發射載具的重力轉彎與姿態控制

Abstract

發射載具通常是以垂直或接近垂直的角度發射升空，在酬載入軌前除了高度及速度的需求外還要作適當的轉彎將飛行路徑角控制到接近零度。載具的轉彎通常利用推力向量控制系統來達成。在大氣層的飛行由於動態壓力相當大，控制的目標之一是防止轉彎造成的側向力矩太大導致載具結構損壞。因此載具在大氣層的初期飛行常採所謂重力轉彎的方式，即保持載具的速度方向與機身一致。本論文探討重力轉彎控制系統的設計。載具氣動力模式的時變及非線性的特性，使其不方便直接用來作控制系統設計。本論文提一個建立近似線性模式的方式，並根據線性模式設計以推力向量為致動的控制系統。垂直發射的載具在進行重力轉彎前必須透過姿態控制改變俯仰角。本文以幾個數值例子，探討姿態控制及重力轉彎控制系統的設計。模擬結果顯示，所提出的設計能維持載具的穩定飛行並達到姿態及重力轉彎的設計目標。

To put a payload into orbit, a launch vehicle must meet altitude, speed and flight path angle specifications. Usually the flight path angle is near zero, which means the vehicle must turn from its vertical or near vertical launch attitude. The turning of vehicle is usually achieved by a thrust vector control system. Due to the large dynamic pressure during atmospheric flight, one of the control objective during this phase of flight is to prevent the induced bending moment from damaging the vehicle structure. Hence most vehicles adopt the so called gravity turn during the early atmospheric part of flight, that is, to maintain zero angle o attack and zero sideslip angle. This thesis investigates gravity turn control system design. Nonlinear and time-varying nature of aerodynamic model makes it inconvenient for control system design. This thesis proposes a method that construct approximate linear model and use it for control system design. Vertically launched vehicles need attitude control to achieve a certain pitch angle before gravity turn. There numerical examples are used to demonstrate the design attitude control system and gravity turn control system. Simulation results show that the designed control systems yield stable flight and achieve attitude and gravity turn design objectives.