在那个悲惨的日子在1997年1月，洛蒂是越俎代庖通过园区自己的生意闲庭信步，当-BAM-命中由德尔塔II火箭燃料箱的一大块。她没有丝毫受伤。可以说，人们可以感到乐观，并说，洛蒂实际上是最幸运的人在世界上生存直接命中的太空垃圾，而不是最不幸的人在世界上有被打的太空垃圾。
Deliberations aside, let’s talk about …
Your chances of being hit by space junk
你总被打受伤的一块碎片重新输入的风险估计是不到一万亿美元。
Let’s break this down to further illustrate just how small this is: Your chances of winning Powerball are much higher—one in 292 million. Your chance of being hit by lightning in the U.S. is one in 1.4 million, and being killed in a hurricane is one in six million. Over the last 40 years, more than 5,400 metric tons of materials are predicted to have survived reentry—even over populated areas—with no reported casualties. The largest object to reenter was the Russian Space station, Mir, weighing 120,000 kg.
Preventing harm to life and property on Earth
For those old enough to remember, the 1979 reentry of the U.S. space station Skylab was rife with worldwide fanfare and some hysteria—it seemed everyone had some sort of “plan” to avoid the impending debris hit. But thanks to NASA controllers who fine-tuned the space station’s attitude (orientation) during its final orbits, Skylab reentered in an orbit that passed over as few populated areas as possible. Its debris eventually reentered on the southern Australian coast, and no one was hit.
美国宇航局太空实验室的碎片足迹(地面控制area containing all its fallen debris) by performing a “deorbit maneuver.” If a satellite or rocket stage has propulsive capability, it can be commanded to execute one burn or a series of burns to lower its orbit so that the object will reenter at a specific location. For objects that pose a hazard to people and property on the ground, a deorbit maneuver is crucial, since this technique assures that the debris hits the ocean.
Another example is NASA’s controlled deorbit of the 14,000-kg Compton Gamma Ray Observatory (CGRO) into the south Pacific Ocean. More than 35 percent of CGRO’s mass was anticipated to survive reentry, and the falling debris would have been profoundly damaging to humans and property. On June 4, 2000, NASA deorbited CGRO with four thruster burns, safely landing its debris in the Pacific Ocean.
This begs the question …
Can you make an exact debris landing prediction?
您不容没有细微的精度，这是。由于预测发生灰尘将土地是非常困难的，分析师只能预测在一定程度上占用空间碎片的位置指示碎片将土地总面积。
A one-minute error in predicting the reentry time changes the debris’ location by nearly 300 miles. The surviving pieces of the object will be spread over a long footprint, so that two nearly identical fragments may impact many miles apart. For instance, four components on the Delta stages left debris in Texas and South Africa!
The main difficulty in predicting footprint location relates to uncertainties in forecasting the object’s lifetime in orbit. Still, given sufficient tracking of the object during the orbit decay, combined with measurements of solar activity over extended time, it’s possible to obtain a fairly good approximation of the date and time (but not location) of an object’s final reentry.
还有最后再入时的±10％的不确定性。考虑到轨道物体在超过7公里/秒行进时，在该对象的最后一个轨道的开始时所作的预测可以通过多达±9分钟，相当于超过7000公里在地面上被关闭。这意味着碎片足迹可以在任何地方沿着这条7000公里长的道路位于！
Why satellites deorbit and fall to Earth
In orbit, objects are exposed to atmospheric drag, just like aircraft and cars are on Earth—except that in space, there is much less drag. Still, even a tiny amount of drag can cause a satellite to reenter into a denser atmosphere.
一旦重新进入大气中，大的碎屑物体经受引起其与大气-在折返点，该对象被移动超过一个子弹快20倍以上相互作用极端加热和负荷。The temperature of the object eventually reaches a critical point, aerodynamic loads increase, and the object breaks up. The first major breakup generally occurs at an altitude between 74 and 83 km. At this point, the object fractures into several smaller objects.
一个卫星的大约10％至40％存活再入;它只是依赖于对象的结构中使用的材料。例如，如果对象包括由不锈钢或钛空燃料箱，两者都具有非常高的熔点的，许多材料将生存。如果该结构由铝制成，其具有低的熔点，一个小得多的百分比将生存。
And just as air will slow a piece of paper more than it will a lead ball, a light piece of debris will slow rapidly and hit the ground at a slower speed than a heavier piece of debris. In general, impact velocities will range from about 30 km/hr for lightweight debris to 300 km/hr or more for heavier objects.
