Multifunctional Robot Test Facility for on-orbit and extraterrestrial surface exploration
Benjamin Girault, Sebastian Bartsch, Frank Kirchner
In Proceedings of Ground-based Space facilities symposium, (GBSF-2013), 12.6.-14.6.2013, Paris, o.A., Jun/2013.
This paper describes a test facility that was developed at the DFKI Robotics Innovation Center in order to test and simulate various kinds of space robotics scenarios, from lunar crater exploration using mobile robots to satellite rendezvous in orbit. Test data obtained from different projects using the facility are presented as well. The paper starts with a State of the Art overview of test facilities for space environments. Afterwards the developed facility which is 24m long, 12m wide and 10m high and has two levels is described in detail. A reproduction of a lunar crater goes from the lower level to the gallery. This crater is 8m long, 9m wide and 4m high and has a carrying capacity of 500 kg/m2. The crater area has been reconstructed based on data of real lunar craters and photos of the Apollo missions. Its slope varies between 15% and 45&, with three continuous paths of 25%, 35%, and 45%. Small craters with diameters of 5 cm to 50 cm are spread over the whole surface. Boulders of varying size can be placed in different locations. An adjustable test ramp can be found on the gallery. It is 6m long, 3m wide and can be tilted up from 0% to 45%. The surface imitates a lunar rocky surface and can be covered by an additional layer of regolith-like sand. Both, the crater and the ramp allow a wide range of climbing experiments with wheeled or legged free-climbing robots. The test facility can also simulate the relative position and orientation of two bodies in free space, such as satellites or space debris. One body of up to 60 kg is held by a 6 degree-of-freedom manipulator arm, placed on the lower part of the hall. The other body is fixed underneath a cable robot that can perform 3D translational movements and rotate along its vertical axis. Both objects can carry a payload, for example cameras or lasers, and embed computing units. This system allows the simulation of the last 15m approach between the bodies. Seven motion tracking cameras placed all around the hall are used to measure the position and orientation accuracy of simulation. The manipulator arm and the cable robot are controlled by a real-time capable control unit that can be interfaced with the trajectory generator and the payloads. Realistic lighting conditions are needed to evaluate optical sensors and algorithms based on these sensors. Therefore the walls, the floor, the ceiling and the different systems have been covered with a light-absorbing black painting. The hall is equipped with 6 motorized spotlights. These lights provide parallel light beams that create sharp shadows and large differences in light intensity between illuminated and dark regions. The test facility has been used already for different research projects. The crater and the ramp have been used to evaluate and optimize the locomotion capabilities of the six-legged freeclimbing robot developed in the project SpaceClimber. The relative pose simulation system was developed during the project Inveritas in order to simulate autonomous rendezvous and capture manoeuvres between two satellites. Visual servoing algorithmsusing stereo cameras and a LIDAR have been tested. Experiments to measure the accuracy of both, arm and cable robot, have also been conducted to evaluate the degree of realism of the system and are presented in this paper as well. Finally, an outlook depicts the next steps and possible modifications to improve the characteristics of this facility are presented.