Optimal Whole Body Trajectory Planning for Mobile Manipulators in Planetary Exploration and Construction

TL;DR

This work tackles offline whole-body trajectory planning for mobile manipulators in planetary exploration under stringent energy and computation constraints. It introduces OptiWB, a two-stage planner that uses Discrete Dynamic Programming to search over time and redundancy, followed by optimal interpolation to produce smooth, feasible trajectories while respecting collision, forbidden-area, and shadowing constraints; the objective combines target visibility and energy-like movement penalties via $\phi = \sigma \zeta_{TV} + (1 - \sigma) \zeta_{SNV}$. The approach is demonstrated on a space-robotics use case with a 10-DOF rover-arm platform, showing significant improvement in trajectory smoothness and constraint satisfaction after interpolation, and it is integrated with ESA's 3DROCS mission planning system for offline planning. The results indicate that whole-body planning can reliably generate synchronized base-arm motions that preserve target visibility and avoid shaded targets, offering a practical path toward more autonomous and efficient planetary missions. Overall, OptiWB advances space robotics planning by delivering feasible, energy-conscious, and visually optimal trajectories that leverage kinematic redundancy and integrate with established mission-planning tools like 3DROCS and Space ROS.

Abstract

Space robotics poses unique challenges arising from the limitation of energy and computational resources, and the complexity of the environment and employed platforms. At the control center, offline motion planning is fundamental in the computation of optimized trajectories accounting for the system's constraints. Smooth movements, collision and forbidden areas avoidance, target visibility and energy consumption are all important factors to consider to be able to generate feasible and optimal plans. When mobile manipulators (terrestrial, aerial) are employed, the base and the arm movements are often separately planned, ultimately resulting in sub-optimal solutions. We propose an Optimal Whole Body Planner (OptiWB) based on Discrete Dynamic Programming (DDP) and optimal interpolation. Kinematic redundancy is exploited for collision and forbidden areas avoidance, and to improve target illumination and visibility from onboard cameras. The planner, implemented in ROS (Robot Operating System), interfaces 3DROCS, a mission planner used in several programs of the European Space Agency (ESA) to support planetary exploration surface missions and part of the ExoMars Rover's planning software. The proposed approach is exercised on a simplified version of the Analog-1 Interact rover by ESA, a 7-DOFs robotic arm mounted on a four wheels non-holonomic platform.

Figures (7)

• Figure 1: Optimal Whole-Body Planner (OptiWB) architecture.
• Figure 2: Planning scenario with the indication of reference frames used for planning; $\eta$ is the line passing through the origins of $\mathcal{F}_c$ and $\mathcal{F}_t$, $\gamma$ that passing through the origins of $\mathcal{F}_s$ and $\mathcal{F}_t$.
• Figure 3: Data interface between 3DROCS and OptiWB.
• Figure 4: Assigned task space trajectory (solid, blue) and its projection on the $x$-$y$ plane (dashed, black). Frames for each waypoint represent the end-effector orientation.
• Figure 5: (a) Robot joint trajectory ${\bf q}(t)$ planned with DDP and (b) corresponding base path in the $x$-$y$ plane. Red arrows represent the base heading while circles represent the points where the base stops and performs a turn-in-place maneuver.