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
The great advance in rocket theory 40 years ago showed that liquid-fuel rockets were far superior in every respect to the skyroc
The great advance in rocket theory 40 years ago showed that liquid-fuel rockets were far superior in every respect to the skyroc
admin
2010-02-21
93
问题
The great advance in rocket theory 40 years ago showed that liquid-fuel rockets were far superior in every respect to the skyrocket with its weak solid fuel, the only kind of rocket then known. However, during the last decade, large solid-fuel rockets with solid fuels about as powerful as liquid fuels have made their appearance, and it is a favorite layman’s question to inquire which one is "better". The question is meaningless; one might as well ask whether a gasoline or a diesel engine is "better". It all depends on the purpose. A liquid-fuel rocket is complicated, but has the advantage that it can be controlled beautifully. The burning of the rocket engine can be stopped completely: it can be re-ignited when desired. In addition, the thrust can be made to vary by adjusting the speed of the fuel pumps. A solid-fuel rocket, on the other hand, is rather simple in construction, though hard to build when a really large size is desired. But once you have a solid-fuel rocket, it is ready for action at very short notice. A liquid-fuel rocket has to be fueled first and cannot be held in readiness for very long after it has been fueled. However, once a solid-fuel rocket has been ignited, it will keep burning. It cannot be stopped and re-ignited whenever desired (it could conceivably be stopped and re-ignited after a pre-calculated time of burning has elapsed) and its thrust cannot be varied. Because a solid-fuel rocket can be kept ready for a long time, most military missiles employ solid fuels, but manned space flight needs the fine adjustments that can only be provided by liquid fuels. It may be added that a liquid-fuel rocket is an expensive device; a large solid-fuel rocket is, by comparison, cheap. But the solid fuel, pound per pound; costs about 10 times as much as the liquid fuel. So you have, on the one, hand, an expensive rocket with a cheep fuel and on the other hand a comparatively cheap rocket with an expensive fuel.
Solid fuel rockets are expensive to operate because of their ______.
选项
A、size
B、fuel
C、construction
D、complicated engines
答案
B
解析
文中提到相比之下,液体燃料驱动的火箭造价更高,但the solid fuel,pound per pound;costs about 10 times as much as the liquid fuel,可以判断固体燃料驱动火箭昂贵之处在于其燃料。
转载请注明原文地址:https://kaotiyun.com/show/QvIO777K
0
考博英语
相关试题推荐
•YouwillhearaninterviewwithMrSchuman,ajobrecruitmentadvisor.•Foreachquestion23-30,markoneletter(A,BorC)fo
•Youwillhearaboutacarpurchaseonthephone.•Foreachquestion,fillinthemissinginformationinthenumberedspace,u
•Lockatthenotesbelow.•Someinformationismissing.•Youwillhearawomantalkingaboutpersonalexperience.•Foreach
ENOUGHELECTRICITY
Lookatthenotesbelow.Someinformationismissing.Youwillheartwopeoplediscusshowtosavearacecourse.Foreachquesti
ElizabethEltingNameofHerBusiness:【B1】______RevenuesoftheBusiness:【B2】______millionDegree:【B3】Bachelorof______Co-f
Lookatthenotesonbeingasuccessfulentrepreneur.Someinformationismissing.Youwillhearpartofthespeechbya
Whilethesectorgraduallyfellback,withaslightrecoveryattheendoftheweek,thiscompanygenerallyperformedmuchbette
Ofwhathistoricandcontemporaryconcernisitthatthearchitectureprofessionhasbeen,andcontinuestobe,stronglymaledo
随机试题
A.PGl2B.PGF2C.PGH2D.PGE2E.PGG2在血管内皮中由15-OH-—PGDH催化代谢的是:
冠心病的危险因素有
下列各项中属于胆碱能神经纤维的有()(2002年)
最适合血管缝合的材料是
以下哪一肌肉不参与软腭的构成
信息公开不够、缺少制度规范、处罚没有威慑等,都是浪费之风形成的原因。其中。监督环节是核心。一些地方部门公开“三公经费”、晒出财政预算,无疑能从花钱的________上管住浪费的发生。纪检、审计、财政一起给力,才能在事中________过度消费的冲动。填入划
根据以下资料,回答下列问题。2012年国家发布新修订的《环境空气质量标准》,将大气污染综合防治作为重点工作。根据这一新标准,空气质量指数(AQI)将替代原有的空气污染指数(API),作为定量描述空气质量状况的无量纲指数。2016年
已知λ1,λ2,λ3是A的特征值,α1,α2,α3是相应的特征向量且线性无关,如α1+α2+α3仍是A的特征向量,则λ1=λ2=λ3.
Thiscountryisfullycommittedtotheintroductionofcomputersintoschools.Thisisdemonstratedbythefactthatvirtuallya
A、Itisveryeffective.B、Itisenforcedstrictly.C、Itistoostricttoobey.D、Ithasmanyloopholes.B由句(3)可知,男士过去每天开一个半小时的车去
最新回复
(
0
)