The intense heat caused by friction is also a problem in space travel. If you rub your hand hard on your forehead, you will feel this kind of heat. Once a spaceship is in outer space, there is no friction because there is no air to press against. But when the spaceship returns to the earth, it must go through air again. At first the air is very thin . But the closer the ship comes to the earth, the denser the air it meets. A spaceship entering the earth's atmosphere at full speed would get so hot that it would burn up completely and disappear.

由于磨擦作用而引起的高熱也是空間旅行中的一個問題。用手在前額部使勁擦，會感到這種磨擦產(chǎn)生的熱。當宇宙飛船在外層空間飛行時，因為沒有空氣緊貼著它，所以不會碰到磨擦的問題。但是，當飛船返回地面時，它必須再穿過大氣層。一開始，空氣非常稀薄；飛船越飛近地面，遇到的空氣就越稠密。以全速飛入地球大氣層的宇宙飛船會變得如此灼熱，以致使它完全燒毀而消失掉。

Today, scientists are working harder than ever to solve the problems of space travel. In 1971, the Soviet Union sent into orbit the first experimental manned space station, Salyut. (On May 14. 1973, the United States sent its first space station, Skylab 1, into orbit 270 miles above the earth. This laboratory in the sky, larger than a three-bedroom house, provided living quarters for three successive teams of three men each. These teams stayed in space for weeks at a time to perform various scientific experiments. One project was to survey some of the earth's surface in order to discover unknown natural resources, such as deposits of coal and oil. Another project was to map fault lines so that earthquakes can be predicted more accurately. Still another involved the observation of the atmospheric disturbances of the sun by telescope. These disturbances have an effect on the earth's weather.

But the main purpose of Skylab was to find out how people could live and work in space for long periods of time. The effects of prolonged weightlessness on the human body must be determined before people can make long space flights. 

目前，科學(xué)家們?yōu)榱私鉀Q空間旅行中的這些問題，而比以往更加努力地工作著。1971年，蘇聯(lián)把第一個實驗載人空間站禮炮號送入了軌道。1973年5月14日，美國將其第一個空間站天空實驗室1號送入了地球上空270英里的軌道。這個在天空中飛行的實驗室，比一幢三居室的房子還要大，它為每組三人，相繼三組字航員提供了生活空間。這三組宇航員一次在空間逗留了數(shù)周，進行了各種科學(xué)實驗。一項計劃是對地球的表面進行觀測，以發(fā)現(xiàn)未探明的自然資源，例如煤田油田。另一項計劃是對地層斷裂線進行測給，以便更準確地預(yù)測地震。再一項計劃是用望遠鏡對太陽引起的大氣擾動進行現(xiàn)測，這種擾動對地面的氣象有影響。

不過，天空實驗室的主要目的是找到人類長時期在空間生活與工作的辦法。因為人類首先必須弄清持久的失重狀態(tài)對于人體的影響，然后才能進行長時期的空間飛行。

責(zé)任編輯：admin