英语作文：jourery to space不要太多难的生词

英语作文：jourery to space不要太多难的生词
英语作文：jourery to space
不要太多难的生词

英语作文：jourery to space不要太多难的生词
Our physiological journey into space actually begins several days before launch.To avoid last minute exposure to colds and flu,you and your crew mates have been in partial isolation at Kennedy Space Center.During isolation,you have gradually adjusted your circadian rhythm to match the sleep-rest cycle required for the mission.
Now,a rookie astronaut,you have already boarded the Space Shuttle Orbiter and,dressed in an orange launch and entry suit,lie in a reclined position strapped into one of the middeck seats.The change in your orientation with respect to gravity produces a headward fluid shift.During launch,you experience as much as 3 Gs of acceleration,but the reclined position preserves blood flow to your brain and you remain conscious and alert throughout the nine minutes it takes to reach orbit.
On entry into weightlessness,the lack of a hydrostatic gradient causes a continuation of this headward fluid shift,leading to puffiness of your face and a feeling of fullness in your head.Your body perceives this fluid shift as excessive fluid volume.To get rid of the excess fluid,sodium excretion is increased leading to increased urine flow.In addition,stimulation of the hypothalmic receptors reduces thirst and so you drink less water.
Transitioning from Earth's gravity to weightlessness disrupts your body's spatial orientation and posture control systems.You experience disorientation and motion sickness during the first few days in space.You also find that the lack of regular 24 hour cycles of light and dark disrupts your circadian rhythm.Combined with a busy work schedule,cramped quarters and the other physiological stresses,which disrupts your sleep patterns and you lose about 2 hours of sleep a day for a short duration space mission.
Your mission,however,is long-duration and involves a three month stay on the International Space Station.After a month of weightlessness,additional changes in physiological systems begin to become apparent as you are fully adapted to the microgravity environment.You now get around using mostly your arms and you don't need to use your legs to support the weight of your body.The reduced work load on weight-bearing muscles leads to muscle wasting (or atrophy) with an associated strength loss that could be 30% to 40%.The small forces used to get around require reduced gross muscle activity and increased fine muscle activity leading to a conversion of muscle fibers from slow twitch type to fast twitch type.Measurements of astronaut intravehicular activity (IVA) reveals average force magnitudes of 9 N (2 lb) with maximum lods of 60 N (13.5 lb).Your heart no longer has to pump blood against the pull of gravity and the reduced load leads to atrophy of your heart muscle.Lack of weight bearing also reduces stress levels in your bones leading to bone breakdown and release of calcium.Loss of bone mineral density at a rate of 1­2% per month in critical areas significantly reduces the strength of your bones.
Through some combination of factors,your immune system gets weaker,and you realize that you are now more prone to infection and perhaps even at risk for reactivation of latent viruses.
These profound changes in your body in response to the weightless environment can pose serious health risks upon return to Earth.For most physiological systems,your body readapts to the 1-g environment,although often at a slower rate than on entry into weightlessness.You might experience orthostatic intolerance brought on by the hydrostatic gradient and a reduced fluid volume.Your muscle strength will probably return to normal within 4-8 weeks.Your bone mass should also recover within approximately 8 months or a year,but may never recover it's original strength for the same amount of mass.You may also encounter difficulties with postural equilibrium due to weightlessness induced changes to your neurovestibular system.
Research needs to be performed to assess astronaut performance for long-duration space missions with particular emphasis on developing countermeasures to spaceflight-induced deconditioning.Pre-,inflight,and postflight investigations of astronauts exposed to long-duration space flight aboard the International Space Station will help answer the question of what are the basic mechanisms underlying adapation to microgravity.This information has implications for future countermeasure interventions.If long-duration space flight leads to general deterioration in astroanut performance then inflight countermeasures that enhance performance can be envisioned.Some combination of exercise,medication,and perhaps,artificial gravity,will be prescribed as countermeasures for long-duration space missions,especially for future missions to the moon or Mars.