Below is a brief description of some of the problems and following is how we are currently dealing with them and any future countermeasures.
Bones When in space, it is no longer necessary for astronauts to walk as they move about the spacecraft, they simply float. Obviously the portions of the skeleton in the lower part of the body – the legs, hips and spine – experience some changes from the lack of weight on them. Over time this leads to a bone breakdown and a release of calcium, which is the body reabsorbs becoming brittle and weak as a result. Additional risks from the calcium loss are the formation of kidney stones and bone fractures. To better understand this, postmenopausal women can have a bone loss of 1 to 1.5 percent in one year - an astronaut loses the same amount in a single month. Additionally, radiation exposure may also impact bone loss.
Muscles The same thing that results in bone loss, not having a need to inflict weight on the lower extremities, results in less of a load on the muscles. The leg & back muscles begin to weaken or atrophy, leaving the astronaut open to injuries that are fall-related during exploration missions. Attempts to exercise by Astronauts do help maintain muscle mass, but it is purely a help, not a fix.
Fluid Shift The downward pull of gravity that distributes the blood and other body fluids to the lower part of the body, does not occur in space. A redistribution of fluids to the upper portion of the body from the lower extremities happens and this shift in fluids in space leads to astronauts having a puffy face. The fluid shift to the head also leads to a feeling of congestion.
Cardiovascular System Although the cardiovascular system generally functions well in space, because the heart doesn’t have to work as hard in the microgravity environment heart atrophy due to the fluid shift and loss of plasma (water in the bloodstream) which accounts for about 20% of the usually 60% constant of the body does happen. On the astronauts return to Earth this contributes to the inability to stand for long periods of time which often results in passing out; something that returns to normal after time. Over time, this could lead to deconditioning and a decrease in the size of the heart. There is also a concern that space radiation may affect endothelial cells, the lining of blood vessels, which might initiate or accelerate coronary heart disease.
The Spine (Taller in Space-3% or ~2 inches) On Earth, the disks of the spinal column can become compressed due to gravity. In space, that is not the case. In fact quite the opposite; compression is no longer present causing the disks to expand. Because the spine lengthens, the astronaut becomes taller. Back pain is one of the side-affects that may be associated with the lengthening of the spine.
Inner Ear and Balance System There is a complex set of neural circuits which allow humans to maintain balance, stabilize vision and understand body orientation in terms of location and direction, but that is on Earth. The pattern for receiving and interpreting information particularly the eyes, inner ear vestibular organs and data that comes from muscles and joints. In space, this pattern of data exchange is altered. The inner ear no longer functions as intended. At first, when the mission begins, astronauts may experience disorientation, motion sickness and at times and at times a loss of sense of direction. Upon returning to Earth, while adjusting to the 1g of the Earth’s gravity the Astronaut may experience problems standing up, stabilizing their gaze, walking and turning. Certainly this problem is increased if the duration of time in space is increased. However affected can be activities that may require these functions for the return to earth. (ie. approach and landing, docking, remote manipulation, extravehicular activity or even exiting the craft.)
Sleep and Performance On the ISS the day as the Astronaut knows it on Earth does not exist. The Astronauts experience 16 sunsets & sunrises a day. Beautiful of course, but it grows old fast. Sleeping becomes impossible for some and in the confined environment an astronaut’s ability to work well in space can be compromised from the lack of sleep. Add to this that an exploration crew will attempt to shift their internal clocks from Earth time to the schedule of the destination. Everyone is familiar with Seasonal Disorders that occur in some cases as a result of the loss of the Sunlight for long periods of time. Hoping to increase the Astronaut’s alertness and reduce performance errors scientists have placed improvements to spacecraft lighting, sleep schedules and the scheduling of work shifts.
Radiation Radiation besides having effects listed above and in addition damage lymphocytes which are necessary to the immune system. Cataracts is something that is experienced by astronauts with far more frequency due to radiation. Also there is a significant health threat from galactic cosmic rays which increase the incidence of cancer. Solar flares are of concern due to their ability to give a fatal dose within mere minutes, but protective shielding and drugs may eradicate or at least minimize that risk.
The Sense of Taste The disruption of the fluids in the body has an effect on the astronaut’s sense of taste. However this is not guaranteed. Some do not experience any change. Scientists are not really positive of why this is but theories such as the congestion (resulting from water redistribution), food degradation, or perhaps psychological reasons. It is for this reason that Astronauts often choose a strong tasting food to make up for the loss of taste.
Better bones through supplements? Pharmaceutical agents such as a high calcium intake and vitamin D supplements does prevent the elevation of serum calcium levels. Vitamin K counteracts the reduction in bone formation and there are indications that bone metabolism and calcium balance can be stabilized during space flight. Currently Bisphosphonate, a therapeutic agent that has been used to treat osteoporosis, hormone therapy and various other things have been tried. Additionally exercise by Astronauts in the not so distant future may have greater benefit thanks to the exoskeleton suit designed by NASA and The Florida Institute for Human and Machine Cognition in Pennsacola, Florida.
Muscles There is evidence that suggests that the muscle atrophy may be arrested by the use of the exoskeleton devices mentioned above.
Fluid Shift A formal research into the problems of the eyes and other complaints resulting from the fluid shift as well as from radiation at this time; back in January of this year it was first implemented.
Cardiovascular System, sense of taste, & a change in sleeping habits All these are currently being looked at as NASA plans spending longer time in outer space. The answer isn’t always to solve the individual’s problems but instead we may look at…
The Bubble Developed at University of Washington, Seattle, the Bubble is a shield that holds many answers for space travel and for re-entering the atmosphere. Forget the heavy metal protective gear and look instead to a shield of plasma that will weigh less and hence make fuel expense reduced. While the Earth’s magnetic field lends protection to anything in low Earth orbit Astronauts travelling to outer space are at risk of cancer and other medical problems due to exposure to cosmic rays.
Granted this is not available today, but the basics are understood. A spacecraft would have a high-voltage device that would tear hydrogen into protons and electrons and form a cloud that extends around the spacecraft. The cloud would necessitate a wire mesh enclosing it and electricity would power the mesh keeping the plasma contained. The resulting magnetic field would deflect cosmic rays and is being looked at as protection for the space-elevator as well.
The mesh would need to be deployed well after launch and would need to be made of superconducting material as it would also need to operate at high temperatures. This material is something that already exists and is available commercially. As it would appear that future spaceships will be powered by some advanced engine type that uses plasma for propellant, excess or discarded plasma could be recycled and used as a radiation shield. This actually would solve the greatest threat to an Astronauts health. Most of the other effects either disapates when he/she returns or can be mediated currently through medication.
Medical Benefits of Space To be completely fair, one must also consider the benefits of living in zero G. The likelihood of space hospitals existing next to the planned space hotels is great. Many surgeries will become easier or safer in zero gravity, painful backs will gain some relief, poor circulation may be improved, but all that won’t be researched further until first we prepare the Astronaut for log visits in space. Then come the space tourists!