fence

Thousands of manmade pieces of space junk orbit the Earth, threatening astronauts and unmanned missions alike. Now the U.S. Air Force Space Command wants an electronic "space fence" that could track any orbital object larger than two inches in width.

Such a surveillance system would require a global network of sensitive S-band radar stations that operate in the gigahertz range of the electromagnetic spectrum. The U.S. Air Force currently relies on a system dating back to 1961, which only covers the continental United States, and can only track objects 20 inches in width or larger.

Since the bombing of the U.S.S. Cole in 2000, protecting docked ships-both military and commercial-has been a big priority in the fight against terrorism. The Department of Homeland Security has already awarded $489 million to help guard the nation´s ports, spurring a number of innovative ideas, the latest of which is an underwater system that blasts enemy swimmers with painful acoustic waves. Patented by the Raytheon Corporation last October, the system is the brainchild of former Navy and Raytheon acoustics expert Frederick Di Napoli. His scheme is simple: Generate a region of high-pressure, low-frequency sound around the ship, creating a sort of sonic fence that â€shocks†anything that swims through it. Although a diver would probably flee from pain, Di Napoli says, "you could really dial up the pressure and make it lethal if you had to."