Simple adaptive re-entry guidance for path-constraint tracking

To limit the mass of the vehicle’s thermal protection system, an optimal trajectory that minimises the total integrated heat load should be own. This means that the maxi- mum heat- ux constraint is followed for as long as possible, until the maximum mechanical load is encountered. Flying as close to this load as possible contributes to minimising the heat load as well. The guidance system to track the path constraints includes three components: a semi-analytical guidance that produces nominal bank-angle commands, an inner-loop tracking system based on linearised output feedback, and an outer-loop system based on simple adaptive control to remove the remaining error. The former two guidance components have been taken from an earlier design, and the performance gain after adding the adaptive system is studied in detail. The ight system under consideration is a hyper- sonic test vehicle of which the stagnation heat- ux should not exceed 1,700 kW/m2, with a limit of the mechanical load of 5g. The results show that the adaptive tracking system extends the duration of heat- ux tracking and is able to track tighter at even less guidance effort, but reduces the fiight range because of that. A simultaneous optimisation of these two con icting objectives should be pursued to reFIne the guidance-system design in case both have requirements to be met. In none of the cases considered, the g-load constraint was violated, although a more detailed analysis is required to make this part of the guid- ance more robust. In all other aspects, the combination of an inner-loop and outer-loop tracking has made the path-constraint tracking more robust and keeps the errors below acceptable levels.