Summary: Hypersonic projectiles, missiles moving at five times the speed of sound, have become a high priority across the Defense Department. You've got two basic ways of getting projectiles to go that fast. One is the electromagnetic rail gun. The other is the use of hat planners call air breathing engines, and those are the topic of a new effort at the Defense Advanced Research Projects Agency. Project manager Andrew Knoedler spoke with Tom Temin. Learn more about your ad choices. Visit megaphone.fm/adchoices
