An artistic rendering of ROSAT (German Aerospace Center)

The demise of ROSAT comes just weeks after NASA’s Upper Atmosphere Research Satellite (UARS) debris harmlessly plunged into the southwest Pacific (September 24). The German Aerospace Center writes the probability of someone somewhere on Earth getting smacked by satellite debris is 1 in 2,000. By comparison, NASA said the odds of UARS beaning a person were 1 in 3,200.

Launched by the U.S. on June 1, 1990, ROSAT’s payload includes an x-ray telescope and a wide field camera. Weighing 2.4 tons, some of ROSAT’s mass will disintegrate during its descent, entering the atmosphere at a speed of 17,400 miles per hour, says the German Aerospace Center. But 30 individual pieces may survive, including the satellite’s 1.7 ton heat resistant mirror.

Here’s how the European Space Agency says it will go down:

The lightweight objects fall to Earth first, similar to leaves from a tree. The really heavy objects land later, because they ultimately have to drill their way through the atmosphere. Generally speaking, whenever a satellite re-enters the atmosphere, about 20 to 40 percent of its mass actually reaches the Earth’s surface. In the case of ROSAT, this figure could be slightly higher because one of its characteristic features is that it carries heat-resistant mirror structures on board. Which means that more than 20 to 40 percent of its total weight could reach the ground.

ESA says it’s impossible to say where ROSAT’s trail of debris will hit until about one or two hours before impact. But it is known that the debris will fall somewhere between 53 degrees north and south latitude. The German Aerospace Center notes most of ROSAT’s debris will fall within a 50 mile (or 80 km) wide path along the satellite’s track.

As far as timing, the German Aerospace Center offers this detail:

At present, scientists expect the X-ray satellite, which completes an orbit around Earth in about 90 minutes, to re-enter around between 22 and 23 October 2011. Currently, the re-entry date can only be calculated to within plus/minus two days. This time slot of uncertainty will be reduced as the date of re-entry approaches. However, even one day before re-entry, the estimate will only be accurate to within plus/minus five hours. projects re-entry will occur during the early hours of the day on October 23.


Take cover: Another satellite is plunging to Earth (USA Today)

ROSAT re-entry tracking page