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Abstract: Preliminary results of an ongoing study examining the effects of space flight on astronauts' motion perception induced by independent tilt and translation motions are presented. This experiment used a sled and a variable radius centrifuge that translated the subjects forward-backward or laterally, and simultaneously tilted them in pitch or roll, respectively. Tests were performed on the ground prior to and immediately after landing. The astronauts were asked to report about their perceived motion in response to different combinations of body tilt and translation in darkness. Their ability to manually control their own orientation was also evaluated using a joystick with which they nulled out the perceived tilt while the sled and centrifuge were in motion. Preliminary results confirm that the magnitude of perceived tilt increased during static tilt in roll after space flight. A deterioration in the crewmember to control tilt using non-visual inertial cues was also observed post-flight. However, the use of a tactile prosthesis indicating the direction of down on the subject's trunk improved manual control performance both before and after space flight. [Copyright &y& Elsevier]

Abstract: This investigation examined depth and distance perception of 3-D objects presented in stereoscopic vision. The results obtained in normal gravity and microgravity in parabolic flight were compared. This experiment was performed during an ESA campaign of parabolic flight on the Airbus A300 Zero-G on six free-floating subjects. The subjects were first presented with a 3-D cube and were instructed to adjust one dimension (width, length, or height) of the cube so that all three dimensions had the same perceived length. The subjects perceived a normal cube to be taller, thinner, and shallower in microgravity compared to normal gravity. Consequently, when they adjusted its dimension so that it looked “normal” to them, they made it shorter, wider, and deeper. A simple distance perception test confirmed that the subjects underestimated the distance of objects in the depth plane in microgravity. These results confirm a role of the gravitational reference in the 3-D perception of the objects and the environment. [Copyright &y& Elsevier]

Abstract: Many experts believe that artificial gravity will be required for an interplanetary mission. However, despite its attractiveness as an efficient, multi-system countermeasure and its potential for simplifying operational activities, much still needs to be learned regarding the human response to rotating environments before artificial gravity can be successfully implemented. The European Space Agency (ESA) Topical Team on Artificial Gravity recommended a comprehensive program to determine the gravity threshold required to reverse or prevent the detrimental effects of microgravity and to evaluate the effects of centrifugation on various physiological functions. Part of the required research can be accomplished using animal models on a dedicated centrifuge in low Earth orbit. Studies of human responses to centrifugation could be performed during ambulatory, short- and long-duration bed rest, and in-flight studies. Artificial-gravity scenarios should not be a priori discarded in Moon and Mars mission designs. One major step is to determine the relationship between the artificial gravity dose level, duration, and frequency and the physiological responses of the major body functions affected by spaceflight. Once its regime characteristics are defined and a dose–response curve is established, artificial gravity should serve as the standard against which all other countermeasure candidates are evaluated, first on Earth and then in space. [Copyright &y& Elsevier]

Abstract: The occurrence of geometric orientation illusions and the perception of ambiguous figures were analyzed in 24 subjects during static body tilt relative to gravity on Earth. Results showed that illusions such as the Rock''s diamond/square, the Ponzo illusion, and orientation contrast illusions occurred less frequently, and that depth reversal of ambiguous figures took more time when subjects were lying on their side or supine compared to upright, thus suggesting that the gravitational reference plays a significant role in these “visual” illusions. The structure of images, our representation of the environment, and orientation relative to gravity are all integral parts in interpreting visual images. In a weightless environment where no gravitational reference can be used, it is expected that similar alterations in visual perception will occur. [Copyright &y& Elsevier]

Abstract: One of the most significant problems associated with long duration space missions is mitigating the harmful effects of microgravity on the human body. These effects include loss of bone, muscle mass, and red blood cells; fluid shifts; cardiovascular and sensory-motor deconditioning; and changes in the immune system. If the long-duration exploration missions currently envisioned are to be successfully achieved, countermeasures to address the deleterious effects of microgravity must be developed, tested, and proven. A possible experiment to determine what level of artificial gravity is required for human perception is explored in this paper and involves creating artificial gravity onboard the Space Shuttle. Two methods are examined using Matlab analysis and simulation studies. The first requires putting the Shuttle into an eccentric orbit about its nominal orbit that would generate the centripetal forces necessary to simulate a gravitational environment. The other is a tumble maneuver, similar to the standard maneuver performed prior to Shuttle re-entry. Results indicate that the later maneuver is well within the capability of the Space Shuttle orbital control system, while the former is not. [Copyright &y& Elsevier]