Modern Marvels: Where can you fire a missile without scaring the neighbors? Or lift millions of pounds in pursuit of a couple of ounces of gold? On a proving ground, of course, where performance is the only thing that matters. Because in the heat of battle or head-to-head competition, no excuses can be given. We'll visit the US military's Cold Regions Testing Center in Alaska and desert proving grounds in Arizona, the Olympic Complex in Colorado, and the now-defunct Packard proving grounds in Michigan.