In general, space robots are more floppier (mechanically flexible) than robots used on the ground.  This is because it is expensive to launch a lot of mass (weight) into space, and the microgravity environment in space allows the joints of the arm to be much weaker than a ground robot.  As a result of these factors, space robots tend to be long and comparatively floppy.  A commonly known example of this is the Space Shuttle Remote Manipulator (SRMS).

The above traits also means that it can be difficult to use the space robot on the ground.  This is true in the case of the robotic systems for the HRSDM.  Both the long Grapple Arm and the Dexterous Robot arms cannot be used on earth.  In order to completely verify that our tools and procedures will work, we need to either hang the robot with cables to reduce the effect of gravity, or we need to simulate its motion with mathematical models of the robot arm.

This second approach is what we intend to pursue to verify our tools and procedures.  I proposed to the HST project that we build a robotic simulator that uses mathematical models to preduct the motion of the flexible robot system, but use a strong industrial robot arm to execute the motions.  In this manner, we can pick up heavy tools and instrument simulators without worrying about how to reduce the effects of gravity.  Since this system will be used to verify tasks with contact dynamics, I have named this laboratory, the HRSDM Contact Dynamics Facility (CDF).

This kind of approach to tools and task verification is similar to that used by other space agencies such as the Canadian Space Agency.

In March 2005, during our PDR, Dr. Riccardo Giacconi, a Nobel Laureate visited our Robotics Lab facility and operated the simulator.  In the fore ground, from left to right: Steve Queen (one of the developers of the simulator), Dr. Giacconi, Dr. Weiler (GSFC Director), Frank Cepollina (Hubble Mission Manager - with hand waving), John Lymer (Chief Engineer), Jill Holz (Robotics Program Manager).  In the background, we can see a model of the entire Ejection Module with a model of the Dexterous Robot visible (white).

We asked Dr. Giacconi to have a try at the simulator.  Here, he is holding the Rotational Hand Controller (RHC).  This commands the robot end-effector in the rotational degrees-of-freedom. In the background from left to right: Jim Corbo (Lead Systems), Frank Cepollina, Jill Holz, John Lymer, Carol Wong (Johnson Space Center).