BRECKENRIDGE, Colo. The already untidy mass of orbital debris that litters low Earth orbit nearly got nastier last month. A head-on collision was averted between a spent upper stage from a Chinese rocket and the European Space Agency's (ESA) huge Envisat Earth remote-sensing spacecraft. Space junk tracking information supplied by the U.S. military, as well as confirming German radar data, showed that the two space objects would speed by each other at a nail-biting distance of roughly 160 feet (50 meters). ESA's Envisat tips the scales at 8 tons, with China's discarded rocket body weighing some 3.8 tons. A couple of tweaks of maneuvering propellant were used to nudge the large ESA spacecraft to a more comfortable miss distance. But what if the two objects had tangled? Such a space collision would have caused mayhem in the heavens, adding clutter to an orbit altitude where there are big problems already, said Heiner Klinkrad, head of the European Space Agency's Space Debris Office in Darmstadt, Germany. It turns out, Klinkrad told SPACE.com, that 50 percent of all the close conjunctions that Envisat faces are due to the lethal leftovers from China's January 2007 anti-satellite test, as well as chunks of junk resulting from last year's smashup between an active U.S. Iridium satellite and a defunct Russian Cosmos spacecraft. Klinkrad joined several orbital debris experts that took part in the 33rd Annual Guidance and Control Conference organized by the Rocky Mountain Section of the American Astronautical Society. The five-day meeting began Feb. 5. Avoidance maneuvers Significant progress has been made by the U.S. and the international aerospace communities in recognizing the hazards of orbital debris, reported Nicholas Johnson, chief scientist for orbital debris at the NASA Johnson Space Center in Houston, Texas. Johnson added that steps are being taken to reduce or eliminate the potential for the creation of new debris. However, "the future environment is expected to worsen without additional corrective measures," he noted. During 2009, Johnson reported, five different NASA robotic spacecraft carried out collision avoidance maneuvers: a Tracking and Data Relay Satellite (TDRS-3), Cloudsat, Earth Observing Mission 1, Aqua, and Landsat 7. Also, the space shuttle and the International Space Station took collision avoidance actions, he said. The worst thing that could happen, according to ESA's Klinkrad, is the International Space Station (ISS) receiving a fatal hit. The space station is currently home to five astronauts representing the U.S., Russia and Japan. "A penetrating object hitting the ISS, and possibly causing a casualty onboard . . . I think that would be the most dramatic case we could have," Klinkrad suggested. Such an incident might turn public opinion against human spaceflight, he said.