Attitude Control of satellites with deployable structures using inverse simulation

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.