They range from a $1 billion U.S. Air Force so-called space fence radar tracking system, to a proposed European Space Agency spacecraft that would spray loose rockets with cushioning foam, to an Italian probe equipped with robot arms to help de-orbit the biggest pieces of debris, USA Today reported Wednesday.
The Obama administration has urged nations with space programs to confront space junk and help protect assets belonging to both nations and private firms, with the latter more and more involved in launches now that the U.S. space shuttle program has ended.
"The problem is worse now than it was 10 years ago," NASA engineer LeRoy Cain said at one of the final space shuttle mission briefings. "And in 10 years it will be worse still."
Scientists estimate there are roughly 22,000 objects bigger than 4 inches and ranging up to car-sized rocket boosters weighing 9 tons in orbit.
"Orbital debris is part of the cost of doing business in space," said space scientist Nicholas Johnson of NASA's Johnson Space Center in Houston.
While most of the orbiting junk and satellites have plenty of room to pass each other at great distances, any collision could be serious, experts say.
"Even something as small as a paint chip moving at 17,000 miles per hour can be a big problem," orbital debris analyst Roger Thompson of The Aerospace Corp. in El Segundo, Calif., says.