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What happens to the human body during space flight? John F. Graham tells us that, (Graham, 1995) “Upon entry into space the first obvious environment an astronaut encounters is weightlessness due to microgravity. The rocket ship and all of its contents are virtually “falling” around the Earth. It’s like being in a runaway elevator that never hits the basement floor or being in a perpetual sky dive without hitting the ground.” We realize that there must be many variant changes in the body, during space flight. We are also told that “The human body changes when it encounters weightlessness and several space shuttle missions have been dedicated to determine what happens to the body and whether or not any of the seemingly temporary changes become permanent as explorers venture farther and longer out into space.”Space flight isn’t all about fun and adventure. We understand that there are many risks to the human body while traveling in space. Of course, there is a more critical and dangerous portion of the space environment which is studied greatly, before humans can journey much beyond our immediate planetary system.Graham tells us that “Radiation occurs in several different forms. First, there is the normal radiation which is emitted from the Sun and all other stars called electromagnetic radiation (EM). EM can destroy body cells and eventually human life with exposure for even short periods. Cosmic rays are emitted from the rest of the galaxy and are thought to come from super novas or exploding stars. As the space explorer goes farther from the Sun the EM becomes less of a problem and galactic cosmic rays become greater problems. Once again, the unshielded human body becomes extremely vulnerable to radiation.”Howard Bartner (Bartner, 2003) offers many different illustrations of what the body experiences during space flight and tells us that the Spacelab, is  “a reusable laboratory module inside the space shuttle, has provided space life scientists with a more regular opportunity to conduct experiments aimed at a deeper understanding of the human body.” Specific, dedicated missions have been made to appear more completely at the human and animal physiology. These missions have very often tried to determine, in detail, how space flight influences living things, so that the health and productivity of space travelers can be maintained and so that lessons in medicine and physiology learned in space can be transferred back to Earth to enrich all our of lives.We realize that scientists don’t have enough information from space to specifically explain what causes the cardiovascular system to change, while in space flight. There is so much evidence to show that it does change the way it operates, even on a short journey into space and examines a true space flight investigation which flew in both the SLS-1 mission and the SLS-2 mission and was designed to examine how the operation of the cardiovascular system is changed in space when astronauts are at rest and when they are exercising. Prior to this investigation, a review is included covering the normal functions of the heart, lungs, and blood vessels as they exist on Earth.      Examination of the blood does begin by looking at its various components and then focusing in on how the red blood cells are produced and destroyed in our bodies. Following an investigation designed by Dr. Clarence Alfrey, the principal investigator, the Focus examines how blood is affected by space flight and, more specifically, how red blood cell activity changes in space flight.Gravity affects the distribution of fluids inside the body by pulling the various body fluids down towards the feet, on Earth. When entering into space, the virtual absence of gravity causes these fluids to redistribute upwards towards the chest and the head. This perceived increase in fluid volume in the upper part of the body causes multiple physiologic changes in the kidneys and associated fluid-regulating hormones, in the cardiovascular system, and in the red blood system. The Focus examines how your kidneys, working with certain hormones, adapt to space flight and regulate the levels of fluids and electrolytes in the body. It is believed that astronaut’s muscles weaken while in space because they do not have to use them as they normally would on Earth. When the astronauts return home, they experience gravity as much more of a force to reckon with than they had ever noticed before. This Focus starts with a description of the structure and mechanical action of muscles. It then looks at the chemical activities that take place in the muscles to assure that they receive the appropriate levels of energy to keep us moving. And finally, it illustrates an important space study that was carried out to see how and why the muscles of astronauts can change their very character as they adapt to the new environment of space where the natural gravitational pull is absent.What must astronauts do to protect themselves, while in flight, in outer space? We learn from Lift Off to Learning that, “When astronauts travel into space, they must carry part of Earth’s environment with them. Air for breathing and for exerting pressure, food and water, and moderate temperatures are contained in a physical shell called a spacecraft. This shell also provides protection against high speed micrometeoroid particles. On some space missions the shell is deliberately opened and astronauts pass through an airlock to venture outside. When doing so, they must still be protected, but by a smaller and specialized version of their spacecraft called the Extravehicular Mobility Unit (EMU). This smaller spacecraft is composed of a spacesuit with a life-support system. It is different from the larger spacecraft by being anthropomorphic (human) in shape and flexible. Flexibility permits movement of arms and legs and operation of many types of scientific apparatus, taking pictures, assembling equipment and structures, piloting the Manned Maneuvering Unit (MMU), and repairing and servicing defective and worn-out satellites and other space hardware. All these tasks are called Extravehicular Activities, or EVAs.”There are, of course, other-environmental problems encountered in outer space include weightlessness, which are (Compton; Benson, 1983)  “electrically charged particle radiation from the Sun, ultraviolet radiation, and micrometeoroids.  Micrometeoroids are usually very small bits of rock and metal left over from the formation of the solar system and from the collisions of comets and asteroids. Though small in mass, these particles travel at very high velocities and can easily penetrate human skin and thin metal. Equally dangerous is debris from previous space missions. A tiny paint chip, traveling at thousands of kilometers per hour, can do substantial damage.”We learn from scientists that spacesuits were initially utilized by the United States manned space flight program for EVAs and that was during the Gemini missions. These suits were then custom built to each astronaut’s body size. In the Apollo program, an astronaut had 3 custom suits. One was used for flight, one for training, and another for flight backup. Space Shuttle spacesuits, however, are tailored from a stock of standard size parts to fit astronauts over a long range of specialized variations. When making the Shuttle spacesuit, developers could concentrate each of their designs toward a single function, going EVA. Mohler shows us that (Mohler, 1971) “Spacesuits in earlier manned spaceflight programs had to serve multiple functions. They had to provide backup pressure in case the cabin lost pressure, protection if ejection became necessary during launch, EVA in weightlessness, and EVA while walking on the Moon in one-sixth Earth’s gravity. Suits were worn during lift-off and re-entry and had to be comfortable under the high-G forces experienced during acceleration and deceleration.”Specialized spacesuits are necessary in space for all astronauts. Our human bodies just weren’t made to fly into space, unprotected. In some cases, astronauts are going by an established tradition for pilots, to tell their official doctors as little as they can. Many of the astronauts are physicians, and persistent stories tell of astronaut-physicians being consulted on medical issues by their fellow astronauts, without the knowledge of the official NASA flight surgeons.Space flight is a miraculous and wonderful journey, and many astronauts will tell you that they wouldn’t trade the experience for anything. We must study more about the effects of space flight on humans to understand more but for now scientists continue to use the spacesuits that have already been constructed. There will always be risks to the human body, during space flight, but some chances, according to astronauts, are just worth the risk.

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