Solar Sailing: Attitude, Orbit, and Shape Control

宇宙飞船有三种不同的运动形式。 它们在空间位置的演变是轨道动力学的课题。 它们相对于某些参照物（如地球）的定向演化由姿态动力学描述。 较大的航天器可能相当灵活，人们关心的是它们的结构动力学，它描述了振动和摇摆类型的行为。 控制这三种类型的运动通常需要反馈控制系统，该系统使用传感器来监测航天器运动，然后使用产生力和扭矩的适当致动器来校正误差。 需要力来控制轨道，而需要力矩来控制方向（也称为姿态）。 在某些问题中，航天器的姿态对其轨道有很大的影响。 一个有趣的例子是太阳帆，它是一个巨大的、脆弱的薄纱结构，它像一面镜子一样反射作用在它上面的太阳辐射，这在帆上产生了一个反作用力。控制太阳帆是一个具有挑战性的应用，因为轨道动力学，姿态动力学和结构动力学是高度耦合的。 轨道路径和帆的定向是耦合的，因为来自辐射压力的力作用在取决于帆姿态的方向上。 这类似于帆船在风中在湖面上移动的运动。 太阳帆的一个有用的目的地是太阳和地球之间的一个点，太阳帆可以用来探测太阳风暴，并在风暴到达之前向地球发出警告。放置太阳帆的另一个有用的点是在一个“坐极”的位置，即帆不绕地球轨道运行，而是坐在北极上方，并随着地球绕太阳运行。为了使用这些特殊的轨道，需要制定实现它们的转向策略。 我们希望确定姿态运动，以便在尽可能短的时间内到达这些地方。 鉴于前一个问题的解决方案，我们想确定控制方法，按照规定的姿态运动。将研究两种驱动方法：使用叶尖叶片（用万向节固定在主帆角上的小型太阳帆）和使用平衡质量。 首先需要解决的关键问题是确定提供控制系统所需的控制力矩所需的致动器运动。 在处理了姿态-轨道耦合控制问题之后，下一个要研究的问题是形状控制。 有两个子问题需要考虑：振动抑制和起皱预防。 两者都是复杂的缺乏分布式的驱动和传感和事实，即驱动是物理noncollocated与典型的感测，其中一个假设将包括在中心的帆测量的姿态和角速率信息。

Spacecraft exhibit three distinct types of motion. The evolution of their position in space is the subject of orbital dynamics. The evolution of their orientation with respect to some reference, such as the Earth, is described by attitude dynamics. Larger spacecraft can be quite flexible and one is concerned with their structural dynamics which describes vibrational and wrinkling types of behaviour. Controlling these three types of motion typically requires feedback control systems which use sensors to monitor the spacecraft motion and then correct errors using appropriate actuators which produce forces and torques. Forces are required to control orbits whereas torques are needed to control orientation (also called attitude). In some problems, the spacecraft's attitude can have a large effect on its orbit. An interesting example is a solar sail, which is a large, flimsy gossamer structure which acts a mirror to reflect the solar radiation acting upon it. This produces a reaction force on the sail. Controlling solar sails is a challenging application because the orbital dynamics, attitude dynamics, and structural dynamics are highly coupled. The orbital path and the orientation of the sail are coupled because the forces stemming from radiation pressure act in a direction that depends on the sail attitude. This is analogous to the motion of a sailboat moving on the surface of a lake in wind. A useful destination for a solar sail is a point between the Sun and the Earth where the solar sail can be used to detect solar storms and communicate a warning to the Earth before the storm arrives. Another useful point to place a solar sail is in a "pole-sitter" position whereby the sail does not orbit the Earth but rather sits above the North Pole and moves with the Earth as it moves around the Sun. In order to use these special orbits, one needs to develop steering strategies to achieve them. We would like to determine attitude motions to reach these places in the shortest time possible. Given the solution of the previous problem, we would like to determine control approaches to follow a prescribed attitude motion. Two actuation approaches will be studied: the use of tip vanes (little miniature solar sails gimballed to the corners of the main sail) and the use of balance masses. The key problem that needs to be solved initially is the determination of the actuator motion required to provide the control torques required by the control system. Having handled the coupled attitude-orbit control problem, the next problem in the hierarchy to be studied brings shape control into play. There are two subproblems to be considered: vibration suppression and wrinkle prevention. Both are complicated by the lack of distributed actuation and sensing and the fact that the actuation is physically noncollocated with the typical sensing which one assumes would include the attitude and angular rate information measured at the centre of the sail.