航天器姿态机动过程中同时满足约束的运行时间保证
Run Time Assurance for Simultaneous Constraint Satisfaction During Spacecraft Attitude Maneuvering
AI总结：
本文针对航天器自主姿态机动中的多重安全约束问题，提出一种基于控制屏障函数和主动集不变性滤波器的运行时间保证方法，并通过松弛变量处理约束不可行情况，经蒙特卡洛仿真验证其有效性。
摘要：
在轨服务、组装与制造（OSAM）的一项基本能力是对待服务航天器或正在组装的结构进行检测。本研究假设采用自主回转（slewing）来维持对近距离运行的多个航天器的态势感知，其中必须满足若干安全约束。多种技术可用作主控制器。本研究的重点是开发运行时间保证（Run Time Assurance, RTA）滤波器，用于监测系统行为和主控制器的输出，以强制执行安全约束满足。具体而言，本研究探索将约束的一个子集组合到一个使用控制屏障函数定义的主动集不变性滤波器（Active Set Invariance Filter, ASIF）RTA中。该方法通过最小化与主控制器期望控制输出的偏差，对主控制的侵入性最小，同时强制执行所有安全约束。该RTA旨在确保航天器在预定通信窗口期间维持与地面站通信和数据传输的姿态要求，遵守圆锥形姿态禁区（keep out zones），限制热不利姿态持续时间，维持足够发电的姿态要求，确保机动低于造成结构损伤的阈值，确保最大角速度低于限制以维持快速响应新回转指令的能力，并在可能时节约执行器使用以防止磨损。当所有安全约束的解不可行时，在ASIF控制器中引入松弛变量以对安全约束进行优先级排序。针对具有反作用轮姿态控制的三自由度航天器，给出了蒙特卡洛仿真结果以及示例案例的曲线图并进行了评估。
英文摘要：
A fundamental capability for On-orbit Servicing, Assembly, and Manufacturing (OSAM) is inspection of the vehicle to be serviced, or the structure being assembled. This research assumes autonomous slewing to maintain situational awareness of multiple vehicles operating in close proximity where several safety constraints must be satisfied. A variety of techniques may be used as the primary controller. The focus of this research is developing Run Time Assurance (RTA) filters that monitor system behavior and the output of the primary controller to enforce safety constraint satisfaction. Specifically, this research explores combining a subset of the constraints into an Active Set Invariance Filter (ASIF) RTA defined using control barrier functions. This method is minimally invasive to the primary control by minimizing deviation from the desired control output of the primary controller, while simultaneously enforcing all safety constraints. The RTA is designed to ensure the spacecraft maintains attitude requirements for communication and data transfer with a ground station during scheduled communication windows, adheres to conical attitude keep out zones, limits thermally unfavorable attitude duration, maintains attitude requirements for sufficient power generation, ensures maneuvers are below threshold to cause structural damage, ensures maximum angular velocity is below limits to maintain ability to respond quickly to new slewing commands, and conserves actuator use to prevent wear when possible. Slack variables are introduced into the ASIF controller to prioritize safety constraints when a solution to all safety constraints is infeasible. Monte Carlo simulation results as well as plots of example cases are shown and evaluated for a three degree of freedom spacecraft with reaction wheel attitude control.
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