Unit 7Exploration is an important survival strategy in evolution. 探索是进化过程中一个重要的生存策略 The migration of expansive species depends on exploring their immediate or distant surroundings for new food sources or safe habitats; it can also come as a result of population pressures or environmental changes. 数量不断扩张的物种的迁移有赖于对临近或遥远的新的食物来源或安全的栖息地进行探索，这是人口压力或是环境变化的结果The human species has added another reason for exploration, namely curiosity. This intellectual urge to explore the unknown led the great European explorers to the Americas, Australia and Antarctica between the fifteenth and seventeenth centuries. 而人类还增加了另外一个探索的原因，即好奇心。
这种对未知事物进行探索的思想冲动引领着伟大的欧洲探险家们在15世纪到17世纪之间来到了美洲，澳大利亚和南极洲Inquisitiveness about nature is also the driving force behind humans exploring the polar caps, climbing mountain peaks and diving into the abysses of the oceans. 对大自然的好奇心同样也是人类探索极地冰冠，攀登山峰和潜入海底背后的驱动力Now, the ultimate frontier to explore in the twenty-first century is space. Astronomical observations and satellites have already yielded immense knowledge about our solar system and the universe beyond. 现在二十一世纪探索的最终前沿便是太空天文观测和人造卫星已经为我们提供了关于太阳系内外的宇宙的丰富知识。
But these technologies can provide only a limited picture of what is out there; eventually humans themselves will have to travel to other planets to investigate them in more intimate detail. 但是这些技术只能提供一些有限的概况，让我们知道那里都有些什么最终人类还是要亲自前往其他星球以进行更详细的研究Tremendous advances in rocket and spaceship technologies during the past 50 years, driven mainly by national security considerations, the need for better communication or a desire to observe environmental changes and human activity on the ground, have made it possible to send humans into near-Earth orbit and to the Moon.过去五十年间国家安全方面的考虑促使火箭和飞船技术取得了巨大进步。
现在，人类已经能够进入近地轨道和月球以便能够更好地实现通讯效果或是观察环境变化以及地面人类活动 Conceivably, these advances will eventually make it possible to transport astronauts to other planets, and Mars in particular.可以想象，这些进展将最终能将宇航员送至其他星球，尤其是火星 But there are significant differences between exploring Earth and exploring space. First and foremost, space is an unforgiving environment that does not tolerate human errors or technical failure. For humans leaving Earth’s orbit for extended periods, there are even more dangers. One is the near absence of gravity in space; the presence of high-energy, ionizing cosmic ray (HZE) nuclei is another. 但是探索地球和探索太空有着巨大的差异。
首先，太空是一个不容许任何人为错误或技术故障的无情的环境对于长时间离开地球轨道的人而言风险会更多一个是太空中几近全无的重力，而另外一个则是高能量电离宇宙射线（HZE）核子的存在Because both zero gravity and cosmic rays would have severe health implications for astronauts on a Mars-bound spaceship, we first need to investigate their effects on cells, tissues and our hormonal and immune systems. 由于零重力和宇宙射线会对前往火星的飞船上的宇航员有着严重的健康影响，我们首先要研究它们对细胞，组织和人类荷尔蒙与免疫系统的影响However, although we are able to produce HZE nuclei on Earth and study their effects on biological material, we cannot simulate extended periods of low gravity and their additive effects on cells and tissues. 然而，尽管我们能够在地面制造HZE核子并研究其对生物材料的影响，但是我们无法长久的模拟低重力时段以及它们二者对细胞和组织的累加效应。
Thus, the International Space Station (ISS) will have an enormously important role in assessing the health dangers for humans in space and in the development of potential countermeasures. 因此，国际空间站（ISS）将会为人类在太空进行健康风险评估以及制定应对措施方面扮演重要的角色here is much information on the adaptation of astronauts to zero gravity (0g) in space and on their return to 1g on Earth. 关于宇航员是如何适应从太空中的零重力（0g）到地球的1g的信息已经有了很多，Nevertheless, our understanding of these effects is not complete; nor have countermeasures to mitigate them been identified. 但是我们对这些影响的了解还是不够全面，也不明了有那些对策能够减轻这些影响。
Observations of astronauts travelling on the Space Shuttle and Russian cosmonauts’ long-term visits to the Mir space station indicate that time spent in 0g has serious effects on bone and muscle physiology and the cardiovascular system. For instance, the return from 0g to 1g leads to an inability to maintain an appropriate blood pressure when in an upright position — orthostatic intolerance—and insufficient blood flow to the brain. 通过对在航天飞船上和长期驻扎在俄罗斯和平号空间站上宇航员的观察发现零重力对骨骼和肌肉生理以及心血管系统都有着严重的影响例如，由0g返回至1g会导致人无法在直立的体位维持正常的血压，即直立耐受不良，还会导致脑部供血不足。
Astronauts returning from orbit therefore have to rest for several minutes, and the time needed to normalize their blood pressure increases with the time spent in 0g. 因此，宇航员从轨道返回后需要休息几分钟恢复正常血压所需的时间和他们在零重力环境中所处的时间成正比This could mean that astronauts travelling to Mars—which would take at least one year in 0g—would need considerable time to readapt to gravity after landing there or after their return to Earth, unless we find a technological solution to the creation of artificial gravity on a spaceship. 这就意味着前往火星的宇航员无论是在登陆后还是在返回地球后都将需要相当长的时间来重新适应重力，因为他们至少将有一年的时间处于零重力状态，除非我们可以找到一个技术解决方案能在宇宙飞船上人工建立重力。
Moreover, there are other cardiovascular effects, such as cardiac arrhythmia and atrophy, which need to be studied in more detail before we can ensure the safety of astronauts on a Mars mission. Other effects of extende。