BIOMEDICAL RESULTS FROM SKYLAB http://lsda.jsc.nasa.gov/books/skylab/ch04.htm
"…One feels this strange fullness in the head and this sensation of having a cold, and one sees the puffy look on the faces of his fellow crewmen and hears their nasal voices. He feels his body assume the strange posture that one has in weightlessness, with the shoulders hunched up, the hands out in the front and the knees bent….Closing one’s eyes made everything go away. And now one’s body is like a planet all to itself, and one really doesn’t know where the outside world is. The first time I tried it, my instinct was to grab hold of whatever was nearest and just hang on, lest I fall. It was the only time in the mission when I had anything like a sensation of falling. I was telling that to my wife, and she pointed out that that’s like the reflex that a baby has. When you begin to drop it, it just reaches out and clutches. And we thought, it would be nice to write a story about a sort of evolution of the human being in zero-g, because one certainly gets used to it in a hurry and it certainly is different"
"The very first system that gave us a pleasant surprise was the vestibular system. All of us keep talking about it because not only was it so different from what was expected but it remains, subjectively, one of the primary memories that one gets from this "Alice in Wonderland" world of weightlessness."
"Our crew was fortunate enough not to run into the motion sickness problem in any clinical or full-blown form. Therefore, among our first pleasant or different impressions was the impression of a very changed relationship between ourselves and the outside world and, I would say there was no vestibular sense of the upright whatsoever. I certainly had no idea of where the Earth was at any time unless I happened to be looking at it. I had no idea of the relationship between one compartment of the spacecraft and another in terms of a feeling for "up or down"; this has some peculiar effects when one passes from one compartment into the other and walls turn into ceilings and ceilings turn into floors in a very arbitrary way. But all one had to do is rotate one’s body to the more familiar orientation and it all comes to right. What one thinks is up, is up. After a few days of getting used to this, one plays with it all the time; one just stands there and does a slow roll around his bellybutton. The feeling is that one could take the whole room and by pushing a button, just rotate it around so that the screens up here would be the floor. It’s a marvelous feeling of power over space—over the space around one." "We discovered that after a few days of decreased appetite in flight we were able to eat all our food. Indeed, as the missions progressed the amount of food the crew was allowed to eat increased and their exercise increased, they were essentially eating the same amount of food as they ate on the ground. That to me is a mystery. I still don’t understand how in an environment in which certainly muscular work is reduced, the caloric demand and the relationship between caloric intake and body weight remain just about the same as they do on the ground, I think that’s a very interesting problem that we haven’t yet been able to solve." A World Without Gravity http://www.busoc.be/general/microgravity/chap2.11.pdf "…Our sixth sense, the sense of motion, is mediated by the vestibular system. The inner ear contains two balance-sensing organs, both of which are designed to keep the individual upright, orientated, and moving smoothly. One organ, comprised of the saccule and utricle, sends messages to the brain as to how the head is positioned relative to the force of gravity (Fig. 2.1.6.3). The saccule and utricle are tiny sacs, lined with hair cells. Small calcium-carbonate particles, the otoliths, rest on these hair cells. When the head moves relative to gravity, the weight and movement of these otoliths stimulate the hair cells and give the brain information on ‘up’, ‘down’, ‘tilt’ and ‘translation’ in a particular direction. The other balance-sensing organ is comprised of three semicircular canals. It provides the brain with information on rotation about the three axes of yaw, pitch and roll… The question is whether the part of the vestibular system that is sensitive to gravity continues to operate in weightlessness. Head tilt is not sensed by the otoliths in the absence of gravitational force, but they are still activated by the inertial force of translational motion. Experiments performed in space to date, including those using the ESA 4 m-long Sled moving with very low accelerations, have not shown significant changes in sensitivity to linear acceleration during and after space flight. Since the brain receives inputs from the otoliths only when there is a translational head motion in weightlessness, it has been proposed that the brain re-interprets tilt-related otolith information as translation during space flight. This has been the theoretical basis of much space research for the last 15 years. Only recently has this hypothesis actually been tested, using a centrifuge installed onboard the Space Shuttle…"
