Most people think of flying in space as an experience that would be fun and exciting. It also involves much more than what meets the eye.
Most people think of flying in space as an experience that would be fun and exciting. And they would be correct. It also involves much more than what meets the eye. Astronauts train for many years to learn the basics of what their jobs require. Once assigned to a mission they come together as a crew and train together for about one year. As the flight approaches all that they have trained for comes together and they are ready to go.
Prelaunch the crew begins sleep shifting, adjusting to the jet lag of the time change, for up to a week before their planned launch. Due to orbital dynamics, each work day is reset to twenty two minutes earlier each calendar day. This effect is due to the relative change in the spacecraft’s workday compared to the orbit of the earth. The crew is quarantined before launch to help prevent them from contracting a contagious disease which could make them sick during their mission. Crew quarantine begins one week before launch, usually at the quarantine facility at Johnson Space Center. A few days before launch the crew will fly to Kennedy Space Center in Florida and quarantine there until launch day.
Stressors at launch include reaching a peak g (gravity equivalent) of 2.8 g’s during the 8 plus minute ride to orbit. For example a 170 pound person feels like they weigh about 480 pounds. Vibration is moderate but not enough to affect the ability of the crew to read check lists and flight deck instruments.
Weightless adaptation includes space motion sickness, fluid shift, muscle deconditioning, and sleep adaptation. Space Adaptation Syndrome (space motion sickness) affecting about 2/3 of crew and generally lasts a few hours or up to 3-4 days. Treatment may include the use of medication, such as promethazine. It is chosen because it is very effective in this environment and is long acting.
Microgravity on orbit results in the astronaut’s body fluid to shift from the lower extremities to the mid body and head. Fluid shift is characterized by fullness in head, nasal congestion, and swelling of face. Some crewmembers report that it feels like hanging upside down on earth. Fluid shift results in excess fluid excretion by the kidneys of up to approximately 20% of the circulating blood volume during the first 1 to 2 days in space.
Floating around in the weightlessness of space makes the skeletal muscles and heart work less than what is normal on the ground. This can result in skeletal and heart muscle deconditioning, and the loss of bone mass. One important countermeasure that we prescribe is a daily exercise workout for every crewmember. They do about 1.5 hours of resistive and aerobic exercise with equipment on the International Space Station. Restful sleep adaptation often take a few days due to sleep shifting, adjusting to floating, environmental noises, and the natural excitement of being and working in space.
Spacewalks are often done during missions to build or repair equipment outside the spacecraft. Hazards during spacewalks include dehydration, decompression sickness, radiation exposure consisting of unfiltered ionizing radiation and solar flares. Dehydration is a potential hazard because the spacesuit has a very low relative humidity. When combined with water loss through the skin, lungs and urine, dehydration can be a problem. The astronaut carries a drink bag with 32 oz. of water, not quite enough to prevent dehydration. Therefore, we train the crew to prehydrate with oral fluids before donning their space suit.
Decompression sickness (DCS) is a risk because the spacesuit pressure is less than 1/3 of an atmosphere to permit meaningful work in space. DCS can result if the nitrogen dissolved in the blood bubbles out when the pressure is reduced. The risk of decompression sickness is mitigated by a pre-oxygenation process and the use of 100% oxygen in the spacesuit. This flushes most of the nitrogen out of the body before the astronauts decompress and go outside in space. There has not been a case of decompression sickness reported in space.
While working in space the crew is not fully protected from solar radiation exposure because they work outside of the earth’s atmosphere. Solar activity is monitored by NASA during all manned missions, especially if a spacewalk or EVA (Extravehicular Activity) is scheduled. If a solar event threatens to expose an EVA astronaut, shielding behind structure or termination of the EVA are considered. It takes about 20 minutes for a solar event to reach earth orbit.
What preparation does the crew make to readjust to gravity on return? Exercise and conditioning sessions are critical to keep the muscles and cardiovascular system in tone to resume 1 g activities after landing. They also help to reduce the loss of bone mass. Oral fluid loading of an isotonic salt solution is taken pre-landing. It is a NASA flight rule that crewmembers consume approximately one to two liters of water and eight salt tablets, or some other approved isotonic drink, during the two hours before Shuttle landing as a countermeasure to orthostatic intolerance. This replenishes the fluid volume lost during the body’s adjustment to zero gravity.
After return to earth the crew often reports feeling very heavy. They may also experience light-headedness, dizziness, nausea, and unsteadiness. Immediately after landing, the crew flight surgeon supervises rehydration (oral or IV as required), and the management of motion sickness which usually resolves within hours of landing. Reconditioning can take up to a month post landing. Their reconditioning program focuses on neurovestibular, cardiovascular, skeletal muscle, and bone re-calcification. Once home in Houston, the crew goes about their post flight testing, debriefings and many other post mission activities. After these are completed crewmembers are available for their next assignment.