Hypersonic Missiles: A Work in Progress and No Break-Through Yet

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Hypersonic missiles | Speed Is the New Stealth. Hypersonic weapons: Building vehicles that fly at five times the speed of sound is amazingly hard, but researchers are trying. Economist, June 1, 2013.
http://www.economist.com/news/te ... e-times-speed-sound
(ramjet; supersonic-combustion ramjet, or scramjet

Quote: "The term hypersonic technically refers to speeds faster than five times the speed of sound, or Mach 5, equivalent to around 6,200kph at sea level and 5,300kph at high altitudes (where the colder, thinner air means the speed of sound is lower).