couple of years. A hybrid rocket motor is propelled by the use of a solid fuel and a liquid oxidizer. The fundamental principle of the hybrid propelled system is that the liquid oxidizer is injected into a combustion chamber to enable the combustion of the solid fuel. The exhaust gases are then accelerated through a nozzle to supersonic velocity to produce the desired level of thrust. To describe the overall performance of a propulsion system, it is common use the specifc impulse which expresses the performance as the total impulse per mass unit of propellant. However, in order to optimize a propulsion system, it is necessary to consider the entire system with the oxidizer tank, feed system, combustion chamber and nozzle. The issue with using the specifc impulse as a performance index is that it does not consider the total mass of the propulsion system. Therefore, this thesis will instead analyze the system specifc impulse, which expresses the performance as the total impulse per mass unit of propulsion system. By studying the entire hybrid propulsion system it is possible to determine the relations between the various parameters of the diferent components and should therefore be able to optimize the mass, volume and system specifc impulse of the system. This master’s thesis aims to illustrate how the hybrid propulsion system can be optimized depending on various fxed parameters. This analysis studies a generic hybrid propulsion systemwith Hydroxyl-terminated polybutadiene (HTPB) as a solid fuel with diferent combinations ofoxidizers. Each oxidizer- and fuel confguration shall have identical combustion chamber presssures and shall generate the same total impulse. Nevertheless, each combination will result indiferent specifc impulses since the optimal confguration for each combination will generate diffferent oxidizer and fuel masses. It is then desirable to analyze how the diferent components ofthe propulsion system are affected by the required oxidizer and fuel for each optimal confgurationand how it drives the design of the system and generates diferent system specifc impulses.

This work is motivated by the Variable Specific Impulse Magnetoplasma Rocket (VASIMR) experiment. This device uses a helicon antenna to generate a plasma inside a dielectric tube, which is radially confined and directed towards the rocket nozzle by an axial magnetic field. An ion cyclotron heating antenna further heats the ions, and a magnetic nozzle accelerates the plasma along the confining magnetic field as it leaves the rocket, ultimately allowing it to detach from the magnetic field and produce thrust. The experimental research presented here provides insight into the physical mechanisms of power flow in a helicon system by providing an overall system power balance in the form of heat flux measurements, and exploring changes in the heat fluxes in different parts of the system in response to varying operational parameters. An infrared (IR) camera measures the total heat flux into the dielectric tube surface, and axially scanned bolometer and UV photodiode probes measure the radial power loss from particles and radiation. Results from IR camera measurements on three different helicon systems are presented: the VASIMR VX-50 experiment, the VASIMR VX-CR experiment, and the University of Texas at Austin (UT) helicon experiment. These results demonstrate the development of the IR camera diagnostic for use on helicon systems of varying scale and geometry, and show reasonable agreement as to the fraction of input power lost to the dielectric tube walls. On the UT experiment, the results presented account for essentially all of the input power, providing a full system power balance. The data from all three experiments indicate that radial transport of ions to the interior wall is the dominant mechanism of power loss, with UV radiation contributing a small percentage. Additional experiments on the UT helicon explore energy and particle transport to the wall due to capacitive coupling of ions near the antenna. These experiments show clear damage to the dielectric tube surface directly under the antenna, due to physical plasma etching of the surface by bombarding ions that are accelerated into the wall by local electric fields from the antenna. / text

<p>Development of complex aerospace systems often takes decades of research and testing. High  performing propellants are important to the success of rocket propulsion systems. Development  and testing of new propellants can be expensive and dangerous. Full scale tests are often required  to understand the performance of new propellants. Many industries have started using data science  tools to learn from previous work and conduct smarter tests. Material scientists have started using  these tools to speed up the development of new materials. These data science tools can be used to  speed up the development and design better propellants. I approach the development of new solid  propellants through two steps: Prediction of delivered performance from available literature tests,  prediction of ideal performance using physics-based models. Random Forest models are used to  correlate the ideal performance to delivered performance of a propellant based on the composition  and motor properties. I use Parsimonious Neural Networks (PNNs) to learn interpretable models  for the ideal performance of propellants. I find that the available open literature data is too biased  for the models to learn from and discover families of interpretable models to predict the ideal  performance of propellants. </p>

Ce travail est consacré au développement de composés polyazotés de la famille des tétrazènes, pour des applications dans le domaine de la propulsion spatiale. Compte tenu de la forte toxicité des hydrazines utilisées actuellement dans les systèmes à biergols stockables, il devient absolument nécessaire de les remplacer par de nouveaux ergols verts, performants au niveau propulsion, et ne présentant pas d'impact significatif sur la santé humaine et l'environnement. Aujourd'hui, le candidat idéal pour remplacer les hydrazines spatiales n'a pas été identifié, mais un premier candidat a été proposé par le CNES en raison de ses performances théoriques et d'une toxicité moindre, il s'agit du 1,1,4,4-tétraméthyl-2-tétrazène (TMTZ). Dans cette thèse, une caractérisation complète de ce composé a été effectuée, afin de valider son intérêt en tant qu'ergol. Une étude cinétique et thermodynamique a permis de proposer un procédé de synthèse du TMTZ propre, performant en continu, intégrant les phases de synthèse, d'extraction et de purification. Pour aller plus loin dans cette démarche, de nouvelles cibles polyazotées ont été identifiées, dans le but d'atteindre des performances plus importantes en élaborant des structures tétrazènes plus riches en atomes d'azote que le TMTZ. Les différentes voies de synthèse de ces tétrazènes densifiés sont présentées, ainsi que la réactivité de leurs précurseurs potentiels. En appui de ces recherches, des outils théoriques et expérimentaux de prédiction et de détermination des performances énergétiques des composés polyazotés sont présentés / This work aims at the development of polynitrogen-based compounds of the tetrazene family for space propulsion applications. Due to the high toxicity of hydrazines used currently in stockable bipropellant systems, there is a need to replace them by new green propellants with high propulsion performance and low impact towards human health and the environment.So far, the ideal candidate to replace space-use hydrazines has not been identified. However, the French Space Agency (CNES) proposed a first candidate, namely, 1,1,4,4-tetramethyl-2-tetrazene (TMTZ), which has a high theoretical performance and exhibits lower toxicity. In this work the latter compound was fully characterized in order to validate its interest as a propellant. Kinetic and thermodynamic studies allowed to propose a continuous synthesis process for pure TMTZ, which involves a synthesis, an extraction and a purification steps. In this context, new polynitrogen-based target molecules were identified in order to achieve higher performances than TMTZ and tetrazene derivatives with a higher nitrogen content were synthesized. Herein, the different synthesis pathways of these tetrazene derivatives with higher density as well as the reactivity of their potential building blocks are presented. To complete the above research, theoretical and experimental methods for the prediction and measurement of the energetic performance of the polynitrogen-based compounds are also presented