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Strategies & Market Trends : 2026 TeoTwawKi ... 2032 Darkest Interregnum -- Ignore unavailable to you. Want to Upgrade?

To: elmatador who wrote (46360)	2/15/2009 4:51:26 AM
From: TobagoJack	Read Replies (4) \| Respond to of 217815

the remaining iridiums are as bad as doomed newscientist.com Satellite collision 'more powerful than China's ASAT test' 20:39 13 February 2009 by Paul Marks For similar stories, visit the Spaceflight Topic Guide Space weapons are dangerous - but out-of-control, defunct satellites can do just as much damage, if not more. So says a leading space scientist who has calculated that Tuesday's collision between an Iridium communications satellite and the defunct Soviet-era Cosmos 2251 spacecraft expended a great deal more destructive energy than China's infamous anti-satellite missile test did in January 2007. In 2003, space debris expert Hugh Lewis and colleagues at the University of Southampton in the UK ran predictions on the debris field that would be created in a hypothetical Iridium satellite break-up owing to a collision with just 1 kilogram of space junk (Acta Astronautica, doi:10.1016/S0094-5765(02)00290-4). Now he has fed Cosmos 2251's orbital data, mass and velocity into that computer model. To be completely obliterated, a spacecraft must be hit with an energy of 40 joules for every gram of its mass. In China's anti-satellite (ASAT) test, a defunct weather satellite called Fengyun-1C was destroyed by a missile that imparted an estimated 350 joules per gram of its mass. (The figure is an estimate because the missile's mass is not known for certain.) But the Iridium and Cosmos satellites collided at 42,120 kilometres per hour, Lewis calculates, imparting 50,000 joules per gram of their mass. 10,000 tennis balls The resulting "unprecedented" debris field, says Lewis, is still being analysed by space agencies. But he expects it to create an extra 10,000 tennis-ball-sized debris shards - more than triple the number created in the ASAT test. "There was more energy here than in the Chinese ASAT test so we'll see more debris," Lewis says. Nicholas Johnson, chief scientist for orbital debris at NASA's Johnson Space Center in Houston, Texas, says the exact amount of debris generated in the collision depends on the geometry of the smashup, which is not yet known. "If they collided main body to main body, that would create the maximum amount of debris," Johnson told New Scientist. "It is possible that one satellite hit an appendage of the other or only a small portion of the other - think about the different ways that two cars can collide and how that affects the extent of damage." Further collisions Worryingly, the new debris will raise the collision risk for other Iridium satellites. That's because the 65 remaining satellites in the Iridium network move in circular orbits that cross each other at the Earth's poles. "The debris cloud that is forming will create a torus [doughnut] of high-density debris that Iridium satellites will now need to pass through," warns Richard Crowther of the British National Space Centre. Lewis estimates that the collision risk to other Iridium satellites over the next 30 days has jumped to about 1 in 7000 from the previously quoted chance of 1 in millions. "The risk is now going to be significantly higher than the background risk," says Lewis. 'Unfortunate but inevitable' Observers expected a collision sooner or later, given the number of dead and defunct satellites beyond anyone's control in various orbits. Less than 10% of the 18,000 objects monitored in low- and high-Earth orbits are working satellites - the rest are dead craft, spent rocket stages and debris. "It was unfortunate but inevitable", says Crowther, the UK delegate on the Inter-Agency Space Debris Coordinating Committee, an umbrella group of 11 space agencies that presses satellite operators to deploy measures to mitigate debris creation. Such measures include ensuring end-of-life craft have the capacity to either be de-orbited - burned up in the atmosphere - or have fuel and guidance to reach a safe 'graveyard' orbit beyond the geostationary ring. Without such measures, debris remains in orbit for a long time. 'Critical infrastructure' "The concern now is the orbital lifetime of the Iridium and Cosmos 2251 debris. It will take many tens of years to decay," Crowther says. "Given we rely so much on space-based assets for communications, navigation and Earth observation as part of our critical national infrastructure, this is one of the weak links in the chain that needs more attention," Crowther adds. Lewis agrees: "I think now this has happened, it's much more likely that governments are going to take this issue seriously."