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The author:(作者)aaapublished in(发表于) 2013/12/16 0:35:21 Experts unscramble chang 3 River moonfall five difficulty
The night of December 14 to become immortal, the third will implement a soft landing on the lunar surface, which is the largest in the Chang-third mission difficulty, is also key to the success or failure of the task. It is reported that Chang, third in recent months, some 15 km from the parabola declined relative speed is gradually reduced from 1.7 kilometers per second to zero. The whole process takes about 12 minutes.
"Transmission, brakes, axles and in recent months compared to a lunar landing, which is the key issue. This is a brand new for us, and is also one of the most important tests. "Said Wu Weiren, Chief Designer of China's lunar exploration engineering.
Difficulties in
The Rainbow Bay area could fall on the specified
Ability to specify accurate Lunar Rainbow Bay region fell, is Chang the third probe, the implementation of soft landing face first challenge.
Zhiqian, Chang e, first He Change second satellite has solved the technical problems of flight around the moon. This time, Chang the third spacecraft to resolve around the months after successful issues can fall in designated areas.
It's like driving a car, the highway runs, slow, delay, speed is too fast and could not brake in time; or missed destination, or it'll be a hit, you cannot successfully complete the task.
Therefore, Chang e, third "brake" is appropriate, whether the distance accurately, all the technical difficulties of the launch mission, and key.
Difficulties in the second
Ultimate Moon locations select still has difficulty
Chang third landing sites chosen at the Rainbow Bay area smooth. But because of the uncertainty of the Lunar terrain and eventually fall months the choice of venue, there is still a certain degree of difficulty.
"The surface of the Moon from the macro side are relatively flat, but small range, like 50 m × m or 10 m × m micro-environment, topography is what it looks like, we are not very clear, nor does it know where eventually landed, it was a big test for us. Despite taking a number of measures, but the risk is still relatively large, where months of many rocks, craters, may encounter the stone may also run into ditches, these conditions can exist. "Wu Weiren said.
Difficulties in three
Cannot be realized by air friction reduction
The moon has no atmosphere, which determines how the moon landing and the Earth landing entirely different, it is the vacuum State of a soft landing.
"No atmosphere realization also means that you cannot use the air friction slows down. Chang the third spacecraft to achieve the surface safe and soft landing, conventional rocket engine and propulsion system to complete this task. Because the Moon, a celestial body to a soft landing on the surface of the atmosphere-free maneuvers, the traditional engine thrust of change cannot be achieved. "Chang-third said Sun Zezhou, Chief Designer of the spacecraft system.
This newly developed variable thrust engine 7,500 cattle can continuously adjustable variable thrust, and thus to the goddess, third to achieve precise control, solved this problem very well. As it is developed and used for the first time, 7,500 n variable thrust engine eventually does, has yet to be a soft landing test for the day.
Difficulty IV
Almost zero human intervention
During the fall months, to real time measurement detector movement speed, height, adjust, and surface topography is complex, but also in search of a safe landing zone, "these works were completed in a very short period of time, and depends entirely on detector independently complete, autonomous navigation control is difficult. "Sun Zezhou said.
Starting 15 km "power fall" stage, been described by insiders as the most thrilling aspect. Chang, third to rely entirely on autonomous navigation control, complete the reduced height, landing place, the implementation of a soft landing and a series of key actions identified, almost zero possibility of manual intervention.
"In this period of measurement and control are kept up with only program set in advance. "Tan Mei Chang-detector systems, third Deputy Commander said.
Difficulties in five
Moon dust or attached to the probe fault
Lunar soil has a certain thickness, the lander landing, moon walk caused by man-made factors, such as dust, surface of Lunar dust attached to the probe, which can cause decreased sensitivity of optical systems, sideng mechanical structure failure.
In addition, the fall months when the detector, enormous energy from the moon have a plume and the detector itself the greatest threat was its safe landing. Landing cushion body can withstand the test of the detector, and moon seen in the day.
12月14日晚，嫦娥三号将在月球表面实施软着陆，这是此次嫦娥三号任务最大的难点，也是任务成败的关键所在。据悉，嫦娥三号将在近月点15公里处以抛物线下降，相对速度从每秒1.7公里逐渐降为零。整个过程大概需要12分钟。
“发射、近月制动、变轨和月面降落比较起来，后者更为关键。这对我们来说是一个全新的，也是一个最重要的考验。”中国探月工程总设计师吴伟仁表示。
难点一
能否落在指定的虹湾区域
能否在指定的月球虹湾区域准确落下，是嫦娥三号探测器实施软着陆首先面临的难题。
之前，嫦娥一号和嫦娥二号卫星已经解决了绕月飞行的技术问题。这一次，嫦娥三号探测器则要解决绕月成功后，能不能在指定区域落下来的问题。
这好比开汽车，在高速路上跑，速度慢了，耽误时间，速度太快，又不能及时刹车；要不就错过了目的地，要不就一头撞上去，不能成功完成任务。
所以，嫦娥三号的“刹车”时间是否合适、远近距离是否准确，都是此次发射任务的技术难点和关键。
难点二
最终落月地点选择仍有难度
嫦娥三号着陆地点，选在较为平坦的虹湾区域。但由于月球地形的不确定性，最终落月地点的选择，仍存在一定难度。
“月球表面从宏观的方面来说相对还是比较平坦的，但小范围，比如50米×50米或者10米×10米的小环境，它的地形地貌是什么样子，我们不是很清楚，也不知道最终会降落到什么地方，这对我们而言是一个很大的考验。尽管采取了很多措施，但风险还是比较大，因为那里的月石、月坑很多，可能碰到石头，也可能碰到壕沟，这些情况都可能存在。”吴伟仁说。
难点三
不能用空气摩擦实现减速
月球上没有大气，这就决定了月面着陆与地球着陆方式完全不同，它是真空状态下的软着陆。
“没有大气也就意味着不能利用空气摩擦实现减速。嫦娥三号探测器要实现月面安全软着陆，传统火箭发动机和推进系统无法完成这一任务。因为在月球这一无大气天体表面进行的软着陆机动飞行中，传统发动机无法实现推力的变化。”嫦娥三号探测器系统总设计师孙泽洲说。
为此次任务新研制的7500牛变推力发动机，能够进行连续可调节变推力，进而对嫦娥三号实现精准控制，很好地解决了这一难题。但由于是首次研制和使用，7500牛变推力发动机最终的表现如何，还有待软着陆当天的考验。
难点四
人工干预几乎为零
落月过程中，要实时测量探测器运动的速度、高度，随时调整，而且月面地形地貌很复杂，还要寻找安全的着陆区等，“这些工作都要在很短的时间内完成，而且完全靠探测器自主完成，所以自主导航控制是个难点。”孙泽洲说。
15公里开始的“动力下降”阶段，被业内人士形容为最惊心动魄的环节。嫦娥三号要完全依靠自主导航控制，完成降低高度、确定着陆点、实施软着陆等一系列关键动作，人工干预的可能性几乎为零。
“在这个时间段内测控都跟不上了，只能事先把程序都设定好。”嫦娥三号探测器系统副总指挥谭梅表示。
难点五
月尘附着或致探测器故障
月壤具有一定的厚度，着陆器着陆、月球车行走等人为因素也会造成尘埃飞扬，月球尘埃如果附着于探测器表面，能引起光学系统灵敏度下降、机械结构卡死等故障。
此外，探测器落月时，来自月面的巨大冲击能量及探测器自身产生羽流是其安全着陆的最大威胁。探测器的着陆缓冲机构能否经受住考验，还得落月当天见分晓。
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