The Air Force wants to rebuild a “fence” around Earth to keep the riff-raff out.

Sounds like a Hollywood script to counter aliens or asteroids but it's a real program the military wants to update at an estimated cost of $3.5 billion.

Just don't expect any space cowboys digging post holes and wrangling barbed wire in orbit.

The Space Fence program is a series of radar signals managed by the Air Force since the early 1960's that has been tracking an ever-growing pile of rocket and satellite parts and other man-made fragments that zoom around Earth’s vicinity at thousands of miles per hour.

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