在20世纪开始时,人们经常问:“人类能不能去太空旅行?”现在,21世纪开始了,过去的问题有了肯定的答案。现在的问题是:“人类什么时候经常去太空旅行呢?” 对于这个问题,不同的人有不同的答案,有的说要2年后,有的说要30年后。英国布里斯托航天飞机公司把太空旅行分为两种。一种是亚轨道太空旅行,即达到太空的高度,绕地球轨道飞行不到一圈的短暂旅行;另一种是环绕地球轨道的太空旅行,就像卫星一样在太空中沿着轨道飞行。根据该公司的分析,6年后可能会开始亚轨道太空旅行,而环绕地球轨道的太空旅行则要等到10年以后。太空旅行的费用很高, At the beginning of the twentieth century, people often asked: “Can humans travel in space?” Now that the 21st century has begun, past questions have been answered in the affirmative. The question now is: “When do humans travel often in space?” Different people have different answers to this question, some say two years later, and some say 30 years later. Bristol Space Flight Company of the United Kingdom divided space travel into two types. One is sub-orbital space travel, that is, to reach the height of space, less than a circle orbiting the Earth orbit a short trip; the other is the orbital space travel orbit, like a satellite orbiting in space. According to the company’s analysis, sub-orbital space travel may start 6 years later, while space travel around orbit around Earth would have to wait 10 years later. Space travel is expensive,