Attitude guidance using on-board optimisation

The ability to autonomously plan and execute highly constrained slew trajectories will be a critical asset for many of the future space missions.​ ESA’s THESEUS mission (M5 & M7 candidate) will have to respond rapidly to gamma ray burst targets by executing fast constrained slews and ESA’s Comet Interceptor mission requires a high-rate slew (originally entirely with reaction wheels) to track the comet during fly-by with perturbations from dust impacts.

By leveraging these autonomous planning capabilities, spacecraft can safely cope with dynamic environments, failures scenarios and complex objectives.

A TDE activity with OHB in Sweden has proved that on-board optimisation of attitude guidance is possible and can maximise the use of the actuation authority envelope whilst respecting system constraints.

The activity developed a methodology and corresponding set of tools to perform on-line constrained attitude guidance that relies on embedded optimisation​. It also wanted to demonstrate the benefit of these novel guidance algorithms compared to heritage techniques on benchmark cases​.

There are several challenges to developing these tools. Firstly, slew time is limited by actuator authority and ad hoc on-board planning algorithms do not use the full envelope. Secondly, large slew planning must consider attitude constraints such as avoiding the sun blinding instruments. Finally, some missions perform one-time-only science. A failure or unexpected condition on-board during fly-by can be devastating without on-board re-planning.

The activity solved the problem using convex optimisation as a core technology resulting in faster slews and more time-on-target in contigency.

Next the activity will investigate algorithmic improvements to speed up computation time and repeat the exercise with different optimizer software toolsets.

T205-125SA, 4000133640 was presented at the final sharing days in 2023.