Autonomous Robots for Space: Trajectory Learning and Adaptation Using Imitation

Abstract

This paper adds on to the on-going efforts to provide more autonomy to space robots and introduces the concept of programming by demonstration or imitation learning for trajectory planning of manipulators on free-floating spacecraft. A redundant 7-DoF robotic arm is mounted on small spacecraft dedicated for debris removal, on-orbit servicing and assembly, autonomous and rendezvous docking. The motion of robot (or manipulator) arm induces reaction forces on the spacecraft and hence its attitude changes prompting the Attitude Determination and Control System (ADCS) to take large corrective action. The method introduced here is capable of finding the trajectory that minimizes the attitudinal changes thereby reducing the load on ADCS. One of the critical elements in spacecraft trajectory planning and control is the power consumption. The approach introduced in this work carry out trajectory learning offline by collecting data from demonstrations and encoding it as a probabilistic distribution of trajectories. The learned trajectory distribution can be used for planning in previously unseen situations by conditioning the probabilistic distribution. Hence almost no power is required for computations after deployment. Sampling from a conditioned distribution provides several possible trajectories from the same start to goal state. To determine the trajectory that minimizes attitudinal changes, a cost term is defined and the trajectory which minimizes this cost is considered the optimal one.

Passivity based nonlinear model predictive control (PNMPC) of multi-robot systems for space applications

“…Through a robotic arm, the satellite was able to grasp and send the object it collected back on a re-entry trajectory. Small-scale robotic systems, exemplified by the Future Space Debris Removal Orbital Manipulator (FSDROM), are poised to make a significant contribution to upcoming space debris removal missions, according to Shyam et al (2021) . As reported by the European Space Agency (ESA) in 2019, the amount of space debris in Earth’s orbit has exceeded 8,000 tons and continues to rise, posing a significant threat to both satellites and astronauts ( Chatterjee, 2014 ).…”