ESA GNC Conference Papers Repository
Forces-RTP: a tool for on-board real-time autonomous trajectory planning
For many space flight scenarios optimal trajectories must be found to satisfy the vehicle and mission constraints and meet the mission specifications. The optimality criterion is usually the amount of fuel needed or the time for mission completion. Currently, these trajectories are computed on the ground departing from initial conditions and assuming no failure in the vehicle or changes in the mission. The process usually takes months, assumes idealistic conditions and does not allow for re-planning in case of noncritical failures or mission changes. In order to cope with operational uncertainty, increase the operational flexibility, add fault tolerance capabilities, and increase the flight envelope, it is necessary to bring optimal trajectory planning from being an off-board design tool to becoming a real-time autonomous operational tool on-board. Despite the obvious advantages, this technology has not yet been implemented, in Europe, because it is too computationally intensive to solve the original GNC problems on a typical flight computer and there are reliability concerns for using these kind of algorithms in flight critical software. We have created a design tool that allows the user to define a GNC problem, including its performance metrics, and automatically generate tailored real-time capable software implementing trajectory re-planning functionality. Internally, the tool applies various mathematically sound approximations to improve the reliability of the underlying algorithms, and automatically generates customized numerical code using https://www.embotech.com/FORCES-Pro - a tool already used in autonomous driving, robotics and energy management applications. In addition, it is possible to validate the behavior of the closed-loop system and evaluate different planning strategies in a hardware-in-the-loop setting with a flight representative mother-board. The developed software tool will be evaluated on two space guidance and control scenarios: large angle reorientation maneuvers for an orbiting spacecraft under multiple attitude-constrained zones; and an attitude constrained ascent, powered descent and pinpoint landing scenario, similar to the capabilities displayed by the SpaceX Falcon9 launcher vehicle.