Two large tethered helium blimps carrying surveillance gear will be deployed for testing by the North American Aerospace Defense Command, known as NORAD, somewhere near Washington, D.C.'s airspace by the end of September, Reuters reported this week. The blimps, each of them about 243 feet long, can reach altitudes up to 10,000 feet and stay aloft for up to 30 days at a time. They will carry radar and other surveillance gear that enables them to detect ground targets, manned and unmanned aircraft, boats, and cruise missiles at distances up to 340 miles. They cost about $450 million for the pair.
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