Solar Sailing: Attitude, Orbit, and Shape Control

航天器表现出三种不同类型的运动。它们在太空中的位置的演变是轨道动力学的主题。姿态动力学描述了它们相对于某些参考的方向的演变，例如地球。较大的航天器可以非常灵活，人们关心的是它们的结构动力学，这描述了振动和褶皱类型的行为。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的运动，然后使用产生力和扭矩的适当的致动器来校正误差。力是用来控制轨道的，而力矩是用来控制方向(也叫姿态)的。在一些问题上，航天器的姿态可能会对其轨道产生很大影响。一个有趣的例子是太阳帆，这是一个巨大而脆弱的薄薄的结构，它像镜子一样反射作用在上面的太阳辐射。这会在帆上产生反作用力。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。轨道路径和帆的方向是耦合的，因为辐射压力产生的力的作用方向取决于帆的姿态。这类似于帆船在风中在湖面上移动。太阳帆的一个有用的目的地是太阳和地球之间的一个点，在那里太阳帆可以用来探测太阳风暴，并在风暴到来之前向地球发出警告。放置太阳帆的另一个有用的位置是“极点位置”，在这个位置上，太阳帆不绕地球运行，而是位于北极上方，随着地球绕太阳运行。为了使用这些特殊的轨道，人们需要制定转向策略来实现它们。我们想要确定在尽可能短的时间内到达这些地方的姿态运动。给出了前面问题的解决方案，我们想确定遵循规定姿态运动的控制方法。将研究两种驱动方法：使用尖端叶片(在主帆的角部安装小型微型太阳帆)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执行器运动。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：振动抑制和防皱。两者都很复杂，因为缺乏分布式激励和传感，而且激励在物理上与典型的传感不协调，人们认为典型的传感将包括在风帆中心测量的姿态和角速度信息。

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.