首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
Space enthusiasts look to the day when ordinary people, as well professional astronauts and members of Congress, can leave Earth
Space enthusiasts look to the day when ordinary people, as well professional astronauts and members of Congress, can leave Earth
admin
2009-04-23
97
问题
Space enthusiasts look to the day when ordinary people, as well professional astronauts and members of Congress, can leave Earth behind and head for a space station resort, or maybe a base on the moon or Mars. The Space transportation Association, an industry lobbying group, recently created a division devoted to promoting space tourism, which it sees as a possible way to spur economic development beyond Earth.
The great stumbling block in this road to stars, however, is the sheer difficulty of getting anywhere in space. Merely achieving orbit is an expensive and risky proposition. Current space propulsion(推进)technologies make it a stretch to send probes to distant destinations within the solar system. Spacecraft have to follow multiyear, indirect paths that loop around several planes in order to gain velocity from gravity assists. Then the craft lack the energy to come back. Sending spacecraft to other solar systems would take many centuries.
Fortunately, engineers have no shortage of inventive plans for new propulsion systems that might someday expand human presence beyond this planet. Some axe radical refinements of current rocket or jet technologies. Others harness nuclear energies or would ride on powerful laser beams. Even the equivalents of "space elevators" for hoisting cargoes into orbit are on the drawing board.
"Reach low orbit and you are halfway to anywhere in the Solar System," science-fiction author Robert A. Heinlein wrote, and virtually all analysts agree that inexpensive access to low-Earth orbit is vital first step, because most possible situations for expanding humankind’s reach depend on the orbital assembly of massive spacecraft or other equipment, involving multiple launches.
The need for better launch systems is already immediate, driven, by private and public sector demand. Most commercial payloads(有效荷载) are destined either for the now crowded stationary orbit, where satellites push for elbow room 36,000 kilometers above the equator, or for low-Earth orbit, just a few hundred kilometers up. Low-Earth orbit is rapidly becoming a space enterprise zone, because satellites that close can transmit signals to handheld receivers. Scientific payloads are also taking off in a big way. More than 50 major observatories and explorations to other solar systems bodies will lift off within the next decade.
选项
A、the development of space’ technology
B、the obstacles and prospects of space transportation
C、the public interests in space travel
D、the growth of space business
答案
B
解析
主旨题。本文首段讲述了人们对太空旅行很感兴趣,接着第二、三段讲述了太空旅行的障碍及可能的技术改进方法。末段又讲述了太空旅行的必要条件是良好的发射系统,因此B“太空飞行的困难和前景”为本题的中心思想。
转载请注明原文地址:https://kaotiyun.com/show/svZK777K
0
大学英语六级
相关试题推荐
ThereisanoldsayinginEnglish;"Laughteristhebestmedicine".Untilrecently,fewpeopletookthesayingveryseriously.N
Thusfar,thereislittleevidencetosuggestthattechnologywillreduceinequality;indeeditmayonlyintensifyinequality.T
ManyChinesestudentswantto【T1】______theirMastersorPh.D.sdegreeinforeignuniversities,especiallyinAmericanschool
ManyChinesestudentswantto【T1】______theirMastersorPh.D.sdegreeinforeignuniversities,especiallyinAmericanschool
ManyChinesestudentswantto【T1】______theirMastersorPh.D.sdegreeinforeignuniversities,especiallyinAmericanschool
Ifyouare【T1】______atafancyplace,youmightfindamintorsomelittlecandiesonyourpillow.Thesearefreeandnice.Som
A、ThewomanhasjustbeentoChicago.B、ThemanknowslittleaboutChicago.C、ThewomanlikesChicagoverymuch.D、Themandoesn
A、Hedrovetowork.B、Hetookataxitowork.C、Hetookabustowork.D、Hegotaliftfromothers.D男士说谢谢女士开车送他去上班,女士说不用谢,并表示在上
随机试题
杜摩兰的()原则,现在已成为选择契约准据法的一项普遍接受的原则。
消食药配伍化湿药,用于消食药配伍温里药,用于
根据诉讼的基本理论,刑事诉讼活动的中心内容是:()
某储运公司仓储区占地面积为90000m2,共有8个库房,原用于存放一般货物。3年前,该储运公司未经任何技术改造和审批,擅自将1号、4号和6号库房改存危险化学品。2008年3月14日12时18分,仓储区4号库房内首先发生爆炸,12分钟后,6号库房也发生了爆炸
在财产清查过程中,应当注意的问题表述正确的是()。
擅自设立金融机构罪侵犯的客体是()。
教育的发展必然能够推动社会的发展。()
【给定资料】关于推动全省文化产业加快发展的若干意见我省“十三五”规划明确提出,到2020年全省文化产业增加值占生产总值的比重超过5%,成为国民经济支柱性产业。为实现这一目标,助力经济强省、美丽××建设,现就推动全省文化产业加快发展提出如
如果央行允许人民币继续贬值,那么市场对于人民币贬值的预期就容易强化。如果市场形成较强的人民币贬值预期,大量的资金就会流出我国。资金流出我国,不仅会强化这种人民币的贬值预期,导致更多的资金流出我国,而且可能会导致我国资产价格全面下跌,继而可能引爆金融市场的区
TheUnitedStates【C1】______alargepartoftheNorthAmericancontinent.ItsneighborsareCanada【C2】______thenorth,andMexico
最新回复
(
0
)