Spacecraft Control Systems: Hybrid Continuous/Impulsive 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，人们还关注其结构动力学，它描述了振动类型的行为。 通常，需要反馈控制系统来控制航天器运动，该反馈控制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。一个想要控制航天器轨道的例子是编队飞行，其中需要控制多个卫星之间的相对运动。在这种情况下，一种可能的力致动器是一种推进器，它利用燃料的大量排出在航天器上产生反作用力。 这种方法的问题在于，它依赖于一种经常短缺的消耗品（燃料）。 一个创新的力的来源是由磁场对航天器携带的电荷产生的洛伦兹力。 事实证明，并非航天器编队中的所有相对运动都可以用洛伦兹力控制--其中一些是无法控制的。 这就意味着可以将连续作用的洛仑兹力与推进器的使用联合收割机结合起来。 推进器可以在短时间内使用;我们说它们是冲动的。 我们希望解决这个混合控制问题，其中一个要尽量减少使用连续和脉冲控制输入。 另一个航天器控制问题是磁姿态控制问题。 在这里，人们使用地球磁场作用于卫星上的载流线圈所产生的扭矩，以及成对推进器所产生的脉冲扭矩。

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 also concerned with their structural dynamics which describes vibrational type behaviour.    Usually, feedback control systems are required to control spacecraft motion which use sensors to monitor the spacecraft motion and then correct errors using appropriate actuators which produce forces and torques. An example where one wants to control the spacecraft orbit is formation flying where the relative motion between multiple satellites needs to be controlled. A possible force actuator in this case is a thruster which uses the mass expulsion of fuel to produce reaction forces on the spacecraft.  The problem with this approach is that it relies on an expendable (the fuel) which is often in short supply.  An innovative source of force is the Lorentz force produced by a magnetic field on the charge carried by a spacecraft.   It turns out that not all of the relative motion in a spacecraft formation can be controlled with the Lorentz force - some of it is uncontrollable.  This suggests that one might combine the Lorentz force, which acts continuously,  with the use of thrusters.  Thrusters can be used over short durations; we say that they act impulsively.  We wish to solve this hybrid control problem where one wants to minimize the use of both continuous and impulsive control inputs.  Another spacecraft control problem is the magnetic attitude control  problem.  Here one uses the torques  produced by the Earth's magnetic field acting on current-carrying loops of wire on-board the satellite in conjunction with  impulsive torques produced by pairs of thrusters.