On Tuesday two satellites, one Russian and one American, collided by accident at about 10 km/s over Siberia (CNN story).
The US Space Surveillance Network uses radar and optical sensors to track all of the satellites and thousands of pieces of “space junk” that orbit the Earth. From the SSN space surveillance description page:
The SSN has been tracking space objects since 1957 when the Soviets opened the space age with the launch of Sputnik I. Since then, the SSN has tracked more than 24,500 space objects orbiting Earth. Of that number, the SSN currently tracks more than 8,000 orbiting objects. The rest have re-entered Earth’s turbulent atmosphere and disintegrated, or survived re-enty and impacted the Earth. The space objects now orbiting Earth range from satellites weighting several tons to pieces of spent rocket bodies weighing only 10 pounds. About seven percent of the space objects are operational satellites, the rest are debris. USSPACECOM is primarily interested in the active satellites, but also tracks space debris. The SSN tracks space objects which are 10 centimeters in diameter (baseball size) or larger.
Eight thousand pieces of space junk sounds like a lot, but space is a big place. The page states that the probability of one of these objects striking the space shuttle is about once every ten thousand years. The probability of a smaller object that is too small to be tracked striking the shuttle—or another operating satellite—is greater.
Earlier this week, NASA’s Image of the Day Gallery had an artist’s conception of the cloud of satellites orbiting the Earth:
Remember that at this scale each satellite is really an almost atom-sized speck.
Grace and Peace