Tuesday, October 4, 2016

The Emerging Problem of Space Debris: What Are the Chances of Being Hit By a Falling Satellite?

A CGI snapshot of the space junk orbiting high above our heads in low-Earth orbit. Image credit: Space Junk 3D website.

From time to time, when a defunct spacecraft is about to plunge into the Earth's atmosphere, ending its operational life with a fiery reentry, many fears and worries recur here on the ground. One of the returning questions is about the odds of being struck by a piece of metal that hadn't entirely burned up in the atmosphere.

It may seem that more than 500,000 pieces of the so-called "space junk" currently floating around our planet, guarantee a very high chance of "winning" an imminent hit, causing a serious injury, but according to calculations made by NASA, the chances are extremely small. Scientists in the agency's Orbital Debris Program Office, estimate that the odds of a person being struck by a piece of a de-orbited satellite are approximately 1 in 3,200. Moreover, the chance for one particular person of being hit by a falling debris is 1 in several trillion.

To put that in some perspective, the odds of a ball landing on a given number in American roulette, like the one available on Netbet, are 1 in 37. Even winning any single number two times a row statistically happens 1 in 1,369 – that's still more probable than a piece of space garbage hitting someone on Earth.

In Texas Hold'em Poker, the probability of being dealt suited Ace-King is 1 in 331. But how about the same situation four time a row? Turns out it's about 1 in 12 billion, thus still more feasible that that you in particular will be hit by some leftover fragment of a defunct spacecraft. So, it seems that instead of being worried about space debris that may someday fall into Earth, we should try to beat the odds at casino and card games.

Extremely low odds of being struck by a piece of space junk are due to the fact that only 29 percent of Earth's surface is land – mostly uninhabited, as people congregate mainly in cities. However, the chances could get higher in the future as more and more satellites are being sent into orbit. Moreover, the spacecraft that are currently orbiting Earth sometimes collide with each other, producing additional debris. For example, in February 2009 a defunct Russian spacecraft collided with and destroyed a functioning U.S. commercial satellite, what added more than 2,000 pieces of in-orbit space junk.

NASA and the Department of Defense are constantly monitoring the risk that satellites pose to Earth. The space agency reveals that currently, total number of tracked objects exceeds 21,000.


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