Formulación y validación de modelo de actitud de un cubesat en interacción dinámica con carga útil líquida.
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Date
2024
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Universidad de Concepción
Abstract
Durante las últimas décadas, el crecimiento del sector espacial ha sido significativo ya que se han desarrollado alternativas cada vez más económicas para desplegar carga útil en el espacio; una de ellas son los cubesats. Estos satélites que nacieron como un concepto para la academia, se han masificado en diversas aplicaciones, sin embargo, un problema de estos satélites, y en general de los vehículos espaciales es cuando llevan carga útil líquida, ya que se genera una interacción dinámica compleja entre el movimiento del fluido y la actitud del vehículo espacial, de esto surge la necesidad de controlar este movimiento.
Es importante mencionar que esta interacción dinámica es un tópico que plantea más preguntas que respuestas, por ejemplo, ¿Cuánto tarda un satélite con una carga útil liquida en hacer detumbling?. En esta memoria de título se decidió abordar este tópico de forma experimental, diseñando, fabricando y operando un banco de ensayo de rotación de un cubesat 2U con carga útil líquida en un grado de libertad. Se ejecutaron una serie de pruebas variando volumen y viscosidad del fluido, el objetivo fue cuantificar una relación entre la rotación del banco y las propiedades de la carga útil líquida, volumen y viscosidad.
El banco de ensayo, diseñado como una plataforma rotatoria sobre una base utilizando un rodamiento, durante su operación presentó una serie de dificultades, tales como el alto valor de roce del rodamiento de la plataforma en relación al coeficiente de disipación de energía del fluido. Además, se observó un leve pero no despreciable aumento del roce del rodamiento luego de unas 10 pruebas sucesivas. En respuesta a estos problemas, se hicieron modificaciones en algunos componentes y cambios en la metodología experimental. Con el banco en su versión final y la metodología bien definida se hizo el entrenamiento de un modelo de 2°orden para caracterizar el banco de ensayo con y sin líquidos y de esta forma, determinar el efecto de los líquidos en la rotación. No se observó una tendencia clara del factor de factor de disipación de energía en función del porcentaje de llenado del frasco, pero el punto en común de los resultados fue el orden de magnitud de 10−3 del coeficiente de disipación de energía para todos los fluidos.
En respuesta a los resultados poco claros obtenidos con el banco de ensayo, se hizo un trabajo de una semana en la Universidad de Chile operando un air bearing semiesférico para experimentar la interacción dinámica entre fluidos y un cuerpo en rotación. La ventaja de utilizar este equipo fue el menor roce que ten ́ıa en comparación al banco de ensayo desarrollado en esta memoria. En los resultados se observó una tendencia lineal en la curva de descenso de la velocidad angular en el eje Z del body frame de la plataforma del air bearing. Mediante el entrenamiento de un modelo lineal de 2° orden se determinó que la tasa de descenso de la velocidad angular fue hasta un 28% mayor en un setup con líquidos en comparación a un setup rígido. Además se analizó el movimiento oscilatorio de la rotación en el airbearing mediante el cálculo del espectro en frecuencia, con esta técnica se determinaron la primera y la segunda frecuencia natural del sistema y se compararon las frecuencias de los setup rígido y con agua, sin embargo, no se observaron resultados concluyentes en este análisis.
Over the last few decades, the growth of the space sector has been significant, with increasingly cost- effective alternatives being developed to deploy payloads in space; one such alternative is cubesats. Origi- nally conceived as an academic concept, these satellites have been widely adopted for various applications. However, a persistent issue with these satellites, and spacecraft in general, is when they carry liquid pay- loads, as this leads to complex dynamic interactions between the fluid movement and the spacecraft’s attitude, necessitating control over this movement. It is important to note that this dynamic interaction raises more questions than answers, for example, how long does it take for a satellite with a liquid payload to achieve detumbling? This thesis addresses this topic experimentally by designing, manufacturing, and operating a rotation test bench for a 2U cubesat with a liquid payload in one degree of freedom. A series of tests were conducted varying the fluid’s volume and viscosity, aiming to quantify a relationship between the rotation of the test bench and the properties of the liquid payload, volume, and viscosity. The test bench, designed as a rotary platform on a base using a bearing, faced several challenges du- ring operation, such as the high friction value of the bearing compared to the fluid’s energy dissipation coefficient. Additionally, a slight but noticeable increase in bearing friction was observed after about 10 consecutive tests. In response to these issues, modifications were made to some components and changes in the experimental methodology. With the final version of the bench and a well-defined methodology, training of a second-order model was conducted to characterize the test bench with and without liquids, thereby determining the effect of the liquids on rotation. No clear trend in the energy dissipation factor was observed based on the filling percentage of the container, but the common denominator of the results was the order of magnitude of 10−3 of the energy dissipation coefficient for all fluids. In response to the unclear results from the test bench, a week-long study was conducted at the University of Chile operating a hemispherical air bearing to experiment with the dynamic interaction between fluids and a rotating body. The advantage of using this equipment was the lower friction compared to the test bench developed in this thesis. The results showed a linear trend in the angular velocity decay curve on the Z-axis of the air bearing’s body frame. By training a linear second-order model, it was determined that the rate of angular velocity decay was up to 28 % higher in a setup with liquids compared to a rigid setup. Additionally, the oscillatory motion of the rotation on the air bearing was analyzed by calculating the frequency spectrum, with this technique determining the first and second natural frequencies of the system and comparing the frequencies of the rigid and water-filled setups; however, no conclusive results were observed in this analysis.
Over the last few decades, the growth of the space sector has been significant, with increasingly cost- effective alternatives being developed to deploy payloads in space; one such alternative is cubesats. Origi- nally conceived as an academic concept, these satellites have been widely adopted for various applications. However, a persistent issue with these satellites, and spacecraft in general, is when they carry liquid pay- loads, as this leads to complex dynamic interactions between the fluid movement and the spacecraft’s attitude, necessitating control over this movement. It is important to note that this dynamic interaction raises more questions than answers, for example, how long does it take for a satellite with a liquid payload to achieve detumbling? This thesis addresses this topic experimentally by designing, manufacturing, and operating a rotation test bench for a 2U cubesat with a liquid payload in one degree of freedom. A series of tests were conducted varying the fluid’s volume and viscosity, aiming to quantify a relationship between the rotation of the test bench and the properties of the liquid payload, volume, and viscosity. The test bench, designed as a rotary platform on a base using a bearing, faced several challenges du- ring operation, such as the high friction value of the bearing compared to the fluid’s energy dissipation coefficient. Additionally, a slight but noticeable increase in bearing friction was observed after about 10 consecutive tests. In response to these issues, modifications were made to some components and changes in the experimental methodology. With the final version of the bench and a well-defined methodology, training of a second-order model was conducted to characterize the test bench with and without liquids, thereby determining the effect of the liquids on rotation. No clear trend in the energy dissipation factor was observed based on the filling percentage of the container, but the common denominator of the results was the order of magnitude of 10−3 of the energy dissipation coefficient for all fluids. In response to the unclear results from the test bench, a week-long study was conducted at the University of Chile operating a hemispherical air bearing to experiment with the dynamic interaction between fluids and a rotating body. The advantage of using this equipment was the lower friction compared to the test bench developed in this thesis. The results showed a linear trend in the angular velocity decay curve on the Z-axis of the air bearing’s body frame. By training a linear second-order model, it was determined that the rate of angular velocity decay was up to 28 % higher in a setup with liquids compared to a rigid setup. Additionally, the oscillatory motion of the rotation on the air bearing was analyzed by calculating the frequency spectrum, with this technique determining the first and second natural frequencies of the system and comparing the frequencies of the rigid and water-filled setups; however, no conclusive results were observed in this analysis.
Description
Tesis presentada para optar al Título de Ingeniero Civil Aeroespacial
Keywords
Satélites, Líquidos, Satélites científicos