Space rendezvous and capture testbed

This paper presents a testbed for autonomous rendezvous and capture of small, high-speed, passive objects. While there have been several successful autonomous rendezvous and docking flight systems, a compact and standardized solution for the retrieval of very small passive objects has yet to be demonstrated. Development of a notional standard, on-orbit sample capture/return architecture would not only enable NASA missions such as potential Mars Sample Return and lunar sample return, but it could also minimize the cost and risks associated with those future missions. The testbed presented in this paper was designed for the Space Rendezvous And Capture Competition (Space RACE), a candidate competition being developed for NASA Centennial Challenges. The competition, in which competitors would build mobile robotic platforms to autonomously chase and capture a mock Orbital Sample (OS), emulates major aspects of proposed on-orbit sample capture: locating and tracking a passive target using limited fiducials, developing an approach algorithm, grappling the target, and manipulating the target for insertion into a notional Sample Return Capsule. These elements would also be pertinent to orbital debris cleanup and terrestrial applications such as warehouse packaging and autonomous harvesting. A prototype was built and successfully used to test the Space RACE concept. The prototype consists of a flat, circular track 17m in diameter, four PulsON 410 Ultra Wideband ranging radios, and a four-wheeled robotic platform called the OS-Bot. An on-board autonomous controller uses the ranging radios in the prototype to calculate the position of the OS-Bot in real-time and follow a predefined, arbitrary path. This method of navigation avoids the use of track-fixed fiducials and allows the simulation of any orbital scenario. The system also supports mounting of additional radios on competitor platforms, allowing for minimally invasive monitoring of competitor position and velocity. These aspects both prevent competitors from merely “line-following” to the OS and allow the simulation of numerous mission scenarios which approximate orbital dynamics. Results are presented in this paper for the successful testing of this platform using low resolution sensors in an environment subject to frequent multi-path ranging errors. In addition, a filter is presented which could improve the response of the controller and deliver more robust operation.