超小型深宇宙探査機のための超軽量熱制御システムに関する研究

摘要

Deep space exploration has one of its motivations in the human endeavor to explore the resources of the Solar System, while the space exploration programs motivate the young people to study in science and engineering. Recently, the size and cost of the satellites missions have been reduced and nowadays many universities have the capability to build small satellites and spacecraft. The continuous improvement in micro spacecraft technologies can increase the space travel reliability. Also, through the small deep space probes missions which aim in collecting space flight data and returning them to Earth, the thermal protection systems for the future human space missions can be validated. Some of the biggest challenges related to these missions are the harsh thermal environment of deep space and the atmospheric re-entry. The aim of this research is to address the two aspects, the one related to the harsh thermal environment of outer space, for which the study case will be represented by Shinen2 deep space mission, and the one related to atmospheric re-entry, focused on the validation of the ablative materials called LATS (Light-weight Ablator Series for Transport Vehicle Systems). The both studies are contributing in enhancing the knowledge and in developing new technologies related to a future small spacecraft mission, led by universities. To accomplish the objectives of the research, the following studies have been done: ・Development of a passive thermal control method for a deep space probe (Shinen2), having an outer structure made of CFRTP (Carbon Fiber Reinforced Thermoplastics) materials (first time used for a space vehicle); ・ Development and validation of empirical and numerical methods to estimate the recession rate of LATS materials during re-entry; The thesis include five chapters. First chapter is the Introduction Chapter, describing the motivation for ultra-small spacecraft missions led by universities, the harsh environment of deep space and during atmospheric reentry, the challenges in designing the thermal system, and also the objectives and the structure of the thesis. Chapter two presents a description of the various methods to design a thermal control system, suitable for a deep space mission like Shinen2, about the thermomechanical properties of CFRTP and LATS materials and about the numerical and empirical methods used to test the efficiency of LATS materials. Chapter three comprises the orbit analysis, the thermal design, analysis and validation of the ultra-small deep space probe, Shinen2, developed by Kyushu Institute of Technology in collaboration with Kagoshima University and launched on December 2014. For reasons of weight saving and power saving, Shinen2 did not carry a heater to warm itself. A passive thermal control of a deep space probe is very difficult to be attained and the thermal design of Shinen2 didn’t have a precedent model. Chapter four focuses on the study of light thermal protection systems for re-entry spacecraft, using LATS materials. To study the thermal performances of LATS materials, numerical and empirical studies were performed using the flight data of USERS spacecraft and the results of high enthalpy heating tests, performed at Japan Aerospace Exploration Agency (JAXA, Japan). The Conclusions chapter, Chapter five, summarizes the findings of the research and describes a conceptual design of the thermal system for a future ultra-small spacecraft mission, led by universities. Also, Chapter five describes the recommendations for future studies. The main findings of the research are that the developed passive thermal control of Shinen2 was proven reliable in deep space and LATS ablative materials were proven to have high thermal efficiency and they can well function as heat shield materials even under a highenthalpy flow, in spite of their low density.