Attitude Control of satellites with deployable structures using inverse simulation

纳米和皮科卫星平台正变得越来越受欢迎，允许以成本效益的方式进入太空。在这些较小的平台上添加更广泛的仪器可以增加功能，传统上只有在较大的卫星上才能提供，价格只有一小部分。然而，这些仪器，如高增益天线和光学有效载荷，往往需要精确的定向平台指向。为了实现这种精确指向，需要三轴姿态控制。纳米和皮科卫星通常在致动器功率方面受到限制，因此开发有效的姿态控制技术至关重要。使用流行的控制技术，如PID，可以允许实现所需的姿态，但是对所采取的精确姿态轨迹几乎没有控制。在许多情况下，可能需要卫星避免指向某个方向，例如朝向太阳以保护敏感仪器，或者避免指向太阳以外的太阳，用于太阳能电池板。逆仿真是一种利用期望的输出轨道来产生给定轨道所需的控制动作的替代方法。首先，将产生高度精确的卫星动力学数学模型，该模型将控制动作作为系统的输入并输出卫星轨道。然后在逆模拟中使用数学模型，以允许生成所需输入的时间序列，从而实现期望的输出。逆模拟的闭环性质减少了模型和真实的飞行器完全发散的机会，可以更深入地了解模型在实际操作中的保真度。由于纳和皮科卫星的形状因素有限，许多正在使用的附加仪器将需要可展开的结构。部署过程和由于部署而引起的卫星惯性变化将需要一种控制系统，该控制系统能够产生适当的致动器控制，该致动器控制能够不作出反应而是规划适当的机动，以确保考虑到对运动的任何限制或公差。逆模拟适合于这一任务。逆仿真的另一个应用是探索其应用，以尽量减少振动的附件和柔性结构，如可展开的太阳能电池板和天线，这可能会影响整体指向误差。这个博士项目将包括分析和实验研究，利用亥姆霍兹笼和空气轴承来测试控制系统，并验证生成的数学模型。3D打印还可以用于物理组件的快速原型制作。

Nano and pico satellite platforms are becoming ever more popular, allowing cost efficient access to space. Adding a wider range of instruments to these smaller platforms allows for increased functionality, traditionally only available on larger satellites, at a fraction of the price. However, these instruments, such as high-gain antennas and optical payloads, often require accurate directional pointing of the platform. To achieve this accurate pointing, 3 axis attitude control is required. Nano and pico satellites are normally limited in in relation to actuator power, making development of efficient attitude control techniques vital. Using popular control techniques, such as PID, could allow for a required attitude to be achieved, however there is little to no control over the exact attitude trajectory taken. In many cases, it may be required for the satellite to avoid pointing in a certain direction, such as to wards the sun to protect sensitive instruments, or avoid pointing away from the sun, for the solar panels. Inverse simulation is an alternative method that uses a desired output trajectory to produce the required control actions for the given trajectory.Firstly, a highly accurate mathematical model of the satellites dynamics will be produced which takes control actions as an input to the system and outputs the satellites trajectory. The mathematical model is then used within an inverse simulation to allow the generation of a time series of the required input to enable the desired output. The closed loop nature of inverse simulation reduces the chances of the complete divergence of the model and the real vehicle, and more insight into the fidelity of the model in actual operation can be obtained.Many of the additional instruments that are being used will require deployable structures due to the limited form factor of nano and pico satellites. The process of deployment and the changes in inertia of the satellite as a result of deployment, will require a control system that can generate suitable actuator controls that are able to, not react, but to plan a suitable manoeuvre that ensures any restrictions or tolerances on movement are considered. Inverse Simulation is suited to this task. A further application of inverse simulation is to explore its application to minimise oscillations on appendages and flexible structures, such as deployable solar panels and antennas, which can impact on the overall pointing error.This PhD project will include analytical and experimental research, making use of a Helmholtz cage and air bearing to test the control system and for validation of the mathematical model generated. 3D printing could also be used for rapid prototyping of physical components.