"Space Debris"
(excerpted and adapted)
In the folktale "Chicken Little," the title character becomes convinced the sky is falling when an acorn falls on her head. While she is demonstrably wrong in the story, in reality objects from outer space do fall to Earth. On average, a total of 200-400 tracked objects enter Earth’s atmosphere every year. [A] Thankfully, human populations are rarely affected by these falling objects. This is because only a relatively small percentage of Earth’s total surface area is inhabited. So, any objects that do not burn up and disintegrate during atmospheric reentry are likely to fall into the open ocean or 46on a land area that is sparsely populated.
The U.S. federal agencies charged with monitoring near-Earth space estimate there are over 170 million pieces of space debris orbiting the Earth. [B] Space debris is the collection of man-made objects like old 47satellites, spent rocket stages, and fragments, from disintegration, erosion, and collisions. The majority of these objects are tiny, but roughly 30,000 are larger than a softball. Only about 1,000 are actual spacecraft.
The smallest bits of space debris cannot even be detected by 48censors. Despite their lack of mass, 49spacecraft are at risk from these tiny pieces of debris. [C] This is because objects orbit the Earth at extremely high velocity. [D] 50Consequently, a seemingly insignificant bit of metal can easily punch through the protective covering on satellites or spacecraft.
There have been two major space collisions involving debris. The first occurred in 1996 when a French military reconnaissance satellite Cerise was struck by debris from a French rocket that had exploded a decade earlier. In 2009, the first collision 51of two intact satellites occurred when Iridium 33, a U.S. satellite, collided with the 52extinct Russian Cosmos-2251 at a speed of over 26,000 mph. 53This produced over 2,000 new pieces of space debris. A piece of space debris from the collision passed close to the International Space Station in March 2012. The crew took shelter in two docked Soyuz rendezvous spacecraft until the debris passed.
54In 1978, NASA scientist Donald Kessler proposed a worst-case scenario for space collisions. This 55scenario, that is now known as the Kessler syndrome, involves debris created from a collision impacting other satellites. Impact follows impact like a row of dominos, eventually resulting in mass satellite destruction.
In an effort to prevent the Kessler syndrome, many satellite mission teams safely maneuver retired satellites back into Earth’s atmosphere so that one of two things occur. For satellites orbiting close to Earth, operators lower the orbit of a decommissioned satellite so that 56they will naturally re-enter the atmosphere within 25 years. As the satellite begins to fall back toward Earth and loses altitude, the compression and friction in the dense region of the atmosphere closest to the Earth 57generate intense heat that breaks up and burns most of the satellite machinery.
If the satellite has enough fuel, it can be directed to fly back through the atmosphere and crash into a predetermined location in the Pacific Ocean. This place has several names, including Point Nemo (Latin for "no one") and the Oceanic Pole of Inaccessibility. These names are 58felicitous: The nearest land mass is 1,450 nautical miles away.
46
A.
NO CHANGE
B.
an area of sparsely populated land
C.
a land area that is sparsely populated
D.
onto a sparsely populated land area
