Robonaut 2 and you: Specifying and executing complex operations

Crew time is a precious resource due to the expense of trained human operators in space. Efficient caretaker robots could lessen the manual labor load required by frequent vehicular and life support maintenance tasks, freeing astronaut time for scientific mission objectives. Humanoid robots can fluidly exist alongside human counterparts due to their form, but they are complex and high-dimensional platforms. This paper describes a system that human operators can use to maneuver Robonaut 2 (R2), a dexterous humanoid robot developed by NASA to research co-robotic applications. The system includes a specification of constraints used to describe operations, and the supporting planning framework that solves constrained problems on R2 at interactive speeds. The paper is developed in reference to an illustrative, typical example of an operation R2 performs to highlight the challenges inherent to the problems R2 must face. Finally, the interface and planner is validated through a case-study using the guiding example on the physical robot in a simulated microgravity environment. This work reveals the complexity of employing humanoid caretaker robots and suggest solutions that are broadly applicable.

I. Introduction

Robonaut 2 (R2), shown in Figure 1, is a complex humanoid robot capable of dexterous manipulation [1]. It is composed of an anthropomorphic upper body and two leglike appendages that each feature seven degrees-of- freedom, for a total of 34 degrees-of-freedom in the main body. Its twelve degree-of-freedom hands can execute dexterous manipulation tasks like using human tools and handling fabric surfaces [2]. The end-effector on the legs has a multi-purpose gripper that can attach to the ubiquitous handrails in the International Space Station (ISS). R2 is designed to be an assistant to the crew currently stationed on-board the ISS, as well as a test-bed for robotic caretaker technology that is required in future space exploration [3]. Repetitive and dangerous operations required for space exploration could be accomplished by R2 and other robots, allowing more time for astronauts to achieve scientific mission objectives. For example, the logistics and organization of cargo takes an immense fraction of crew time and is physically strenuous. In future space exploration, robots like R2 could unload a dormant logistics module for a spacecraft in cislunar orbit in advance of crew arrival. On the ISS today, cargo is stored within a general purpose container called a Cargo Transfer Fig. 1.

R2 executing the CTB retrieval scenario. R2 has to respect many different constraints when planning motions along the course of the operation. For example, when holding the CTB with both hands, there is a constraint imposed on the hands as to not drop the CTB. The system allows consideration of constraints such as the example given and provides means for the operator to easily specify novel ones without leaving the high-level interface. There are four stills superimposed in this image, from back to front: R2 approaching the cargo rack, R2 unbuckling the restraint holding the CTB, R2 grabbing the CTB with both hands, and the final image of R2 bimanually manipulating the CTB.