By Tuan Nguyen
Posting in Aerospace
The Roentgen Satellite (ROSAT) will be in a state of aimless free fall sometime in late October or early November, scientists predict.
We, as in all 6 billion of us, dodged a potential catastrophe last week when debris from a 6-ton satellite plummeted into a remote area of the south Pacific Ocean. Now scientists are hoping we'll be just as lucky the second time around when another one is scheduled to drop as early as next month.
This time it's the defunct German Roentgen Satellite (ROSAT) that will be in a state of aimless free fall sometime in late October or early November. The X-ray space observatory is less than half the weight (2.4-tons) of the fallen UARS, but has an orbit that ranges from latitudes of 53 degrees north and south, putting it in a position where it can threaten a wide region that stretches from Canada to South America. And while much of the spacecraft will disintegrate during it's rapid descent, German Aerospace Agency officials predict that as many as 30 large chunks of debris -- a combined mass of 1.6 tons -- is expected to survive re-entry.
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The agency estimates that there is a 1 in 2,000 chance that anyone will be pelted by one of these pieces -- a slightly more nerve-wracking figure than the one posed by the UARS, which had a 1 in 3,200 possibility.
So it really begs the question: why can't satellites like the ROSAT find a more peaceful way to put itself out of commission? In this case, it has to do with built-in durability features that are sometimes necessary.
In an official statement, ESA's senior space debris expert Heiner Klinkrad explains:
"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."
The silver lining in this whole business of out-of-control satellites is that NASA really did do a bang-up job of tracking the previous dead satellite and providing timely updates on the situation. The German Aerospace Agency plans to follow suit as a way of assuaging any fears and to perhaps help further minimize the risks, which, as it stands, is extremely slight. For instance, Klinkrad said that it will "be possible to predict, about one day in advance, which geographical regions will definitely not be affected."
Scientists are already actively tracking ROSAT's final descent, but the specifics of how everything will play out shall remain uncertain until roughly one to two hours before the big crash.
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Sep 28, 2011
With a little planning, military forces using anti-satellite (ASAT) weapons could destroy the satellites like ROSAT at a convenient location that would provide the least threat to inhabitants. But then, they might be giving away secrets or setting theemselves up for litigation if something goes wrong.
Why don't they just send these expired satellites toward the sun? When they get close to being useless they should fire the retros to move it out of orbit and send it toward the sun, let the sun burn them up.
that we can observe stars and even planets lightyears away, but have no idea where our own satellites are going to hit. So much for american and german "Hi-tech". Why don't they practice with some sharp shooting on those satellites. The smaller the pieces are the faster they burn up on re-entry to our atmosphere. Who dares go to Mars with technology this uncertain?