Space Flight: Travel beyond the earth's atmosphere.Astronauts: Members of spacecraft crew including those who travel in space, and those in training for space flight. (From Webster, 10th ed; Jane's Aerospace Dictionary, 3d ed)Weightlessness: Condition in which no acceleration, whether due to gravity or any other force, can be detected by an observer within a system. It also means the absence of weight or the absence of the force of gravity acting on a body. Microgravity, gravitational force between 0 and 10 -6 g, is included here. (From NASA Thesaurus, 1988)Flight, Animal: The use of wings or wing-like appendages to remain aloft and move through the air.Aerospace Medicine: That branch of medicine dealing with the studies and effects of flight through the atmosphere or in space upon the human body and with the prevention or cure of physiological or psychological malfunctions arising from these effects. (from NASA Thesaurus)Weightlessness Simulation: Condition under normal Earth gravity where the force of gravity itself is not actually altered but its influence or effect may be modified and studied. (From ASGSB Bull 1992;5(2):27)Space Motion Sickness: Disorder characterized by nausea, vomiting, and dizziness, possibly in response to vestibular disorientation or fluid shifts associated with space flight. (From Webster's New World Dictionary)Decalcification, Pathologic: The loss of calcium salts from bones and teeth. Bacteria may be responsible for this occurrence in teeth. Old age may be a factor contributing to calcium loss, as is the presence of diseases such as rheumatoid arthritis.Weightlessness Countermeasures: Techniques and routines designed to prevent or reverse unwanted effects of weightlessness experienced during actual and simulated space flight, including physiologic changes related to removal of gravitational loading. Specific measures include creation of artificial gravity, exercise, low-level lower body negative pressure, and use of anti-deconditioning devices. (From Nicogossian, Space Physiology and Medicine, 2d ed, pp294-297)Space Simulation: An environment simulating one or more parameters of the space environment, applied in testing space systems or components. Often, a closed chamber is used, capable of approximating the vacuum and normal environments of space. (From NASA Thesaurus, 1988) This also includes simulated EXTRAVEHICULAR ACTIVITY studies in atmosphere exposure chambers or water tanks.Cosmic Radiation: High-energy radiation or particles from extraterrestrial space that strike the earth, its atmosphere, or spacecraft and may create secondary radiation as a result of collisions with the atmosphere or spacecraft.Foods, Specialized: Foods and beverages prepared for use to meet specific needs such as infant foods.United States National Aeronautics and Space Administration: An independent Federal agency established in 1958. It conducts research for the solution of problems of flight within and outside the Earth's atmosphere and develops, constructs, tests, and operates aeronautical and space vehicles. (From U.S. Government Manual, 1993)Spacecraft: Devices, manned and unmanned, which are designed to be placed into an orbit about the Earth or into a trajectory to another celestial body. (NASA Thesaurus, 1988)Gravitation: Acceleration produced by the mutual attraction of two masses, and of magnitude inversely proportional to the square of the distance between the two centers of mass. It is also the force imparted by the earth, moon, or a planet to an object near its surface. (From NASA Thesaurus, 1988)Dimenhydrinate: A drug combination that contains diphenhydramine and theophylline. It is used for treating VERTIGO, MOTION SICKNESS, and NAUSEA associated with PREGNANCY.Bed Rest: Confinement of an individual to bed for therapeutic or experimental reasons.Bone Resorption: Bone loss due to osteoclastic activity.Oxygen Isotopes: Stable oxygen atoms that have the same atomic number as the element oxygen, but differ in atomic weight. O-17 and 18 are stable oxygen isotopes.Bone and Bones: A specialized CONNECTIVE TISSUE that is the main constituent of the SKELETON. The principle cellular component of bone is comprised of OSTEOBLASTS; OSTEOCYTES; and OSTEOCLASTS, while FIBRILLAR COLLAGENS and hydroxyapatite crystals form the BONE MATRIX.Wing