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
A rocket thruster based on an engine designed to power a lunar lander on an expedition to the Moon has been successfully tested
A rocket thruster based on an engine designed to power a lunar lander on an expedition to the Moon has been successfully tested
admin
2009-06-24
62
问题
A rocket thruster based on an engine designed to power a lunar lander on an expedition to the Moon has been successfully tested by the Northrop Grumman aerospace company in the U.S.
The thruster runs on a mix of liquid methane and liquid oxygen, which has the potential to be more efficient than other engines, but has never before been used to power or steer a spacecraft.
Methane engines are a candidate for powering the liftoff vehicle NASA is developing to return astronauts from the lunar surface. Methane thrusters could be used for steering in space.
Missions such as landing on and taking off from the Moon put stringent requirements on engines. Importantly, rockets must be liquid-fuelled so they can be shut down and restarted if needed.
The Apollo lunar landers used exotic mixtures called "hypergolic" fuels, which ignite when they come into contact with a matched oxidizer. Because they are liquids at or near room temperature, hypergolic fuels don’t require heavy cryogenics or pressurized tanks, and can be stored longer than liquid hydrogen and liquid oxygen (LOX) without boiling away.
But the specific impulse—a measure of propulsion power—of hypergolic engines is only 260 to 310 seconds, compared to 425 to 455 seconds from liquid hydrogen and LOX. And hypergolic engines require the use of compounds such as nitrogen tetroxide and hydrazine, which are extremely toxic for astronauts and ground crews.
Methane requires cooling to -161.6℃, close to the temperature of LOX, but well above the -252.9 degrees C needed for liquid hydrogen, reducing the mass of insulation and cooling equipment.
Liquid methane is also denser than liquid hydrogen, so fuel tanks can be smaller than those for liquid hydrogen. And Northrop’s test engine has already beaten the specific impulse of hypergolic fuels, although it can’t match that of a liquid-hydrogen engine.
The Northrop tests are a step toward answering NASA concerns about the ease of igniting methane, crucial for engine function, and have earned the company a 10-month contract for further engine development. "The engine far exceeded performance requirements", said Northrop programme manager Mark Trinidad. It was fired more than 50 times, a key capability for thrusters, which are used repeatedly.
Meanwhile other teams are also working on more powerful methane/LOX engines suitable for lunar liftoff. Last year, NASA engineers fired a methane-LOX engine for 103 seconds and XCOR Aerospace test-fired a methane-LOX engine that generated 33,400 newtons (7,500 pounds) of thrust in shorter bursts lasting about one second.
The XCOR engine is soon to be test-fired in a vacuum—a necessary test for space use. The company is developing another lower-powered methane/LOX engine for the MarsFlyer aircraft being developed by Aurora Flight Systems, which may one day take to the skies over the red planet.
选项
A、Liquid methane and liquid oxygen.
B、Methane.
C、Liquid hydrogen and liquid oxygen.
D、LOX.
答案
A
解析
转载请注明原文地址:https://kaotiyun.com/show/K5Hd777K
本试题收录于:
公共英语五级笔试题库公共英语(PETS)分类
0
公共英语五级笔试
公共英语(PETS)
相关试题推荐
MargaretSangerandBirthControlMargaretSanger,anAmericannurse,wasthefirsttostartthemodernbirthcontrolmoveme
WorkingMothersCarefullyconductedresearchesthathavefollowedthechildrenofworkingmothershavenotbeenabletoshow
TheFamilyThestructureofafamilytakesdifferentformsaroundtheworldandeveninthesamesociety.Thefamily’sformc
WhichofthefollowingisNOTrequiredofacontainer?HowdidhegotoNewYorkCity?
WhichofthefollowingisNOTacharacteristicoftheBrazilianstyleofplayingfootball?WhichofthefollowingisNOTtrueo
Marketcanbeclassifiedaccordingtowhatissoldonamarketandhowgoodsaresold.Thedefinitionofmarketforbusinesspu
Hehasestablishedhimselftobeacompetentmanagerbyhissuccessfullyhandlingseveraldifficulttasks.
TeachingPoetryNopoemshouldeverbediscussedor"analyzed",untilithasbeenreadaloudbysomeone,teacherorstudent
Therepresentativewasaskedtoverifyhisearlierstatement.
HowWeFormFirstImpressionWeallhavefirstimpressionofsomeonewejustmet.Butwhy?Whydoweformanopinionabouts
随机试题
同一个领导层次的机关团体,或者一个机关团体中的各个构成单位,完全集中于一位上级领导或一个上级机关团体的指挥、控制和监督。这种领导体制我们称作
已知某厂生产x件产品的成本为C(x)=25000+200x+x2(元),产品产量x与价格P之间的关系为:P(x)=440一x(元)。求:要使平均成本最小,应生产多少件产品?
24岁,农民,10天前劳动中砍伤足背,未特殊处理。今日觉乏力,烦躁,饮水时张口费力。应考虑的诊断是
根据三级预防的原则,在劳动卫生及职业病工作中,不属于第二级预防工作的是哪一项
在我国基本建设所用的“三大建筑材料”通常是指:[1995年第002题][2006年第001题]
某上市公司针对经常出现中小股东质询管理层的情况,拟采取措施协调所有者与经营者的矛盾。下列各项中,不能实现上述目的的是()。
下列关于企业所得税适用税率的说法中,不正确的是()。
【2016下】美国学者孟禄根据原始社会没有学校、没有教师、没有教材的史实,断言教育起源于儿童对成人的无意识的模仿。这种观点被称为()。
A、 B、 C、 D、 A分数数列。原式可化为,分子是公差为4的等差数列,分母是公差为3的等差数列,因此中间项为。
从所给的四个选项中,选择最合适的一个填入问号处,使之呈现一定的规律性。()
最新回复
(
0
)