Scientists in the US have warned Nasa that the amount of so-called space junk orbiting Earth is at tipping point. A report by the National Research Council says the debris could cause fatal leaks in spaceships or destroy valuable satellites. It calls for international regulations to limit the junk and more research into the possible use of launching large magnetic nets or giant umbrellas. The debris includes clouds of minuscule fragments, old boosters and satellites. Some computer models show the amount of orbital rubbish has reached a tipping point, with enough currently in orbit to continually collide and create even more debris, raising the risk of spacecraft failures, the research council said in a statement on Thursday. In 2007, China conducted an anti-satellite weapon test which destroyed a decommissioned weather satellite, smashing the object into 150,000 pieces larger than 1cm. Two years later, two satellites - one defunct and one active - crashed in orbit, creating even more debris. Those two single events doubled the amount of fragments in Earth orbit and completely wiped out what we had done in the last 25 years, said Donald Kessler, who led the research. MO