微衛星低成本重力梯度桿設計分析

The Design of a Low-Cost Gravity-Gradient Boom for Microsatellite

本文主要針對TUUSAT-1A (Taiwan University-United Satellite-1)下一代微衛星（體積小於40cm×40cm×40cm、重量小於40kg）開發重力梯度穩定機構，衛星主要任務目標為拍攝氣象雲圖，設計的機構必須符合衛星需求和低成本且適合在大學裡發展的微衛星使用，指向精度以能夠提供任務所需5度做設計。設計首先將定義衛星任務目標、需求以及系統需求與限制，接著參考國外現有機構的設計方法作為依據，並估算出所需之重力梯度力矩、桿長和慣性矩，機構將完全自行開發與設計，且符合安裝簡單、可提供試驗數據和容易伸展的特性，最後對機構進行伸展功能測試以及利用有限元素軟體進行振頻模擬驗證設計成果，開發過程中每一階段皆需和系統需求、限制比較，直到設計結果滿足設計需求為止。

This paper focuses on the design of a gravity-gradient boom for the next generation of the microsat, TUUSAT-1 (Taiwan University-United Satellite-1), which is less than 40 cm by 40 cm by 40 cm in size, and 40 kg in weight. The primary mission objective is to acquire weather images. The design of a gravity-gradient boom must be low-cost and applicable to the microsat developed by the university programs. The attitude control system of the microsat must provide off-nadir pointing with less than 5 degree of deviation when the stationary phase of attitude is approached.The functional requirements of the gravity-gradient boom are defined according to the requirements of the attitude control system. The gravity-gradient torque of the microsat, which meets functional requirements, is calculated to obtain a proper length and weight of tip-mass for the boom. A stainless steel tapeline is adopted as the main structure of the boom. The boom has been developed and fabricated in-house, and possesses the characteristics of low-cost, ease of assembly and ease of deployment. The deployment of the gravity-gradient boom is then tested to verify the functionalities. The result shows that the gravity-gradient boom using steel tapeline can be successfully deployed.