Alton Yates says the trip on the high-speed sled could be painful, and frightening. But he also says, "We were anxious to get strapped into that seat to conduct the next experiment." Courtesy of Alton Yates hide caption

itoggle caption Courtesy of Alton Yates

A Minuteman III intercontinental ballistic missile can hit almost any target on earth ... but only if it flies through Russian airspace. This unarmed test version was launched from Vandenberg Air Force Base in California. V.A. Mouzon/Tech Sgt. Vincent Mouzon/U.S. Air Force hide caption

itoggle caption V.A. Mouzon/Tech Sgt. Vincent Mouzon/U.S. Air Force

First Lt. Patrick Romanofski (center) and 2nd Lt. Andrew Beckner (left) practice the launch of nuclear weapons. Promotions are now more strongly influenced by hands-on performance in this simulator. R.J. Oriez/U.S. Air Force hide caption

itoggle caption R.J. Oriez/U.S. Air Force

An intercontinental ballistic missile in its silo at Malmstrom Air Force Base in Montana. Airman John Parie/U.S. Air Force hide caption

itoggle caption Airman John Parie/U.S. Air Force

A computer image generated by NASA shows objects orbiting Earth, including those in geosynchronous orbit at a high altitude. The objects are not to scale. NASA hide caption

itoggle caption NASA

A rendering of objects currently in Low Earth Orbit (not illustrated to scale). According to NASA, "approximately 95 percent of the objects in this illustration are orbital debris, i.e., not functional satellites." NASA hide caption

itoggle caption NASA