Evaluation of Various Hand Controllers for Use by a Space Suited Subject

The Space Systems Lab has evaluated several different types of generic hand controllers to see which performs the best when used by a suited subject. This paper outlines the types of hand controllers selected for this experiment and the results of the performance testing. The evaluation was conducted by subjects wearing spacesuit gloves in a partial pressure glovebox at a pressure differential of 4.3 pounds/square inch. Performance for each hand controller was measured by the completion of several one degree-of-freedom (DOF) tasks presented to the subject on a computer screen. Performance metrics for this experiment included the error associated with attempting to follow an ideal trajectory and a subjective Cooper-Harper questionnaire given after each session was complete. The same information was also collected for unpressurized suit gloves and for the bare hand. INTRODUCTION The goals of spaceflight today are somewhat different than our earlier goals. Originally, our goals were to simply prove that we could reach the heights we were aiming for; each step simply took us higher than before. Today, we've graduated to research goals on-orbit and have begun looking toward manned bases on both the moon and Mars. With the advent of the International Space Station (ISS), the number of hours spent on-orbit and involved with extravehicular activity (EVA) will dramatically increase. Just the number of hours slated for the construction of the ISS will more than double the total number of hours of EVA in the previous US history of spaceflight [1]. This increase has become known as the ``EVA Wall.” This unprecedented increase poses many challenges to the EVA community. Among these are to make the most of limited resources, to make astronauts more efficient in completing tasks, and to provide ease of movement without sacrificing safety. The goals of this research included examining input devices to evaluate their appropriateness for use by suited subjects. In doing so, it was hoped that this might further illuminate how tasks are accomplished while wearing gloves and what types of movement are the most accurate and least fatiguing. This information could be used in the future to design input devices for specific tasks or even in the design of new gloves. HISTORY Our hands are not just another part of our anatomy; they are our tools and our means of expression. We continuously use them to interact with our environment and shape it to our needs. Consequently, the need for gloves to protect our hands in space has also hindered our interaction with that environment. Gloves, in general, account for a decrease in dexterity and tactility. Early studies using gloves of leather or wool showed that ``the efficiency with which instrument controls may be operated by a gloved hand depends on certain measurable glove characteristics" [2]. Bradley reported that previous comparisons between barehanded and gloved manipulability showed a marked difference between the two; for all six types of gloves tested, performance was significantly lower than barehanded performance [3]. Space suit gloves are comprised of several layers of material, including a pressure bladder, a restraint layer, and a thermal micrometeorite layer. Also, fingertips are coated in rubber to help increase friction. While protecting the hand well, these layers prohibit the suited subject from being able to accurately sense the objects that they are manipulating. In addition, space suit gloves do not maintain a constant volume. Motions by the hands and fingers tend to change the volume. This, coupled with the pressurization of the suit, leads to the gloves having a preferred position. The subject then has to constantly fight against that preferred position when trying to accomplish a task. This type of compensation can lead to muscle fatigue, especially in the fingers and wrist [4]. In the next hundred years of space exploration, we are looking toward larger scale missions and more complicated tasks than ever before in our history. Future exploration of both the Moon and Mars will require a great deal of planning and development of new technology in order to be carried out successfully. Given the success of smaller robots, such as Sojourner, on Mars, it seems only logical that robots would play a role in future planetary exploration missions. It has been proposed [5], [6], [7] that a larger robot would be useful as an astronaut assistant for planetary exploration. Such a robot would be capable of carrying scientific equipment, storing samples, and carrying consumables for the astronaut. It could also serve as a terrain scout or take video of an interesting area. Field testing has shown that it would be advantageous that the ``EVA crewmember be provided with some control of the rover" and future study was recommended to develop ``methods for the suited subject to control the robotic rover" [8]. Gloves hold their own unique limitations, such as limited range of motion and dexterity. These impact the performance of hand controllers designed for nude body performance. To this end, a control method appropriate to a suited subject would need to be found. This experiment was designed to illustrate which basic type of hand controller would be the most appropriate for use by a suited subject. Also, it is hoped that the results may provide insight into designing hand controllers for future missions, both for EVA and planetary surface exploration. In addition, these experiments may provide insight into the performance of space suit gloves.